1-05-09 final version - ex forklift handbook

GOOD PRACTICE HANDBOOK

Protecting Powered Industrial Equipment Operating in and Around

Explosion Hazardous AreasAnd Explosive Atmospheres

January 2009

This document is for educational/informative purpose only and has not be used to determined suitability of powered industrial equipment. Please contact your local authority having jurisdiction to verify equipment

fire safety

FOREWORD

History has shown that flammable vapor ignitions in a number of cases have been proven to reside in mobile equipment working in or around a facility. “Industrial Loader and Forklift Fires,” an NFPA report published in January 2009, states that between 2003 and 2006, an average of 1,340 fires were ignited by heat or ignition sources found on powered industrial loaders and forklifts.

PYROBAN has provided explosion protection and environmental solutions to industry for almost 40 years. Through continued investment in technology, product development, and as an active member in regulatory committees, Pyroban has made significant contributions to the development and implementation of codes and regulations such as the European standards EN1755:2000 and EN1834:2000, the Chinese GB19854:2005, the American NFPA 505, and UL STP583. Our efforts to improve public and employee safety through our products and innovative developments have earned us global respect and a reputation as an authority in the field of ignition source protection on powered industrial equipment.

Codes and regulations relating to the use of powered industrial equipment in potentially explosion hazardous areas can be complicated and difficult to understand. It is our experience that, even though local codes and regulations might show minor deviations from each other, they all serve the same common goals of preventing catastrophic incidents and loss of human life.

When approving and protecting powered industrial equipment for use in explosion hazardous areas, it is critical that ALL potential ignition sources have been addressed. The level of protection required is determined by the classification of explosion hazardous areas in which the equipment will operate and the probability that an ignitable atmosphere will develop.

Protecting the ignition sources found on mobile powered industrial equipment is a complicated process. Because mobile equipment can often travel between areas with different hazardous area classifications, the chances that the equipment will encounter an explosive atmosphere are significantly increased. Great care should be given to ensure that the appropriate level of equipment protection is applied to ensure safe operation of the equipment.

Modifying, testing, and certifying equipment for use in explosion hazardous areas has, by some users, been considered cost prohibitive. Economic justification and an incident-free history entice owners/operators to use equipment which may not be intended, protected, or certified for use in explosive atmospheres. If these liabilities are combined with such items as human error, equipment wear and tear, component failure, and under-classifying explosion hazardous areas, then the risk of an incident taking place is increased significantly.

Determining the appropriate level of ignition protection for powered industrial equipment should be based on a risk assessment. It should take into account the type of flammable material encountered, the frequency in which an explosive atmosphere develops, and the ability of equipment to operate in this explosive atmosphere.

The only way to ensure the safety of people, their investments, and our environment is to demand that appropriate levels of ignition source protection are applied and that hazardous area compliance has been guaranteed.

Contents

INTRODUCTION..............................................................................................................................................................................7

Scope.....................................................................................................................................................................................................7

Assumptions.........................................................................................................................................................................................8

TERMINOLOGY...............................................................................................................................................................................8

Testing laboratory.................................................................................................................................................................................8

Approved..............................................................................................................................................................................................8

Explosion hazardous AREA.................................................................................................................................................................8

Explosion hazardous ATMOSPHERE.................................................................................................................................................8

Hours of exposure.................................................................................................................................................................................8

Potential ignition sources on powered industrial equipment................................................................................................................8

Other risk factors..................................................................................................................................................................................8

ACTIVE equipment protection.............................................................................................................................................................8

PASSIVE equipment protection...........................................................................................................................................................9

CREATING A FIRE OR AN EXPLOSION....................................................................................................................................9

Oxygen..................................................................................................................................................................................................9

Flammable materials.............................................................................................................................................................................9

Ignition source......................................................................................................................................................................................9

EXPLOSION HAZARDOUS AREAS..............................................................................................................................................9

Hazardous Materials Classes and Zones.............................................................................................................................................10

Divisions.............................................................................................................................................................................................10

Division 1 or Zone 0 (gas & liquids) or Zone 20 (dust & fibers).......................................................................................................11



Unrated areas in potentially explosion hazardous locations...............................................................................................................11

NON hazardous areas.........................................................................................................................................................................11

Groups of flammable materials..........................................................................................................................................................12

Hazardous areas in facilities...............................................................................................................................................................12

Division 1 or Zone 0/20......................................................................................................................................................................12

Division 1 or Zone 1/21......................................................................................................................................................................12

Division 2 or Zone 2/22......................................................................................................................................................................13

Unrated potentially explosion hazardous areas..................................................................................................................................13

EXPLOSION HAZARDOUS ATMOSPHERES...........................................................................................................................14

Flammable Gasses and Liquids..........................................................................................................................................................14

Flash Point..........................................................................................................................................................................................14

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Open-Cup Flash Point.........................................................................................................................................................................14

Auto-ignition Temperature.................................................................................................................................................................14

Lower Explosive Limit (LEL) or Lower Flammable Limit (LFL).....................................................................................................15

Explosive Range.................................................................................................................................................................................15

Upper Explosive Limit (UEL) or Upper Flammable Limit (UFL).....................................................................................................15

Vapor Density.....................................................................................................................................................................................15

Common Flammable Industrial Gases................................................................................................................................................15

Acetylene............................................................................................................................................................................................15

Hydrogen............................................................................................................................................................................................15

Liquefied Petroleum Gas (LPG..........................................................................................................................................................15

Flammable and Combustible Liquids.................................................................................................................................................15

Flammable Dusts and Fibers:.............................................................................................................................................................16

Elements of a Dust Explosion.............................................................................................................................................................16

Facility Dust Hazard Assessment.......................................................................................................................................................16

Facility Analysis Components............................................................................................................................................................16

Dust Combustibility............................................................................................................................................................................17

Electrical Classification......................................................................................................................................................................17

Other Hazard Analysis Considerations...............................................................................................................................................17

Dust Control........................................................................................................................................................................................18

Ignition Control..................................................................................................................................................................................18

EQUIPMENT IGNITION SOURCES...........................................................................................................................................18

PRECAUTIONS FOR IC POWERED (DIESEL) INDUSTRIAL EQUIPMENT.....................................................................19

PRECAUTIONS FOR BATTERY POWERED LIFT TRUCKS................................................................................................21

Ignition hazards..................................................................................................................................................................................21

Protection methods.............................................................................................................................................................................21

Electrical protection............................................................................................................................................................................21

Gas detection system..........................................................................................................................................................................21

Other precautions................................................................................................................................................................................21

Equipment use in Class I, Division 1 or Zone 0 explosion hazardous areas......................................................................................21

Equipment use in Class I, Division 1 or Zone 1 explosion hazardous areas......................................................................................22

Class I, Division 1 or Zone 1 approved equipment protection methods............................................................................................22

Identification.......................................................................................................................................................................................22

Surface temperatures..........................................................................................................................................................................22

Cooling and temperature monitoring of equipment “hotspots”..........................................................................................................22

EX enclosures.....................................................................................................................................................................................22

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Special purpose EX enclosures...........................................................................................................................................................22

Increased safety enclosures.................................................................................................................................................................23

Encapsulation......................................................................................................................................................................................23

Wiring.................................................................................................................................................................................................23

Intrinsically safe (IS) wiring, circuits or apparatus............................................................................................................................23

Cable glands or seals..........................................................................................................................................................................23

Frame leakage detection/monitoring..................................................................................................................................................23

Flame arrestors....................................................................................................................................................................................23

Spark arrestors....................................................................................................................................................................................24

Vapor ingestion and over-speeding....................................................................................................................................................24

Elimination or protection of spark-producing components and static buildup...................................................................................24

Protection of load contact and impact points......................................................................................................................................24

Batteries and connectors.....................................................................................................................................................................24

Allowed equipment recommendation.................................................................................................................................................25

Class I, Division 2 or Zone 2 approved equipment protection methods............................................................................................25

Identification:.....................................................................................................................................................................................25



Purged or Increased safety enclosures................................................................................................................................................25

Other enclosures.................................................................................................................................................................................25

Encapsulation......................................................................................................................................................................................26

Wiring.................................................................................................................................................................................................26

Nonincendive wiring, components or equipment...............................................................................................................................26


Flame arrestors....................................................................................................................................................................................26

Spark arrestors....................................................................................................................................................................................26

Vapor ingestion and over-speeding....................................................................................................................................................26



Gas Detection......................................................................................................................................................................................27

Unrated potentially explosion hazardous Class I areas......................................................................................................................27

Gas detection with automatic shutdown risk reduction......................................................................................................................28

Equipment used in Class II & 3, Division 1 or Zone 20 explosion hazardous areas..........................................................................29

Equipment use in Class II&3, Division 1 or Zone 21 explosion hazardous areas..............................................................................29

Class II, Division 1 or Zone 21 approved equipment protection methods.........................................................................................29

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EX enclosures.....................................................................................................................................................................................30

Special purpose EX enclosures...........................................................................................................................................................30

Increased safety enclosures.................................................................................................................................................................30

Encapsulation:.....................................................................................................................................................................................30

Wiring.................................................................................................................................................................................................30

Intrinsically safe (IS) wiring, circuits or apparatus............................................................................................................................31


Frame leakage detection.....................................................................................................................................................................31

Spark arrestors....................................................................................................................................................................................31

Air inlet filter......................................................................................................................................................................................31




Allowed equipment recommendation.................................................................................................................................................32

Class II, Division 2 or Zone 22 approved equipment protection methods.........................................................................................32

Identification.......................................................................................................................................................................................32



Other enclosures:................................................................................................................................................................................32

Encapsulation:.....................................................................................................................................................................................33

Wiring:................................................................................................................................................................................................33


Spark arrestors....................................................................................................................................................................................33




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INTRODUCTION

Scope:Dangers resulting from manufacturing, handling, processing, storing, or distributing flammable materials pose a global problem. Regardless of where these functions or processes take place, the risks of igniting (accidental) releases of flammables by powered industrial equipment are real.

This handbook was written to assist Authority Having Jurisdictions, manufacturers, end users and other interested parties in determining suitable equipment protection levels for their particular applications. The goal of this handbook is to assist the reader in reducing the exposure that results from operating powered industrial equipment around flammable and explosive materials. Recommended practices are based on ignition protection methods and system safety rather than guideline interpretation, cross referencing of codes & regulations, or possible misrepresentation of UL equipment type designations.

This handbook will not differentiate between borders, codes, or regulations. It simply aims to educate the reader about methods to protect powered industrial equipment used in (potentially) explosive atmospheres.

Protection methods described in this handbook focus on explosion protection and explosion prevention through the elimination of arcing/sparking components, hot surfaces, and other known equipment ignition sources. All protection methods and philosophies described in this handbook are based on tested, certified, and proven principles used to minimize ignition risks in case the powered industrial equipment encounters an explosive atmosphere. This handbook will quantify differences between potentially explosive areas, explosive atmospheres, ignition risks, and protection methods required.

This handbook covers:- flammable material- ignition risks- facilities handling explosive material- descriptions of explosion hazardous- common equipment ignition sources- equipment protection methods- equipment designations- protection requirements - justification of equipment suitability through elimination of ignition sources

Ignition sources found on mobile powered industrial equipment and vehicles will be compared, and minimum protection recommendations will be made. This handbook does not contain detailed technical specifications, construction details, or testing requirements. Please consult recognized codes, regulations, and applicable construction requirements for more details.

All protection methods and systems described in this manual should be tested, certified, and approved by a recognized third party testing laboratory according to accepted codes or standard. In most cases, this handbook will recommend safeguards meeting or exceeding regional requirements, while in other instances the equipment protection levels recommendations may contradict local requirements or common practice.

There is a growing trend in the industry to differentiate between ACTIVE and PASSIVE equipment protection methods. ACTIVE equipment protection systems do not allow operation of powered industrial equipment in explosive Gas or Vapor atmospheres. Equipment will be de-energized prior to the development of ignitable gas or vapor levels. A significant benefit of ACTIVE protection is that it offers a solution against human error (driving into explosive hazardous areas for which the equipment is not intended to operate) and equipment misuse.

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Equipment protected by PASSIVE protection method can be operated in explosive atmospheres. These vehicles will NOT be de-energized when an explosive atmosphere develops. Unless the operators wear special breathing equipment when operating equipment in explosive atmospheres, the health implications to the operator may be serious.

Assumptions:It is assumed that all equipment referred to in this handbook is tested and certified for general purpose application prior to making any modification, which will ensure safe operation in potentially explosion hazardous areas. Adding ignition protection should under no circumstance interfere or change any existing equipment stability and safety design specifications.

TERMINOLOGY:

Testing laboratory:Any recognized third party testing laboratory that tests and certifies equipment according to local or internationally recognized codes and regulations.

Approved:Equipment constructed, tested, and certified for its purpose by a recognized testing laboratory according to local or internationally recognized codes and regulations.

Explosion hazardous AREA:Area designation/classification based on the probability that an explosive atmosphere may develop.

Explosive ATMOSPHERES:Explosive atmospheres develop when the mixture of flammables and oxygen are combined to create an ignitable atmosphere. The dangers posed by explosive or ignitable atmospheric conditions vary significantly depending on the flammable material encountered. The lowest percentage of flammable gas or vapor required to allow ignition often is identified as the Lower Explosive Limit (LEL) or LFL level.

Hours of exposure:The total number of hours per year during which an explosive atmosphere is present in a certain predetermined area.

Potential ignition sources on powered industrial equipment:The most common equipment ignition sources are:

Flashback from the air inlet system (IC engine power) Flame or spark emission from the exhaust system (IC engine power) Over-speeding from vapor ingestion (IC engine power) Surface temperatures Arcs and sparks from electrical equipment Sparks from the discharge of static electricity High temperature from friction Sparks from impact

Other liabilities:Besides the known ignition sources, a number of additional risk factors influence the safety of equipment use in potentially explosive areas.

These are: Human error Equipment abuse/misuse Noncompliant repairs Equipment failure

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ACTIVE equipment protection:ACTIVE equipment protection systems prevent the operation of powered industrial equipment in explosive gas or vapor atmospheres. By de-energizing equipment before an explosive atmosphere develops, equipment ignition sources will be eliminated. ACTIVE protection systems should prevent restarting of powered industrial equipment in explosive gas or vapor atmospheres. ACTIVE protection will significantly reduce the risk due to human error, equipment failure, equipment misuse, noncompliant repairs, and operator poisoning by overriding the operator’s actions and alarming the operator of the danger at hand.

PASSIVE equipment protection:PASSIVE equipment protection methods will NOT prevent the operation of powered industrial equipment in explosive atmospheres. Equipment protected by only PASSIVE protection methods will remain energized, even if an explosive and possibly toxic atmosphere develops. PASSIVE protection methods are used when equipment must be able to operate in explosive atmospheres. If equipment is operated in an explosive atmosphere, it is recommended that approved breathing apparatus is worn by the operator at all times. All Class I, Division 1 and Zone 1 rated equipment, as well as equipment used in dust hazardous areas, use PASSIVE protection methodology.

CREATING A FIRE OR AN EXPLOSIONIn order to start a fire or create an explosion the right combination of the following three elements must be present:

1. Oxygen2. Flammable material3. Ignition source

These three elements combined form the fire or explosion triangle. Physics has proven that if any one of these items is not present, ignition will not take place.

Oxygen This very abundant element is almost impossible to remove in a normal manufacturing environment. In normal manufacturing environments where mobile industrial equipment operates, oxygen is always present in sufficient quantities to support ignition. Prevention of ignition therefore must eliminate either the flammable material or the ignition sources.

Flammable materialsFlammable materials can be gases, liquids, fibers, and dusts. Any one of these materials needs to be present in the right mixture before combustion takes place. In certain cases, an initial explosion can create an environment that leads to a more catastrophic explosion. This is especially the case with dusts and fibers, where secondary explosions are common due to changes in environments caused by the initial explosion (floating dust and overpressure). Ignition sourceIgnition sources can be found throughout facilities manufacturing, processing, handling, storing, or distributing flammable materials. One often underestimated source for ignitions is mobile powered industrial equipment. Unlike fixed equipment, mobile equipment can travel easily throughout a facility, moving in and out of explosion hazardous areas while they may or may not have the proper level of ignition protection.

Different levels of protection methods have been developed to minimize the ignition sources based on the probability that explosive atmosphere is encountered by powered industrial equipment. The responsibility and judgment for ensuring safe operation most often rests on the shoulders of the equipment operators. History, however, has shown that most incidents occur when accidental releases, misjudgment, and/or human error come together..

EXPLOSION HAZARDOUS AREASAlso see appendix XYZ NEC exert or NEC 2008 article 500.

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Steve Noakes, 12/23/09,

What is the reference to use here ?

Around the world, a variety of rating systems are used to indentify explosion hazardous areas. The most commonly used rating systems are the international system that divides explosion hazardous areas into zones and the U.S. system that divides explosion hazardous areas into Classes, Divisions, and Groups.

Ultimately the dangers and risks faced as a result of manufacturing, handling, processing, storing, or distributing flammable materials are basically identical, regardless of geographic locations. For more than 20 years, the IEC has made an effort to develop global codes, regulations, guidelines, and an area classification rating system. Global acceptance and enforcement of these codes would ensure a harmonized uniform global safety standard. Even though significant progress has been made, it appears that the ultimate goal of a single global code will not be achieved any time soon.

Hazardous materials protection classificationExplosion hazardous materials in the U.S. are split into three major categories called classes. International (IEC) coding does not differentiate between dust and fiber due to the likelihood that they both are present in environments at the same time. Therefore, in international coding, areas are classified as either gas/vapor hazard and/or dust hazards.

The international coding also differentiates between area classification and equipment classification.

Hazardous material US

International (IEC)

Area marking Equipment marking

Gas or vapor Class I Zone 0, 1, or 2 1G, 2G, 3G

Dust Class IIZone 20, 21, or 22 1D, 2D, 3D

Fibers Class IIITable 1: Classes, area and equipment marking

Divisions and ZonesClasses are divided into divisions. There are 3 Zone levels. The frequency and length of time in which ignitable levels occur in the atmosphere determine the division rating or zone level. As the hours of the existence of an explosive atmosphere increase, the level of equipment protection required also must be increased.

At first look, there appears to be a significant difference between the U.S. hazardous area designation in classes and divisions and the internationally used zoning concept. However, once one takes the time to read the hazardous area descriptions and compare them to the allowed use of mobile powered industrial equipment in explosion hazardous areas, it becomes clear that the differences are minimal and appear to be based on interpretation rather than physical differences.

When you compare the allowed use of powered industrial equipment to the protection methods applied and likelihood that an explosive atmosphere will develop, five (5) levels of explosion hazardous areas become clear. For the protection of powered industrial equipment, these five levels provide a good indication of the minimum level of protection required to operate powered industrial equipment safely in these areas:

1. Division 1 or Zone 0 (gas & vapor) or Zone 20 (dust & fibers)2. Division 1 or Zone 1 (gas & vapor) or Zone 21 (dust & fibers)3. Division 2 or Zone 2 (gas & vapor) or Zone 22 (dust & fibers)4. Unrated areas where large quantities of flammable materials are stored or handled5. NON hazardous areas

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Presence of flammable material

Area DesignationHrs. of

exposure/yr.US International

Likely to exist MOST of the time

Division 1

Zone 0(Gas & Liquids)

Zone 20(Dust & Fibers)

>1000

Likely to exist SOME of the time

Division 1



>100< 1000

Might but are unlikely to exist

Division 2



> 10<100

Very unlikely to exists

No designation



<1

NON hazardous areas

No designation

No designation

0

Table: 2: Hazardous area overview and the likelihood in hours of explosion hazardous environments existing in these areas during normal working conditions.

Division 1 or Zone 0 (gas & liquids) or Zone 20 (dust & fibers)Areas where ignitable concentrations of flammable materials are LIKELY TO EXIST MOST OF THE TIME under normal operating conditions.

Exposure to ignitable levels of flammable materials: >1000 hours per year.

Division 1 or Zone 1 (gas & liquids) or Zone 21 (dust & fibers)Areas where ignitable concentrations of flammable materials are LIKELY TO EXIST SOME OF THE TIME under normal operating conditions.

Exposure to ignitable levels of flammable materials: >10 <1000 hours per year.

Division 2 or Zone 2 (gas & liquids) or Zone 22 (dust & fibers)Areas where ignitable concentrations of flammable materials MIGHT BUT ARE NOT LIKELY TO EXIST under normal operating conditions.

Exposure to ignitable levels of flammable materials: <10 hours per year.

Unrated areas where flammable materials are stored or handledAreas where ignitable concentrations of flammable gas, vapors, and liquid MIGHT BUT ARE VERY UNLIKELY TO EXIST under normal operating conditions unless there is a spill, accident, or equipment failure. Unrated areas are not formally acknowledged in area classifications.

Exposure to ignitable levels of flammable materials: <1 hour per year.

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NON hazardous areasAreas where ignitable concentrations of flammable gas, vapors and liquid WILL NEVER EXIST.

Exposure to ignitable levels of flammable materials: 0 hours per year.

Groups of flammable materialsFlammable materials are divided into groups based on the differences in explosion and ignition characteristics. This type of grouping allows the equipment to be protected, tested, and certified based on a representative flammable material. The groupings and representative materials reflect the differences in ease of ignition and the resulting explosion forces between the many flammable materials.

Representative Hazardous material

US International

Acetylene AIIC

Hydrogen B

Ethylene C IIB

Propane D IIA

Metal Dust EConductive

Carbon Dust F

Flour & Grain Dust

G Non conductive

Table3 Flammable material groups

Hazardous areas in facilitiesA typical hazardous facility will have a number of different hazardous areas ratings. In some facilities, the different levels of hazardous area classification are not separated by physical barriers. Due to variances in code interpretations and explosion hazardous area ratings, equivalent levels of equipment protection have not been established. This makes many facilities that manufacture, process, store, distribute, or handle flammable materials extremely vulnerable to incidents caused by powered industrial equipment, which can travel freely between different hazardous areas. With both the U.S. and international coding systems, industrial equipment protection should be based on the assumption that an explosive atmosphere can develop at any time anywhere in or around a facility where flammable materials are handled. Therefore unprotected equipment is not recommended in such cases.

Division 1 or Zone 0/20In areas where ignitable concentrations of flammable materials are LIKELY TO EXIST MOST OF THE TIME (greater than 1000 hrs/yr) under normal operating conditions, the risk of ignitable levels of flammable materials existing is extremely high. In the United States these areas are classified as Class I, II, or III, Division 1. The international community identifies them as Zone 0 (gas and liquids) or Zone 20 (dust & fibers).

The use of powered industrial equipment is not allowed in these areas unless intrinsically safe or encapsulated.

Examples of these areas are (NFPA-70-2008 page 70-357):- Inside an inadequately vented enclosure containing instruments normally venting flammable material to the

interior or exterior.- Inside vented tanks containing volatile flammable materials- Inadequately vented areas within spraying or coating operations using flammable material- Interior of exhausts ducts that are used to vent ignitable concentrations of flammables.

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Division 1 or Zone 1/21In areas where ignitable concentrations of flammable materials are LIKELY TO EXIST SOME OF THE TIME IN NORMAL OPERATION (10–1000 hrs/yr), the risk that ignitable levels of flammable materials exist is high. In the United States, these areas area classified as Class I, II, or III, Division 1. The international community identifies them as Zone 1 (gas and liquids) or Zone 21 (dust & fibers).

The use of properly tested and certified electric and diesel powered industrial equipment is allowed in these explosion hazardous areas. Because the international community differentiates between Zone 0 and Zone 1 classified areas, it is possible to protect, test, and certify electric and diesel powered equipment for use in Zone 1 Group IIA (U.S. group D), IIB (U.S. group C), and even IIC (US group A&B) hazardous areas.

Equipment tested and certified for use in Zone 1 Group IIA (U.S. group D), IIB (U.S. group C), or IIC (U.S. group A&B) hazardous areas may be considered a suitable solution for applications such as areas described in NFPA-70-2008 (pages 70–356):- Where flammable materials are transferred from one container to another- Interiors of spray booths and areas in the vicinity of spraying and paining operations- Locations containing open vats or containers of flammable materials- Drying rooms or compartments for evaporating flammable materials- Locations containing vat- and oil-extraction equipment using volatile flammable solvents- Portions of cleaning and dyeing plants where flammable materials are used- Gas generator rooms and other portions of gas manufacturing plants where flammable gas may escape- Inadequately ventilated pump rooms for flammable materials or volatile liquids- The interiors of refrigerators and freezers in which flammable materials are stored in open, lightly stopper, or

easily ruptured containers- All locations where ignitable concentrations of flammable materials are likely during the course of normal

operations- All locations surrounding areas where ignitable concentrations of flammable materials are LIKELY TO EXIST

MOST OF THE TIME (greater than 100 hours) under normal operating conditions; may exist frequently because of repair, maintenance, or leakage; or may exist due to breakdowns and failure of equipment.

Division 2 or Zone 2/22In areas where ignitable concentrations of flammable materials MIGHT BUT ARE NOT LIKELY TO EXIST (less than 100 hrs/yr) under normal operating conditions, the risk is low that ignitable levels of flammable materials will exist is low. In the United States, these areas area classified as Class I, II, or III, Division 2. The international community indentifies them as Zone 2 (gas and liquids) or Zone 22 (dust & fibers).

A variety of powered industrial equipment protected with a range of ignition protection methodologies can be used in these potential explosion hazardous areas. It is recommended that equipment tested and certified for use in Class I, Division 2 or Zone 2 be shut down when an explosive atmosphere develops.

Examples of these areas are:- All areas where flammable materials are stored, handle,d or transported in closed containers- Areas surrounding outdoor bulk storage of flammable materials- Al areas surrounding areas where ignitable concentrations of flammables are LIKELY TO EXIST SOME OF THE

TIME (10–100 hours/yr) under normal operating conditions; may exist frequently because of repair, maintenance, or leakage; or may exist due to breakdowns and failure of equipment.

A major item of concern in Division 2 or Zone 2 hazardous areas, especially on internal combustion powered equipment, is the surface temperature of manifolds, exhaust systems, and catalytic converters.

Unrated potentially explosion hazardous areas Unrated potentially explosion hazardous areas are areas where significant volumes of ignitable gas, vapors, and liquids MIGHT BUT ARE VERY UNLIKELY TO EXIST under normal operating conditions. Exposure usually does

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not occur unless there is an accidental spill or release. The risk of igniting flammable materials in these areas is extremely high due to a lack of equipment protection requirements and the volume of flammables involved.

The operation of unprotected powered industrial equipment near large quantities of flammables materials can have devastating consequences, as was proven by the large number of incidents that have occurred in these areas over the past eight years. A Pyroban analysis of the 2003–2007 NFIRS shows that during this time period, more than 13,000 fires were started by heat sources on powered industrial equipment. It is recommended that all powered industrial equipment used in and around areas where Class I flammables are stored be protected and equipped with an automatic shutdown system to reduce the risk of igniting these accidental gas, vapor, or liquid releases.

Examples of these areas are:- Property surrounding facilities that handle or store flammable materials- Fuel terminals- All open air locations storing, handling and processing open or sealed containers of flammable materials

As these areas are not formally classified, unrated areas often are referred to as nonhazardous areas. However, based on accident statistics, should such areas be regarded as non hazardous requiring no protection at all?

Nonhazardous areaBy definition, the only nonhazardous area is one where either no flammable materials are present or no ignition sources are present.

EXPLOSION HAZARDOUS ATMOSPHERESUnlike the definition “explosion hazardous areas,” the term “explosive atmospheres” provides a more accurate representation of the risks associated with the use of powered industrial equipment in explosion hazardous areas. The overall accepted industry standard for explosion hazardous atmospheres is that any atmosphere below 20 percent LEL (Lower Explosion Level) is regarded as nonhazardous or ignitable. LEL represents the percentage of flammable gas mixed with oxygen.

When eliminating ignition sources on powered industrial equipment, it can be more fruitful to utilize protection methods that focus on the detection of the development of explosive atmospheres and ignition prevention rather than attempting to package and contain the explosion in explosion-proof (EX) housings or enclosures. Today, only equipment protected by Division 1 or Zone 1/21 protection methods are constructed to operate safely in an explosion hazardous atmosphere. Equipment that is protection with Division 2 or Zone 2/22 protection methods should never be allowed to operate in an explosive atmosphere for an extended time period.

Flammable Gases and Liquids Source: General Monitors’ “A Guide to the Characteristics of Combustible Gases and Applicable Detection Technologies”

The following properties represent those that are important in evaluating protection methods of industrial equipment used in potentially Class I explosion hazardous environments.

Flash PointThis is the lowest temperature at which a liquid gives off sufficient vapor at its surface to form a flammable or an explosive mixture. Many hazardous liquids have flash points at or below room temperature and are covered by a layer of flammable vapors that will ignite immediately if exposed to an ignition source. Vaporization increases as temperature rises and consequently they are more hazardous at elevated temperatures.

Open-Cup Flash PointThis is the lowest temperature at which a liquid gives off sufficient vapor at its surface to form a flammable or an explosive mixture. Open cup testing is a method to determine this flash point, and although less accurate than closed cup testing, it is necessary for certain substances.

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Auto-ignition TemperatureSometimes referred to as spontaneous ignition temperature, or “SIT,” this is the minimum temperature for self-sustained combustion of a substance, independent of the heating or heated element. This temperature generally is well above the open-cup flash point.

Lower Explosive Limit (LEL) or Lower Flammable Limit (LFL)This is the minimum concentration of a flammable gas or vapor that will propagate flame when exposed to a source of ignition. Commonly abbreviated as LEL or LFL, a mixture below this concentration level is considered too “lean” to burn. An increase in atmospheric temperature or pressure will decrease the LEL of a gas or vapor.

Explosive RangeThis includes all concentrations (measured as a percent of volume in air) of a flammable gas or vapor that will propagate flame when exposed to a source of ignition. Many common flammable liquids have very wide explosive ranges. The explosive range of all flammable gases and vapors will vary with temperature and pressure.

Upper Explosive Limit (UEL) or Upper Flammable Limit (UFL)This is the maximum concentration of gas or vapor in air that will combust. Any higher percentage of combustible gas or lower amount of oxygen in the mixture of the two will make the mixture too “rich” to sustain combustion.

Vapor DensityThis is the relative density of the vapor as compared with air. It is calculated as the ratio of the molecular weight of the vapor to the molecular weight of air. A vapor density less than one indicates a substance lighter than air; conversely, densities greater than one indicates a substance heavier than air.

Common Flammable Industrial GasesFor our purpose, we will use the term “industrial gases” to refer to a variety of compressed gases and liquids used in manufacturing processes. Under this definition, a particular gas may have a variety of applications, such as a source of heat or power generation or as a solvent or for medical applications. As a rule, these gases and liquids are manufactured elsewhere and then transported to and stored at the end users’ facility. We will limit our consideration to flammable gases. A flammable gas is one that can burn when brought in contact with heat or flame. A flammable compressed gas is one in which a mixture of 13 percent or less (by volume) with air is flammable or the flammable range with air is under 12 percent. Under certain conditions, flame velocities of these gases after ignition can progress to detonation speeds producing violent explosions and damage.

AcetyleneAcetylene is colorless and odorless in its pure state, lighter than air, and highly flammable. Its low LFL and wide flammability range make it extremely easy to ignite. In the presence of moisture, acetylene can react with copper, silver, and mercury to form metallic acetylates that are shock-sensitive, explosive compounds.

HydrogenHydrogen is a highly flammable, extremely light elemental gas with a wide flammability and explosive range. It also has low ignition temperature and low minimum ignition energy. Static electricity can ignite leaking or venting hydrogen.

Liquefied Petroleum Gas (LPG)This is the generic name for a number of low-pressure, liquefied hydrocarbon gases. The most common are butane and propane. They are readily liquefied by pressurizing at atmospheric temperatures and are used in the vapor phase as a fuel with air or oxygen.

Flammable and Combustible Liquids

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Almost every industrial plant has some quantity of flammable and combustible liquids stored in its facility. A flammable liquid is defined as one having a flash point below 100°F (37.8°C) with a vapor pressure not exceeding 40 psi (276 kPa). They are volatile in nature, constantly giving off heavier-than-air vapors that cannot be seen with the naked eye. Combustible liquids have a flash point at or above 100°F (37.8°C). When heated above their flash points, these liquids take on many of the characteristics of flammable liquids.

One significant difference between flammable and combustible liquids concerns the behavior of their vapors. Vapors from flammable liquids tend to flow along slopes and inclines, much like a liquid, and collect in low areas. Vapors from combustible liquids, on the other hand, do not readily travel away from the source of a leak or spill unless the atmospheric temperature remains above the flash point of the liquid. This distinction must be taken into account when determining sensor use and positioning because liquids themselves do not burn or explode; the flammable vapors resulting from evaporation that do. The site of the spill or leak may not be the only zone of danger.

In evaluating the hazardous potential of a particular liquid, the flash point generally is considered the most important criterion to consider. However other factors – ignition temperature, explosive range, vapor density, and rate of evaporation – have a bearing on the liquid’s hazardous potential. For example, the concentrations of a vapor in air determine the intensity of an explosion. Concentrations near the lower and upper limits of flammability are less violent than those occurring when concentrations are near the median range.

FLAMMABLE DUSTS AND FIBERSSource: OSHA SHIB 07-31-2005 “Combustible Dust in Industry: Preventing and Mitigating the Effects of Fire and Explosions”

Elements of a Dust Explosion

Elements needed for a fire (the familiar "Fire Triangle"):1. Combustible dust (fuel)2. Ignition source (heat) 3. Oxygen in air (oxidizer)

Additional elements needed for a combustible dust explosion:4. Dispersion of dust particles in sufficient quantity and concentration 5. Confinement of the dust cloud

The addition of the latter two elements to the fire triangle creates what is known as the "explosion pentagon." If a dust cloud (diffused fuel) is ignited within a confined or semi-confined vessel, area, or building, it burns very rapidly and may explode. The safety of employees is threatened by the ensuing fires, additional explosions, flying debris, and collapsing building components.

An initial (primary) explosion in processing equipment or in an area where fugitive dust has accumulated may shake loose more accumulated dust, or damage a containment system (such as a duct, vessel, or collector). As a result, if ignited, the additional dust dispersed into the air may cause one or more secondary explosions. These can be far more destructive than a primary explosion due to the increased quantity and concentration of dispersed combustible dust.

If one of the elements of the explosion pentagon is missing, a catastrophic explosion cannot occur. Two of the elements in the explosion pentagon are difficult to eliminate: oxygen (within air), and confinement of the dust cloud (within processes or buildings). However, the other three elements of the pentagon can be controlled to a significant extent, which will be discussed further in this document.

Facility Dust Hazard AssessmentA combustible dust explosion hazard may exist in a variety of industries, including: food (e.g., candy, starch, flour, feed), plastics, wood, rubber, furniture, textiles, pesticides, pharmaceuticals, dyes, coal, metals (e.g., aluminum, chromium, iron, magnesium, and zinc), and fossil fuel power generation. The vast majority of natural and synthetic

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organic materials, as well as some metals, can form combustible dust. NFPA’s Industrial Fire Hazards Handbook states that "any industrial process that produces a combustible material and some normally noncombustible materials to a finely divided state presents a potential for a serious fire or explosion."

Facility Analysis ComponentsFacilities should carefully identify the following in order to assess their potential for dust explosions:

Materials that can be combustible when finely divided Processes that use, consume, or produce combustible dusts Open areas where combustible dusts may build up Hidden areas where combustible dusts may accumulate Means by which dust may be dispersed in the air Potential ignition sources

The applicable federal, state, and local laws and regulations must be identified and followed. The two predominant model fire codes that have been adopted by many jurisdictions in the US are the International Code Council’s International Fire Code and NFPA’s Uniform Fire Code. Both of these model codes reference many of the NFPA consensus standards related to dust explosion prevention and mitigation, which are discussed below. In the absence of a legal mandate to comply with these consensus standards, they should be considered a very useful source of guidance on this topic.

Dust CombustibilityThe primary factor in an assessment of these hazards is whether the dust is in fact combustible. Any "material that will burn in air" in a solid form can be explosive when in a finely divided form. Combustible dust is defined by NFPA 654 as: "Any finely divided solid material that is 420 microns or smaller in diameter (material passing a U.S. No. 40 standard sieve) and presents a fire or explosion hazard when dispersed and ignited in air." The same definition is used for combustible metal dust in NFPA 484, Standard for Combustible Metals, Metal Powders, and Metal Dusts. One possible source for information on combustibility is the Material Safety Data Sheet (MSDS) for the material. In some cases, additional information such as test results will be available from chemical manufacturers.

Different dusts of the same chemical material will have different ignitability and explosive characteristics, depending upon many variables such as particle size, shape, and moisture content. Additionally, these variables can change while the material is passing through processing equipment. For this reason, published tables of dust explosive data may be of limited practical value. In some cases, dusts will be combustible even if the particle size is larger than that specified in the NFPA definition, especially if the material is fibrous.

Industrial settings may contain high-energy ignition sources such as welding torches. In these situations, test methods for dust ignition and explosion characteristics from ASTM International (originally the American Society for Testing and Materials) would be of value. A discussion of these test methods is in reference 8, and the relevant OSHA and other standards are listed in the "Sources of Additional Information" section of this document.

Electrical ClassificationThe facility analysis must identify areas requiring special electrical equipment classification due to the presence (or potential presence) of combustible dust.

Other Hazard Analysis ConsiderationsThe amount of dust accumulation necessary to cause an explosive concentration can vary greatly. This is because there are so many variables – the particle size of the dust, the method of dispersion, ventilation system modes, air currents, physical barriers, and the volume of the area in which the dust cloud exists or may exist. As a result, simple rules of thumb regarding accumulation (such as writing in the dust or visibility in a dust cloud) can be subjective and misleading. The hazard analysis should be tailored to the specific circumstances in each facility and the full range of variables affecting the hazard.

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Many locations need to be considered in an assessment. One obvious place for a dust explosion to initiate is where dust is concentrated. In equipment such as dust collectors, a combustible mixture could be present whenever the equipment is operating. Other locations to consider are those where dust can settle, both in occupied areas and in hidden concealed spaces. A thorough analysis will consider all possible scenarios in which dust can be dispersed, both in the normal process and potential failure modes.

After hazards have been assessed and hazardous locations are identified, one or more of the following prevention, protection, and/or mitigation methods may be applied. The references and information sources at the end of this document will assist in the decision process for the methods suitable to specific work sites. Additional guidance and requirements may be available from local or state fire and building code officials, as well as OSHA area or regional offices.

Dust ControlNFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, contains comprehensive guidance on the control of dusts to prevent explosions. The following are some of its recommendations:

Minimize the escape of dust from process equipment or ventilation systems Use dust collection systems and filters Utilize surfaces that minimize dust accumulation and facilitate cleaning Provide access to all hidden areas to permit inspection Inspect regularly for dust residues in open and hidden areas Clean dust residues regularly Use cleaning methods that do not generate dust clouds if ignition sources are present Only use vacuum cleaners approved for dust collection Locate relief valves away from dust hazard areas Develop and implement a hazardous dust inspection, testing, housekeeping, and control program (preferably in

writing with established frequency and methods).

The OSHA ventilation standard, 29 CFR 1910.94, contains ventilation requirements for certain types of operations (such as abrasives, blasting, grinding, or buffing) which involve dusts, including combustible dusts. Additionally, 29 CFR 1910.22(a) (1) requires employers to keep work places and other areas clean, which includes the removal of dust accumulations.

Ignition ControlNFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, also contains comprehensive guidance on the control of ignition sources to prevent explosions. The following are some of its recommendations:

Use appropriate electrical equipment and wiring methods Control static electricity, including bonding of equipment to ground Control smoking, open flames, and sparks Control mechanical sparks and friction Use separator devices to remove foreign materials capable of igniting combustibles from process materials Separate heated surfaces from dusts Separate heating systems from dusts Proper use and type of industrial trucks Proper use of cartridge activated tools Adequately maintain all the above equipment

The use of proper electrical equipment in hazardous locations is crucial to eliminating a common ignition source. The classification of areas requiring special electrical equipment is discussed in the Facility Dust Hazard Assessment section above. Once these areas have been identified, special Class II wiring methods and equipment (such as "dust ignition-proof" and "dust-tight") must be used as required by 29 CFR 1910.307 and as detailed in NFPA 70 Article

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500. It is important not to confuse Class II equipment with Class I explosion-proof equipment, as Class II addresses dust hazards, while Class I addresses gas, vapor, and liquid hazards.

EQUIPMENT IGNITION SOURCES

Ignitions, though exceptionally rare, have been proven in a number of cases to have been caused by mobile equipment working in or around a facility that manufactures, processes, stores, or distributes flammable materials. Ignition sources that can be found on most powered industrial equipment are:

a) Arcing and sparking of unprotected electrical component Arcs or sparks may arise from unprotected electrical equipment such as starters, batteries, instrumentation, switches, sensors, and motors.

b) Hot surfaces (including brakes) The surface temperature of the engine, exhaust, electrical equipment, brakes, and any other “hot spots” on the equipment should be kept below the lowest ignition temperature of any flammable materials likely to be encountered.

c) Sparks from static build up, friction or impact Non-electrical items can cause electrostatic build up or frictional sparks by rubbing or impact.

d) Flames or sparks from the exhaust system Internal combustion engine powered equipment run the risk of backfiring or emitting hot carbon particles from the exhaust system.

e) Flames from the air inlet systemIf flammable vapor is drawn into the air inlet system, it may be ignited in the combustion chamber and blow back through the inlet manifold.

f) Engine over-speeding and overloadIngestion of flammable vapor also may result in over-speeding of the engine. Such overload conditions may lead to hot surfaces or flames, and damage or destruction of the engine.

g) Human errorThis includes equipment misuse, faulty repairs, uncorrected wear and tear and, incorrect area classifications.

PRECAUTIONS FOR IC POWERED (DIESEL) INDUSTRIAL EQUIPMENTa) Elimination or protection of electrical equipment Arcs or sparks may arise from unprotected electrical equipment such as starters, batteries, and instrumentation. The vehicle should be supplied with electrical equipment suitable for use in explosion hazardous areas, depending

on the level of protection required. The temperature classification of the equipment should be appropriate for the range of gases and vapors likely to be encountered.

Care should be taken to ensure that vulnerable items, such as lights, are durable enough to withstand damage. Electrical equipment may be eliminated by the use of mechanical alternatives, for example mechanical fuel,

temperature, and pressure gauges or starters operated by spring recoil, hydraulic fluid, or compressed air (ensuring the mechanical alternatives do not pose an ignition source themselves).

Vehicles may be fitted with electric starters which are specially wired to a plug and socket connection for use with a starter battery that is stored and used in a safe area.

b) Control of surface temperature The surface temperature of the engine, exhaust, electrical equipment, brakes, and any other “hot spots” on the

equipment should be kept below the lowest ignition temperature of any flammable materials likely to be encountered. The supplier will provide details of the maximum surface temperature the equipment may reach.

The exhaust manifold and associated piping may be cooled by using a water jacket or water-cooled heat exchanger, or by passing the exhaust gases through a water bath. Water levels should be monitored regularly and maintained at the recommended level.

Air cooling may be provided for hot spots such as the friction surfaces of brakes and clutches and the outer casings of electrical equipment. In extreme cases (for example, equipment required for heavy work-cycles in an

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area where materials with a low ignition temperature are present), oil-filled or labyrinth-type brake enclosures may be required.

Thermal sensors may be used to detect overheating, as well as to trigger audible or visual alarms and to provide automatic shutdown of the engine and equipment.

The use of standard insulation cladding to provide protection from hot surfaces is not recommended because it is liable to be damaged and may be penetrated by flammable liquids and vapors.

c) Elimination or protection of spark-producing components Non-electrical items can cause electrostatic or frictional sparks by rubbing or impact. Therefore, adequate

clearance is needed between fixed and rotating parts, with allowance made for engine movement during normal operation. Engine-cooling fans often are made from non-metallic material such as anti-static plastic.

The use of aluminum, magnesium, titanium, and light alloys generally is minimized because of the risk of sparks from a thermal reaction (this may occur on impact between light metals and rust). If such components are used, they must be shielded from impact by an enclosure. Surface coatings incorporating these materials normally are considered unsuitable.

The risks of sparks from static build-up are minimized by the use of electrically conductive or anti-static materials for drive belts, tires, and other components.

The forks of lift trucks may cause frictional sparks when they contact a metal drum or other object or are allowed to impact on concrete floors. They often are fitted within brass or stainless steel sleeves.

d) Prevention of spark emission from the exhaust system A spark arrester fitted between the flame arrester and the atmosphere will prevent sparks from being emitted from

the exhaust system. Spark arresters are designed to trap (usually in a series of baffles) hot burning particles, normally of carbon, emitted from a sooty engine.

Suppliers generally will supply certification demonstrating that spark arresters have been tested against recognized standards.

e) Prevention of flashback from the air inlet system If flammable vapor is drawn into the air inlet system, it may be ignited in the combustion chamber. A flame

arrester is used to prevent flashback to the atmosphere. A flame arrester is a device containing narrow passages or apertures through which the flame will be extinguished before it reaches the atmosphere.

The inlet system is constructed, tested, and certified to withstand the pressures generated from an ignition. The inlet system ensures that the flame must pass through the flame arrester, thus ensuring that the flame is extinguished safely.

To remain effective, flame arresters should be cleaned regularly. Sharp objects should not be inserted into the flame arrester element as this may cause damage and impair its performance.

f) Prevention of flashback from the exhaust system If flammable vapor is drawn into the air inlet system, it may be ignited in the combustion chamber and backfire

through the exhaust system. A flame arrester is used to prevent flashback to atmosphere. The exhaust system is constructed, tested, and certified to withstand the pressures generated from an ignition. The

exhaust system ensures the flame must pass through the flame arrester, thereby ensuring that the flame is extinguished safely.


g) Vapor ingestion and over-speeding (also known as runaway engine) Ingestion of flammable vapor also may result in over-speeding of the engine. Such over-speed conditions may

lead to hot surfaces or flames, and may damage or destroy the engine. Turning off the fuel supply alone may not stop the engine, as it may continue to run on the ingested vapor.

An air inlet shutoff valve can be used to stop the engine if vapor ingestion leads to over-speeding. The valve may be operated manually by the driver or automatically after detection of engine over-speed. Automatic shutdown

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may be triggered either by a differential pressure sensor or by a speed detection device. In both methods, it is important that the operating parameters are set according to the supplier’s instructions.

h) Gas detection system (helps reduce risks due to human error) This method of protection applies to vehicles (both electric and diesel powered) that operate in Zone 2 areas only.

If flammable vapor or gas is detected by the system, the vehicle is shut down automatically. The gas detection system itself is constructed to an explosion proof standard. It should normally be set to activate

shutdown at a maximum of 20 or 25 percent of the lower explosive limit (LEL) of the gas or vapor likely to be encountered (or representative gas). If there are several potential gas or vapor hazards, then it is important to check with the supplier that the setting is suitable for all the materials used. A setting corresponding to 20 to 25 percent of the LEL for propane generally is satisfactory for the majority of gases and vapors.

It may be useful to have an early warning alarm (audible and/or visual) set at a lower level (for example 10 percent) to enable the vehicle to be driven away from the source of the vapor before automatic shutdown occurs.

If automatic shutdown does occur, then it should not be possible to restart the vehicle until the detection system has retested the atmosphere and confirmed that the gas hazard has dispersed. If there is a possibility that the flammable gas may be trapped inside enclosures on the vehicle, these should be purged before the vehicle and/or engine is restarted. Some systems may be fitted with an automatic purge. As a rule, restart of the engine should not be attempted until the cause of the shutdown has been investigated and rectified (for example, spills should be cleaned up before the engine is restarted).

Regular testing and maintenance of the gas sensing devices is necessary, as they may suffer catalyst poisoning from airborne contaminants, blockage of the sensing paths, or calibration drift. Some systems incorporate a compulsory gas response test before the vehicle can be put into use.

The safety of this type of system depends on its response time. Clearly, it is essential that the vehicle has shut down before flammable vapors can reach potential sources of ignition. All components that may produce sparks or hot spots are therefore enclosed to limit the rate of access of flammable vapors. These enclosures are designed and tested to prevent the entry of flammable concentrations of vapor for at least 60 seconds after the gas detection system alarm has been activated. The covers may be fitted with locking devices to prevent casual access.

PRECAUTIONS FOR BATTERY POWERED LIFT TRUCKS

Ignition hazardsThe main ignition hazards from electric vehicles are the arcing and sparking of unprotected electrical components, hot surfaces, and sparks from static buildup of friction.

Protection methodsThere are two approaches to the protection of battery-powered trucks for use in potentially flammable atmospheres. The first approach is to ensure that the truck is fully protected to EX standard. The second approach is to use a gas detection system, which will automatically shut down the truck in the event of a spill or release of flammable vapor. The use of a gas detection system is only suitable for trucks operated in flammable gas and liquids hazardous areas.

Electrical protectionFull electrical protection is provided primarily for trucks designed to operate in Zone 1 areas. Motors and other electrical components that are arcing or sparking in normal operation are housed in explosion-proof enclosures. For switches and control circuits outside the enclosure, a method of protection is to use low energy (intrinsic safety) circuits that ensure the power is no longer ignition capable. The battery and battery connections also are explosion-protected.

Gas detection systemAnother protection method is to use a gas detection system, which triggers automatic shutdown of the truck in the event of a release of flammable vapors.

Other precautions

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a) Thermal sensors are used to detect overheating under overload or fault conditions and are linked to the alarm and automatic system shutdown.

b) Measures to prevent sparking from static buildup or from friction also may be necessary. c) The changing and charging of batteries may result in sparks; therefore, these operations should be carried out in

nonhazardous areas.

PROTECTION METHODS FOR POWERED INDUSTRIAL EQUIPMENT USED IN CLASS I, DIVISION 1 OR ZONE 0 EXPLOSION HAZARDOUS AREASIn areas where ignitable concentrations of flammable gases, vapors, or liquids are LIKELY TO EXIST MOST OF THE TIME under normal operating conditions, the risk of reaching igniting levels of flammables is EXTREMELY HIGH.

United States classification: Class I, Division 1 International classification: Zone 0 Estimated time of exposure to hazardous gas, vapor, or liquid: greater than 1000 hrs/yr

The used of powered industrial equipment is not allowed in these areas.

PROTECTION METHODS FOR POWERED INDUSTRIAL EQUIPMENT USED IN CLASS I, DIVISION 1 OR ZONE 1 EXPLOSION HAZARDOUS AREASIn areas where ignitable concentrations of flammable gas, liquids, or vapors are LIKELY TO EXIST SOME OF THE TIME under normal operating conditions, the risk of encountering igniting levels of flammables in these areas is HIGH.

United States classification: Class I, Division 1. International classification: Zone 1 Estimated time of exposure to explosive gas, liquids, or vapors atmospheres: 100–1000 hrs/yr

The use of Class I, Division 1 or Zone 1 certified powered industrial equipment is allowed in Class I, Division 1 explosion hazardous areas. Protection methods focus on the actual operation of the equipment in explosion hazardous atmospheres. Due to the level of protection required, only electric and diesel powered equipment can be modified for the use in these potentially volatile areas.

Class I, Division 1 or Zone 1 approved equipment protection methods

IdentificationBesides the standard required equipment information, the ID tag shall provide detailed information regarding the manufacturer, the temperature class, gas group protection, and hazardous area suitability rating.

Surface temperaturesThe surface temperature of the engine, exhaust, drive or hydraulic motors, electrical equipment, brakes, and any other “hot spots” on the truck should be kept below the lowest ignition temperature of any flammable materials likely to be encountered.

The maximum surface temperatures allowed depends upon the hazardous gas, vapor, or liquids that the equipment will encounter; T3 (200oC/392oF) or T4 (135 oC/275oF) are common limits for these hazardous areas.

Cooling and temperature monitoring of equipment “hotspots”The exhaust manifold and associated piping may be cooled by using a water jacket or water-cooled heat exchanger or by passing the exhaust gases through a water bath. Water levels should be monitored regularly and maintained at the recommended level. (The waste residues from cleaning the water bath cooling system may pose a health and environmental hazard.)

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Air cooling may be provided for hot spots such as the friction surfaces of brakes and clutches and the outer casings of electrical equipment. In extreme cases (for example, a truck required for heavy work-cycles in an area where materials with low ignition temperatures are present), oil-filled or labyrinth-type brake enclosures may be required.

Thermal sensors should be used to detect overheating of potential hotspots. These thermal sensors must trigger audible or visual alarms and provide automatic shutdown of the equipment when necessary.

EX enclosuresAll sparking and arcing electrical components must be housed in approved explosion proof enclosures. This includes controllers, DC motors, Zener barriers, contactors, and fuses. The EX enclosures must be approved for the areas in which they are used.

Special purpose EX enclosuresDrive motors, starter motors, alternators, auxiliaries (lights, etc), instruments, and all other spark, arc, or heat generating components must be housed in approved custom EX housing. The EX enclosures must be approved for the areas in which they are used. .

Increased safety enclosuresIncreased safety enclosures are water and dust ingress protected, yet not EX approved. Increased safety enclosures cannot withstand an internal explosion and are therefore used only where the equipment inside does not generate sparks or high temperatures such as connector or termination boxes for wiring in Class I, Division 1 or Zone 1 explosion hazardous areas.

EncapsulationEncapsulation is a process that hermetically seals and enclose electrical components in an approved compound. Encapsulation seals the components/parts completely from the outside atmosphere. Encapsulated components cannot be repaired and must be replaced in their entirety when defective. Parts that are suitable for encapsulation are controllers, interface PCBs, and solenoid valves coils.

WiringThe following wiring methods are suitable for use in industrial equipment that is used in Class I, Division 1 or Zone 1 explosion hazardous areas. Installation and application should be in accordance with codes and regulations. Conduit and flexible conduit Mineral insulated (MI) cable MC-HL cable Extra hard duty flexible cable

Due to cable movement and restricted compartment space, the use of Conduit, MI, or MC-HL cable often is not practical when converting mobile industrial equipment. Due to these limitations, the use of extra hard duty flexible conductors is a suitable alternative when wiring equipment. It is important that flexible cables are protected from impact and are placed within the chassis of the equipment. When using extra hard duty flexible cable, it is critical that the conductor is protected from impact by the steel body of the equipment. All enclosure entries must be through approved EX cable glands or cable seals.

Intrinsically safe (IS) wiring, circuits, or apparatusIntrinsically safe wiring, circuits, or apparatus are unable to create arcs or sparks capable of igniting a flammable gas or vapor. Intrinsically safe wiring is used predominantly for the operational functions of the equipment. Intrinsically safe wiring, circuits or apparatus must be protected through an approved Zener barrier type interface.

Cable glands or sealsEX approved cable glands or seals must be used for cable entries into certified enclosures. Cable glands are preferred due to their ease of use, and the fact that they offer guaranteed seal without the need for special skills. Care must be given to the fact that overtightening of approved cable glands might lead to cable damage.

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Frame leakage detection/monitoringA frame leakage detection system should continuously monitor the chassis potential to detect leakage of either battery positive or negative to the chassis.

Frame leakages can be caused by: Carbon dust deposits built up inside EX DC motors Liquid (electrolyte or water) within the battery case A trapped or exposed electrical conductor touching a metal component

Frame leakage can result in the creation of sparks and arcs and should therefore be monitored

Flame arrestorsIf flammable vapors are drawn into the air inlet system, they may be ignited in the combustion chamber. A flame arrester is a device containing narrow passages or apertures through which gases or vapors can flow but that are too small for a flame to pass through. Flame arresters also are used to prevent flames from the exhaust system from reaching the outside atmosphere. Use of approved flame arresters is required to guarantee the prevention of flashback from the inlet or exhaust system into atmosphere. Approved flame arrestors are designed to withstand internal explosions.


Spark arrestorsA spark arrester fitted between the flame arrester and the atmosphere will prevent sparks from being emitted from the exhaust system. Spark arresters are designed to trap (usually in a series of baffles) hot burning particles, normally of carbon, emitted from a sooty engine. Spark arrestors must be approved for use in the explosion hazardous area in which it will be deployed.

Vapor ingestion and over-speeding (also known as runaway engine)Ingestion of flammable vapor may result in over-speeding of the engine. Such over-speed conditions may lead to hot surfaces or flames, and may damage or destroy the engine. Turning off the fuel supply alone may not stop the engine, as it may continue to run on the ingested vapor. An air inlet shutoff valve can be used to stop the engine if vapor ingestion leads to over-speeding.

Elimination or protection of spark-producing components and static buildup:Non-electrical items can cause electrostatic or frictional sparks by rubbing or impact. Therefore, adequate clearance is needed between fixed and rotating parts, with allowance made for engine movement during normal operation. Engine-cooling fans often are made from non-metallic material such as plastic. The risks of sparks from static buildup are minimized by the use of electrically conductive materials for drive belts, tires, and other components. The use of aluminum, magnesium, titanium, and light alloys generally is minimized because of the risk of sparks from a thermal reaction (this may occur on impact between light metals and rust). If such components are used, they must be shielded from impact by an enclosure. Surface coatings incorporating these materials normally are considered unsuitable.

Protection of load contact and impact pointsThe load contact points (forks or clamp surfaces) of lift trucks may cause frictional sparks when they contact a metal drum, the ground, or another object. They often are fitted within brass or stainless steel sleeves. The risk of high velocity impact sparks is extremely low. Protecting the entire machine with a non-sparking “bumper” is impractical in most cases, while the use of a two-inch wide quarter-inch thick bumper on the furthest extruding points of the equipment offers a false sense of security. This can be proven easily by analyzing the wear, tear, and paint damage shown on equipment that has been in operation for a period of time.

Batteries and connectors

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Only approved EX batteries should be used on equipment used in Class I, Division 1 or Zone 1 explosion hazardous areas. It is impossible to house batteries in EX-rated housing because they require ventilation. The design of the approved batteries is such that it minimizes the chances of creating a spark due the special cell construction, inter-cell connections, locking battery lids, and special battery connectors. Batteries must be tested and certified for use in the explosive areas in which they operate. BATTERIES NEVER SHOULD BE DISCONNECTED OR CHARGED IN EXPLOSION HAZARDOUS AREAS.

Battery connectors must be approved for use in Class I, Division 1 or Zone 1 hazardous environments and must be locked in place. Connectors never should be opened in ANY hazardous area.

PROTECTION METHODS FOR POWERED INDUSTRIAL EQUIPMENT USED IN CLASS I , DIVISION 2 OR ZONE 2 EXPLOSION HAZARDOUS AREASIn areas where ignitable concentrations of flammable gas, liquids, or vapors MIGHT BUT ARE NOT LIKELY TO EXIST (less than 100 hrs/yr) under normal operating conditions, the risk of encountering igniting levels of flammables in these areas is LOW; however, ignition risks are equivalent to those found in any explosive atmosphere after an accidental release or spill takes place.

United States classification: Class I, Division 2 International classification: Zone 2 Estimated time of exposure to explosive gas, liquids or vapors atmospheres: less than 100 hrs/yr

Allowed equipment recommendationOnly approved and certified diesel and electric powered equipment should be operated in Class I, Division 2 explosion hazardous areas. The protection of diesel powered equipment is very similar to that of Class I, Division 1 or Zone 1 equipment, with differences only reflected in the protection of the electrical components. Adding integrated gas detection with automatic shutdown to equipment used in Class I, Division 2 or Zone 2 explosion hazardous areas will guarantee equipment shutdown before an explosive atmosphere develops.

Class I, Division 2 or Zone 2 approved equipment protection methods

IdentificationBesides the standard required equipment information, the ID tag shall provide detailed information regarding the manufacturer, the temperature class, gas group protection, and hazardous area suitability rating.

Surface temperaturesThe surface temperatures of the engine, exhaust, drive or hydraulic motors, electrical equipment, brakes and any other “hot spots” on the powered industrial equipment should be kept below the lowest ignition temperature of any flammable materials likely to be encountered.

Cooling and temperature monitoring of equipment “hot spots”Cooling of internal combustion equipment “hot spots” faces the same challenges and protection principles as equipment used in Class I, Division 1 or Zone 1 hazardous locations. The exhaust manifold and associated piping may be cooled by using a water jacket or water-cooled heat exchanger or by passing the exhaust gases through a water bath. Water levels should be monitored regularly and maintained at the recommended level. (The waste residues from cleaning the water bath cooling system may pose a health and environmental hazard.)

Air cooling may be provided for hot spots such as the friction surfaces of brakes and clutches and the outer casings of electrical equipment. In extreme cases (for example, a truck required for heavy work-cycles in an area where materials with low ignition temperatures are present), oil-filled or labyrinth-type brake enclosures may be required.

The use of approved thermal barriers is allowed if this material is approved and permanently attached the parts or components protected by this barrier.

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Thermal sensors should be used to detect overheating of potential hot spots. These thermal sensors must trigger audible or visual alarms and provide automatic shutdown of the equipment when necessary.

Increased safety enclosuresThese are approved for use in Class I, Division 2 or Zone 2 flammable areas. Increased safety enclosure cannot withstand an internal explosion, but are used where the internal components are non-spark generating and do not create high temperatures.

Other enclosures following an approved standardThe use of approved enclosed components that prevent contact of the arcing and sparking components with the outside atmosphere must be used on Class I, Division 2 or Zone 2 equipment; especially if used in conjunction with an approved gas detection system.

Special enclosure designs following an approved standard or conceptIn some applications, for example DC motors used in Class I Division 2 explosive hazardous areas, the motor must be uniquely modified and sealed to form an enclosure as they contain sparking and arcing components.

Class I, Division 2 or Zone 2 approved AC motors may not require to be sealed since they should not contain sparking or arcing components. Determination of suitability is based on a technical risk assessment.

All enclosures should be tested and certified for use in Class I, Division 2 or Zone 2 hazardous areas.

Encapsulation:Encapsulation is the enclosure of an arcing or sparking electrical component or part in an approved compound that hermetically seals the component/part from the outside atmosphere. Encapsulation is an accepted and approved method of protection for Class I, Division 2 or Zone 2 explosion hazardous areas.

WiringAll types of approved wiring can be used on Class I, Division 2 or Zone 2 approved equipment. It is important that all wiring is protected from impact by the chassis of the equipment or a metal guard. All enclosure entries must be through approved cable glands. Installation of the wiring must be in accordance with applicable electrical codes and regulations.

Nonincendive wiring, components, or equipmentApproved nonincendive wiring, components, or equipment are incapable, under normal operating conditions, of causing an arc or spark that will ignite a flammable material. Approved nonincendive components and wiring can be utilized in Class I, Division 2 or Zone 2 explosion hazardous areas.

Cable glands or sealsApproved cable glands or seals must be used for cable entries into certified enclosures. Care must be not to over-tighten cable glands as this may lead to cable damage.

Flame arrestorsIf flammable vapors are drawn into the air inlet system, they may be ignited in the combustion chamber. A flame arrester is a device containing narrow passages or apertures through which gases or vapors can flow but which are too small for a flame to pass through. Flame arresters also are used to prevent flames from the exhaust system from reaching the outside atmosphere. Use of flame arresters is required to assure prevention of flashback from the inlet or exhaust system into atmosphere.


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Spark arrestorsA spark arrester fitted between the flame arrester and the atmosphere will prevent sparks from being emitted from the exhaust system. Spark arresters are designed to trap (usually in a series of baffles) hot burning particles, normally of carbon, emitted from a sooty engine. Spark arrestors must be approved for use in the explosion hazardous area in which it will be deployed.

Vapor ingestion and over-speedingIngestion of flammable vapor may result in over-speeding of the engine. Such over-speed conditions may lead to hot surfaces or flames, and may damage or destroy the engine. Turning off the fuel supply alone may not stop the engine, as it may continue to run on the ingested vapor. An air inlet shutoff valve can be used to stop the engine in vapor ingestion leads to over-speeding. For dust explosion hazardous areas (Class II, Divisions 1 & 2 or Zones 21 & 22), an air inlet dust filter must be added.

Elimination or protection of spark-producing components and static buildupNonelectrical items can cause electrostatic or frictional sparks by rubbing or impact. Therefore, adequate clearance is needed between fixed and rotating parts, with allowance made for engine movement during normal operation. Engine-cooling fans often are made from non-metallic material such as plastic. The risks of sparks from static buildup are minimized by the use of electrically conductive materials for drive belts, tires, and other components. The use of aluminum, magnesium, titanium, and light alloys generally is minimized because of the risk of sparks from a thermal reaction (this may occur on impact between light metals and rust). If such components are used, they must be shielded from impact by an enclosure. Surface coatings incorporating these materials normally are considered unsuitable.

Protection of load contact and impact pointsThe load contact points of powered industrial equipment may cause frictional sparks when they contact a metal drum or other object. The most common method of protecting load contact points is to plate them with a non-sparking material. This can be brass or stainless steel. Protecting the entire machine with a non-sparking “bumper” is impractical and cost prohibitive in most cases.

Batteries and connectorsSpecific OEM batteries may be use in Zone 2 equipment if they satisfy the requirements for Class 1, Division 2 or Zone 2. The battery plugs must be locked together if they are easily accessible to the operator. Batteries never should be disconnected or charged in explosion hazardous areas.

Gas DetectionA self-calibrating gas detection system with audible alarm and automatic equipment shutoff is recommended for powered industrial equipment used in Class I, Division 2 or Zone 2 explosive hazardous areas. Misuse, limited protection methods, wear and tear, equipment mobility, and human error all result in increased ignition risks. An equipment integrated gas detection system with automatic shutoff will prevent the operation of equipment in explosive atmospheres for which it is not properly protected, tested, or certified.

UNRATED AREAS WHERE FLAMMABLE GAS, VAPORS, OR LIQUIDS ARE HANDLED OR STOREDAreas where large concentrations of flammable gas, liquids or vapors are handled or stored in open air often are unrated. Exposure to explosive atmospheres is UNLIKELY under normal operating conditions.

Due to the lack of equipment protection requirements, if there is a release of flammable material, the risks of the unprotected equipment igniting the material is extremely high.

History has shown that these unrated or “safe” areas in facilities handling flammable gases or liquids are the locations most susceptible to a catastrophic event or incident. “Industrial Loader and Forklift Fires,” an NFPA report published in January 2009, states that between 2003 and 2006, an average of 1,340 fires were ignited by heat or ignition sources found on powered industrial loaders and forklift.

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Examples of these areas are: Manufacturing, storage and shipping/receiving areas inside a facility handling flammable material Property surrounding facilities that handle or store flammable materials All open air locations storing, handling and processing of flammable materials Fuel terminals Aircraft hangers

Gas detection systems with alarm and automatic equipment shutdownA gas detection system with automatic shutdown is recommended to be installed on all types of powered industrial equipment that operates in and around facilities that handle, process, manufacture, or store flammable gases, liquids, or vapors and that is not itself tested and certified for use in Class I, Division 1 or Zone 1 hazardous areas.

When flammable vapor or gases are detected by the system, the equipment should be shut down automatically before an ignitable atmosphere has developed, thereby significantly reducing or eliminating the chance of ignition by heat or other ignition sources from the powered industrial equipment.

The gas detection system itself must be constructed, tested, and certified according to a minimum of a Class I, Division 2 and/or Zone 2 standards. The gas detection system must be set to operate at a maximum of 20–25 percent of the lower explosive limit (LEL) of the gas or vapor likely to be encountered. If there are several potential gas or vapor hazards, then it is important to check with the supplier that the setting is suitable for all the materials on the premises. A setting corresponding to 20–25 percent of the LEL for propane generally is satisfactory for the majority of gases and vapors.

Note:20 percent LEL for equipment with no additional ignition source protection or surface temperature limitations25 percent LEL for equipment with some ignition source protection and monitored surface temperature limitation

The gas sensing head must be placed in close proximity to the most likely ignition sources on the equipment. In most cases, this will be the engine compartment or motor. On some equipment, it might be recommended to install a second gas detection head in the air inlet system (when the air intake is located at a significant distance from the engine compartment), or a secondary location with ignitable components may be created during normal operation (man-lifts, order pickers, etc.). At least one gas sensing head should be installed no more than 20 inches off the ground to ensure detection of flammable gases and vapors that are heavier then air.

An early warning alarm (audible and/or visual) set at a lower level (for example 10 percent), which enables the equipment to be driven away from the gas or vapor source before automatic shutdown occurs, is recommended.

If automatic shutdown occurs, then it should not be possible to restart the vehicle until the detection system has retested the atmosphere and confirmed that the gas or vapor hazard has dispersed. There is a possibility that the flammable gas may be trapped inside enclosures on the vehicle. It is recommended that enclosures are purged and potential gas pockets are ventilated before the equipment is restarted. Restart of the engine should not be attempted until the cause of the shutdown has been investigated and rectified (for example, spills should be cleaned up before the engine is restarted). Approved and independent gas/LEL detection systems should be utilized to ensure the safety of the environment before a restart of the equipment is attempted.

Regular testing and maintenance of the gas detection devices is necessary as they are liable to catalyst poisoning from airborne contaminants. Ideally, the systems will incorporate a compulsory gas response and calibration test every time before the equipment can be put into use. This will prevent the use of unprotected equipment and floating of the detection levels.

It is essential that the equipment is shut down before flammable vapors can reach potential equipment ignition sources. Because in most cases none of the components of the equipment protected by the gas detection system have any additional safeguards against equipment ignition sources, a gas detection system with automatic

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shutdown will eliminate only 90 percent of all ignition sources found on powered industrial equipment. The only ignition sources not be immediately affected by equipment shutdown are surfaces temperatures or hot spots.

By shutting down equipment automatically before ignitable levels of flammable gas or vapors develop, the following ignition sources will be eliminated by de-energizing the equipment:

Arcing and sparking of unprotected electrical component Sparks from static buildup, friction, or impact Flames or sparks from the exhaust system Flames from the air inlet system Hot surfaces (including brakes) Engine over-speeding and overload

Gas detection with automatic shutdown risk reductionUtilizing gas detection with an automatic shutdown as an equipment protection method will provide significant risk reduction by virtually eliminating the risk of human error.

By taking the decision to shut down equipment away from the operator, risk of ignition because of the following liabilities will be addressed when shutdown takes place:

Human error Equipment non compliant and/or faulty repairs Sparks resulting from equipment wear and tear Sparks resulting from component failure

Inhalation of (high levels of) flammable gases and vapors is unhealthy for humans. Because equipment integrated gas detection systems monitor the atmosphere and alert the operator to increasing flammable materials levels, the chance of vacating the facility without being poisoned is increased significantly.

PROTECTION METHODS FOR POWERED INDUSTRIAL EQUIPMENT USED IN CLASS II & III, DIVISION 1 OR ZONE 20 EXPLOSION HAZARDOUS AREASIn areas where ignitable concentrations of flammable Dusts or fibers are LIKELY TO EXIST MOST OF THE TIME under normal operating conditions, the risk of igniting flammable materials through smoldering is HIGH.

United States classification: Class II or III, Division 1. International classification: Zone 20 Estimated time of exposure to hazardous dust/fiber: greater than 1000 hrs/yr

In most cases, very high density dust or fiber atmospheres makes operating equipment inside these areas impossible. One must be aware that once these high levels of dust are disturbed and particles become airborne, a Class II, Division 1 or Zone 21 environments can develop quickly.

PROTECTION METHODS FOR POWERED INDUSTRIAL EQUIPMENT USED IN CLASS II & III, DIVISION 1 OR ZONE 21 EXPLOSION HAZARDOUS AREASIn areas where ignitable concentrations of flammable dusts or fibers are LIKELY TO EXIST SOME OF THE TIME under normal operating conditions, the risk of igniting flammable materials is HIGH under the right conditions.

United States classification: Class II, Division 1. International classification: Zone 21

Estimated time of exposure to hazardous dusts or fibers: between 10–1000 hrs/yr

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Powered industrial equipment used in Class II, Division 1 or Zone 21 explosion hazardous areas requires extensive protection. Due to the level of protection required, only electric and diesel powered equipment can be modified for use in these potentially volatile areas. A major difference in protection against dust compared to gas is the fact that continued housekeeping plays a critical role in the safety of the equipment. Dust buildup on hot surfaces must be prevented by regular cleaning to prevent ignition and smoldering.

Class II, Division 1 or Zone 21 approved equipment protection methods

IdentificationBesides the standard requirement for equipment information, the ID tag shall provide detailed information regarding the manufacturer, the temperature class, hazardous material group, the hazardous area for which the equipment has been tested, certified, and approved, and the testing laboratory that conducted this testing.

Surface temperaturesThe surface temperature of the engine, exhaust, drive or hydraulic motors, electrical equipment, brakes, and any other “hot spots” on the truck should be kept 75°C below the lowest ignition temperature of any flammable materials likely to be encountered.

The maximum surface temperatures allowed depends upon the hazardous material that the equipment will encounter (see chart XYZ). It is recommended that no surface temperature exceeds the temperature class T3D or 200oC / 392oF for dust or fiber in these hazardous areas. This operating temperature allows the protection and certification of equipment for safe use in dust/fiber Groups E, F, or G in Class II, Division 2 or Zone 21 explosion hazardous areas.

Cooling and temperature monitoring of equipment “hot spots”The exhaust manifold and associated piping may be cooled by using a water jacket or water-cooled heat exchanger or by passing the exhaust gases through a water bath. Water levels should be monitored regularly and maintained at the recommended level. (The waste residues from cleaning the water bath cooling system may pose a health and environmental hazard.)

Air cooling may be provided for hot spots such as the friction surfaces of brakes and clutches and the outer casings of electrical equipment. In extreme cases (for example, a truck required for heavy work-cycles in an area where materials with a low ignition temperature are present), oil-filled or labyrinth-type brake enclosures may be required.

The introduction of catalytic converters has created extreme surface temperatures to IC powered industrial equipment. In general, the installation of catalytic converters should be avoided when equipment is used in dust or fiber hazardous environments.

Thermal sensors should be used to detect overheating of potential hotspots. These thermal sensors must trigger audible or visual alarms and provide automatic shutdown of the equipment when necessary.

The use of insulation cladding to provide protection from hot surfaces is not recommended because it is liable to be damaged and may be penetrated by liquids, dusts, and vapors, which can lead to corrosion of these parts.

EX enclosuresAll sparking and arcing electrical components must be housed in approved explosion proof enclosures. This includes controllers, Zener barriers, contacts, and fuses. The EX enclosures must be approved for the areas in which they are used. In Class II, Division 1 or Zone 21 explosion hazardous atmospheres, purged enclosures may be used.

Special purpose EX enclosuresDrive motors, starter motors, alternators, auxiliaries (lights, etc.), instruments, heater terminations, and all other sparks, arcs or heat generation components must be housed in approved custom EX housing.

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Steve Noakes, 12/23/09,

Need chart

Increased safety enclosuresIncreased safety enclosures are water and dust ingress protected yet not EX approved. Increased safety enclosures cannot withstand an internal explosion. These types of enclosures may be used in Class II, Division 1 or Zone 21 explosion hazardous areas only as connector boxes for wiring.

EncapsulationEncapsulation is the enclosure of an electrical component or part in an approved compound that hermetically seals the component/part from the outside atmosphere. Encapsulation is approved, but should be used only if other protection methods cannot be utilized. Encapsulated components cannot be repaired and must be replaced in their entirety when defective. Parts that are suitable for encapsulation are controllers and solenoid valves.

WiringThe following wiring methods are suitable for the use in industrial equipment that is used in Class II, Division 1 or Zone 21 explosive areas. Installation and application should be in accordance with codes and regulations.

Conduit and flexible conduit Mineral insulated (MI) cable MC-HL cable Extra hard duty flexible cable

Due to cable movement and restricted compartment space, the use of Conduit, MI, or MC-HL cable often is not practical when converting industrial equipment. When using extra hard duty flexible cable, it is imperative that the conductor is protected from impact by the steel body of the equipment. All enclosure entries and exits must be performed through approved EX-rated cable glands or cable seals.

Intrinsically safe (IS) wiring, circuits or apparatusWhere sealed components such as switches, sensors, etc., are not possible to source, intrinsic safety wiring principles can be used even for dust atmospheres. The low energy circuit prevents ignition capable sparks from the devices.

Cable glands or sealsApproved cable glands or seals must be used for enclosure cable entries. Cable glands are preferred due to their ease of use, and the fact that they offer guaranteed seal without the need for special skills. Care must be given to the fact that over tightening of approved cable glands might lead to cable damage.

Frame leakage detectionA frame leakage detection system continuously monitors the chassis potential to detect a leakage of either battery positive or negative to chassis.

Frame leakages can be caused by: Carbon dust deposits built up inside sealed motors Liquid (electrolyte or water) within the battery case A trapped or exposed electrical conductor touching a metal component

Frame leakage can result in the creation of sparks and arcs and should therefore be monitored.

Spark arrestorsA spark arrester is fitted between the engine and the atmosphere to prevent sparks being emitted from the exhaust system. Spark arresters are designed to trap (usually in a series of baffles) hot burning particles, normally of carbon, emitted from a sooty engine. Spark arrestors must be approved for use in the explosion hazardous area in which it will be deployed.

Air inlet filter

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An air filter with a two or more stage filter is located as close as possible to the engine inlet manifold and with efficiencies better or equal to 85 percent for the first stage and 95 percent for the second stage.

Elimination or protection of spark-producing components and static buildupNon-electrical items can cause electrostatic or frictional sparks by rubbing or impact. Therefore, adequate clearance is needed between fixed and rotating parts, with allowance made for engine movement during normal operation. Engine-cooling fans often are made from non-metallic material such as plastic. The risks of sparks from static buildup are minimized by the use of electrically conductive materials for drive belts, tires and other components. The use of aluminum, magnesium, titanium, and light alloys generally is minimized because of the risk of sparks from a thermal reaction (this may occur on impact between light metals and rust). If such components are used, they must be shielded from impact by an enclosure. Surface coatings incorporating these materials normally are considered unsuitable.

Protection of load contact and impact pointsThe forks of lift trucks may cause frictional sparks when they contact a metal drum, ground, or other object, and often are fitted within brass or stainless steel sleeves. The risk of high velocity impact sparks is extremely low. Protecting the entire machine with a non sparking “bumper” is impractical in most cases, while the use of a two-inch wide, quarter-inch thick bumper on the furthest extruding points of the equipment offers a false sense of security. This can be proven easily by analyzing the wear, tear, and paint damages on equipment that has been in operation for a period of time.

Batteries and connectorsOnly approved batteries should be used on equipment used in Class II, Division 1 or Zone 21 explosion hazardous areas. It is impossible to house batteries in fully sealed housing because they require ventilation. Batteries used must be tested and certified for use in the explosion hazardous areas in which they operate. Batteries never should be charged in explosion hazardous areas.

Battery connectors may be approved for use in Class II, Division 1 or Zone 21 hazardous environments and must be locked in place.

PROTECTION METHODS FOR POWERED INDUSTRIAL EQUIPMENT USED IN CLASS II & III, DIVISION 2 OR ZONE 22 EXPLOSION HAZARDOUS AREASIn areas where ignitable concentrations of dusts or fibers MIGHT BUT ARE NOT LIKELY TO EXIST (less than 100 hrs/yr) under normal operating conditions, the risk of igniting flammable materials is relatively low.

United States classification: Class II, Division 2. International classification: Zone 22 Estimated time of exposure to hazardous gas, liquids or vapors: less than 100 hrs/yr

Allowed equipment recommendationOnly approved diesel and electric powered equipment is operated in Class II, Division 2 or Zone 22 explosion hazardous areas.

Class II, Division 2 or Zone 22 approved equipment protection methods

IdentificationBesides the standard required equipment information, the ID tag shall provide detailed information regarding the manufacturer, the temperature class, gas group protection, and explosion hazardous area suitability rating.

Surface temperaturesThe surface temperature of the engine, exhaust, drive or hydraulic motors, electrical equipment, brakes, and any other “hot spots” on the truck should be kept 75°C below the lowest ignition temperature of any flammable materials likely to be encountered. Surface temperatures should not exceed the temperature class of the truck.

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Cooling and temperature monitoring of equipment “hot spots”The exhaust manifold and associated piping may be cooled by using a water jacket or water-cooled heat exchanger or by passing the exhaust gases through a water bath. Water levels should be monitored regularly and maintained at the recommended level. (The waste residues from cleaning the water bath cooling system may pose a health and environmental hazard.)

Thermal sensors should be used to detect overheating of potential hot spots. These thermal sensors must trigger audible or visual alarms and to provide automatic shutdown of the equipment when necessary.

Other enclosuresThe use of approved enclosed components that prevent the contact of the arcing and sparking components with the outside atmosphere may be used on Class II, Division 2 or Zone 22 equipment.

DC electric motors used in Class II, Division 2 or Zone 22 explosive areas must be sealed with a metal clamp band. Enclosing the motors will prevent the buildup of dust inside the motor. The surface temperature of the motor must be monitored by temperature sensors that will shut down the equipment automatically when the T class for which the equipment is certified is reached. Regular cleaning of these motor housing is required to reduce the hazards caused by dust buildup. Approved AC motors can be used if they meet the requirements of a technical risk assessment.

EncapsulationEncapsulation is the enclosure of a sparking or arcing electrical component or part in an approved compound that hermetically seals the component/part from the outside atmosphere. Encapsulation is an accepted and approved method of protection for Class II, Division 2 or Zone 22 explosion hazardous areas.

WiringAll types of approved wiring can be used on Class II, Division 2 or Zone 22 approved equipment. It is important that all wiring is protected from impact by the chassis of the equipment. Wiring connections should be made in approved junction boxes or inside approved component housing. All enclosure cable entries must be through approved cable glands. Installation of the wiring must be in accordance with applicable codes.

Cable glands or sealsApproved cable glands or seals must be used for cable entries of enclosures or junction boxes. Care must be given to the fact that over-tightening of cable glands might lead to cable damage

Spark arrestorsA spark arrester fitted between the engine exhaust and the atmosphere will prevent sparks being emitted from the exhaust system. Spark arresters are designed to trap (usually in a series of baffles) hot burning particles, normally of carbon, emitted from a sooty engine and they should be cleaned regularly. Spark arrestors must be approved for use in the explosion hazardous area in which it will be deployed.

Elimination or protection of spark-producing components and static buildupNon-electrical items can cause electrostatic or frictional sparks by rubbing or impact. Therefore, adequate clearance is needed between fixed and rotating parts, with allowance made for engine movement during normal operation. Engine-cooling fans often are made from non-metallic material such as plastic. The risks of sparks from static buildup are minimized by the use of electrically conductive materials for drive belts. The use of aluminum, magnesium, titanium, and light alloys should be minimized to reduce the risk of sparks resulting from thermal reaction (this may occur on impact between light metals and rust). If such components are used, they must be shielded from impact. Surface coatings that contain these types of materials normally are considered unsuitable for use on Class II, Division 2 or Zone 22 rated equipment.

Protection of load contact and impact points

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The forks of lift trucks may cause frictional sparks when they get into contact with a metal drum, other object, or are dragged over the floor. Forks must be fitted with a brass or stainless steel sleeves or coating. Protecting the entire machine with a non sparking “bumper” is impractical in most cases. Installing a two-inch wide, quarter-inch thick bumper on the furthest extruding points of the equipment serves little purpose, as is shown by analyzing the wear, tear, and paint damages on equipment that has been in operation for a period of time.

Batteries and connectorsOnly approved batteries should be used on equipment used in Class I, Division 2 or Zone 22 explosion hazardous areas. Because batteries require ventilation, it is impossible to enclose them in fully sealed housings. Batteries used must be tested and certified for use in the explosion hazardous areas in which they operate. Batteries never should be charged in explosion hazardous areas.

Approved and rated battery connectors should be in Class I, Division 2 or Zone 22 hazardous environments. Battery connectors on powered industrial equipment NEVER should be disconnected in an explosion hazardous area.

QUICK REFERENCE GUIDE TO EQUIPMENT SUITABILITY

To determine if powered industrial equipment is suitable and safe for use in and around facilities that store, manufacture, process, distribute, or handle flammable or explosion hazardous materials, you should take the following items into consideration.

1. Hazardous area classification Likelihood that equipment encounters an explosive atmosphere

2. Presence and volume of flammable material stored and/or handled regardless of the hazardous areas classificationAre flammable materials being stored in significant volumes and does powered industrial equipment handle or operate around these flammables?

3. Accessibility to flammable materials or hazardous areasHow easy is it for any equipment to enter and operate in an area with a higher EX classification?

4. Type of hazardous materials encounteredGas, liquid, dust, or fibers and material group (A, B, C, D, E, F, or G)

5. Have all the equipment ignition sources been eliminated?The more equipment ignition sources have been eliminated, the safer the equipment

6. Third party testing and certificationHas the equipment been tested and certified for use in explosion hazardous areas? Check for hazardous area rating on equipment ID tag. The ID tag must state the hazardous area for which it has been tested and certified, and what testing laboratory approved the equipment

7. Risk of human errorsMisuse, lack of awareness, faulty repairs, lack of preventive maintenance

8. Protection methods use to prevent the operation of equipment in explosive atmospheresIs the equipment prevented from operating in an ignitable atmosphere?

9. Will the equipment enter the location temporarily or remain in the potentially explosion hazardous area at all times?If equipment will enter a hazardous location only to make a delivery, the reduced chance of encountering an explosive atmosphere may justify the use of a lower level of a certified equipment protection compared to equipment that will remain in the hazardous area at all times.

10. Air quality, air changes and flammable material toxicityDepending on the air quality, the number of air changes that occur, and the toxicity levels of the flammable materials handled, the use of ACTIVE protection methods that warn and shut down equipment automatically before levels of flammable materials increase above the LEL may be considered a preferred method of protection, especially when the material encounters are toxic.

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References

The following documents/publications were used as references in the writing of this handbook:

United States – NFPA 70/2008: National Electrical Codes – Article 500

United States – NFPA 505/2006: Fire Safety Standards for Powered Industrial Trucks, including Type designations, Areas of Use, Conversions, Maintenance, and Operations.

United States – UL 583/2007: Battery Powered Industrial Trucks

United States – UL 558/2008: Industrial Trucks, Internal Combustion (IC) Engine Powered

United States – UL 1203: Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Division 1 Hazardous (Classified) Locations

United States – UL 1604: Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Division 2 Hazardous (Classified) Locations

United States – ANSI/ITSDF B56.1: Safety Standards for Low Lift and High Lift Trucks

United States – OSHA 1910.178: Powered Industrial Trucks

United States – OSHA SHIB 07-31-2005: Combustible Dust in Industry: Preventing and Mitigating the Effects of Fire and Explosions

British Health and Safety Handbook: “Lift trucks in potentially flammable atmospheres.” ISBN 9780717607068

European – ATEX 94/9/EC: Approximation of the Laws of the Member States Concerning Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres

European – EN 1755:2000: Safety of Industrial Trucks. Operation in Potentially Explosive Atmospheres. Use in Flammable Gas, Vapor, Mist and Dust

Chinese – GB19854:2005: General Rules of Explosion-proof Techniques of Industrial Trucks for Explosive Atmospheres

The following documents are highly recommended reading material if you would like to learn more about industrial equipment protection:

British Health and Safety Handbook: “Lift trucks in potentially flammable atmospheres.” ISBN 9780717607068

European – EN 1755:2000:- Safety of Industrial Trucks. Operation in Potentially Explosive Atmospheres. Use in Flammable Gas, Vapor, Mist and Dust

United States – NFPA 70/2008: National Electrical Codes – Article 500

United States – UL 583/2007: Battery Powered Industrial Trucks

United States – UL 558/2008: Industrial Trucks, Internal Combustion (IC) Engine Powered

Unites States – NFPA report “Industrial Loader and Forklift Fires,” by Marty Ahrens, published January 2009

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1-05-09 final version - ex forklift handbook

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