ep fa ha 01 st rev 1 company standard for areas classification 2008-09-04

Standard Petrom EP EP FA HA 01 ST

Company Standard for Areas Classification Page 2 of 182 In force since: 04.09.08 Edition: 01

Note:

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Content

1. FOREWORD........................................................................................................................................................................................5

1.1 Extent............................................................................................................................................................................................5 1.2. Scope...........................................................................................................................................................................................5

2. STANDARD CONTENTS.....................................................................................................................................................................5

1. ESSENTIAL CIRCUMSTANCES FOR AN EXPLOSION OR FIRE TO TAKE PLACE .....................................................................5 a. Explosion Prone Mixtures ..........................................................................................................................................................5 b. Oxidizing Substance ..................................................................................................................................................................7 c. Ignition Sources .........................................................................................................................................................................7

2. FIRE AND EXPLOSION HAZARDS PREVENTION AND PROTECTION......................................................................................8 1. Basic Principles for Fires and Explosions Prevention and Protection.............................................................................................8 2. Prevention and Protection Measures for:.....................................................................................................................................9

a. Forming of Explosion Atmospheres............................................................................................................................................9 b. Ignition of Explosion Atmospheres .............................................................................................................................................9

1. Hot Surfaces.......................................................................................................................................................................10 2. Flames and Hot Gases .......................................................................................................................................................11 3. Mechanically Generated Sparks .........................................................................................................................................11 4. Electric Systems .................................................................................................................................................................13 5. Parasitic Electric Circuits. Cathodic Protection....................................................................................................................13 6. Static Electricity ..................................................................................................................................................................14 7. Atmosphere Discharges......................................................................................................................................................15 8. Radio Frequency Electromagnetic Waves (10

4 Hz 3

. 10

12 Hz)........................................................................................15

9. Electromagnetic Waves within Range of Frequencies 3 . 10

11 Hz 3

. 10

15 Hz...................................................................16

10. Ionising Radiations ...........................................................................................................................................................18 11. Ultrasounds ......................................................................................................................................................................19 12. Adiabatic Compression and Shock Waves........................................................................................................................19 13. Chemical Reactions..........................................................................................................................................................20

c. Mitigation of Effects of an Explosion Event ..............................................................................................................................21 1. Explosion Resistant Constructions and Plants ....................................................................................................................22 2. Explosion Decompression ..................................................................................................................................................23 3. Explosion Suppression .......................................................................................................................................................24 4. Prevention of Explosion from Propagating ..........................................................................................................................24 5. Devices for Preventing Explosion from Propagating............................................................................................................26

d. Emergency Action....................................................................................................................................................................26 3. Measuring & Control Systems in Order to Prevent and Provide Protection for Explosion Hazard...............................................26 4. Crisis Management ...................................................................................................................................................................27

3. HAZARDOUS AREAS CAUSED BY FLAMMABLE AND COMBUSTIBLE LIQUIDS, FLAMMABLE GASES AND VAPOURS .......29

a. Flammable and Combustible Liquids, Flammable Gases and Vapours .........................................................................................29 b. Decisive Factors for Hazardous Areas Categorizing......................................................................................................................31

1. Emissions degree and flow rate ...............................................................................................................................................32 2. Low/high Limits ........................................................................................................................................................................33 3. Sources for Emissions .............................................................................................................................................................33 4. Venting ....................................................................................................................................................................................33 5. Gas or Flammable Vapours Relative Density during Releasing and Atmospheric Dispersion Behaviour ..................................34 6. Other Parameters Considered .................................................................................................................................................34

c. Methods for Hazardous Areas Classification .................................................................................................................................34 1. Emission Sources Analyzing Method (Detailed Classifying Areas) ...........................................................................................34 2. Generalized Method (Areas Classifying on the Whole).............................................................................................................35

d . Types of Hazardous Area Locations.............................................................................................................................................35 e. The Extent of Hazardous Areas.....................................................................................................................................................40

1. Hazardous Areas Located in Open Air .....................................................................................................................................40 2. Enclosed Spaces .....................................................................................................................................................................41

f. Open Areas (Openings) .................................................................................................................................................................41 g. Non-Hazardous Areas..................................................................................................................................................................42 h. Methods for Classified Areas Diminishing or de-Classification.......................................................................................................43

4. CLASSIFICATION OF EXISTING HAZARDOUS AREAS FOR THE MAIN FACILITIES PERTAINING TO PETROM.....................44

a. Areas Classifying on the Ensambly ...............................................................................................................................................45 A.1. Drilling Wells.........................................................................................................................................................................45 A.2. Naturally Flowing Wells ........................................................................................................................................................45 A.3. Pumping Wells......................................................................................................................................................................45 A.4. Gas Lift Wells .......................................................................................................................................................................45 A.5. Water Injection Wells ............................................................................................................................................................46 A.6. Reservoir Combustion Wells.................................................................................................................................................46 A.7. Crude Oil and Gas Gathering Facilities.................................................................................................................................46



A.8. Crude Oil Pump Stations ......................................................................................................................................................46 A.9. Compressor Stations ............................................................................................................................................................46 A.10. Crude Oil Treatment and Storage Facilities........................................................................................................................47 A.11. Reservoir Water Treating and Injection Facilities ................................................................................................................47 A.12. Road Trucks Loading/Unloading Facilities for Oil Products and Liquefied Gas....................................................................47 A.13. Railway Tanks Loading/Unloading Facilities for Crude and Oil Products.............................................................................47 A.14. Storage Yard and Loading/Unloading Ramp for Liquefied Petroleum Gas (LPG)................................................................48 A.15. Gas Dehydration Plants ......................................................................................................................................................48 A.16. C3 C4+ Fractions Recovery Plants Through Adsorption and Absorption Methods..............................................................48 A.17. Natural Gas Decarbonizing and Ethane Recovery Plants ...................................................................................................48 A.18. Gas Regulating, Measuring and Delivery Stations ..............................................................................................................49 A.19. Facilities Related to Petroleum Gas, Liquids and Liquefied Gas Pipelines ..........................................................................49 A.20. Offshore Petroleum Dedicated Facilities .............................................................................................................................49 A.21. Risk Assesment for Production Wells Using Mobile Equipment for Intervention (IC-5, etc) .................................................49

b. Comprehensive Classifying of Hazardous Areas ...........................................................................................................................49 1. Hazardous Zone Radius ..........................................................................................................................................................50 2. Classification of Flammable and Combustible Materials Based on Volatility .............................................................................51

2.1. Category G of volatility.....................................................................................................................................................52 2.2. Category 1 of volatility......................................................................................................................................................52 2.3. Category 2 of volatility......................................................................................................................................................52 2.4. Category 3 of volatility......................................................................................................................................................52 2.5. Category 4 of volatility......................................................................................................................................................53

3. Determination of the Hazard Radius for Area Classification Purposes......................................................................................53 4. Example of Classification for the Space around a Source Releasing Heavier-than-Air Gases or Vapours ................................53

4.1. Hazard Source Located Near or Above Grade................................................................................................................54 4.1.1. Pumps ..........................................................................................................................................................................56 4.1.2. Compressors ................................................................................................................................................................56 4.1.3. Instrument and Process Vents and Drains to Atmosphere ...........................................................................................56 4.1.4. Flanges and Valves ......................................................................................................................................................57 4.1.5. Restriction devices (orifices, drains, etc) installed on the low or medium preassure vessels..........................................57

5. Example of classification the area around the source releasing gasses or flamable vapour lighter than air ..............................57 5.1. Releasing Sources Located at the Ground Level (compressors) ......................................................................................58

6. Releasing Sources Located in Inadequately Ventilated Areas..................................................................................................58

5. MANAGEMENT OF PLANTS IN HAZARDOUS AREAS ...................................................................................................................58

a. Hazardous Areas Monitoring and Evaluation.................................................................................................................................58 b. Responsibilities and Obligations for Employer and Employees that Carries on their Activity on Classified Areas...........................59

1. Responsibilities and Obligations for Employer..........................................................................................................................59 2. Responsibilities and Obligations for Employee that Carries on their Activity on Classified Areas..............................................60 3. Responsibilities and Obligations for Employee who Develops occasionally his Activity in Classified Areas ..............................61

c. Minimum requirements that shall be taken in scope of improving of health and safety protection of workers present in potentially hazard in explosive atmospheres are materialized by:..............................................................................................61

1. Executive measures ...........................................................................................................................................................61 2. Protective measures against explosions..............................................................................................................................61

6. DEFINITIONS AND ABBREVIATIONS..............................................................................................................................................62

1. Definitions .....................................................................................................................................................................................62 2. Abbreviations ................................................................................................................................................................................65

7. SUPPORT DOCUMENTS (LAWS, DECISIONS, ORDERS, SR EN, SR ISO, ANOTHER REGULATIONS) ......................................65

8. MODIFICATIONS FROM THE REGULATIONS IN FORCE ...............................................................................................................68

9. APPENDIX.........................................................................................................................................................................................68

Appendix A: Calculation Examples for Determination of Ventilation Degree Appendix B: List of Drawings Appendix C: Case Studies

1. Practical Example for Hazardous Area Classification of One Park for Oil - Gas Separators - Park 250 Nineasa

2. Practical Example for Hazardous Area Classification of One Gas Compression Station Compression Station Satchinez

Appendix D: Main Crude Oils from PETROM Appendix E: Characteristics of the Main Combustible Substances from PETROM

(see Romanian Language)



1. FOREWORD

1.1 Extent

The company standard applies for designing, construction, commissioning, operation, maintenance of equipment and plants carrying, processing, producing and handling flammable substances, gas and liquid, which in certain conditions can cause explosive and/or flammable mixtures. This company standard applies also for existing plants for identifying the explosion hazard and adopting of adequate measures for management, avoidance and prevention of explosive atmospheres. Any modification performed within a plant after commissioning, imposes the reassessment of plant from the point of view of explosive atmosphere prevention. The assessment can be performed from the point of view by certified / licensed personnel only, according to the legislation in force, valid on the date of assessment, shall be checked by the designer of the plant and approved by certified PETROM personnel, in charge of HSEQ department.

1.2. Scope

Delimitation and classification of hazardous zones from E&P Objectives of S.C. PETROM S.A. OMV GROUP MEMBER, hereinafter named PETROM.

2. STANDARD CONTENTS

1. ESSENTIAL CIRCUMSTANCES FOR AN EXPLOSION OR FIRE TO TAKE PLACE

For occurrence of explosion or fire there must be three factors at the same time and over the same space (triangle of ignition).

- Explosive atmosphere: flammable gas, vapours, mists and/or flammable powders at the

critical concentration (in case of explosions)or a fuel material (in case of fire) - Oxidizing substance: as support of violent combustion (explosion): air, pure oxygen,

oxidizing substances (potassium permanganate, etc) - Ignition source

a. Explosion Prone Mixtures

Explosive atmospheres are represented by air mixture of flammable substances under form of gas, vapours, mist or powders where after ignition has occurred combustion propagates in the whole available mixture. Potentially explosive atmosphere is represented by atmosphere likely to become explosive due to local and operational conditions.



European directive no. 94/9/EG (ATEX 100a) requires a full separation of zones presenting potential explosion hazard into two distinct groups:

- Zones of protection against explosion hazard caused by existence of gas, vapours, mists - Zones of protection against explosion hazard caused by existence of dust

Explosive atmospheres are divided into two groups:

- Group I: explosive atmospheres in gassy mines - Group II: explosive atmospheres, other than present in gassy mines that divide into three

subgroups depending on the minimum ignition criterion namely:

Group Representative Substance Min. Ignition Power ,J

IIA Propane 180

IIB Ethylene 60

IIC Hydrogen, acetylene 20

Conditions of flammability of explosion atmosphere (ATEX) are as follows:

- existence of contribution by an ignition source(e.g. electric or mechanical sparks, hot

surfaces, electrostatic discharges, flames, etc); - sufficient onset energy (energy supplied by source should be higher than minimum energy of

initiating deflagration and temperature of the explosive mixture should be higher than self-ignition temperature)

Within the ATEX concept flammable substances are very strictly classified:

a) upon gas combustible characteristics and b) upon maximum temperature at surface

Ignition temperature of a gaseous explosive atmosphere is defined as being the lowest temperature of a heated surface where ignition may occur for flammable substance located under the form of gas or vapour air mixture. Duty temperature is defined as temperature reached when the device operates at regular service conditions. Maximum surface temperature is defined as the highest temperature reached under the most unfavourable conditions on either side or surface of electrical device susceptible to cause ignition of surrounding explosive atmosphere.

Flammable Substances Classification upon Temperature Groups and Classes

Group Substances Equipment max allowable surface temperature

0 1 2

I methane 450C (T1)

IIA

acetone ethane propane

ethyl acetate ammoniac

benzene (pure) acetic acid carbon oxide methanol toluene

450C (T1)



0 1 2

Ethyl alcohol isoamyl acetate n-butane

n-butyl alcohol n-hexane

300C (T2)

gasoline gas-oil

kerosene n-hexane

200C (T3)

acetaldehyde ethyl ether 135C (T4)

IIA

hydroxylamine 100 C (T5)

IIB ethylene cracking gas 450C (T1)

IIC hydrogen acetylene

carbon sulphide

450C (T1) 300C (T2) 85C (T6)

b. Oxidizing Substance

Gas or vapours shall be into air mixture or oxygen to ratios or amounts in which the so occurred mixture should be flammable. This condition is essential to determine the extent of hazardous areas.

Also other factors shall be considered such as:

amount of material that may release

physical features of this material

operating pressure and temperature

natural trend of gas or flammable vapours to spread within atmosphere c. Ignition Sources

Ignition source is represented by an energy source causing burning that can be physical, chemical or other nature phenomenon generating an amount of energy capable to initiate the ignition of fuel material or environment.

The ignition source may be represented by: hot surfaces, hot flames and gas, mechanically caused sparks, electric installation, balancing currents, static electricity, lightning, ultrasounds, electromagnetic waves, ionizing radiations, adiabatic compressions, exothermal reactions (according to Community legislation they are defined in standard SR EN 1127-1:2008).

An energy source becomes ignition source whenever it supplies sufficient energy for the ignition process to be initiated (energy supplied by source shall be higher than minimum energy for deflagration onset and temperature of explosive mixture shall be higher than self-ignition temperature).

Ignition sources shall be classified upon their nature, as follows

a) sources of flame ignition: flame of matches, candle, welding apparatus, etc; b) sources of thermal nature ignition: incandescent objects, heat released by thermal

equipment / devices, thermal effect of electric current, etc; c) sources of electric nature ignition: electric arcs and sparks, short-circuit, static electricity, etc d) sources of mechanical nature ignition: mechanical sparks, friction, etc



e) sources of natural ignition: solar heat, lightning, etc f) sources of self-ignition of chemical, physical-chemical and biological nature, exothermal

chemical reactions; g) sources of ignition due to explosions and firing materials; h) sources of indirect ignition: radiation of a fire point and other alike

2. FIRE AND EXPLOSION HAZARDS PREVENTION AND PROTECTION

1. Basic Principles for Fires and Explosions Prevention and Protection

Plants where flammable materials are processed, stored and circulated shall be designed, operated and maintained so that all possible release of such materials and implicitly extent of hazardous areas should be maintained at a minimum as regarding frequency, duration and quantity regardless if operation is or not normal. In case of maintenance activities other than necessary in normal operation, extent of hazardous areas may be affected in respect of limit increase but this issue is assumed to be settled by working instructions proper to such activities.

Basic principles of fire prevention and protection are as follows: - control of fire hazards - monitoring fire hazard

Control of fire hazards represents the assembly of technical and organizational action designed to maintain or mitigate hazards within the set out limits of acceptability. In the order of their adoption they are:

- establishment of priorities in action - implementation of control action - management and monitoring of hazards

Establishment of priorities in action consist of decision adoption process referring hazard categories on which there is priority of action. In establishing priorities in action criteria will be considered used in risk assessment of fire, respectively probability of fire occurrence and severity of consequences.

Implementation of fire hazard control Is achieved upon case by:

a) ensuring a systemic and qualified examination of hazard determined factors; b) establishment and preparation of responsibilities, tasks, rules, instructions and measures

concerning fire fighting and having employees, users and concerned people acquainted with;

c) estabilishing people with attributions on placing in practice of the fire fighting measures. d) ensuring the technical means for fire-fighting, the personnel required for intervention and the

due conditions for training of such; e) resumption of steps in fire hazard identifying and assessing at change of preliminary

conditions; f) permanent updating of the list with hazardous substances used in production activity

Monitoring of fire hazards is consisting of the assembly of the activities for background, preparation and implementation of a coherent strategy of fire prevention, limiting and consequence fighting including also the process of supervising the manner steps are run concerning identification, assessment and control of hazards, review of efficiency got in action undertaken versus results got and required decisions to take.



2. Prevention and Protection Measures for:

- prevent from occurrence of explosive atmospheres - prevent from ignition of explosive atmospheres - limiting and stopping the effects of an explosion

a. Forming of Explosion Atmospheres

All plants handling substances generating explosive atmospheres shall satisfy the following essential requirements required within the design phase:

- observe minimum distances required to locate plant component elements that handling

substances that may generate explosive atmospheres - handling of the substances generating explosive atmospheres should be achieved into a

closed system - should some explosive environment contain several types of gas, vapours, mist or

flammable or fuel powders, then protection measures shall be proper to the highest hazard possible.

- corrosion resistant materials to be used - to withstand the foreseen regimes of pressure proper materials shall be used that should not

significantly alter their properties under action of circulated substances. The producers shall supply all details concerning the influence of various substances on materials that could affect the integrity of the plant;

- offer proper resistance to the fuel penetration of the material in order to limit the quantity of vapours being transferred to the environment. Trials of permeability shall be carried out for oilfield fuels in order to ensure that the admissible limits are not exceeded;

- be able to support all stress which they are subject to during storage, transportation, installation and operation of the system. Significant tests shall include pulling, collapsing, twisting, impact and bending;

- provide for venting of rooms wherever occurrence is possible of explosive atmosphere - provide for possibility of discharging electrostatic loads accumulated

Also the prevention from occurrence of flammable atmosphere and at the same time of ignition hazards may be done by:

avoiding in as much possible to have spaces without liquid within a system;

getting the respective space inert by using inert gas such as nitrogen, CO2, of purified flue gases(in table no.2 the limit value are specified for some gases and fuel vapours)

achievement and maintenance of tightness in systems through which are circulated substances susceptible to from an explosion mixture

purging with inert gas or process gas at starting up of the systems or whenever needed

replacement in case it is possible of substances generating explosive prone atmosphere by others that do not give place to explosive prone mixtures.

supervision of concentration of substances generating explosive atmosphere so that it should be kept below the lower limit of explosion or above explosion upper limit.

zoning of hazardous areas

utilization of equipment proper to the identified hazardous zones

b. Ignition of Explosion Atmospheres

Since the avoiding the occurrence of explosive atmosphere cannot be ensured totally it is necessary that measures should be applied that is proper for preventing from occurrence of ignition sources. Such measures shall be established depending on the Ex classified zone (according to SR EN 60079-10 or equivalent for detailed zoning or branch standards for assembly zoning).



1. Hot Surfaces

If some explosion prone mixture comes into touch with a hot surface (hot piping, boilers, etc) ignition may occur. The capacity of a heated surface to generate ignition depends on the type and concentration of the respective substance in mixture with air. More the temperature and surface of the hot body and more this capacity. Moreover the temperature initiating ignition depends on the dimension and shape of the heated body, on the gradient of concentration to the surface vicinity and to a certain extent on the material the surface is made of. So, for instance, some gas or vapour explosion prone atmosphere inside some heated spaces considerably high (approximately 1 l or more) may ignite by surface temperature that are lower than the ones measured according to CEI 79-4 or other equivalent methods

On the other side, in case of heated bodies having got surfaces that are convex rather than concave an increased surface temperature is necessary for ignition; for an example in spheres or pipelines the minimum ignition temperature increases with the diameter decrease.

In case of prolonging an explosion atmosphere along a heated surface because of the short time of contact a higher surface temperature may be required for ignition.

Should the explosive atmosphere stay in touch with the hot surface for a relatively long time preliminary reactions may occur, e.g. cold flames so that several products of decomposition occur that are slightly flammable and promote ignition of initial atmospheres.

Beyond hot surfaces easy to recognise such as fans, drying cabinets, heating spools and others, mechanical and processing process may lead also to hazardous temperatures. These processes also include equipment, protection systems and components that convert mechanical power into heat that means all types of friction couplings and mechanical brakes (e.g. on vehicles and centrifuges). Moreover all movable parts in bearings, shaft passages, bushings, etc may become ignition sources should they not be sufficiently lubricated. Inside of tight housings of movable parts ingress of foreign bodies or axis movement may lead also to frictions that in their turn further lead to high surface temperatures which occurs pretty quickly sometimes.

Protection Measures If hazards are identified that are caused by hot surfaces depending on the type of explosion atmosphere (gas/vapours/mist or powder as flammable substance) and on the category of such then the following specific requirements shall be observed as for equipment, protection systems and components:

Category 1: The temperature of all surfaces pertaining to protection equipment, systems and components that may come in touch with explosive atmospheres shall not exceed 80% of the minimum ignition temperature for fuel gases or liquids into C neither for the case of rare malfunctions. Category 2: The temperature of all surfaces of the equipment, protection equipment, systems and components that may come in touch with explosive atmosphere shall not exceed the minimum ignition temperature of fuel gases or liquids (C) during normal operation and in case of malfunctions. If however the possibility cannot be excluded that gas or vapours may heat until the surface temperature, then such surface temperature shall not exceed 80% of the gas ignition minimum temperature measured into C. Such values may only be exceeded in case of rare malfunctions.



Category 3: Temperature of all equipment surfaces protection, systems and components that may come in touch with explosive atmosphere shall not exceed during normal operation the minimum ignition temperature for gases or liquids.

2. Flames and Hot Gases

Flames are exothermal chemical reactions that propagate quickly at about 1000 C or more that are accompanied by bright phenomena and have as reaction products hot gases. Both flames and hot reaction products may ignite explosive atmospheres. Flames even of small dimensions are numbered among the most efficient sources of ignition. Should inside or outside a piece of equipment, construction or across neighbouring areas exist some explosion prone atmosphere in case of some ignition within one of the areas the flame may propagate from one area to another through orifices (venting ducts). To prevent flames from propagating special constructive protection measures shall be taken providing for fire resistant elements in the project.

Also welding droplets occurring in welding or cutting are sparks with a very large surface and so they represent of the most efficient sources of ignition.

Protective Measures

If hazards are identified caused by flames or hot gases depending on category the following requirements shall be taken into respect for protection equipment, systems and components: All categories. No open flames are allowed except as described below: Category 1. Besides removal of open flames, gases from flames (e.g. exhaust flue gases for inertization) or other gases heated are not allowed but only if special prevention measures are taken such as restriction of temperature or removal of firing prone particles. Category 2 and 3. Flame devices are only allowed if the flames are safely closed and do not exceed temperature specified under previous item onto external surfaces of plant parts.

Moreover assurance shall be given that in protection equipment, systems and components with closed flames (e.g. special heating systems) closure is properly resistant to flame effect and propagation cannot occur of flame at the hazardous place. Category 2 and 3. The air required for combustion may be taken out from zones 1 and 2 but only if hazards are prevented from by implementing proper protection measures. Hot gases may be only introduced if the minimum ignition temperature is assured not to be reached for explosive atmosphere. Assurance shall be given that the deposited powder shall not ignite. Moreover prevention measures shall be taken (e.g. utilisation of spark arrester devices) to assure the exclusion of hot solid particles out of exhaust gases.

3. Mechanically Generated Sparks

By friction, polishing, hitting processes particles may detach of solid materials that may reach high temperatures based on energy consumed in separation process. Should such particles be composed of oxidable substances (iron or steel) based on oxidation process they could reach temperatures of above 1000 C thus becoming sparks. Such particles (sparks) may ignite fuel gases and flammable vapours with an ignition energy of min. 0,1 mJ (10

-4 W.s) and less.

At 200 J and stronger hits of a tough steel onto a very tough metal and by using cutting disks sparks are generated having a energy much higher than the above mentioned ignition energy.



Sparks may be generated with a higher capacity of ignition and by slight hits (1J) of a random material onto rusty steel if there are any traces of aluminium or magnesium at the hitting place. Even hitting tools made of the so-called anti-spark materials (copper, monel, beryllium bronze) may cause sparks. An efficient manner may be initiated by aluminothermy reaction (reaction between iron oxide and aluminium). The amount of aluminium or magnesium shall not be over 10

-3 g.

Sparks resulted out of welding process are the most efficient sources of ignition. Pervasion shall be considered of foreign matters inside the equipment protection, equipment systems and components, for instance stones or metals that may generate sparks. Friction between ferrous similar metals and certain ceramic products may generate hot spots and sparks similar to the one in polishing jobs. They may lead to ignition of explosion prone atmospheres. Light metals, titanium and zirconium may also generate firing sparks at impact with or friction onto sufficiently tough materials even in absence of rust.

Protection Measures

Should hazards be identified that are due to mechanically generated sparks depending on the explosion atmosphere type (gas/vapours/mist or powder as flammable substance) and upon category the following specific requirements shall be taken into respect as for protection equipment, systems and components: Category 1. Must be excluded the equipments protection, systems and components that even in case of rare malfunctions may give birth to friction, impact or abrasion firing sparks. Especially friction shall be avoided between aluminium and magnesium, (excluded alloys with less 10 % Al and paints and convering material with less than 25% Al in mass) and iron or steel (except for stainless steel, when presence may be excluded of rust particles). Friction and impact shall be avoided between titanium or zirconium and any tough material. Category 2. Whenever possible requirements shall be observed for category 1. Sparks shall be excluded also in case of regular operation and malfunctions. Category 3. It is enough to implement protection measures against friction, impact or abrasion firing sparks during regular operation.

All categories. Utilisation shall be forbidden of explosion atmosphere gas/air, vapours/air and mist/air for equipment that may generate mechanic sparks if the possible explosion atmosphere may include one or several of gases: acetylene, carbon sulphide, hydrogen, hydrogen sulphide and ethylene oxide except for the case that there are proofs that there is no explosion hazard. Requirements for tools that may be used in explosion atmosphere shall be as follows:

a) tools that may generate only single sparks in utilisation (screwdrivers, fixed spanners, impact screwdrivers);

b) tools that in utilisation during cutting or grinding jobs generate spark sprinkling (saw).

Tools that may generate sparks are not allowed in zone 0. Tools are allowed across zone 1 and 2 but only if made of steel of a) type. Tools b) type are only allowed if no hazardous explosion atmosphere is ensured not to be present at the working place. However utilisation of any kind of tools made of steel is completely forbidden in zone 1 if there is any explosion hazard due to presence of substances pertaining to II C group of explosion (acetylene, carbon bisulphide, hydrogen) and hydrogen sulphide, ethylene oxide and carbon monoxide except



for the case that assurance is given that there isnt no hazardous explosion atmosphere at the working place during work with such tools. NOTE 1: In some cases protection is possible for light metals against coming in touch with rust by plating. Should it be plated with non-conductive materials such as plastics then precautions may be required against static electricity. The coating layer is recommended not to contain a high percentage of aluminium. NOTE 2: Probability can be reduced for firing spark occurrence mechanically generated for an example by wetting. Possible reactions shall be considered with the wetting medium (e.g. generate hydrogen in case of water and light metals).

4. Electric Systems

Electric systems are means of production either individual or interconnected causing, conduction, transforming, storing, transportation, distribution, measuring, controlling or consuming electric power.

In case of switchgear sparks may occur and hot surfaces as sources of ignition in the following cases:

- at electric circuits shut-off or opening - existence of insufficiently tightened connections - stray currents

To be specified explicitly that extra low voltage (ELV, e.g. below 50 V) is provided for people protection against electrocution and not as measure designated to protect against explosions, voltage values lower than this value being capable to cause sufficient energy to ignite some explosion atmosphere. At electric installations also other sources of ignition must be considered (e.g. mechanically generated sparks).

Protection Measures

If hazards are identified caused by electrical devices, then requirements shall be observed that are specific to protection equipment, systems and components as present in laws, norms and standards in force within this field of activity. All categories. Electrical devices shall be designed, built, installed and maintained according to specific European standards.

5. Parasitic Electric Circuits. Cathodic Protection

Through electric installations or through some parts of the systems leakage currents may leak off temporary or on longer time, that are also named parasitic or stray currents. Stray currents may circulate in electrically conductive systems or parts of systems:

- under the form of return currents in power generating systems especially in vicinity of

electrified railways and large welding systems whenever for instance components of conductive electric system such as rails and cable coatings lied in underground decrease the path resistance of such return current;

- as a result of a short-circuit or earth short-circuit caused by damages in electric systems; - as a result of magnetic induction (e.g. close to electric systems with high values of the

current or radio frequency; - as a result of meteorological discharges



If separating, unifying or shunting such parts of an electric system sparks may occur at even small differences of potential that may ignite an explosion atmosphere. Ignitions are also possible by heating of such current conductors. At utilisation of cathodic protection against corrosion having the electric current supply from outside there also may be ignition hazard. However if sacrificial anodes are used ignition hazards are improbable to be caused by electric sparks except for the case anodes are made of aluminium or magnesium.

Protection Measures

If hazards are identified that are caused by stray currents and/or cathodic protection against corrosion, depending on the explosion prone atmosphere (gas/vapours/mist or powder as flammable substance) and on category then the following specific requirements shall be observed as for protection equipment, systems or components: All categories. All conductive parts of a system taking part in electric switchgear or being in vicinity of such must be protected according to EN 50154.

Special protection measures shall be ensured for corrosion proof systems under impact of electric current. For corrosion cathodic protection systems (except for the ones with sacrificial anodes) special protection measures are necessary. It is necessary that between all parts of conductible systems as well as other operating means that are not close to electrical ones, a potential balancing shall be carried out in construction according to standard. Such conditions may only be deviated from whenever the range is surrounded by potential compensation built in walls. If throughout zone 1 conductible parts of system are connected, for example venting or suction lines in a tank they shall be included in potential compensation. Throughout zone 1 same measures are required as for zone 0. In case of parts of system having electric conductibility not being located close to electric means of operation, may rennounced to special measures for potential compensation (e.g. supplementary shunting) if within the network of the system conductible parts (e.g. line network, earthing network) there is already a potential compensation. Before connections are shut off or opened between good conductivity parts of system (e.g. dismounting fittings or line parts) shunting shall be carried out between lines with sufficient section to the extent that the compensation network could be interrupted. Throughout zone 2 as a rule potential compensation may be given up.

6. Static Electricity

Further to separating processes to which at least one substance may electrostatically charged ignitions may occur under certain conditions by discharge of this electricity. Such discharges may lead to sparks capable to ignite conductible system parts that are isolated but charged electrostatically. In case of electrostatically charged parts made of non-conductible materials, category including the majority of synthetic materials, as well as other materials, concomitant discharges are possible over the whole surface(bundle) and in special situations within quick separating processes concentrated discharges may take place (sliding bundle) for instance plastic sheets of roll mills, driving belts.



Bundle discharges (over the whole surface) may ignite gas and vapour explosion prone mixtures. Protection Measures

If hazards are identified as generated by static electricity depending on the type of explosion atmosphere (gas/vapours/mist or powder as flammable substance) and upon category the following specific requirements shall be observed as for protection equipment, systems and components: All categories. The most significant measure of protection is the equipotential connection of all conductive elements that might hazardously charge and their earthing. This protection measure is not however sufficient in presence of non conductive materials. In this case hazardous levels shall be avoided as for charging of non conductive elements and materials, including solids, liquids and powders. Such information shall be included in instructions of utilisation. Category 1. Firing discharges shall be removed and rare malfunctions shall be taken into respect. Category 2. Firing discharges shall not occur during installations utilisation including maintenance and cleaning or during malfunctions that may be reasonably anticipated.

Category 3. As a rule, other measures are necessary than the ones of earthing but only if firing discharges frequently occur (e.g. in case of insufficiently conductive driving belts).

7. Atmosphere Discharges

If lightning hits explosion prone atmosphere this one will always get on fire. Another way of getting on fire is the place of lightning discharge by heating. Strong currents start from the place of lightning penetration that spread in all directions and may cause flammable sparks. In case of lightning storms high voltages may be cause inside protection equipment, systems and components.

Protection Measures

If hazards caused by lightning are identified the following specific requirements shall be observed as for protection equipment, systems and components: All categories. Systems must be protected by proper measures of lightning protection. Effects shall be prevented from of lightning occurring outside zones 0 for instance surge protection systems may be installed in proper places. In tank systems covered with earth or in components of an electrically conductive system that are electrically isolated from tank equipotential connections shall be carried out and a system shall be ensured of earthing electrodes into belt. Such requirements shall be included in instructions of utilisation. Protection measures against lightning shall not affect cathodic protection against corrosion.

8. Radio Frequency Electromagnetic Waves (104 Hz 3 10

12 Hz)

Electromagnetic waves are emitted by all systems supplying and using frequency radio electric power (frequency radio systems) e.g. radio emission stations or industrial generators of frequency radio for heating, drying, quenching, welding, cutting, etc. All conductor parts located through radiation field act as receiving aerials. Should this field be sufficiently strong and receiving aerial sufficient large then such conductive parts may cause explosion atmosphere to get on fire.



For an example the received frequency radio energy may lead to heating of thin conductors or in case of connection, respectively to interruption of conductor parties thus causing sparks. In case of especially strong high frequency fields as for instance close to high frequency large capacity generators even non-conductible parties may get hot thus becoming sources of ignition. The energy stored in the receiving aerial that may cause ignitions depends at a given length of wave and a certain high frequency power first of all on the distance between transmitter and receiving aerial and on dimensions of receiving aerial.

Protection Measures

If hazards are identified caused by radio-frequency electromagnetic waves then the following requirements shall be observed as for protection equipment, systems and components: All categories. As general measures of protection against ignition effect due to electromagnetic waves a safety distance in all direction shall be ensured between the closest emittent part and the receiving aerial. NOTE 1: At direction featured emission systems the fact shall be considered that the safety distance depends on the direction. It is also recommended to mention that the radio-frequency source depending on its output power, aerial amplification and operating frequency may be located at even some km distance.

If there are doubts about then the safety distance shall be determined my measurement. If a proper security distance may not be observed then special protection measures shall be taken as for instance screening. NOTE 2: The operating permit concerning electromagnetic interference issued by the National Communication Authority body, protection label for respective radio interference or information on the degree of interference dont offer any information concerning the fact that the device or irradiation field could lead to ignition hazard. If the safety distance cannot be ensured to be sufficiently large then special protection measures shall be taken (e.g. screening). By effect of radiation field pertaining to high frequency systems with maximum value of high frequency capacity of at most 1 W throughout zone 0 there is no danger of ignition; throughout zones 1 and 2 this limit increases to 2 W. Here are below other measures of protection:

- only high frequency systems are allowed throughout zone 0 that are approved for zone 0. - throughout zones 1 and 2 high frequency devices may be mounted.

At systems having a max. capacity of high frequency of over 2 W there have to be supplementary guaranteed that by influence of the radiant wave capacity (zone 2) respectively even in frequent damages in operation (zone 1) there is no hazard of ignition.

9. Electromagnetic Waves within Range of Frequencies 3 10

11 Hz 3 10

15 Hz

Radiations within this spectral range(optical range) especially by focusing may become sources of ignition by adsorption in explosion atmospheres or onto solid surfaces. Solar light may for instance initiate ignition if objects lead to focusing of rays (glasses operating like lens, focusing projectors, outward cambered mirrors, filled in bottles). In case of laser radiations (e.g. information transmission, telemetry, topometry, utilisation of visible ranger measurement devices) even long distance, density of energy or power even in a non-focused bundle may be so high that an ignition be possible.



Heating may take place and in this case by laser rays meeting the surface of a solid body. Also possible is the coincidence of gas adsorption strips with length of wave of the laser as source of ignition. By a strong focusing temperatures may occur in the focus point much above 1000C. To be mentioned that all protection equipment, systems and components generating radiations (e.g. lamps, electric arcs, lasers, etc) may be in themselves source of ignition.

Protection Measures

If hazards are identified caused by electromagnetic waves then the following specific requirements shall be observed as for protection equipment, systems and components: All categories. No devices are allowed that may cause ignitions by adsorption of resonance. Category 3. Electric equipments are allowed that generate radiations and are approved for such zones or are allowed for such provided that:

a) the energy of a radiant pulse or energy flux of radiation continues to be limited to a value

sufficiently low that not to be able to have explosion atmosphere got on fire b) or the radiation shall be enclosed safely ensuring that:

- prevent under full safety that a radiation that might ignite explosion atmosphere emit since

encapsuling at hazardous place and no hot surface occur that could ignite due to radiations explosion atmosphere located outside encapsuling, and

- explosion atmosphere shall not be able to penetrate the encapsulation or an explosion inside such shall not be able to propagate in the hazardous place

That shall be ensured during normal operation. Category 2. The above conditions shall be ensured also in case of rare situations (e.g. malfunctions) Category 1. The above conditions shall be ensured even in case of very rare situations (e.g. rare malfunctions) Installation is not allowed through zone 0 of devices and laser systems. Other electrical equipment can be however mounted across this zone generating radiations that are allowed for 0 zone. Independently it shall be ensured that radiations penetrating or occurring throughout 0 zone even in damages shall not exceed the following values:

- 5 mW/mm2 for continuous laser and continuous light sources;

- 0,1 mJ/mm2 for pulse laser and light sources with pulse distances of at least 5 seconds

Sources of radiations with below 5 sec pulse intervals within this context may be deemed as continuous sources. Throughout zone 1 radiation and laser generating equipment may be mounted to the extent they satisfy provisions under item 4 (Electric systems). Intensity of radiation respectively irradiation taking place during operation and frequent derangements cannot exceed throughout zone 1 over the whole ray path in no place of its section the value of 10mW/mm

2, respectively 0,5 mJ/mm

2.

Throughout zone 2 all equipment can be mounted that are generating radiations corresponding to item 4 (Electric systems). The radiation intensity respectively irradiation that takes place during operation over its whole path throughout zone 2 cannot exceed in no place of the ray section the value of 10 mW/mm

2, respective 0,5 mJ/mm

2.



10. Ionising Radiations

Ionising radiations generated for instance by UV generators, Roentgen tubes, laser, radioactive substances, accelerators or nuclear reactors may ignite explosion atmospheres as a consequence of energy adsorption. Moreover, the proper-said radioactive source may heat up even by itself by own adsorption of energy of radiation so that it may exceed the ignition temperature of surrounding explosion atmosphere. Ionising radiations may cause chemical decomposition or other reactions that may lead to development of radicals very reactive or instable chemical compounds that may cause ignition. NOTE: Such radiation may generate also explosion atmosphere by decomposition (ex. a mixture of oxygen and hydrogen by water radiolysis).

Protection Measures

If hazards are identified caused by ionising radiations depending on category, the following specific requirements shall be observed as for protection equipment, systems and components: All categories. For switchgear required in operation of radiation sources indications must be followed under 4 (Electric systems). In 9 (Electromagnetic Waves within Range of Frequencies 3

. 10

11 Hz 3

. 10

15 Hz) protection

measures for laser are given.

Category 3. Electrical equipment that generate ionising radiations are allowed provided that:

a) The energy of a pulsing radiations or of continuous flux of energy radiation shall be limited to a so low value that it could not ignite explosion atmosphere,

b) Radiation shall be safety enclosed ensuring that: 1. any radiation leak shall be for sure prevented from since encapsulating towards

hazardous place that might ignite explosion atmosphere and no produce hot surfaces which might ignite explosion atmosphere from outside encapsulating due to radiations,

2. explosion atmosphere shall not be able to penetrate the encapsulation or an explosion from the encapsulation do not propagate to the hazardous place

That shall be ensured during normal operation. Category 2. The above conditions shall also be ensured in case of rare situations(e.g. malfunctions) Category 1. The above conditions shall also be ensured even in case of very rare situations(e.g. rare malfunctions) Throughout zone 0 the following sources of radiations can be used:

- UV stations, if dedicated special design for zone 0 - radioactive substances with activity until 4 10

10 S

-1 (about 1Ci) tightly enclosed so that

penetration shall not be possible of gases from outside. In case of safe exhaustion of heat such values may be exceeded. In case there are any doubts on heat exhaustion to be ensured then the allowable limit is adopted

Intensity of radiation in UV irradiations shall not exceed 0,5 W/cm

2, respectively 50 mJ/cm

2. The

power of irradiation ratio shall not exceed in radioactive substances and Roentgen rays 3 mA/kg (appr. 40 000 R/h).



Throughout zones 1 and 2 UV transmitters may be used according to item 4 (Electric systems). Amounts of radioactive substances allowed as well as power of irradiation respectively irradiation of ionising rays shall be set out on a case to case basis to the extent they exceed values set out for zone 0. In non destructive examinations by IR sources intensities may be used with no special heat removal measures until about 10

12 S

-1 (appr 30 Ci).

11. Ultrasounds

In using ultrasounds, large amounts of energy emitted by electroacoustic transformer are absorbed by solid and liquid substances. In the acoustically irradiated substances a heat occurs further to inside friction that can reach in extreme cases to temperatures exceeding the ignition temperature.

Protection Measures

The indications to follow refer to the ignition hazard by intensity of acoustic irradiation. The related electrical equipment shall correspond to conditions under item 4 (Electric systems) as protection measure the fact shall be considered that electric loads that may occur in utilisation of piezo ceramic parts as transformers in ultrasound devices draw off with no hazard through proper connecting elements. If hazards are identified caused by ultrasounds depending of the category then the following specific requirements shall be observed as for protection equipment, systems and components:

All categories. Ultrasound waves are not allowed if above 10 MHz frequency but only if absence was proven of the ignition hazard for the case concerned by proving that there is no absorption caused by molecular resonance. For up to 10 MHz frequency ultrasound waves the following are required: All categories. Ultrasound waves are only allowed if security is ensured for working procedure. Density of the generated acoustic field power shall not exceed 1 mW/mm

2 but only if for the case

concerned it was proved that no ignition is possible. Categories 2 and 3. In working procedures with conventional ultrasound devices (e.g. ultrasound devices of echo testing) no special protection measures are required against ignition hazards from the respective ultrasound waves but only in case of power density throughout generated acoustic field exceeds 1 mW/mm

2, except for the case it was proved for the concerned case that no ignition is

possible 12. Adiabatic Compression and Shock Waves

In case of a shock wave and an adiabatic or quasi-adiabatic compression temperature can occur so high as they might ignite an explosion prone atmosphere. The rise of temperature depends on the compression rate and not on the pressure difference. NOTE: In pressure lines of air compressors and receivers connected to such lines explosions may occur further to ignition by compression of lubricating oil mists. Shock waves may occur for instance at sudden expansion of high pressure gases in lines. They penetrate to the ultrasound rate within low pressure ranges. At their diffraction or reflection in the piping bends, in stranglings, in the connection flanges particularly high temperatures occur. NOTE: Protection equipment, systems and components containing high power of oxidation gases for instance pure oxygen or gaseous atmospheres with high concentration of oxygen may become efficient source of ignition under action of adiabatic compression, shock waves or simple flowing as



lubricants may ignite, and packings or even construction materials. If that leads to damaging of protection equipment, systems and components then parts of such will ignite an explosion prone atmosphere. An explosion gas mixture such as hydrogen/air or acetylene/air may ignite by compression whenever a fluorescent tube breaks out and the mixture penetrates the tube while heating up even if the tube is not connected to the electric network. Particular feature hazards occur at oxygen handling under pressure; various particles driven at a sufficiently high rate (such as rust) dislocates iron particles out of the pipeline that in compressed oxygen burn by sending over the fire to the line or reinforcements. A particular hazard is represented by handling of gate vales and oxygen valves because of the high flowing rates occurring at their opening and fittings.

Protection Measures

Should hazards be identified as caused by adiabatic compression and shock waves depending on category the following specific requirements shall be observed as for protection equipment, systems and components: Category 1. Processes shall be avoided that can cause compressions or shock waves. That shall be ensured even in case of rare malfunctions. As a rule, hazardous compressions and shock waves may be removed if for instance guides and valves between the system sections where there are high compression coefficients may only slowly be opened. Category 2. Processes that may cause adiabatic compressions or shock waves may only be tolerated in case of rare malfunctions.

Category 3.Only those shock waves and compressions shall be prevented from that occur during regular operation and that might ignite explosion prone mixtures. NOTE: Should protection equipment, systems or components be used that contain very oxidizing gases, then special precautions are recommended to be taken in order to prevent from ignition materials of which they are made along and auxiliary materials

13. Chemical Reactions

By chemical conversions with heat release, the substances or substance mixtures may heat up thus becoming ignition sources. Exothermal reactions may act as ignition sources in such situations that the heat generating rate exceeds the rate of heat transfering to environment. Many chemical reactions are exothermal. Reaching a high temperature at some reaction depends amongst other parameters on the volume/surface ratio of the system that reacts, on environmental temperature and on the retaining time. Such high temperatures may lead to ignition of explosion prone atmospheres and also to initiating smouldering and/or burning. Such reactions include also the ones pertaining to pyrophoric substances with air, of alkali metals with water, self-ignition of fuel powders, self-heating of feeding materials by biologic processes, decomposition of organic peroxides or polymerization reactions. Catalysts may induce also energy generating reactions (e.g. hydrogen/air platinum atmosphere). NOTE: Some chemical reactions (e.g. pyrolysis distillation and biological processes) may lead to the occurrence of flammable substances that in their turn may cause explosion prone atmosphere in mixture with surrounding air.

In some combinations of construction materials with chemical substances (e.g. copper with acetylene, heavy metals with hydrogen peroxide) violent reactions may take place that cause ignitions.



Some combinations of substances especially when they are finely dispersed (e.g. aluminium/rust or sugar/chlorate) violently react in case of impact or friction.

Protection Measures

Should hazards be identified caused by exothermal reactions depending on category the following specific requirements shall be observed for protection equipment, systems and components: All categories. For all the zones is imposed the avoiding of presence in as much possible of substances presenting self-ignition trend. Should substances be used that have a trend of self-ignition, then protection measures shall be set out on a case to case basis. In order to handle under security conditions unstable substances the following protection measures shall be taken:

- inertisation; - stabilizing; - improvement of heat transfer; - division of unstable substance amounts into smaller units; - utilisation of the technique of storing with intermediate rooms; - storage at low temperature; - permanent control of temperature or pressure

The construction materials that react hazardously with the handled substances must be avoided.

WARNING: Under certain conditions pyroforic materials can be generated, for instance in storing oilfield products with contents of sulphur or at milling light metals within inert atmosphere. Preparation and putting into practice of operating instructions that should give possibility to safe operation of the plant including development of security condition at shutdown, start-up and rest stands for a significant protection measure.

c. Mitigation of Effects of an Explosion Event

In many cases avoiding is not possible of explosion prone atmosphere or ignition sources at a sufficient level of security. In such cases measures shall be taken to limit effects of explosions to an acceptable level. Here are below the concerned measures:

- explosion resistant construction; - explosion decompression (release); - explosion suppression - prevention of flame or explosion from propagating

Such measures refer generally to mitigating the hazardous effects of explosions inside protection equipment, systems and components. WARNING: in protection equipment, systems and components, portions of pipelines or elongated connected vessels it is possible that an explosion might propagate throughout the entire system with acceleration of the flame front. Elements or obstacles included that increase turbulence (e.g. deflectors) may accelerate also the flame front. Depending on the system geometry, such acceleration may lead to a transition from deflagration to detonation at which high pressure pulses occur.



1. Explosion Resistant Constructions and Plants

Besides requirements concerning resistance and stability to statical and dynamic strains, operating safety and fire safety, protection equipment, systems and components shall be able to stand internal explosion without getting damaged. Generally distinction is made between the following construction structures:

- construction for maximum explosion pressure - construction for reduced explosion pressure together with explosion discharge

Protection equipment, systems and components may be:

a) resistant to explosion pressure b) resistant to shock of explosion pressure

Should the inside of the equipment, the protection systems and component are divided into sections (e.g. tanks connected by a line pipe) over the duration of explosion in one of the sections, then the pressure in the other sections of protection equipment, systems and components will increase. Consequently an explosion will occur in such sections to high initial pressure. Further pressure peaks will occur that are higher than the anticipated value under atmosphere conditions. In case of such situations, proper measures shall be taken, for instance have a construction proper to explosion withstand or automated disconnecting in case of explosion.

a) Construction resistant to explosion pressure

The equipment protection, protection systems and components that are resistant to explosion pressure shall withstand the explosion anticipated pressure with no permanent deformation. At the dimensioning and construction of such equipment, protection systems and components, the regulations referring to design and calculation of pressure vessels shall be used. Explosion anticipated pressure shall be used as pressure calculation basis. In case that pressure developed during explosion of the mixture contained within the plant under working conditions lies below 10 bar the plant shall be dimensioned properly to such maximum pressure (10 bar). In case the maximum pressure reaches above 10 bar other means of protection shall be provided for such as for instance protection membranes or getting the space of reaction inert. In pipelines or plants having free inner spaces, such as tanks having height/ diameter ratio over 5, for saturated hydrocarbons in mixture with air possibility shall be considered to pass explosion in detonation. Occurrence of detonations is favoured by the shock waves representing a strong sources of ignition as well as a certain type of constructions contributing to increasing the flame turbulence. In detonations in the direction of the flame propagation effects occur of pressure corresponding to static pressure and that may be by 100 times higher than working pressure. The routes of non bent pipelines made of materials resistant to minimum 10 bar over pressure withstand as a rule to the radial pressure resulted further to detonation of an explosion mixture provided that over the route of the pipeline no reductions in section intervene (reducers, gate valves, etc). On curvatures, the bending radius to pipe diameter ratio shall be as high as possible (for saturated hydrocarbons in mixture with air to an at most 90 angle a ratio is required of minimum 5 for bending radins per diameter).



b) Construction resistant to pressure-shock of explosion Protection equipment, systems and components resisting explosion pressure-shock are so built as to be able to withstand the explosion anticipated pressure but with a possible permanent deformation. For design and construction of equipment protection, systems and components consequently the relevant codes and standards shall be applied.

After explosions the affected parts of the systems must be examined in order to assess if protection equipment, systems and components still can operate safely. That shall be included in instructions of utilisation.

2. Explosion Decompression

The notion of decompression of explosion includes all actions required to open for short time or definitively the initial plant where explosion took or takes place immediately after explosion or after explosion has reached a certain pressure and it stands for a protection principle utilising the discharge of the burnt and non-burnt mixture and fuel gases in order to mitigate explosion pressure. Decompression devices has a scope that the plant should not be stressed above its limit of resistance. As decompression devices explosion membranes or flaps may be used. Particularly significant in dimensioning of such devices of decompression is the time relation between explosion propagation and discharge momentum. The discharge area required for a decompression system will mainly depend on:

- vessel resistance; - explosion severity (featured usually referring to the maximum rate of pressure raise and

explosion maximum pressure); - pressure of acting of the discharge device; - type and mass of discharge device; - volume and geometry of the vessel; - dimension of discharge culverts (if any used); - initial turbulence and the one induced into the vessel.

The lower the rate of explosion pressure increase for explosion prone mixture and the quicker decompression begins acting the faster emptying is done for burning products and non-burnt mixture thus avoiding maximum allowed pressure to be reached. Mounting of decompression devices shall be so done as it should be accomplished in non hazardous manner thus avoiding to cause injuries to personnel by the discharge process. For such reason pressure must be directed towards a security area. Discharge of explosion is not allowed inside working rooms but only after it was proved that people may not be endangered (e.g. flames, projected fragments or pressure waves) shall be considered the effects of discharge on the environment. Decompression shall be done over a short and straight route towards outside. The device shall be so dimensioned that to withstand explosion pressures and recoil forces and be mounted at the end of the discharge line. Should discharging stacks be required then individual discharge shall be achieved in as much possible thus avoiding joint emptying of several devices. The decompression devices status shall be periodically checked.



Decompression shall be avoided into working rooms at devices releasing in 0 or 1 classified zones, at devices or pieces of equipment containing beside explosion prone atmosphere also fuel liquids and at instruments where there is hazard of detonations.

3. Explosion Suppression

Systems of explosion suppression prevent an explosion from reaching its maximum pressure by quick injection of fire quenching agents in the protected equipment, systems and components in case of explosion. That means that protection equipment, systems and components protected in such manner can be so designed as to withstand at reduced explosion pressure. Whenever explosion suppression is used its effects are generally limited inside protection equipment, systems and components. Explosion suppression systems essentially consist of a detection system capable to detect explosion in initial stage (phase) and of pressurized extinguisher whose outlets are triggered by the detection system. The contents of extinguisher shall be quickly injected in the equipment, protection systems and components that are to be protected and shall be distributed as evenly as possible. That has an effect of quenching the flames of explosion and mitigate explosion pressure in order to protect the structure of equipment, protection systems and components. Under certain conditions, explosions in tanks may be suppressed fast enough so that not to allow for the burst but of a partial explosion and in this way only maximum mitigated pressures occur. So the pressure increase occurred in partial explosion or in special cases and in flames radiation is signalled by means of proper detectors that introduce from a tank extinction agents.

For the good operation of such suppression systems among others significant are the following: are determinant sort of extinction agent and manner of its spreading, number and location of tanks containing extinction agent, type and place of location of detectors. Explosion is detected by optical detectors which release a gaseous cloud of extinction within which the flame is put off.

Safety in operation of explosion suppression devices inside tanks depends to a great extent on the manner of operating the protected plants. Therefore it is necessary that operation of such plants should be automatically supervised.

4. Prevention of Explosion from Propagating

It is possible the utilisation of active and passive devices in order to prevent explosion from propagating for instance through pipelines, breathing devices or filling and emptying ways. In case of high speeds of flames propagation or if some detonation is anticipated special measure may be necessary. In some cases the preference could be directed for utilisation of passive systems as for instance flame arresters, sluices, explosion divertors, as alternate systems or in combination with active systems. The following devices may be used for various types of explosion prone atmosphere, namely gas, vapours, mist and air hybrid mixtures. They shall be proven to be proper for the foreseen utilisation.



To avoid flame penetration through gas non tight component parts (axes seals, venting devices, filling and emptying lines non permanently filled with liquid) of a plant at ignitions of explosion prone atmospheres, flame proof safety devices may be used. Flame penetration depends on:

- mixture properties - type of fuel - concentration and pressure - limit dimension of safety slot (in gases) - shape of opening, length and width of slot respectively section and length of pipe - slot leakage conditions influenced by shape of orifice and difference between inside and

outside pressure.

In case occurrence of explosion atmosphere inside a tank for flammable liquids that cannot withstand explosions cannot be avoided then all existing openings shall be secured against flames (e.g. venting device, level indicator, filling emptying lines). Should a device operate within explosion environment and some flame can get out of it outside through an opening it shall be flame proof secured ( e.g. small slot shaft passage). Mounting is forbidden of flame arresters onto gas discharging lines from safety fittings mounted on pressure vessels. Here are below the following different constructive types of devices:

a) explosion resistant fittings:

- orifices exposed for only short time to action by flames of an explosion they shall withstand a single explosion and mechanical stress of it

- flame barriers used to such purpose: safety strips, safety plates, syntherized metals, gravel backfills or artificial body backfills whose channels are small and slot length and width pretty large.

b) continuous burning resistant fittings:

- orifices through which on longer time gas mixture are removed such as tank vents during their filling in and emptying, exposed to flames for a longer period of time in case mixture has already got on fire;

- the provided devices in such respect shall prevent the flame from piercing in case of explosion as well as ignition of explosion atmosphere inside the plant whenever emptied mixtures get on fire

Special fittings correspond to such conditions that have safety band and special valves of high speed over pressure. Onto fittings explosion and continuous burning resistant mounting is not allowed onto that part from which explosion is directed of no one pipe (L/D>5) due to the fact that such lines could develop detonations and fittings could be overstressed. a) Detonation resistant fittings. In pipelines or parts of plants having elongated shape (L/D>5), explosions may transform into detonations. Fittings connected through piping (such as in storing tanks) shall withstand stress developed during detonations and prevent from flame penetration in case of explosions and detonations.

Examination of fittings shall be done per certain substances by certified bodies. Their utilisation for other substances is possible if substance features are well known, or a new examination of fittings is required.



Since the fittings against flame penetration are often mounted onto devices resisting only to low overpressure in making use of them it shall be considered that they should not inappropriately make difficult the pressure equalisation between tank and free outside atmosphere.

5. Devices for Preventing Explosion from Propagating

The main types of devices used in respect of preventing explosion from propagating are as follows:

a) Deflagration arresters these devices prevent from causing flame explosion and withstand the explosion pressure and the stress of temperature of deflagration ( flame arresters conta

ep fa ha 01 st rev 1 company standard for areas classification 2008-09-04

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