Presented by: Divan Pretorius, Snr. Engineer, Proconics

SANS 329: Industrial thermoprocessing equipment – Safety

requirements for combustion and fuel-handling systems and

area classification in the context of fired heaters.

Presentation main discussion points

• Problem statement

• What do the International standards say?

• What do the SA standards say?

• What does SANS 329 say?

• Comparison

• Conclusion

Problem Statement

• The purpose of explosion protection is to prevent a ignition source. This can be done in a number of ways:• Energy limiting

• Containment

• Pressurisation (purging)

• Etc…

• What happens when equipment provide an inherent thermal ignition source?

• Examples:• Ovens, furnaces, flares, boilers and fired heaters

Problem Statement(1)

• SANS10108:2005• Hazardous location: “location determined by national regulations or by the

risk assessment of the plant or mine, where there might be a significant risk of the ignition of gas, dust or vapour”

• Fire triangle:

Problem Statement(2)

• Hazardous location zones (API RP505 Table 3)

What do the International standards say?

• NFPA 86, Standard for Ovens and Furnaces, 2007 Edition

“4.1.3.3* The installation of an oven in accordance with the requirements of this standard shall not in and of itself require a change to the classification of the oven location.”

What do the International standards say?

• NFPA 86, Standard for Ovens and Furnaces, 2007 Edition“A.4.1.3.3 Unless otherwise required by the local environment, ovens and furnaces and the surrounding area are not classified as a hazardous (classified) location. The primary source of ignition associated with an oven installation is the oven heating system or equipment or materials heated. The presence of these ignition sources precludes the need for imposing requirements for wiring methods appropriate for a hazardous (classified) location. Refer to Section 3.3 of NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, and Section 3.3 of NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, regarding equipment with open flames or other ignition sources. In addition, ovens or furnaces are considered unclassified internally as proved ventilation is provided to ensure safety.”

What do the International standards say?

• NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, 1997 Edition

“3-3.1 Experience has shown that the release of ignitable mixtures from some operations and apparatus is so infrequent that area classification is not necessary. For example, it is not usually necessary to classify the following areas where combustible materials are processed, stored, or handled:

(a) Areas that have adequate ventilation, where combustible materials are contained within suitable, well-maintained, closed piping systems

(b) Areas that lack adequate ventilation, but where piping systems are without valves, fittings, flanges, and similar accessories that may be prone to leaks

(c) Areas where combustible materials are stored in suitable containers”

What do the International standards say?

• NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, 1997 Edition

“3-3.3 Open flames and hot surfaces associated with the operation of certain equipment, such as boilers and fired heaters, provide inherent thermal ignition sources. Electrical classification is not appropriate in the immediate vicinity of these facilities. However, it is prudent to avoid installing electrical equipment that could be a primary ignition source for potential leak sources in pumps, valves, and so forth, or in waste product and fuel feed lines.”

What do the International standards say?

• API RP 500, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Zone 0, and Zone 2, First Edition, November 1997

“5.4.2 Lighter-than-air gases released from an opening often will disperse rapidly because of their relatively low density and usually will not affect as extensive an

area as the vapors of flammable liquids or heavier-than-air gases. Lighter-than-air gases seldom produce large volumes of ignitible mixtures in open locations close to grade where most electrical installations are made; however, ignitible mixtures can

accumulate inside enclosed spaces.”

• API RP 505, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Zone 0, and Zone 2, First Edition, November 1997

“6.5.9.2 Adequately ventilated locations surrounding equipment that has continuous flame sources(e.g., unprotected fired vessels and flare tips) need not be classified solely by reason of the fuel gas being considered as a source of release.

Note 1: it may be prudent to classify portions of these locations. For example electrical equipment may be exposed to flammable gas during a purge cycle of a fired heater or furnace.

Note 2: The lack of classifications around unprotected fired vessels and flare tips does not imply the safe placement of fired vessels and flare tips in the proximity to other sources of release because unprotected fired vessels and flare tips are themselves sources of ignition. The decision of whether or not it is safe to install the unprotected fired vessel or flare tip at the location is outside the scope of this document.”

What do the International standards say?

What do the International standards say?

• API RP 505, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Zone 0, and Zone 2, First Edition, November 1997

“6.5.9.3 The practice of not classifying locations where non-electrical ignitions sources ( e.g., the open flame of an unprotected fired vessel or flare tip) exist has been utilized in previous issues of RP500. It is recommended that the application of this practice be limited to unprotected fired vessels or flare tips and that the resulting unclassified locations be restricted to their immediate vicinity. Electrical equipment located in these unclassified locations typically is de-energized for the majority of the time that the flame source is not present.”

What do the International standards say?• Health and Safety Executive UK, Hazardous Area Classification and

Control of Ignition Sources

“Direct Fired Heaters, Hot Oil Systems and Processes Operating Above Auto-Ignition Temperatures

A range of petrochemical and refinery processes use direct fired heaters, e.g. steam crackers for ethylene production. Clearly, if the fuel supply to the heater or the pipework carrying the process fluid leaks close to the furnace, any leak must be expected to find a source of ignition, either directly at the flames, or by a surface heated by a flame. In these circumstances, hazardous area classification, and appropriate selection of ATEX equipment is not suitable as a basis of safety for preventing fire and explosion risks.

Instead, safety should be achieved by a combination of a high standard of integrity of fuel and process pipelines, together with a means of rapid detection and isolation of any pipes that do fail. The consequences of the failure of a pipe carrying process materials within the furnace should be considered in any HAZOP study.”

What do the International standards say?

• EN 746-2, Industrial thermoprocessing equipment – Part 2: Safety requirements for combustion and fuel handling systems, 2011-02 (SANS 329 European equivalent)

“This Part of EN 746 assumes that the equipment is not creating any potentially explosive atmosphere and is located in a normally ventilated area.”

What do the SA standards say?

• SANS 10108:2005,The classification of hazardous locations and the selection of apparatus for use in such locations, Edition 5

Does not explicitly mention the issue, but does reference SANS 60079-10-1, API RP 505, etc… in section 4.4.2.

What do the SA standards say?

• SANS 60079-10-1, Table B1, pg. 31: Ventilation Calculations Calc. 6, pg 37

What does SANS 329 say?

• SANS 329:2013, Industrial thermoprocessing equipment – Safety requirements for combustion and fuel-handling systems , Edition 2

"5.7.1 Because of the very low risk of the presence of flammable concentrations of gas in the vicinity of burner pipework and control equipment, this

area shall be considered as non-hazardous."

Back

Quick Comparison between the standardsStandard Hazardous

location?

Comments

Yes No

NFPA 86 Depending on location, already non electrical ignition source present, proved ventilation

NFPA 497 Adequate ventilation, where combustible materials are contained within suitable, well-maintained, closed piping

systems

Also - Electrical classification is not appropriate in the immediate vicinity of these facilities. However, it is prudent to

avoid installing electrical equipment that could be a primary ignition source

API RP 500 Non hazardous as long as area ventilated

API RP 505 Adequately ventilated locations surrounding equipment that has continuous flame sources need not be classified….

May be required to classify portions, Location should be considered

Unclassified locations restricted to their immediate vicinity. Electrical equipment located in these unclassified

locations typically is de-energized for the majority of the time that the flame source is not present

HSE Already non electrical ignition source present, hazardous area classification, and appropriate selection of ATEX

equipment is not suitable as a basis of safety for preventing fire and explosion risks

Instead, safety should be achieved by a combination of a high standard of integrity of fuel and process pipelines,

together with a means of rapid detection and isolation of any pipes that do fail. Should be considered in HAZOP.

EN 746-2 Assumes no potentially explosive atmosphere and is located in a normally ventilated area

SANS 10108 - - SANS 60079-10-1 ventilation

SANS 329 very low risk of the presence of flammable concentrations of gas in the vicinity of burner pipework and control

equipment, this area shall be considered as non-hazardous

Conclusion

• Location of equipment!!!

• Ventilation• SANS 329 & EN 746-2 assume ventilated to a negligible extent

• Installation specific

• How equipment is operated must be considered• Batch

• Continuous

• Purge cycle

Back to SANS 329?

• Scope of SANS 329

• Gas supply to houses, restaurants, bakeries, etc…

• Revisit what it currently says:

• Is this put too simply?

SANS329 pg. 53, Section 5.7.1