Overview and Importance of Protecting Against Fire and Explosion in Hazardous Areas
– A light switch may cause a small spark when switched on or off.
– In the presence of a flammable atmosphere, the spark can start an explosion.
– Protecting against fire and explosion is important for personnel safety and reliability.
– Strategies to minimize risks include reducing electrical equipment in hazardous locations and designing equipment to reduce ignition hazards.
– International standards are slowly converging to approve a wider range of acceptable techniques.
Standards for Electrical Equipment in Hazardous Areas
– The National Fire Protection Association (NFPA) publishes relevant standards in the US.
– NFPA 497 and NFPA 499 provide guidance on assessing explosive gas and dust hazards.
– The American Petroleum Institute publishes similar standards in RP500 and RP505.
– The National Electrical Code (NEC) defines area classification and installation principles in the US.
– NEC articles 500, 505, and 506 describe the NEC Division and Zone classification systems.
– The International Electrotechnical Commission (IEC) publishes the 60079 series of standards.
– IEC 60079-10-1 covers classification of explosive gas atmospheres, and IEC 60079-10-2 covers explosive dust.
– The IEC 60079 standard set has been adapted for use in Australia and New Zealand.
– AS/NZS 60079 is the published standard set for hazardous areas in Australia and New Zealand.
Hazards and Classification of Hazardous Areas
– Industrial plants handling flammable liquids and gases pose exposure risks.
– Coal mines, grain mills, and similar facilities present the risk of dust explosions.
– Locations are classified based on the type and risk of gas, vapor, or dust release.
– Area classification plans identify equipment ratings and installation techniques for each classified area.
– Process changes require regular review and update of area classification documentation.
– Typical gas hazards include hydrocarbon compounds, hydrogen, and ammonia.
– Class I, Division 1 areas encompass Zone 0 and Zone 1 areas with continuous or intermittent ignitable concentrations.
– Zone 0 areas have continuous ignitable concentrations, such as vapor spaces above liquids.
– Zone 1 areas have ignitable concentrations likely to exist under normal operating conditions.
– Class I, Division 2 or Zone 2 areas have ignitable concentrations not likely to exist under normal operating conditions.
– Dust explosions can occur in facilities handling grain, coal, and other combustible materials.
– Different classifications exist for hazardous dust environments.
– Unclassified locations are considered non-hazardous or ordinary.
– Unclassified locations have very low risk of causing an explosion but may pose a fire risk.
– Dilution of hazardous gases below 25% of their lower flammability limit designates unclassified locations.
Equipment Design and Protection Techniques
– Equipment can be designed or modified for safe operation in hazardous locations.
– Two general approaches are intrinsic safety and explosion-proof.
– Intrinsic safety limits the energy present in a system to prevent ignition of a hazardous atmosphere.
– Explosion-proof equipment is sealed and rugged to prevent ignition, despite sparks or explosions within.
– Techniques for flame-proofing include sealing the housing, containing and cooling combustion gases, pressurizing with clean air or inert gas, isolating arc-producing elements, and designing heat-producing elements to limit temperature.
– IEC 60079 is a standard for electrical equipment in hazardous locations.
– Types of protection include flameproof, intrinsically safe, and non-incendive.
– Flameproof equipment is designed to withstand internal explosions and provide relief of external pressure.
– Intrinsically safe equipment has insufficient energy to ignite a vapor.
– Non-incendive equipment is non-sparking.
– NEMA defines standards for enclosure types in the US.
– NEMA enclosure types determine the level of protection offered by the equipment.
Labeling and Certification of Equipment for Hazardous Areas
– All equipment certified for use in hazardous areas must be labeled to show the type and level of protection applied.
– In Europe, the label must show the CE mark and the code number of the certifying/notified body.
– The CE mark is complemented with the Ex mark: A yellow-filled hexagon with the Greek letters εχ (epsilon chi), followed by the Group, Category, and, if Group II, G or D (gas or dust).
– Specific types of protection being used will also be marked.
– Industrial electrical equipment for hazardous areas has to conform to appropriate parts of standard: IEC-60079 for gas hazards, and IEC-61241 for dust hazards.
– In North America, the suitability of equipment for the specific hazardous area must be tested by a Nationally Recognized Testing Laboratory, such as UL, FM Global, CSA Group, or Intertek (ETL).
– The label will always list the class, division and may list the group and temperature code.
– Some manufacturers claim suitability or built-to hazardous areas in their technical literature, but lack the testing agency’s certification.
– All equipment in Division 1 areas must have an approval label.
– Certain materials, such as rigid metallic conduit, do not have a specific label indicating the Cl./Div.1 suitability.
Note: The content has been organized into 5 groups based on the similarity of concepts and information. The headings for each group have been provided for clarity. Source: https://en.wikipedia.org/wiki/Electrical_equipment_in_hazardous_areas
In electrical and safety engineering, hazardous locations (HazLoc, pronounced haz·lōk) are places where fire or explosion hazards may exist. Sources of such hazards include gases, vapors, dust, fibers, and flyings, which are combustible or flammable. Electrical equipment installed in such locations can provide an ignition source, due to electrical arcing, or high temperatures. Standards and regulations exist to identify such locations, classify the hazards, and design equipment for safe use in such locations.
