Hazardous area classification systems identify electrical equipment locations with potential fire and explosion risks and establish the necessary protections and installation methods based on the type, properties, and severity of the hazard. Companies in the USA and Canada use two classification systems: traditionally, the Class/Division/Group system and, increasingly, the Zone system employed throughout the rest of the world.
The Class/Division/Group system uses three designators to categorize hazardous areas:
- Class:The Class designator defines the general nature of the hazard, such as its state of matter or form.
- Division:The Division designator indicates the probability of a hazard igniting or producing an explosion.
- Group:The Group designator describes the type of hazard with greater specificity than the Class designator and identifies precise chemical and material compositions within the surrounding atmosphere.
Hazardous area classifications significantly impact the operations of the power generation industry. However, every industry that uses electrical equipment needs to be aware of the risk of ignition or explosion. Products and components can that be affected by hazardous area classification systems include:
- Battery systems
- Combustion-based electrical generator plants
- Electrical equipment with hot surfaces
- Fuel and ignition systems
- Generator cooling systems
Recognized approval agencies ensure a facility’s electrical equipment is designed, constructed, and installed according to the country’s established laws, regulations, and codes.
National Electrical Code (NEC) Article 500 and National Fire Protection Agency (NFPA) 497 establish the Class/Division/Group system for classifying hazardous areas. This system allows for precise, standardized communication about the types of hazardous locations by classifying them based on the type of material (Class), the probability of explosion or ignition (Division), and the products comprising the hazards (Group).
Each class describes the nature of the hazardous compound. This qualification is important because different material types react to the presence of heat and electricity differently.
- Class I: Gases or vapors.Class I hazardous areas may contain flammable vapors or gases in quantities large enough to cause a fire or an explosion. Examples of these gases and vapors include hydrogen, carbon monoxide, and ethylene oxide.
- Class II: Dust.Class II hazardous areas may contain combustible or conductive dust in quantities large enough to cause a fire or an explosion. Examples of these dusts include metal dusts such as aluminum dust or carbon-based dusts such as coal dust.
- Class III: Fibers and flyings.Class III hazardous areas may contain fibers and flyings (i.e., small airborne parts) in quantities large enough to ignite and cause a fire or an explosion. Examples of these fibers and flyings include wood, plastic, and grain.
Hazardous areas don’t always maintain a constant level of risk. In these circumstances, rather than evaluating these areas along a spectrum or constantly reevaluating at-risk areas, facilities classify them by their likelihood of having hazardous materials.
- Division 1: High probability. Division 1 areas are highly likely to experience a fire or explosion under ordinary operating conditions. Packaging areas within food processing plants that routinely have airborne starch are an example of Division 1 areas.
- Division 2: Low probability. Division 2 areas are highly unlikely to experience a fire or explosion during typical operations. However, under abnormal operating conditions, fire or explosion may still occur. An example of a Division 2 area is closed-loop fluid heating systems that use hot oil as the oil is only present outside of the system during equipment malfunctions.
The seven group designators define the specific type of hazardous compound more precisely than class designations:
- Group A:Contains acetylene.
- Group B:Contains flammable gases, flammable liquid-produced vapors, or aerosolized combustible liquid-produced vapors, in which the Minimum Igniting Current (MIC) ratio <0.40 or the Maximum Experimental Safe Gap (MESG) is <0.45 mm. Examples of Group B contents include acrolein, butadiene, hydrogen, or propylene oxide.
- Group C:Similar contents to Group B but with a MIC ratio of 0.40<MIC≤0.80 or a MESG of 0.45 mm<MESG≤0.75 mm. Examples of Group C contents include carbon monoxide, cyclopropane, ether, or ethylene.
- Group D:Similar to Group B and C conditions but with a MIC ratio >0.80 or a MESG >0.75 mm. Examples of Group D contents include acetone, ammonia, benzene, butane, and gasoline.
- Group E:Contains combustible metal dusts, such as aluminum alloy, bronze, chromium, titanium, and zinc.
- Group F:Contains combustible carbon-based dusts with ≥8% volatile compounds, such as coal and coke.
- Group G:Contains solid dusts, fibers, or flyings not covered by the Groups E or F, such as flour, starch, sugar, wood, and plastic particles.
Under this comprehensive system, hazardous areas are classified as Class [X], Division [Y], Group [Z]. For example, a mine with aluminum dust frequently present is designated as Class II, Division 1, Group E.
While the USA and Canada widely employ the Class/Division/Group classification system, the rest of the world uses the Zone classification system. Based on National Electrical Code (NEC) Articles 505 and 506, this system also uses Zones/Groups method as established by the International Electrotechnical Commission (IEC).
Zones describe the general nature of the compound and the probability of its concentration causing an explosion or igniting. There are six zones: three for gases, vapors, and mists as described under NEC Article 505 and three for dusts as defined under NEC Article 506. The zones are:
For Gases, Vapors, and Mists:
- Zone 0:Continuous or near-continuous presence of ignitable or combustible concentrations of gases and vapors during typical operations.
- Zone 1:Highly likely that ignitable or combustible concentrations of gases and vapors are present during typical operations.
- Zone 2:Unlikely that gases and vapors will be present in ignitable or combustible concentrations during typical operations or the levels may only be present for short durations.
- Zone 20: Continuous or near-continuous presence of combustible dusts or ignitable fibers and flyings during typical operations.
- Zone 21:Highly likely that combustible or ignitable concentrations of dust or fibers and flyings are present during typical operations.
- Zone 22:Unlike that combustible dusts or ignitable fibers and flyings will be present in high enough concentrations during typical operations or may only be present for short durations.
Similar to the Group designator in the Class/Division/Group system, groups in the Zone system describe the type of airborne material with more detail. These designations also specify information about the site of the hazardous area. The groups include:
- Group I: Mines.Mines are susceptible to naturally occurring flammable gas mixtures—i.e., firedamps.
- Group II: Explosive Gas.Group II areas are non-mine areas that are prone to the occurrence of firedamps. These atmospheres contain gases such as petrol and methane (Group IIA), ethylene and ethyl ether (Group IIB), and hydrogen or carbon disulfide (Group IIC).
- Group III: Explosive Dusts.These atmospheres contain non-gaseous hazards such as combustible dusts and ignitable fibers or flyings. Examples of these compounds include combustible flyings (Group IIIA), non-conductive dusts with high electrical resistivity such as cement dust (Group IIIB), and conductive dusts such as aluminum dust (Group IIIC).
Under the Zone system, areas are designated in the following format: Zone [X], Group [Y]. For example, the same mine with continuous aluminum dust is designated as Zone 20, Group IIIC.
Who Certifies Equipment Used in Hazardous Areas
Government or independent approval agencies certify electrical equipment intended for use in various hazardous locations. In North America, three of the principal agencies are:
Underwriters Laboratories (UL)
Underwriters Laboratories (UL) provides certification, evaluation, and testing services. They certify products based on their adherence to both ordinary location safety measures and hazardous area protection methods. UL also requires compliance with ANSI and CAN standards.
Every division marking has an area classification under the Class/Division/Group system and includes the product’s temperature class. UL certified products are marked as UL listed or UL classified.
Factory Mutual (FM)
Factory Mutual (FM) has a global certification program. In addition to certifying equipment for use in hazardous locations, the agency tests and evaluates building materials, roofing and wall assemblies, and construction, electrical, and fire-related detection equipment.
“FM Approved” certifications mark the specific model of approved equipment and the FM approval class.
Canadian Standard Association (CSA)
Canadian Standard Association (CSA) provides testing, inspection, and certification services. The organization employs either the Class/Division/Group system or the Zone system when marking certified equipment and products. CSA marks may also include the temperature class, protection concept code, and gas group as needed.
Contact Dietz Electric Today
At Dietz Electric Co., Inc., we specialize in supplying and servicing motors designed for use in hazardous areas. Our engineers have years of experience with motors that are UL, FM, and CSA certified.