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To understand what is meant by explosion proof, we must look at the context of the term and the organization that defined it. The National Fire Protection Association (NFPA) began publishing the National Electric Code (NEC®) in 1897. The NEC® is also known as NFPA 70 and ANSI/NFPA 70 from its inclusion in the body of NFPA codes.
The NEC® includes definitions for several types of protection techniques acceptable when designing products for use in hazardous (classified) locations: Explosion proof, dust ignition proof, dust tight, purged/pressurized, intrinsically safe, and hermetically sealed. These definitions set the criteria that must be met by all components installed in hazardous (classified) locations.
To meet the criteria for the explosion proof rating, an enclosure must be able to contain any explosion originating within its housing and prevent sparks from within its housing from igniting vapors, gases, dust, or fibers in the air surrounding it. Therefore, explosion proof, when referring to electrical enclosures, does not mean that it is able to withstand an exterior explosion. Instead, it is the enclosures ability to prevent an internal spark or explosion from causing a much larger blast.
Additionally, the NEC states that equipment must meet the temperature requirements of the specific application in which it is to be installed. This means that the operating temperature of the motor (and its enclosure) or other component cannot be greater than the lowest ignition/combustion temperature of the gases or dusts in the atmosphere where the component is to be installed.
All components are labeled on their nameplate with the distinct classification in which they have been tested and approved for installation.
Each of the protection techniques mentioned above is permitted for use only in very specific applications. For example, components and equipment complying to the dust tight specification are approved for use in Class II, Division 2, or Class III, Division 1 or 2 locations, while those listed as explosion proof are approved for use in Class I, Division 1 or 2 locations.
Often, those products listed for a higher classification surpass the requirements for lower classifications. In fact, the NEC® explicitly states “Equipment that has been identified for a Division 1 location shall be permitted in a Division 2 location of the same class, group, and temperature class,” thereby complying with requirements for the Division 2 areas [ANSI/NFPA 70:500.8(A)(2)].
Nationally recognized testing laboratories such as Underwriters Laboratories and Intertek use marks to denote that the products they have tested conform to the standards set by the (NFPA) and by other international standards organizations. These marks, which include UL, CSA, ETL, and others, can be looked for to determine compliance with the standards. Products that do not bear these marks may not meet the requirements of the NEC.
A ready for production prototype is sent to a testing laboratory. Once approved, that laboratory sends inspectors to the manufacturer on occasion to ensure that nothing has been changed in the design or manufacturing of the component.
Unlike systems sold by HVAC modifiers, units fabricated by Specific Systems® are engineered from the sheet metal to the compressor choices to meet the standards laid out in the NEC®. Specific Systems® uses only fully approved and labeled components and wiring methods on all systems.
Some refineries and processing facilities operate in cooler environments. Because of the often cooler ambient temperatures, heat is often required in these applications. However, typical open coil heaters can not be used in hazardous areas due to the explosion hazard. For these applications, explosion proof fin tube heaters must be utilized.
Explosion proof heaters incorporate fin tube heating elements and enclosed electrical connections to meet code and reduce surface temperatures. Specific Systems® explosion proof heaters are CSA C/US approved.
Additionally, explosion proof crankcase heaters are used in these conditions instead of standard crankcase heaters.
Specific Systems® has been building HVAC and pressurization units for hazardous (classified) areas since 1974, and is the oldest and largest manufacturer in the industry. Because we build the units, we will be here to assist with any questions you have post-installation.
Classes, groups, grades, and categories are all used to define usefulness across any industry. Industrial facilities also utilize divisions such as Explosion-Proof classification to denote the required safety within a hazardous environment. Understanding how to read Explosion-Proof classification will allow you to accurately assess your safety circumstances and comply with the safety regulations of your worksite.
Three factors classify a hazardous area.
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Explosion-Proof Classes
There are three classes of hazardous areas that define the type of flammable substances present in the environment. And all class locations ascend from most hazardous gases (class I), dust (class II), to fibers (class III).
Class I
Flammable vapors and gases are or may be continuously present in the atmosphere in ample amounts that can ignite or explode. Additionally, any arcs, sparks, and sufficient thermal energy could ignite the gases into a potential explosion.
Furthermore, class I locations include refineries, oil storages, spraying booths, petroleum plants, fuel services.
Class II
Combustible dust is present in the air, enough to ignite a fire or explosion at the location. Thus, similar to class I, enough electrical and thermal energy can ignite the particles present at a work location.
Example Locations include granaries, candy manufacturers, and plastic manufacturers.
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Class III
Incendiary fibers that may not suspend in the air are present around machinery. Unlike classes I and II, fibers include general fibers and substances that are not necessarily airborne. However, the material is flammable, and energy produced by machinery can ignite a fire.
Divisions
Hazardous locations are classified based on the probability of high concentrations of the dangerous substance being present under working circumstances–enough to react in combustion.
Division 1 signifies a likely chance of hazardous substances being present in the atmosphere during normal work circumstances. Whereas, Division 2 represents a less likely chance of dangerous substances emerging in the air unless the system (machinery, human error, and more) fails. In other words, the first division is concerned with the constant circulation of hazardous substances in the air, and the second division is concerned with hazards that may escape containment.
Groups
Lastly, groups correlate to specific substances present at the location. Specifically, the letters “A” through “G” connote the different groups of substances. Moreover, the letters correspond to their appropriate classification of gas and vapor, dust, and fibers (which do not appear).
Accordingly, each group below defines what substances a location will contain.
Class I Groups – Gases & Vapors
A
: specifies atmospheres containing acetylene
B
: hydrogen, butadiene, acrolein, ethylene oxide, propylene oxide, or other gases or vapors of equivalent hazard
C
: carbon monoxide, cyclopropane, ethyl ether, ethylene, hydrogen sulfide, or the equivalent
D
: acetone, alcohol, ammonia, benzene, benzol, butane, gasoline, hexane, lacquer solvent, naphtha, natural gas, propane, methane, vinyl chloride, or the equivalent
Class II Groups – Dusts & Grains
E
: metals dust like aluminum and alloys
F
: carbon, charcoal, and coal dust clouds
G
: flour, grains, plastics
Now, how do I find the appropriate gear?
Finding the right gear is, luckily, quite simple. Certified protection will always provide information on the appropriate classes, divisions, and groups that are relevant for the piece. For instance, our Intrinsically Safe Ventilator COPPUS VANO page specifies the “hazardous area rating,” which includes the classification rate (zones, classifications, and more) to inform the consumer of the equipment’s intended purpose.
If you require safety equipment for your workforce, check out our Intrinsically Safe Store catalog. We have equipment suitable for many classifications and groups used by industry leaders.
For more information, visit this document provided by the Occupational Safety and Health Administration to learn more about Explosion-Proof Classification. Also, you can comment below or chat with us for more information regarding Explosion-Proof equipment and more.
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