Explanation of Hazardous Locations – Class 1 Div 1, Groups A, B, C, and D

My first job out of the Navy was in industrial & chemical pump repair. Oftentimes, the customer would remove the pump from its installation and send it in for us to fix. Other times, we’d go out to their facility if it was an exceptionally large pump and/or if seeing what it was doing (or not doing) while it was running was beneficial. Sometimes the pump was located in an area that was designated as explosion proof, or classified. There were different precautions we’d need to take, depending on what the particular hazard (or potential for a hazard) was. More often than not, that meant that we had to observe some VERY basic safety rules…no open flame was a biggie…but occasionally, we’d have to take apart a pump in an area that required us to use non-sparking tools. One time, I actually had to attach a grounding strap to my wrist, because even a spark from a static charge could have been bad news.

Electrical products that are operated in such areas have to meet certain requirements, or classifications.  In the United States, the National Electrical Code (NEC) defines these areas in a system of Classes, Divisions, and Groups, depending on the nature of the material that presents the hazard (Class), whether it normally exists or if it’s just possible in abnormal situations (Division), and the specific type of the subject material (Group). Today’s blog is all about what would classify an area as Class I, Division 1, and which Group the specific hazardous material falls under.

A Class I location means that the hazard is a flammable gas or vapor which is present in the area, in a high enough concentration to be considered ignitable. These were the locations that we were required to use non-sparking tools in, and for good reason. Some examples of Class I locations are:

  • Petroleum refineries
  • Gasoline storage or dispensing areas
  • Aircraft hangars and fueling stations
  • Spray finishing rooms or booths

Division 1 means that the flammable gas or vapor that makes the area a Class I location is present in the atmosphere during normal operating conditions and/or when the gas or vapor is released to the atmosphere during maintenance or repair work. These gases & vapors aren’t present in ALL areas of the above listed Class I examples during normal operation, so only the areas where they ARE present during normal operations would be defined as Division 1. For example:

  • Areas where a gasoline tank (in a refinery or gasoline storage/dispensing station, for example) is vented to the atmosphere are Class I Division 1, because the vapor coming out of the vent is doing so by design…you can’t pump a liquid into a non-vented tank.
  • Only the parts of an aircraft hangar where fuel is actually being handled are Division 1. That wouldn’t necessarily apply to a stock or communications room in the hangar, though.
  • The interior of a paint booth is Division 1 because the spray is volatile, as is the immediate vicinity adjacent to an open spray booth.

Class I designation is further divided into four Groups, based on two specific characteristics of the gas or vapor that basically express how easy it is to cause (or how hard it is to prevent) an explosive hazard:

  • Maximum Experimental Safe Gap (MESG) – The gas is put in the interior chamber of a vessel with an adjustable gap that leads to the outer chamber. MESG is the largest gap between the chambers that will prevent ignition of the gas.
  • Minimum Igniting Current (MIC) ratio. This is the ratio of the minimum current from an inductive spark required to ignite the gas, divided by the minimum current from an inductive spark that will ignite methane under the same conditions.
  • Group A: Acetylene
    • MESG = 0.25 mm
    • MIC ratio = 0.017
  • Group B: Hydrogen, butadiene, ethylene oxide, propylene oxide, and acrolein
    • MESG <0.45mm (except acetylene)
    • MIC ratio <0.4 (except acetylene)
  • Group C: Ethylene, cyclopropane and ethyl ether
    • MESG = 0.45mm to 0.75mm
    • MIC ratio = 0.4 – 0.8
  • Group D: Acetone, ammonia, benzene, butane, ethanol, gasoline, hexane, methane, methanol, methane, naphtha, natural gas, propane and toluene
    • MESG >0.75mm
    • MIC ratio >0.8

EXAIR HazLoc Cabinet Cooler Systems are engineered and approved for use on electrical enclosures in these areas, as well as Class II and Class III. Our ATEX Cabinet Cooler Systems are compliant with the European Union’s ATEX Directive (Zones 2 and 22).

Both the HazLoc (left) and ATEX (right) Cabinet Cooler Systems are available from stock in NEMA 4 and NEMA 4X ratings.

Wherever the panel you need cooling for is located, we’ve very likely got a reliable and safe solution. If you’d like to find out more, give me a call.

Russ Bowman, CCASS

Application Engineer
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