Class II Hazardous Areas, Groups E, F and G Explained

The National Electrical Code, or NEC, classifies hazardous areas into three different categories; Class I, Class II, and Class III.  To use equipment in or around these types of areas, caution has to be taken to not cause an explosion or fire.  In the U.S., the Underwriter’s Laboratory, UL, can certify products that can be used safely in these hazardous areas.  EXAIR received our UL Classification for our HazLoc Cabinet Cooler® Systems.  Under certain guidelines, the HazLoc Cabinet Coolers can be used in Class I areas for gases and vapors, Class II areas for flammable dust, and Class III areas for ignitable fibers and flyings.  In this blog, I will cover the Class II hazardous areas.

First, HazLoc Cabinet Coolers are designed to keep electrical components cool during summer months and higher ambient conditions.  They are powered by an EXAIR Vortex Tube which only uses compressed air to generate cold air.  They do not have any moving parts, refrigerant, or refrigerant compressors to fail.  These simple, but effective, cooling devices can be used in the toughest of environments.  With the Vortex Tube as the “engine”, the reliability of the EXAIR HazLoc Cabinet Cooler is unmatched.  It is an easy choice for cooling electrical panels and reduce premature shutdowns.

For a fire to occur, we only need three things as described by the fire triangle; oxygen, fuel, and an ignition source.  For an explosion, we need two other conditions, dust concentration and confinement.  For a Class II area, the fuel is combustible dusts.  “Combustible dusts are fine particles that present an explosion hazard when suspended in air under certain conditions.”1  By NEC standards, dust is categorized into three different groups.  Group E is for metal dust.  This will include aluminum and magnesium dust.   Group F is for carbonaceous dust like charcoal, coal, and carbon black.  And Group G is for non-conductive dust like flour, grain, and plastic.  These fine particles can float and collect on equipment in the surrounding areas.  This collection of material can ignite and cause a fire from a spark or a heat source.  If they are contained like within a panel, then there is a possibility of an explosion.

The ignition source (the second leg of the fire triangle above) is generally from electrical equipment, heat, and static.  Arcs and sparks from motors, contacts, and switches can ignite Class II materials; as well as, high temperatures from equipment.  NEC and UL segregate this hazardous location into two divisions.  Class II Division 1 is in an area where dust material is handled, manufactured, or used.  Class II Division 2 is where the dust material is stored or handled other than in the process of manufacturing.  In both divisions, it is important to protect your electrical systems from these particles “floating” in the surrounding air.

The EXAIR HazLoc Cabinet Cooler Systems are designed to keep your electrical panels cool within hazardous areas like Class II above.  Because system shutdowns from electrical components overheating are costly and potentially dangerous, you can install a HazLoc Cabinet Cooler System without sacrificing your panel’s integrity.  If you would like to discuss in more detail about the different types of EXAIR HazLoc Cabinet Coolers, an Application Engineer at EXAIR will be happy to help you.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

 

Note 1: Osha.gov publication

Photo: Inflammable Sign Hazardous Symbol European by Clker-Free-Vector-Images.  Pixabay License

Class I Div 1, Groups A, B, C, and D – Explained

There are a number of hazards to be considered when using electrical equipment in areas where flammable, combustible, or explosive elements do (or might) exist.  The National Electric Cod (NEC) has a system to delineate areas by Class, Division, and Group, based on the specific nature of the hazard.  There are three Classes, each with two Divisions, and a number of Groups that may apply to each of those Divisions.  Today, we’re going to learn about Class I, Div 1, and the Groups that EXAIR HazLoc Cabinet Cooler Systems are designed for use in.

“Class I” simply means that ignitable concentrations of flammable gases, vapors, or airborne liquids can exist under normal operating conditions.  Examples of such areas include:

  • Refineries
  • Distilleries
  • Fuel storage facilities
  • Spray paint/coating booths

Now, not every single square foot of such areas have ignitable elements in the atmosphere all the time; Class I just means they can have them.  This is where the Divisions come in.

“Div 1” means that these ignitable elements can exist during normal operations, as opposed to “Div 2” which means it’s possible, but not likely.  A good example of the difference here might be a paint booth: inside a paint booth, normal operation is DEFINED as volatile liquid (paint) being discharged into the atmosphere in a spray of fine droplets – hence, that would be Class I, Div 1.  The area adjacent to the paint booth should only have that spray of fine droplets in the air if, say, the exhaust hood of the paint booth failed, or if an operator inadvertently sprayed paint outside the booth, etc…any event or condition that’s possible, but not likely – hence, that would be Div 2.

Not only are hazardous areas classified by Class (nature of the hazardous material,) and Division (likelihood of existence of it,) but they’re further delineated by the type of hazardous material, and these are sorted into Groups.  For Class I (gases, vapors or airborne liquids,) four Groups are applicable.  Materials fall into these groups (with one exception) based on two properties:

  • Maximum Experimental Safe Gap (MESG) – this is a standardized measurement of how easily a gas flame (produced by the ignition of the material) will pass through a narrow gap, bordered by heat-absorbing metal.  
  • Minimum Igniting Current (MIC) ratio, which is the ratio of the minimum electrical current required to ignite the material, by the minimum current required to ignite methane under the same conditions.

Group A is the above mentioned exception.  Because acetylene, of all hazardous materials detailed across the different groups, results in the most violent explosion when ignited, it gets a group all to itself.

Group B is for flammable gases, liquids, and vapors with a MESG less than 0.45mm, and a MIC ratio of 0.40 or less.  Hydrogen, butadiene, ethylene oxide, propylene oxide, and acrolein are popular examples of such materials.

Group C materials have a MESG less than 0.75mm and a MIC ratio less than 0.80 (but greater than 0.40, which would put it in Group B.)  Carbon monoxide, ether, hydrogen sulfide, morphline, cyclopropane, ethyl, isoprene, acetaldhyde and ethylene are some good examples.

Group D consists of all other flammable gases, vapors & liquids with MESG’s over 0.75mm and MIC ratios greater than 0.80.  Gasoline, acetone, ammonia, and benzene are common examples.  Methane is also in Group D, which gives perspective on the materials in the other Groups, which all have a fractionally lower Minimum Igniting Current than methane…the lower the MIC ratio, the lower the current needed for ignition, and therefore, the placement in a more restrictive Group.

EXAIR HazLoc Cabinet Cooler Systems are engineered and approved for use in Class I, Div 1, Groups A, B, C, or D environments.  If you have an electrical panel that needs heat protection in such an area, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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