Explosion-Proof
Guidelines & Nomenclature.
Defining Hazard Environments.
Scientific Systems has been building HVAC, pressurization, and chiller units for hazardous (classified) areas since 1965, and is the oldest manufacturer in the industry. Because we manufacture the units, we will be here to assist with any questions you have post-installation.
“Explosion Proof” is only a generic term. When applied to equipment it does not by itself assure that the item is safe to use in a hazardous location. Required are additional code designations as issued by agencies in the United States, Canada, Europe and other parts of the world.
An “Explosion Proof” designation under the NEC must include a “Class”, a “Group” and a “Division”. Class I refers to gases, Class II to dusts, and Class III to fibers and flyings. Groups relate to the ignitability of the material. Two Divisions are defined as outlined below.
NEC Class & Division Architecture.
Gases
Locations where flammable gases or vapors are, or may be, present in the air in quantities sufficient to produce explosive or ignitable mixtures.
Includes Groups A, B, C, D
Dusts
Locations where the presence of combustible dust present a fire or explosion hazard.
Includes Groups E, F, G
Fibers & Flyings
Locations where easily ignitable fibers or flyings are present but not likely to be suspended in the air in quantities sufficient to produce ignitable mixtures.
The hazardous concentration of flammable gases, vapors or suspended combustible dusts are present continuously, intermittently or periodically under normal operating conditions.
Volatile, flammable liquids or flammable gases present, but normally confined within closed containers or systems from which they can escape only under abnormal operating or fault conditions. Combustible dusts not normally in suspension nor likely to be thrown into suspension.
Classification of Gases, Vapors & Dusts.
Groups are defined by letters. Groups A, B, C and D fall under Class I. Group A is the most easily ignited, Group D the least. Groups E, F, and G fall under Class II. For a more complete summary refer to NFPA 497M “Classification of Gases, Vapors and Dusts for Electrical Equipment in Hazardous (Classified) Locations”.
Group A
Class I / Highest Volatility
- acetylene
Group B
Class I / High Volatility
- formaldehyde (Gas)
- hydrogen
Group C
Class I / Moderate Volatility
- acetaldehyde
- allyl alcohol
- butyl mercaptan
- n-butyraldehyde
- carbon monoxide
- crotonaldehyde
- dicyclopentadiene
- diethyl ether
- diethyl amine
- 1, 1-dimethyl hydrazine
- di-isopropyl amine
- dimethylamine
- 1, 4-dioxane
- di-n-propylamine
- epichlorohydrin
- ethylene
- ethyl mercaptan
- hydrogen cyanide
- hydrogen selenide
- hydrogen sulfide
- isobutyraldehyde
- methylacetylene
- methyl ether
- methyl mercaptan
- monomethyl hydrazine
- morpholine
- nitroethane
- nitromethane
- 2-nitropropane
- propionaldehyde
- n-propyl ether
- tetrahydrofuran
- triethylamine
- valeraldehyde
Group D
Class I / Standard Volatility
- acetic acid (glacial)
- acetone
- acetonitrile
- acrylonitrile
- ammonia
- amyl acetate
- sec-amyl acetate
- benzene
- butane
- butanol (butyl alcohol)
- 2-butanol
- butyl acetate
- sec-butyl acetate
- butylamine
- chlorobenzene
- cyclohexane
- cyclohexene
- cyclopropane
- 1, 1-dichloroethane
- 1, 2-dichloroethylene
- 1, 3-dichloropropene
- di-isobutylene
- ethane
- ethanol (ethyl alcohol)
- ethyl acetate
- ethyl benzene
- ethyl chloride
- gasoline
- heptane
- heptene
- hexane
- hexenes
- isoamyl acetate
- isoprene
- isopropyl ether
- LPG (liquified pet gas)
- methane (natural gas)
- methanol (methyl alcohol)
- methyl acrylate
- methyl amine
- methyl cyclohexane
- methyl ethyl ketone
- methyl isobutyl ketone
- methyl isocyanate
- methyl methacrylate
- 2-methyl-1 propanol
- naphtha (petroleum)
- nonane
- nonene
- octane
- octene
- pentane
- 1-pentanol (amyl alcohol)
- 2-pentanone
- 1-pentene
- propane
- 1-propanol (propyl alcohol)
- 2-propanol (isopropyl alcohol)
- propylene
- styrene
- toluene
- turpentine
- vinyl chloride
- xylenes
Group E
Class II / Combustible Dust
Atmospheres with combustible metal dusts regardless of resistivity, or other combustible dusts of similar hazardous characteristics having resistivity of <10⁵ ohm-cm.
Group F
Class II / Carbon Dust
Atmospheres with carbon black, charcoal, coke or coke dusts which have more than 8% total volatile material(1) or atmospheres containing these dusts sensitized by other materials so that they present an explosion hazard, and having resistivity >10² ohm-cm but equal to or <10⁸ ohm-centimeter.
(1) Carbon Black per ASTM D 1620; charcoal coke and coke dust per ASTM D271.
Group G
Class II / High Resistivity
Atmospheres with combustible dusts with resistivity of 10⁵ ohm-centimeter or greater.
CSA Group HazLoc Poster
Download the comprehensive chart for Canadian Standards Association hazardous location certifications.
Secure Your Infrastructure.
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