Hazards Classified by NEC Group

This list is not exhaustive. It is meant only as an introductory aid to classification.

Certain metal dusts have characteristics which require additional safeguards — such as extremely low ignition temperatures and energies and are therefore not included in Classes I, II or III.

Class I encompasses Groups A, B, C and D; Class II contains Groups E, F, and G. Class III (fibers and "flyings") has no groups, only divisions.

Group A

  • acetylene

Group B

  • formaldehyde (Gas)
  • hydrogen
  • manufactured gases containing >30% hydrogen (by volume)

Group C

  • acetaldehyde
  • allyl alcohol
  • butyl mercaptan
  • n-butyraldehyde
  • carbon monoxide
  • crotonidehyde
  • dicyclopentadiene
  • diethyl ether
  • diethylamine
  • 1, 1-dimethyl hydrazine
  • di-isopropylamine
  • dimethylamine
  • 1, 4-dioxane
  • di-n-propylamine
  • epichlorohydrin
  • ethylene
  • ethylenimine
  • ethyl mercaptan
  • hydrogen cyanide
  • hydrogen selenide
  • hydrogen sulfide
  • isobutyridehyde
  • isopropyl glycidyl ether
  • methylacetylene
  • methyl ether
  • methyl formal
  • methyl mercaptan
  • monomethyl hydrazine
  • morpholine
  • nitroethane
  • nitromethane
  • 2-nitropropane
  • propionaldehyde
  • n-propyl ether
  • tetrahydrofuran
  • triethylamine
  • UDMH 1,1-dimethyl hydrazine
  • valeraldehyde

Group D

  • acetic acid (glacial)
  • acetone
  • acetonitrile
  • acrylonitrile
  • allyl chloride
  • ammonia
  • n-amyl acetate
  • sec-amyl acetate
  • benzene
  • butane
  • 1-butanol (butyl alcohol)
  • 2-butanol
  • n-butyl acetate
  • sec-butyl acetate
  • butylamine
  • butylene
  • chlorobenzene
  • cyclohexane
  • cyclohexene
  • cyclopropane
  • 1, 1-dichloroethane
  • 1, 2-dichloroethylene
  • 1, 3-dichloropropene
  • di-isobutylene
  • ethane
  • ethanol (ethyl alcohol)
  • ethyl acetate
  • ethyl acrylate (inhibited)
  • ethlyamine
  • ethyl benzene
  • ethyl chloride
  • ethylenediamine (anhydrous)
  • ethylene dichloride
  • ethylene glycol monomethyl ether
  • ethyl formate
  • gasoline
  • heptane
  • heptene
  • hexane
  • hexenes
  • isoamyl acetate
  • isoamyl alcohol
  • isobutyl acrylate
  • isoprene
  • isopropyl acetate
  • isopropylamine
  • isopropyl ether
  • LPG (liquefied petroleum gas)
  • methane (natural gas)
  • methanol (methyl alcohol)
  • methyl acetate
  • methyl acrylate
  • methylamine
  • methyl cyclohexane
  • methyl ethyl ketone
  • methyl formate
  • methyl isobutyl ketone
  • methyl isocyanate
  • methyl methacrylate
  • 2-methyl-1-propanol
  • (isobutyl alcohol)
  • 2-methyl-2-propanol
  • naphtha (from petroleum, also benzine, ligroin)
  • nonane
  • nonene
  • octane
  • octene
  • pentane
  • 1-pentanol (amyl alcohol)
  • 2-pentanone
  • 1-pentene
  • propane
  • 1-propanol (propyl alcohol)
  • 2-propanol (isopropyl alcohol)
  • n-propyl acetate
  • propylene
  • propylene dichloride
  • pyridine
  • styrene
  • toluene
  • turpentine
  • vinyl acetate
  • vinyl chloride
  • vinylidene chloride
  • xylenes

Group E

  • Atmospheres containing combustible metal dusts regardless of resistivity, or other combustible dusts of similar hazardous characteristics having resistivity of <105 ohm-cm (only division/zone 1, never 2; includes dusts of aluminum and magnesium and their commercial alloys)

Group F

  • Atmospheres containing carbon black, charcoal, coke or coke dusts which have more than 8% total entrapped volatile material* or atmospheres containing these dusts sensitized by other materials so that they present an explosion hazard, and having resistivity >100 ohm-cm but equal to or < 108 ohm-centimeter.

*Carbon black per ASTM D 1620 and charcoal coke and coke dust per ASTM D271.

Group G

  • Atmospheres containing combustible dusts with resistivity of 105 ohm-centimeter or greater and not included in Groups E or F such as flour, grain, wood, plastic, and chemicals.