Hazardous Area Classifications

Hazardous Area Classifications
Hazardous Locations Guide
Class I – Gases or Vapors
Class II- Dust
Class III-Fibers
Division 1
Hazardous Vapors present
Air Suspended
Fibers handled, manufactured, or stored
Hazardous vapors contained, but may be
present
Surface accumulated, Non-air suspended
Fiber handled or stored
Group A
Atmospheres containing
acetylene
Group E
No Groups for Class III
Group B
Atmospheres containing
hydrogen or gases of vapors
of equivalent hazard such as
manufactured gas
Group C
Atmospheres containing
ethyl-ether vapors, ethylene
or cyclo-Propane
Group F
Atmospheres containing
carbon black, coal, or coke
dust
Group D
Atmospheres containing
gasoline, hexane, naptha,
benzene, butane, propane,
alcohol, acetone, benzol,
lacquer solvent vapors, or
natural gas
Group G
Atmospheres containing
flour, starch, or grain dust
Division 2
Atmospheres containing
metal dust including
aluminum, magnesium, their
commercial alloys, and other
metals of similarly
hazardous characteristics
Atmospheres containing textile, wood or
synthetic fibers
Group Specifics
Group A
Group C
Group D
acetylene
acetaldehyde
allyl alcohol
n-butyraidehyde
carbon monixide
crotonaldehyde
cyclopropane
diethyl ether
diethylamine
epichlorohydrin
ethylene
ethylenimine
ethyl mercaptan
ethyl sulfide
hydrogen cyanide
hydrogen sulfide
morpholine
2-nitropropane
tetrahydrofuran
unsymmetrical dimethyl
hydrazine
(UDMH 1, 1-dimethyl hydrazine)
Acetic acid (glacial)
acetone
acrylonitrile
ammonia 3)
benzene
butane
1-butanol (butyl alcohol)
2-butanol (secondary butyl alcohol)
n-butyl acetate
isobutyl acetate
di-isobutylene
ethane
ethanol (ethyl alcohol)
ethyl acetate
ethyl acrylate (inhibited)
ethylene dichloride
ethylene glycol monomethyl
Group B
acrolein (inhibited) 2)
arsine
butadiene 1)
ethylene oxide 2)
hydrogen
manufactured gases containing more than
30% hydrogen (by volume)
propylene oxide 2)
propyinitrate
Fluid Control Systems
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Hazardous Locations Guide
Group Specifics (continued)
Group D (continued)
Group D (continued)
Group E
ether gasoline
heptanes
hexanes
isoprene
isopropyl ether
mesityl oxide
methane (natural gas)
methanol (methyl alcohol)
3-methyl-1 butanol (isoamyl alcohol)
methyl ethylketone
methyl isobutyl ketone
2-methyl-1 –propanol
(isobutyl alcohol)
2-methyl-2-propanol
(tertiary butyl alcohol)
petroleum naphtha 4)
pyridine
octanes
pentanes
1-pentanol (amyl alcohol)
propane
1-propanol (propyl alcohol)
2-propanol (isopropyl alcohol)
propylene
styrene
toluene
vinyl acetate
vinyl chloride
xylenes
Containing metal dust, including aluminum, magnesium, and their commercial
alloys, and other metals of similarly
hazardous characteristics.
Group F
Containing carbon black, coal or coke
dust.
Group G
Containing flour, starch or grain dust.
Notes:
1) Group D equipment shall be permitted for this atmosphere if such epuipment is isolated in accordance with section 501-5(a) of
National Electric Code by sealing all conduit 1/2 inch size or larger.
2) Group C equipment shall be permitted for this atmosphere if such equipment is isolated in accordance with Section 501-5(a) of
National Electric Code by sealing all conduit 1/2 inch size or larger.
For classification of areas involving ammonia atmosphere:
4) See Safety Code for Mechanical Refrigeration (ANSI/ASHRAE 15-1978) and Safety Requirements for the Storage and Handling of
Anhydrous Ammonia (ANSI/CGA G2.1-1972).
5) A saturated hydrocarbon mixture boiling in the range 68-275ºF (20-135ºC). Also known by the synonyms benzene, ligroin,
petroleum ether, or naphtha.
Intrinsic Safety
Intrinsic safety prevents instruments and low voltage circuits in hazardous areas from releasing sufficient energy to ignite volatile
gases. The excess electrical energy in the form of voltage and current is limited by inserting energy-limiting devices, known as
intrinsically safe barriers, in the circuits. To properly select the correct barrier the field device must be known. These field devices are
classified as either simple (non-energy storing) or complex, which can store energy. Complex devices must be tested and approved by
a third party to be used in intrinsically safe circuits. The entity parameters of approved devices are then compared to the proper safety
parameters of the barrier to ensure an intrinsically safe circuit.
• There are three components to an intrinsically safe circuit: the field device, intrinsically safe barrier and field
wiring.
• Field devices known as intrinsically safe apparatus are classified as simple or complex.
• Simple apparatus, which do not need to be approved, are non-energy storing devices such as contacts, thermocouples, RTDs, LEDs and resistors.
• Complex apparatus such as transmitters, solenoids, relays and transducers may store excess energy and need to
be approved by a third party.
• Contacts, transmitters and temperature sensors are the most commonly used field devices in intrinsically safe
applications.
• The intrinsically safe barrier limits the current with a resistor and the voltage with a zener diode.
• Intrinsically safe circuits are designed so that they operate properly under normal conditions, but keep the
energy levels below the ignition curves when a fault condition occurs.
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