How Do Flame Arrestos Work

LISK Flame Arrestors

Class I, Division 1 location is a location:

In which ignitable concentrations of flammable gases or vapors may exist under normal conditions; or
In which ignitable concentrations of flammable gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or
In which breakdown or faulty operation of equipment or processes might release ignitable concentrations of flammable gases or vapors, and might also cause simultaneous failure of electric equipment.

NOTE: This classification usually includes locations where volatile flammable liquids or liquefied flammable gases are transferred from one container to another; interiors of spray booths and areas in the vicinity of spraying and painting operations where volatile flammable solvents are used; locations containing open tanks or vats of volatile flammable liquids; drying rooms or compartments for the evaporation of flammable solvents; inadequately ventilated pump rooms for flammable gas or volatile flammable liquids; and all other locations where ignitable concentrations of flammable vapors or gases are likely to occur in the course of normal operations.

Class I, Division 2 location is a location:

In which volatile flammable liquids or flammable gases are handled, processed, or used, but in which the hazardous liquids, vapors, or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such container systems, or in case of abnormal operating equipment; or
In which ignitable concentrations of gases or vapors are normally prevented by positive mechanical ventilation, and which might become hazardous through failure or abnormal operations of the ventilating equipment; or
That is adjacent to Class I, Division 1 location, ant to which ignitable concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided.

NOTE: This classification usually includes locations where volatile flammable liquids or flammable gases or vapors are used, but which would become hazardous only in case of an accident or of some unusual operating condition. The quantity of flammable material that might escape in case of an accident, the adequacy of ventilating equipment, the total area involved, and the record of the industry or business with respect to explosions or fires are all factors that merit consideration in determining the classification and extent of each location.

Piping without valves, checks, meters, and similar devices would not ordinarily introduce a hazardous condition even though used for flammable liquids or gases. Locations used for storage of flammable liquids or of liquefied or compressed gases in sealed containers would not normally be considered hazardous unless subject to other hazardous conditions.

Electrical conduits and their associated enclosures separated from process fluids by a single seal barrier are classed as a Division 2 location if the outside of the conduit and enclosures is a nonhazardous location.

NEC Division System Gas & Dust Groups

Area	Group	Representative Materials
Class I, Division 1 & 2	A	Acetylene
	B	Hydrogen
	C	Ethylene
	D	Propane
Class II, Division 1 &2	E (Division 1 only)	Metal dusts, such as magnesium (Division 1 only)
	F	Carbonaceous dusts, such as carbon and charcoal
	G	Non-conductive dusts, such as flour, grain, wood, plastic
Class II, Division 1 & 2	Description	Ignitable fibers/flyings, such as cotton, lint, rayon

NEC & IEC Zone System Gas & Dust Groups

Area	Group	Representative Materials
Zone 0, 1 & 2	IIC	Acetylene & Hydrogen (equivalent to NEC Class I, Groups A and B)
	IIB + H2	Hydrogen (equivalent to NEC Class I, Group B)
	IIB	Ethylene (equivalent to NEC Class I, Group C)
	IIA	Propane (equivalent to NEC Class I, Group D)