Hazardous locations are classified according to the hazardous materials present.

• Class I locations are those in which flammable gasses or vapors are present.
• Class II locations are those in which combustible dust is present
• Class III locations are those in which combustible fibers are present

Classification of Areas

Definition	CENELEC	USA
That part of a hazardous area where a flammable atmosphere is continuously present under normal operating conditions	Zone 0	Division 1
That part of a hazardous area where a flammable atmosphere is likely to occur under normal operating conditions	Zone 1	Division 1
That part of a hazardous area where a flammable atmosphere is unlikely to occur under normal operating conditions	Zone 2	Division 2

Types of Protection for Electrical Equipment

Division 0 (Zone 0)	Division 1 (Zone 1)	Division 2 (Zone 2)
Exia	Exia	Exia
	Exib	Exib
	Exd	Exd
	Exe	Exe
	Exp	Exp
	Exs	Exs
		Exn

Exia	intrinsically safe with two fault conditions
Exib	intrinsically safe with one fault condition
Exd	flame proof or explosion proof
Exe	increased safety
Exp	pressurized
Exn	non incendive
Exs	special, which includes encapsulation

Apparatus Gas Grouping

Typical Gasses	CENELEC	USA
Acetylene Hydrogen	IIC	A B
Ethylene Hydrogen Sulfide	IIB	C
Butane Propane Benzene	IIA	D
Methane (mining)	I

Apparatus Temperature Classes

Temperature Class	Maximum Surface Temperature (ºF)	Maximum Surface Temperature (ºC)
T1 T2 T3 T4 T5 T6	842 572 392 275 212 185	450 300 200 135 100 85

Note that the German authority (PTB) uses a G instead of a T