National Electric Code:
Hazardous Locations - Articles 500-516 Hazardous Locations are areas where a potential for explosion and/or fire exists due to flammable gasses, vapors or finely pulverized dusts in the atmosphere. Easily ignitable fibers or debris in the atmosphere can also cause a location to become Hazardous.
Class I Locations:
Those areas where flammable Gases or Vapors may be present in sufficient quantities to produce explosive or flammable mixtures.
Petroleum Refining - Petrochemical Plants - Utility Gas Plants - Aircraft/fuel servicing Areas, etc.
Class II Locations:
Those areas where combustible Dust is present in sufficient quantities to produce explosive or ignitable mixtures.
Grain Elevators - Magnesium Facilities - Mfg/Storage of Starch - Flour/Feed Mills
Class III Locations:
Those areas where easily ignitable Fibers are present.
Wood burning plants - Textile Mills - Cotton Gins - Cotton Seed Mills
Division 1 Locations:
Those areas where the Hazard is constantly present in the atmosphere
Division 2 Locations:
Those areas where the Hazard is normally contained or stored and can only escape by rupture or deterioration of the containers or systems.
Chemical Groups as defined by NEC - Table 500-2 Groups A,B,C,D Atmospheres containing Hazardous Chemicals/Gases/Vapors
Group E Atmospheres containing Metal Dust
Group F Atmospheres containing Carbon Black, Charcoal, Coal, or Coke Dust
Group G Atmospheres containing Flour, Starch, Grain, Combustible Plastics, or Chemical Dusts

Temperature Codes

Identification Number

Degrees C

Identification Number

Degrees C

T1

450

T3A

180

T2

300

T38

165

T2A

280

T3C

160

T28

260

T4

135

T2C

230

T4A

120

T2D

215

T5

100

T3

200

T6

85

MAXIMUM TEMPERATURE RANGE IDENTIFICATION NUMBERS