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“Avoiding the BOOM!"
It may seem overly complicated at first, but there is another part of the Hazardous Location Classification System: Temperature Classes.

Yes - temperatures are also designated with a class system. And this is a different class system from the Class I, II and III classifications covered earlier. Don’t confuse these two classes!

So – why is a Temperature Class needed?
To answer this, I need to ask a question: What happens if there is a light fixture in a gasoline dispensing area, and the area is classified for gasoline vapors (Class I, Division I) - and the light above it gets very hot?

The gas vapors can get ignited by the hot fixture.

Because Fuel (the gas vapors) in the area came in contact with a very hot surface on the light and ignited the vapors. Since different types of Fuel can be ignited at different temperatures, it’s important to know more about the flammability levels of the Fuels in the different Groups, and also – to know how hot a light fixture can get.This brings us back to the Groups of materials covered in earlier Journals. These Groups are determined in part by a material’s explosiveness and by its flammability. And one key measure of a Group’s flammability is the temperature at which a Group’s material ignites.

Fuel Properties: Temperature

Every Fuel listed in Classes I, II and III has a different temperature where they will start to burn. Technically, this is called spontaneous ignition temperature , SIT (or AIT, auto ignition temperature) at which temperature it will ignite spontaneously.
Next: In Journal 12: Haz Loc Temperature Classes, Part II that will include a quick-reference "T-Rating Chart".
Bill Nagengast, President and Lighting Engineer, Solas Ray Lighting, holds over 20 patents in the lighting industry.
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TJ-12 2.9.18