Thanks for the confidence Jumper
Diesel is a
Class II combustible liquid.
From NFPA 30):
Any liquid that has a closed-cup flash point at or above 37.3?C (100?F)as determined by the test procedures and apparatus outlined in NFPA 30.
Combustible liquids are subdivided as follows:
Class II liquids-are those having flash points at or above 37.3?C (100?F) and below 60?C (140?F).
Class IIIA liquids-are those having flash points at or above 60?C (140?F) and below 93?C (200?F).
Class IIIB liquids-are those having flash points at or above 93?C (200?F)
In general, we don’t consider them flammable (having ignitable vapors at normal temperatures) unless they are stored, processed or handled at or above their flash-point.
One of the reasons I like API RP500 is it discusses the relevant physical properties and behaviors of flammable/combustible materials as they affect their electrical area classification.
From API RP500 [2002]:
5.2.3 Class II Liquids
5.2.3.1 With Class II liquids, the probability of an ignitable vapor-air mixture is low because the liquids typically are handled at temperatures below their flash point and, consequently, do not produce sufficient vapors to form an ignitable mixture. When these liquids are heated above their flash point, additional vapors are generated, and the probability of ignition is increased.
5.2.3.2 The chance of ignition of vapors of Class II liquids is not as great as ignition of the vapors of Class I liquids.
Their vapors normally do not travel as far as the vapors of Class I liquids. Normally, except near points of release, Class II liquids do not produce vapors of sufficient quantity to be considered for electrical classification purposes.
Section 5.2.3.2 above is still true even when the ambient temperature is over 100?F, since diesel vapors are much heavier than air they tend to drop like a rock and hug the ground. In other words, they rarely affect anything unless they are very close to point of release.
I said all that to say this;
in your application, I would treat the diesel storage as Class I, Group D, T2A and use Article 515 as the basis for classifying the location. [Edit add: In my documentation [Section 500.4(B)], I would note it was a
Class II, combustible liquid handled above its flash point] This would be reasonably conservative and I wouldn’t look back. I chose T2A because it was the “common” Group D, T-rating prior to the introduction of Table 500.8(B). If you have an MSDS for the diesel you are using that indicates a lower auto-ignition temperature (VERY unlikely) then use that, of course.
If you also have fuel dispensing in the area, still Class I, Group D, T2A and use Article 514.
