I don’t think I have done a process safety course or a HAZMAT course where I do not have a lengthy sidebar discussion to explain why NH3 is a flammable gas under OSHA definitions, but not under DOT definitions. Yes, NH3 has a LEL of 15-16% and a UEL of 25-28% so it has a flammable range, but it is this same data that exempts us from classifying it as a flammable gas while it is being transported. Both OSHA and DOT have their own way of classifying flammables and this is where so many get lost. Let’s break these down and explain: