There is no PPR for the energy level of instramentation transformers but igniting a flammable vapour can kill you too and that is not arc Flash but flash fire. Your electrical PPR could offer lots of flame resistance but they are rated differently. A lot of early FR was sold as arc flash protection but things like pocket slashes are acting differently in a fire as opposed to an arc flash or Blast.
If the transformer is intrinsically safe output then in theory you can short the wires in an explosive atmosphere without igniting the gas and there is no possibility of an arc. Now if you are installing the transformer into a panel then PPR is coming into play.
