Thanks for the pdf it is interesting.
When I wrote to them it was when the storage of blackpowder was proposed. In their reply they briefly outlined the test and the reason for it. It seems they have done more research into it and more information is now available.
It does surprise me that they did not use the plastic canisters BP comes in. The substitutes they used might be a different grade of plastic that is more heat resistant and may be thicker walled and not give a completely accurate result.