AWOL:
SlightIy OT: I once read an essay (it may have been by Primo Levi) about not smothering a petrol (or I guess any flammable fumes or gas) leak with a CO2 extinguisher - the rush of ice crystals through the nozzle, and the drying effect on the air can cause static charges to build up and spark.
Like the dryness of acetylene when it comes from the tank. Can be quite sensitive to static and create - surprises.
I do wonder how they managed to use hydrogen for balloons back in the day. They must have had some method of hydrating the gas when filling those blimps.