Hydrogen is a pain to work with. Other than being explosive in air, it leaks unless the seal is near perfect. On the flip side, it's easy to obtain via electrolysis. If argon is acceptable it would be much easier to work with. The pdf reads like a mixture was used. I have done some work @ 1300C where we needed an inert atmosphere, so we plumbed an argon tank to the furnace and ran it at a slight positive pressure.