Industrial Health and Safety/nonflammable hydrogen mix
I want to use 4% hydrogen, balance helium gas for an experiment in a furnace at 900C. First I was told by the gas supplier that less than 5% hydrogen was not flammable. Then I was told that it is considered flammable because the balance is helium. But helium is inert, so I don't understand why it would be flammable if it is not flammable with a different balance gas. I wanted helium instead of argon balance gas because helium is lighter than air, like hydrogen, and they should stay somewhat together as they are released to the ambient air, and should escape easily. Argon is heavier than air, and I was afraid the two gases could separate more quickly, either the hydrogen becoming flammable, or the argon collecting near the floor and reducing atmospheric oxygen. Are they telling me wrong? I want to make sure that there is not a fire or explosion. Thanks.
This question is somewhat out of my expertise, but I'll give you some basic information:
The flammable range of hydrogen is 4% through 75% in air. However, since you are mixing with an inert gas, this will change these limits. If no oxygen is present (as would be your case), it is possible that no combustion will occur. Also, if you thoroughly mix your gases, they won't necessarily separate as you describe. Fir example, normal air is about 70% nitrogen, but this does not separate from the denser oxygen under typical conditions.
You should consult a qualified chemist before you proceed.
Best of luck, Steve