We don't look at cesium compounds any more...
Furthermore, we don't just leave chunks of sodium lying out on the bench. When we're using it, we hustle. That probably helps.
I do research work with nickel metal hydride batteries... Those are really fun, because of all the H2 gas boiling off of the metal matrix.
It sounds like you have a fascinating job. Perhaps it will someday lead to efficient electric cars. Wouldn't that be cool? I could come home and plug my car into a windmill and charge it up.
As to that MSDS, it isn't detailed as to why Na will react with air. It's because of humidity. It is a bit of a trick question because it gets down to the water reaction of which you are well aware.
It could be that your lab maintains a dry air environment and that's why you've not seen an air reaction. But, it would seem responsible for your supplier to at least put a warning label to that affect.
As far as H2 goes, I used to evolve it by dissolving Al in a sodium hydroxide solution when I was a kid. As you are probably well aware, H2 has an LEL of only 1% in air (five times lower than methane). I’m very lucky I didn’t blow myself up!
Best regards, Barnacle