Be cautious with old flashbulbs. Be sure that they still yield vacuum.
It will be indicated by a safety dot on the inside of the glass. This should be blue. Don't use a bulb if its dot has turned pink.

To be even more on the safe side, it would be nice if the bulb had a strong varnish on the outer of the glass or would be used in a flashgun which would yield some protection against morsels of glass flying around.