in the context you have it, i would lean towards a fancy noise maker as well- a modern day flash bang. as with its modern day cousin, you still don't want to be near it when it goes off. smoke, lots of noise, i imagine extra sulfur added while being made would make a heck of a smell, the shock wave of it going off, and the sheer terror of seeing something you know will go bang heading in your direction.
On the small arms range (modern weapon), we refer to a squib as a round that does not fire properly. The ammunition has a projectile and a primer, but the powder got left out at the factory. The primer goes off and creates enough force to expel the projectile from the case and enter the barrel, where it promptly looses strength and stops- a dangerous predicament to be in. Compared to L. silvers description, its a similar ignition, just a much different sized purpose.