I don’t see ammo being set off this way unless the torch hits the brass directly. Even then it probably would be just that one round or maybe a handful.
A canister of black powder or maybe some dynamite???
Dynamite is very safe. Unless you use a "blasting cap" or something like "det-cord" dynamite is inert. As a mater of fact you can toss it into a wood stove and it will burn with some vigor, but it will not detonate. There are several types of dynamite, all are based on nitroglycerin which is mixed with a filler substance.
The fillers used range from fullers earth, a type of clay, to mixtures of sawdust and sodium nitrate, to gun-cotton (nitrocellulose aka smokeless powder) with some sodium nitrate. The first two listed can be made in strength ranging from 40% to 60% nitro, the last listed is 100% and is sold as gelignite.
All forms of dynamite are safer than using nitroglycerin alone as a blasting agent, which had superseded black powder.
Regards,
GtG