Wotzdisden

your on the right track john with sprinkler system

It detects a fire/heat hazard and sets off the sprinklers

the first beeswax sprinkler ?

pressure causes the plunger to drop, breaking the glass and this releases some kind of weird stuff.

fire extinguisher bomb type thingy ?

detonator

explain more by detonator

er.. as soon as the glass is broken by the plunger the air causes detonation

pebbly and john i apologise i didnt see your guesses,
yes john described what happens pebbly got what it is .

the Fire grenade. This consisted of a glass sphere filled with CTC, that was intended to be hurled at the base of a fire (early ones used salt-water, but CTC was more effective). Carbon tetrachloride was suitable for liquid and electrical fires and the extinguisers were fitted to motor vehicles. Carbon-tetrachloride extinguishers were withdrawn in the 1950s because of the chemical's toxicity–exposure to high concentrations damages the nervous system and internal organs. Additionally, when used on a fire, the heat can convert CTC to Phosgene gas ,[7] formerly used as a chemical weapon.