A detonator is built into the bomb.
起爆剤として雷管が使われる。
A blasting cap is used as a primer.
Figurative use for something that sets off a major event, change, or reaction. Often used in social, political, or personal contexts.
その事件が戦争の起爆剤となった。
That incident became the trigger for the war.
彼の一言が改革の起爆剤になった。
His single remark sparked the reform.
起爆剤 is literally a detonating agent and is used metaphorically for a catalyst that spurs sudden change, similar to the figurative use of 導火線 but with less sense of a delay before the effect.
起爆剤 (literally 'detonator') is used figuratively for something that sets off a chain of events, much like 触媒 in its figurative sense of a person or event that triggers change.
起爆剤 (literally 'detonator') suggests a sudden, explosive catalyst for change, while 呼び水 has a gentler image of priming or coaxing out a bigger reaction.
Compound of 起爆 (きばく, 'detonation') + 剤 (ざい, 'agent, substance'). The figurative sense is a natural extension from the literal explosive initiator.