火災|かさいkasai[0]heiban (flat)

1. nounconflagration; fire
   火災かさいの理由りゆうは何なんか。↗

   What caused the fire?

• Synonym火事かじNeutralThe everyday word for a fire breaking out, as in 「火事だ！」; 「火災」 is the more formal choice, typical of news and laws.
• Related火難かなんWrittenWritten term for the disaster a fire brings; seen mostly in protective phrases and prayers such as 「火難除け」.
• Related回禄WrittenArchaic written word for a fire, taken from the name of a fire god; rarely used in modern Japanese.
• Antonym鎮火ちんかWrittenWritten word for a fire being put out — the opposite of a 「火災」 occurring, as in 「火災が鎮火する」.

In everyday speech say 「火事」; 「火災」 is the formal word used in news reports, laws and insurance. Use 「鎮火」 when a fire is put out; 「火難」 and 「回禄」 are rare written terms.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 火事かじ。
2. 火事かじによる災害さいがい。