火勢|かせいkasei[0]heiban (flat)

1. nounforce of a fire; force of flames
   暖炉だんろには薪たきぎが足たりず、早はやくも火勢かせいが衰おとろえ始はじめている。↗

   Without enough wood on the fire, the flames are already beginning to die down.

   薪たきぎが足たりず、はやくも火勢かせいが衰おとろえはじめた暖炉だんろ。↗

   The fireplace, lacking firewood, flames already starting to lose their vigour.

• Related激烈げきれつWrittenWritten word for extreme intensity in competition, arguments and the like; not tied to fire. 「火勢」 is a noun naming the force of a burning fire.
• Related凄烈せいれつWrittenRare written word describing fierce, terrifying force. 「火勢」 is a noun for how strongly a fire burns.
• Antonym火力減退WrittenWritten term for a fire losing force and dying down; the opposite of rising-force phrases like 「火勢が強まる」.

Use 「火勢」 (written, common in news reports) for the force of a fire, as in 「火勢が強まる」「火勢が衰える」. Use 「激烈」 for fierce intensity in contests or speech, 「凄烈」 for rare, fierce force, and 「火力減退」 when the fire weakens.

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

1. 火ひが燃焼ねんしょうする勢いきおい。