萬一發生火災，按下按鈕。

In case of fire, push the button.

Source: Tatoeba

Sentence Composition

1 萬一 wànyī
  1. just in case
  2. if by any chance
  3. contingency
2 發生 fāshēng to happen; to occur; to take place; to break out
3 火災 huǒzāi serious fire (in a city or a forest etc)
4 按下 ànxià
  1. to press down
  2. to press a button
5 按鈕 ànniǔ
  1. to push a button
  2. button (one that can be pressed to trigger an action)