"turn off the fire" sounds strange to me. Does it mean to extinguish, or is the fire in a stove or some machinery that can be turned off?

an automatic machine-gun?

Mi diveno estas gasforno en domo.

Ege helpus aldoni iom da kunteksto. Ekzemple:

La instruisto demandis nin: kion vi farus se vi en via hejmo vi flarus gasodoron? Mi respondis: Mi forturnus la fajron ( / fermus la gaskranon ) kaj kurus al sekura loko.

a baby volcano?

My guess is a stove in a house.

It would be a great help to add some more context. For instance:

The teacher asked: What would you do, if there were a smell of gas in your home? I answered: I would turn of the fire, and run to a save place.

@sacredceltic
Im not sure wether this is a baby volcano or bonsai NPP.*

*NUCLEAR POWER PLANT

I just googled "turn off the fire". I guess when you cook with gas, it's a more likely sentence.
Since the Japanese has a wider application than the English, I would translate it again and have an alternative translation in English: "First, I'd put out the fire....etc."