fire door

a door through which a boiler or furnace is fired or through which the fire is inspected.

a fireproof or fire-resistant door in a building, intended to isolate an area from fire.

Origin of fire door

First recorded in 1830–40

Fire-door opening formed by flanging and riveting together the inner and outer sheets.

Illustrated Catalogue of Locomotives |M. Baird, et. al..
The fire-door, for the supply of fuel, appears at M, fig. 116.

The Steam Engine Explained and Illustrated (Seventh Edition) |Dionysius Lardner
The chest is heated from the subjacent grate c, upon which the fuel is laid, through the fire-door d.

A Dictionary of Arts, Manufactures and Mines |Andrew Ure
Old Hobden let himself down on the coals by the fire-door. '

Puck of Pook's Hill |Rudyard Kipling

What is the result of opening the fire-door when the engine is working steam?

The Traveling Engineers' Association |Anonymous

fire door

a door made of noncombustible material, the purpose of which is to prevent a fire from spreading within a building

a similar door, leading to the outside of a building, that can be easily opened from inside; emergency exit