The firemen make up the engine crews alongside the drivers. They together keep their respective engine in control and provide company, in addition a voice of reason when an engine is being difficult.
If the drivers are unwell or are called away for some reason, the firemen usually take over and drive the engine instead.
These crew members are responsible for making sure the engine is properly fuelled and maintained; they stoke the fire by shovelling coal or tossing wood and keep the water level where it needs to be. When the water is running low, the firemen fill up the engine's water tanks, which can either be or not part of a tender. After the day's work is over, they clean out the ash from the firebox. They also couple the engine if a shunter is not available.