One of several long steel implements carried on a steam locomotive to manipulate the burning coal in the firebox. The set typically includes a dart for breaking up clinkers, a rake for leveling the firebed, and a slice bar for lifting the fire off the grates to improve airflow. They are heavy, awkward, and get extremely hot during use.
Heard on the job
Grab the long fire iron and break up that clinker before we lose steam pressure.