CNW: probably a couple of things here.
A hotbox happens when a friction bearing axle end and the metal that it's turning in run short of lubrication. The axle end starts to heat up and may eventually melt off. The journal box (where the axle end turns -- see the square lump at each corner of a truck) contains cotton waste (old undershirts?) that helps pull the oil onto the bearing and this may catch fire. (search for my post on Mississauga derailment)
Anyway, the railroads did 2 things. They replaced the bearings with roller bearings and they installed hotbox detectors that sense when something hotter than expected goes past. Now it just happens that the firebox of a steam loco is nice and hot and down near wheel level, so the hotbox detector picks this up. So there is an immediate message to the effect "Extra 2985 -- Over temperature axle 12" and the train has to slow down to confirm that it's the firebox and not an actual hotbox.
A hotbox happens when a friction bearing axle end and the metal that it's turning in run short of lubrication. The axle end starts to heat up and may eventually melt off. The journal box (where the axle end turns -- see the square lump at each corner of a truck) contains cotton waste (old undershirts?) that helps pull the oil onto the bearing and this may catch fire. (search for my post on Mississauga derailment)
Anyway, the railroads did 2 things. They replaced the bearings with roller bearings and they installed hotbox detectors that sense when something hotter than expected goes past. Now it just happens that the firebox of a steam loco is nice and hot and down near wheel level, so the hotbox detector picks this up. So there is an immediate message to the effect "Extra 2985 -- Over temperature axle 12" and the train has to slow down to confirm that it's the firebox and not an actual hotbox.