The History of One-Piece Boilersuit
Coveralls are most often worn as protective clothing over "street" clothes at work, but sometimes instead of ordinary jacket and trousers.

Boilersuits are so called because they were first worn by men maintaining coal-fired boilers.[citation needed] To check for steam leaks or to clean accumulated soot from inside the firebox of a steam locomotive, someone had to climb inside, through the firehole (where the coal is shovelled in). A one-piece suit avoids the potential problem of loosened soot entering the lower half of one's clothing through the gap in the middle. As the firehole opening is only just large enough for a fit individual to negotiate, a one-piece suit also avoids the problem of the waistband snagging on the firehole as one bends to wriggle through, or of jacket tails snagging if one has to come out backwards.