Common employment was an historical defence in English tort law that said workers implicitly undertook the risks of being injured by their co-workers, with whom they were in "common employment".
The US labor law terminology was the "fellow servant rule".
Corp.[1][2] Bunker Hill Mining Company operated by the fellow servant doctrine.
According to Katherine Aiken, "persons engaged in the same common pursuit for the same employer were fellow servants and companies were not liable for injuries where a fellow servant was at fault.
[3] It was abolished altogether by the Law Reform (Personal Injuries) Act 1948 in the United Kingdom.