The canary girls were the United Kingdom's female trinitrotoluene (TNT) shell makers of World War I (1914–1918). The nickname arose because exposure to TNT is toxic, and repeated exposure can turn the skin an orange-yellow colour reminiscent of the plumage of a bird, the canary (which itself was used by miners to detect toxic carbon monoxide in coal mines.) The canary girls were also referred to by the nickname "munitionettes".