Claim: Shirt of Flame refers to a specific form of the poison dress trope in folklore which were  doused with tar, pitch and oil, and set alight and used on Christians and martyrs in the Roman Empire.
Evidence: The phrase Shirt of Flame refers either to a specific form of the poison dress trope in folklore, or to a particular type of clothing given to people about to face burning at the stake. During the Persecution of Christians in the Roman Empire, many early Christians were executed by being doused with tar, pitch and oil, and set alight in Rome. According to Tacitus, the Roman Emperor Nero used Christians as human torches. As such, they martyrs wore the metaphorical "Shirt of Flame" as they were consumed.