I have always assumed that the belief that haystacks can burst into flames spontaneously was a convenient myth to cover for careless farm workers having a crafty cigarette break while forgetting their surroundings, but a friend insists that it can happen. Surely the only way hay can warm up significantly is if it is wet and bacteria begin to heat the stack as part of the process of biodegradation. But I鈥檇 be amazed if this could generate temperatures hotter than about 40 掳C. So how else could ignition take place?
鈥� Insurance companies in the 18th century insured farmers鈥� haystacks in England, Scotland and Wales, so they clearly believed fire was possible. A standard phrase in the policies reads: 鈥淔ree from loss on such hay or corn as shall be destroyed or damaged by its natural heat.鈥� This clause appears hundreds of times in the policies of Sun Fire Office in London.