1931: On 12 August, the Hawera Star surprised readers with a story about exploding trousers. Richard Buckley, a local farmer, had placed his wet trousers in front of the fire to dry. As they warmed up, they “exploded with a loud report”.
Buckley’s trousers weren’t the only combustible clothing. Elsewhere in New Zealand, a load of laundry burst into flames on a washing line and a farmer’s trousers began to smoulder while he was actually wearing them.
The culprit was a chemical: sodium chlorate, which farmers used against ragwort. Ragwort had been accidentally introduced into New Zealand at the end of the 19th century. Within a few decades it was running riot. Ragwort was more than a nuisance; it could be fatal to livestock.
After a government scientist recommended sodium chlorate as a weedkiller, farmers eagerly began to spray it on ragwort. Some of the chemical got on their clothing, where it combined with fibres in the fabric to form a highly combustible mixture. Then all that was needed was a spark or a lighted match or even just a little warmth.
Source: Agricultural History, Summer 2004