In the 1930s, New Zealand farmers began to face an unusual problem: their pants kept exploding, or else otherwise bursting into flames.
Imagine the scene. You are a worker in the 1930s who has chosen to ride out the depression by heading to the middle of the New Zealand wilderness, where the biggest danger you think you'd face is from sheep. You're working away, when suddenly, you smell something suspiciously like burned butt hair.
You look down and find to your surprise that, with no source of fire for miles around, your pants are alight and possibly even exploding as you try to get them off your body. Similar reports came in from farmers around the country, historian James Watson wrote in an Ig Nobel Prize-winning article. One farmer's pants set on fire as he rode his horse, another looked out on his washing line expecting to see his wet washing and found it to be a lot more on fire than usual.
"A man's pair of trousers exploded with a loud report. Fortunately the owner was not in them at the time" one North Island newspaper reported on August 12, 1931. "Although dazed by the force of the explosion, was able to seize the garment, which was hanging before the fire, and hurl it out on to the grass outside."
"There the trousers smouldered, with a series of minor detonations."
It seemed no farmer's legs, crotch, or butt was safe from our old friend, the trouser. Some deaths were even reported from trousers that set alight houses, killing the occupants.
So, why did our own trousers turn on us, and what could the farmers do to end the plague – other than shepherding the sheep whilst butt naked from the waist down like Winnie the Pooh?
Well, the answer was that they had been done over by trying to rid themselves of ragwort.
Ragwort, brought over from Europe during the 1800s, was spreading around the country like wildfire in the decades preceding the 30s. The weed caused all sorts of problems to livestock who ingested it, damaging their liver and making them susceptible to everything from diarrhea and colic to sunburn, blindness, and death. A solution to the ragwort was sodium chlorate, a chemical that – whilst effective at removing ragwort – came with some unfortunate side effects of the "wait a minute, my butt isn't usually this warm" variety.
The chemical was recommended by the Department of Agriculture and was quickly taken up as a solution by the farmers, who trusted their advice. The problem was, the chemical is highly volatile and needed protective clothing: a message that didn't spread as fast as "this chemical will kill the ragwort".
Sodium chlorate is particularly explosive when mixed with organic materials. Observe what happens, for instance, when you put a gigantic gummy bear into a beaker containing the chemical.
This is a problem for your nether regions if your clothes are made from organic materials such as wool or cotton. The chemical, once it gets into your pants, is incredibly difficult to get out again. Once it's dry, it can explode when near heat, or through friction (of, say, riding a horse or doing farm chores) – and when it does, it bursts into flame extremely rapidly and is difficult to smother out.
Though the Department of Agriculture didn't go as far as to recommend people walk around trouserless, that wasn't because they had any better advice.
"One would prefer to advise workers to wear such loose clothing in such a way that in an emergency these could be stripped off with the least possible delay," one representative said at the time. "Actually the combustion of the chlorate-saturated portion is so nearly instantaneous that there is no time for preventative measures once the fire is started."
In other words, don't even bother wearing loose clothing, because your ass will burn long before you can get your trousers off.