Revisiting the great exploding trousers epidemic of the 1930s.
IT WAS STRANGE BEHAVIOUR FOR “A QUITE RESPECTABLE GARMENT”. ACCORDING TO THE HUTT NEWS, “NOT LONG AGO, IN A COUNTRY TOWNSHIP, A MAN’S PAIR OF TROUSERS EXPLODED WITH A LOUD REPORT.” FORTUNATELY, HE WASN’T WEARING THEM AT THE TIME AND WAS ABLE TO THROW THE OFFENDING PANTS OUTSIDE, WHERE THEY CONTINUED TO SMOULDER. HIS WOULDN’T BE THE ONLY PAIR OF SCORCHED SLACKS TO MAKE THE NEWS.
It all started because of the ragwort. A noxious weed that probably came into Aotearoa mixed with pasture grasses in the late 1800s, ragwort, or Jacobaea vulgaris, is pretty enough, but it spreads like, well, wildfire. It quickly became a pain in the butt for farmers, literally.
Sheep will happily eat ragwort, but the plant is poisonous to horses and cattle, causing everything from liver damage, to blindness, to death. Cows won’t go near the stuff, and when a growing number of farms shifted from sheep to dairy in the early 20th century, meaning fewer sheep around to graze it, ragwort really started to spread. According to the historian James Watson of Massey University, the problem was also a symptom of agricultural labour shortages, which had been exacerbated by factors like restrictive immigration policies, a growing aversion to child labour and higher urban wages.
Enter the Department of Agriculture. They had just the thing: a weedicide in the form of sodium chlorate. It could kill pretty much anything, it was easy to apply, and farmers took to it enthusiastically. But there was a problem. Actually, there were several.
The case referred to in the Hutt News was that of Hawera farmer Richard Buckley. In August of 1931, Mr Buckley had been out spraying with sodium chlorate, after which he hung his clothes up to dry by the fire. He wasn’t hurt when they detonated, though he was “partially stunned”, and probably more than a little confused.
“Cows won’t go near the stuff”
Turns out sodium chlorate is highly volatile in its crystalised form. In order to spray it efficiently, farmers mixed it with water, which tended to soak their trousers if the wind got up. As their pants dried, and the water evaporated, they became encrusted with sodium chlorate crystals, ripe for ignition.
(Don’t-try-this-at-home aside: You can mix sodium chlorate with sucrose to make an even more explosive fuel that will burn in airtight conditions. For a compelling demonstration of this effect, check out the ‘Giant Gummybear Fireball’ video on YouTube, as recommended by the team at IFL Science.)
Following Mr Buckley’s experience, reports of other flaming farmers started to come in from around the country. Many were less fortunate than him, in that they were still wearing their trousers when they caught fire. There were stories of a man whose pants lit up while he was riding a horse, thanks to the heat generated by friction between him and his saddle, and of britches bursting into flames on washing lines. In 1938, ten men employed to do ragwort control for the Ohinemuri County Council had to jump for their lives from a moving lorry after several bags of weed killer they were transporting caught fire – it seems the swinging tailboard of the truck came into contact with a whiff of weedicide, and that was enough.
Warnings from the Department of Agriculture ensued, cautioning users to avoid allowing sodium chlorate to contact their clothing. Also, “care should be taken not to carry matches in one’s pocket.”
Matches aside, as the Hutt News explained (headline: ‘Trousers Explode – Weed-killer Dangers’), cloth fibres soaked in sodium chlorate didn’t even need a direct heat source to set them off:
“There is nothing visible to warn the owner that the affected portion of the dried out clothing may catch fire (or even explode) by coming near a fire (there need not be actual contact with flame or spark), or by friction, or by the concussion of a sudden blow. Even sunheat can cause ignition.”
Even worse, a sodium chlorate fire is hard to extinguish. Because it is rich in oxygen (its chemical formula is NaClO3 – that’s one sodium atom, one chlorine atom and three oxygens), smothering a sodium chlorate fire will not put it out. The old wrap the burning person in a rug and give them a roll trick, which usually works because fire needs oxygen from the air to feed it, isn’t effective. Instead, the Department of Agriculture recommended workers “wear such loose clothing in such a way that in an emergency these could be stripped off with the least possible delay.”
“care should be taken not to carry matches in one’s pocket”
Our burning britches also won the aforementioned scholar James Watson an international prize. His 2004 study ‘The Significance of Mr. Richard Buckley’s Exploding Trousers: Reflections on an Aspect of Technological Change in New Zealand Dairy Farming between the World Wars’ won the Agricultural History Prize at the 15th Ig Nobels. The Ig Nobel prizes are awarded each year at Harvard University for achievements that “make people laugh, then think.” Upon accepting his, James told the audience of more than 1000 that “despite the fact that New Zealand has only four million people but 40 million sheep, rural history does not have a high profile there. Hopefully the publicity from this award will help change that.”
It may have worked. As well as boasting its own Wikipedia listing (find it under ‘Exploding Trousers’), New Zealand’s dance with spontaneous combustion made it onto the American science education show MythBusters in 2006. The MythBusters Build Team tested the flammability of Depression- era herbicides against gunpower, fertiliser, and some sort of acid (which was rejected right away because it just made the pants melt). The conclusion? Only the herbicide ignited under the range of described conditions, including exposure to an open flame or radiant heat, and upon impact. Google the post-experiment photos of Buster, the programme’s resident crash test dummy. He doesn’t look well.