Custard powder makes a delicious dessert but also has a rather less savoury potential – in certain conditions, it can be a powerful explosive.

Instant custard powder is a staple of many kitchens. Just add water and heat, and the powdery mixture of cornstarch and flavourings will transform into an unctuous treat. It's hard to imagine anything more inoffensive. But on 18 November 1981, at the Bird's Custard factory in Oxfordshire, the substance showed its dark side. A hopper of powder overflowed, and the resulting dust cloud ignited, exploding into flame.

Nine people were injured in the explosion. They were lucky – powder explosions can be lethal. Fourteen people were killed in Minnesota in 1871 when a flour mill went up. Forty-four people, including a child, lost their lives to a cornstarch-based explosion in 1919 in Cedar Rapids, Iowa, which levelled part of the town. "The main explosion seemed to lift great buildings and hold them in tension for a moment, letting them drop with their own weight," one observer wrote later.

Dust explosions, of various substances, have continued to take lives – in 2014, 97 people died when dust in a factory in Kunshan, China, ignited. In 2022, one industry report counted 50 such explosions globally, although not all of them involved foodstuffs.

How can the makings for a simple dessert cause carnage, though? In all dust explosions, there are a few common factors. The powder must be made of a flammable substance – that means you're safe from sand, which is made of minerals like silica. But flour, cornstarch, sugar, coal dust, powdered plastic, and aluminium powder can all burn, meaning that if they get airborne, the risk for a truly devastating explosion goes up.

That's because, suspended in a cloud, all those particles have an enormous surface area exposed to oxygen. That makes them swift to combust. If a few of them heat up to ignition – and in each of these cases, there was a source of heat like friction or static electricity involved – then the fire can spread almost instantaneously to the rest of the cloud. Like a pile of confetti ignited in a fireplace, suspended dust burns fast.

That evening at the Bird's Custard........

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