# An explosion in a custard factory

I have a vague memory of a question on the BBC panel game QI which started with a long chemical reaction equation on the screen, asking what it might be.

The answer was definitely "an explosion in a custard factory", due in part to high quantities of fine powders in the air, but also some of the chemical constituents of custard powder.

Does anyone know what that equation would be, or how I might re-find it?

How would one go about getting back from that equation to custard?

but also some of the chemical constituents of custard powder

Don't blame it on the custard. As long as there's

• dust of a combustible material, preferably with a small particle size
• sufficient oxygen in the athmosphere
• an igniter, such as a spark or an open flame

there's a good chance for a devastating dust explosion.

Your combustible material can be something seemingly unspectecular, coal dust, saw dust, flour, or custard powder.

UPDATE

The incident in the BBC game most likely took place at a factory in Banbury, UK in 1981. Their traditional custard powder, known as Bird's Custard, is egg-free and mostly consists of cornflour.

how you might use it to tell that the reaction was an explosion in a custard factory

In risk assessment for dust explosions of organic materials, product analysis rarely plays a role; the "equation" isn't interesting and it is usually assumed that all carbon ends up as $\ce{CO2}$.

In order to establish workplace safety, it is more important to determine, how "strong" a possible dust explosion might get.

A measure for the "strongness" of an explosion is the rate by which the pressure (rapidly) increases. This is expressed in the $\mathrm{K_{St}}$ value (in $\mathrm{bar\cdot m \cdot s^{-1}}$), and experimentally determined in standardized tests.

Based on the $\mathrm{K_{St}}$ value, materials of certain properties (particle size, rest humidity) are assigned to the explosion classes (ST 0 to ST 3), and suitable workplace safety measures are taken.

• The question was about the reaction equation, how you might use it to tell that the reaction was an explosion in a custard factory. @MaxW's answer appears to have focussed on the high energy content of sugar. – AJFaraday Mar 7 '16 at 16:23

A recipe for custard uses the following ingredients

    2 cups whole milk
2 eggs (preferably free-range)
2 egg yolks
1/3 cup sugar
1 teaspoon vanilla extract
Freshly grated or ground nutmeg


In an industrial scale operation the sugar would no doubt be in a large hopper with some sort of auger feed to fill the hopper. The sugar dust can explode due to static electricity in the dust particles. So the reaction is sugar plus oxygen gives a boom!

$$\ce{C12H22O11 + 12O2 -> 12CO2 + 11H2O}$$

Here is an egg free custard powder video.

• You could see an industrial scale custard facility also using some kind of non-dairy creamer or something to cut down on volume/cost, and that would just add to the effect. – SendersReagent Mar 7 '16 at 17:44
• I'd guess that just about any flammable material when reduced to dust could explode when ignited. – MaxW Mar 7 '16 at 18:03
• $$\ce{C12H22O11 + 12O2 -> 12CO2 + 11H2O}$$ Sugar can burn and explode? Never knew that before. – Pritt says Reinstate Monica Aug 20 '17 at 9:20
• @PrittBalagopal Haven't you built any sorbitol rockets as a kid?:) – andselisk Aug 20 '17 at 9:34
• @andselisk Actually no, although I did hear about them before. I wasn't really the DIY type of guy anyway :) – Pritt says Reinstate Monica Aug 20 '17 at 9:36

The reaction given in the QI show was

$$\ce{C6H12O6(s) + 6O2(g) = 6CO2(g) + 6H2O(g)}$$

This basically translates to glucose in solid form with the addition of gaseous oxygen will, with the application of something (I am assuming heat because the show does not say) reacts to form gaseous carbon dioxide and water vapor.

I would like to add that many molecules such as nitrogen and sulfur are excluded from the formula for whatever reason, possibly because they may not have had a role to play. I am not a chemist so I do not know.

What I do know is that in no universe would the chemical formula given lead to the conclusion that it was specifically a custard factory that exploded. It could just as easily have been a chocolate factory or boiled sweet factory or even a marshmallow factory for that matter.

How the contestant rightly guessed a custard factory is beyond my understanding. Besides, unless glucose is used in the production of custard, it is downright impossible to conclude what she did. I assume that they use sugar (sucrose) in the manufacture of custard. Sucrose has the chemical composition of $\ce{C12H22O11}$. And also the presence of lactose (in milk) was not taken into account.

• The way I've heard her God-level answer explained is that in UK schools, it was apparently (or perhaps still is) not uncommon to accompany the explanation of the sugar oxidation reaction with an experiment in which powdered custard was mixed with air and lit in order to create a controlled explosion. To me this seems a reasonable explanation why the contestant immediately connected sugar oxidation to custard, perhaps even without remembering that it was a sugar oxidation formula, just remembering the custard part. (after all, the only things we remember from chemistry class are the times when – McFly Nov 16 '17 at 22:40
• con't "the teacher made something go bang or on fire. Or both.)" – jonsca Nov 17 '17 at 0:25