The Safety of Liquid Nitrogen Cocktails

Cocktails cooled with liquid nitrogen

Cocktails cooled with liquid nitrogen. Picture from Canadian Content

I was horrified to hear of the young woman, Gaby Scanlon, who suffered stomach injuries after drinking a cocktail laced with liquid nitrogen.

My interest in this case is to find out exactly how Ms. Scanlon came to be harmed. I often use liquid nitrogen for both scientific applications (cooling) and for scientific demonstrations. And over 30 years I have never heard of anyone who has suffered anything other than the most minor of injuries, so I was shocked to hear this news. How had it happened?

Liquid nitrogen can cause harm in one of three ways. The first and most obvious way is that it can cause cold burns. The second is that it can displace oxygen in the air and asphyxiate people. And the third is that it when it turns to a room temperature gas – which it can do rapidly – it increases in volume by a factor of roughly 600.

Normally the extreme cold is viewed as the primary hazard, but in fact that is usually not the case. The reason is that even though liquid nitrogen at -196 °C is extremely cold, on contact with objects at room temperature it immediately turns to gas. The gas has a low thermal conductivity and transiently insulates the hot object from the extreme cold. This film-boiling or Leidenfrost effect usually makes the handling of small quantities of liquid nitrogen extremely safe – much safer than the handling of hot coffee.

The effect is so strong that one can pour liquid nitrogen over one’s hand and barely feel the cold. However, after a second or two, the gas film collapses, and the cooling rate of the hot object increases dramatically. So prolonged contact – more than a second or so – with the liquid will rapidly cause cold burns or frostbite.

My speculation is that in this case, Ms. Scanlon swallowed the drink relatively quickly and because of the Leidenfrost effect, she recieved no feedback in her mouth about how cold the liquid was. The nitrogen would have travelled in droplets along with the cocktail into her stomach, probably relatively harmlessly. At this point the liquid – probably only a cubic centimetre of so – was trapped in a confined volume, and would have rapidly turned to more than 500 cubic centimetres of gas. I suspect it was this rapid expansion which caused the damage to her stomach.

Apparently the use liquid nitrogen in cocktails is commonplace. Wow! That passed me by! And so it is somehow shocking that Ms Scanlon was the first casualty – because there is no way to drink liquid nitrogen safely. But there is a way to safely consume drinks which are bubbling with gas and emanating large amounts of mist.

The key is to use dry ice -solid carbon dioxide – not liquid nitrogen. The difference is that liquid nitrogen floats on drinks – and so it is impossible to consume the drink without the possibility of ingesting a small droplet of the liquid nitrogen. In contrast, solid carbon dioxide sinks in water.

Michael de Podesta safely drinking 'potion'

Michael de Podesta preparing to safely drink ‘potion’

But there is a trick! The trick is to use both a glass and a liquid which are transparent and to put in just a single large piece of solid carbon dioxide. By large I mean roughly a cubic centimetre. The reason that a large piece is necessary is that the solid carbon dioxide immediately freezes water around it and if a small piece of solid carbon dioxide is used – the ice will cause the carbon dioxide to float. If prepared correctly one can see the single large piece of dry ice in the base of the beaker – and be sure that there are no other pieces lurking on the surface of the liquid.

Here’s to your health… Cheers

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