Liquid nitrogen is the liquid form of nitrogen gas, produced by cooling nitrogen to -195.8°C at atmospheric pressure. At that temperature, the gas condenses into a clear, colourless liquid with a density of approximately 806 kg/m³. It is non-toxic, non-flammable, and chemically inert at ambient temperatures, which is why it is used safely across a wide range of industries including healthcare, food processing, research, and industrial manufacturing.
The property that defines liquid nitrogen’s usefulness is its extreme cold. When it contacts a warmer surface, it boils instantly, absorbing large quantities of heat in the process. This rapid heat absorption is what makes it effective for flash-freezing biological samples, rapid cooling of equipment, and maintaining the ultra-low temperatures required for long-term cryopreservation.
One physical property that laboratory staff must understand is its expansion ratio. One litre of liquid nitrogen expands to approximately 694 litres of nitrogen gas at room temperature. This is not a minor detail. In a poorly ventilated room, even a small LN2 spill can rapidly displace enough oxygen to trigger the HSE’s asphyxiation threshold, which sits at an oxygen concentration of 19.5 per cent. This is why all UK facilities storing or handling LN2 are required to conduct formal risk assessments under the Management of Health and Safety at Work Regulations 1999, and why fixed oxygen depletion monitors are considered best practice in any room where LN2 is used regularly.
Liquid nitrogen also has a freezing point of -210°C, meaning it can be cooled further to a solid state under vacuum conditions, though this is rarely relevant in laboratory or clinical practice.
For guidance on selecting the right LN2 storage vessel for your laboratory, visit cryolab.co.uk/product-category/storage-vessels/ or speak with the Cryolab team at cryolab.co.uk/contact-us/.
