Flammables and Lab Refrigeration
If you are considering purchasing a fridge or freezer for your laboratory, you need to be aware of the dangers of storing flammables in an ordinary refrigerator.
Flammable liquids are combustible liquids that can readily catch on fire. It isn’t the liquid that ignites but the vapour that has evaporated from the liquid. For the vapour to ignite, it must be between the liquid’s lower explosive limit (LEL) and the upper explosive limit (UEL). Volatility is the measure of the tendency for a substance to vaporise and is related to a substance’s vapour pressure. A liquid with a high vapour pressure will evaporate much faster than a liquid with low vapour pressure.
What is important when it comes to storing flammable liquids in a lab fridge or freezer is the flashpoint of the liquid. The flashpoint is the lowest temperature at which vapour of the material will ignite. Any liquid with a flashpoint below 93°C is considered to be flammable. Here is a table of a few common flammable liquids.
| Liquid | Flashpoint |
| Acetone | −17 °C |
| Benzene | −11 °C |
| Ethanol | 13 °C |
| Ethanol 70% | 17 °C |
| Ethanol 20% | 36 °C |
| Isopropanol | 12 °C |
| Methanol | 12 °C |
| Ethyl Ether | −45 °C |
| Pentane | −49 °C |
Mixtures and solutions of flammable solvents can retain their low flashpoints, even if they have been diluted.
The danger when refrigerating flammables is that vapours can build up to the point that they are above the LEL. Then all it takes is a single spark from a fan, light, thermostat or heater to cause an explosion. A conventional refrigerator should never be used for storing a flammable liquid. Even a minimal volume of flammable liquid if stored in an unapproved fridge or freezer could cause a large explosion. Such an explosion could easily kill people and destroy much of a laboratory.
For safe storage of flammables, it is essential to use either a flammable storage refrigerator or a flammable storage freezer that is specially made for storing flammables. The insides of these fridges and freezers are free of all potential sources of ignition. It is necessary to stress that it is only the inside of these fridges and freezers that are spark-free, and therefore, they can’t be placed in a flammable environment.
