Cryogenic substances are substances that are in an extremely cold state. Contact with the substance or with materials cooled with the substance may cause injuries that are similar to burns. The substance may also cause asphyxiation in a closed room, as it can displace the oxygen in the room when in gaseous form.
In order to avoid such dangers, it is necessary to take the following safety measures, for example:
- Properly ventilate any spaces that are used for the tapping and/or storage of cryogenic fluids;
- Preferably use transport containers and/or stainless Dewar flasks with lid for horizontal movements;
- Wear special cold insulating gloves and a face shield when tapping;
- Always wear safety goggles (monogoggles) when pouring out the fluids;
- Preferably wear closed shoes with insulating rubber insoles or at least shoe covers if you are wearing open shoes.
Cryogenic fluids are generally used as a cooling agent. The most common ones are liquid nitrogen, with a boiling temperature of -196°C at a pressure of 1 bar, and mixtures of dry ice (solid CO2) and a solvent. Liquid helium, oxygen and carbon dioxide are also used in laboratories. Working with cryogenic fluids directly or indirectly involves health hazards. Contact with the skin causes 'burns', contact with the eyes can cause severe damage. Another hazard associated with cryogenic fluids is their toxicity. Toxicity is usually rather low and any damaging effects will therefore only occur if one is exposed to a high concentration (high volume percentage in the air). Large quantities can, however, be produced easily: one litre of liquid nitrogen will, after it has vaporized, turn into around seven hundred litres of gaseous nitrogen.
Cryogenic fluids can, after they have vaporized, displace oxygen from the air. So a quick vaporization (for example, caused by a flask falling over) could therefore result in asphyxiation. As the cold gases accumulate on the floor, you will, at first, not notice anything. However, if a person becomes unwell in the relevant room due to a lack of oxygen and falls, the risk of asphyxiation will be very high. That is why it is forbidden to leave containers inside small, poorly ventilated spaces (a lift, for example), with someone present there.
Some cryogenic fluids require even more attention due to fire risks. This requires little explanation when it comes to liquid hydrogen. The temperature of liquid nitrogen or helium is lower than the boiling point of oxygen. As a result, oxygen from the air could condense into these fluids. Liquid oxygen is very dangerous, as it causes violent and often explosive reactions with a great many materials. The combination of liquid oxygen spilled on clothes and an (electrostatic) spark could cause the clothes to catch fire immediately. The use and creation of liquid oxygen should therefore be avoided as much as possible.
- The requirements set on stationary reservoirs for liquid gases are described in the regulations of the Integrated Environmental Permit (formerly the Environmental Management Act).
- Beware of splashing when transferring cryogenic fluids. Wear safety goggles, preferably monogoggles (sealed!) and special insulating gloves. Wear a face shield if there is any risk of splashes in the face.
- Cryogenic fluids should be stored and transported in double-walled vacuum glass or metal flasks, so-called Dewar flasks.
- Never hold your face above the mouth of a Dewar flask; its contents could suddenly start boiling and gush out.
- Always put a suitable lid on a Dewar flask to prevent the liquid from spilling or splashing over the side. This applies to glass Dewar flasks in particular.
- Vaporizing cryogenic fluids could displace oxygen in poorly ventilated spaces. Risk of asphyxiation. When tapping cryogenic fluids or in case of rapid vaporization, there should always be sufficient ventilation.
- If Dewar flasks are transported in a lift, no persons may be present inside the lift. So a person stepping into the lift during the transport should be avoided as well.
- Tapping metal Dewar flasks is generally always done using a siphon, with a slight overpressure on the flask. The maximum working pressure (often 0.7 bar) may not be exceeded.
Use a suitable siphon, if necessary a siphon with a safety valve. Regularly check the proper functioning of this valve.
- Pouring out metal Dewar flasks should be avoided due to the thermal load of the weld near the mouth.
- When working with liquid oxygen and/or liquid hydrogen, there is an additional risk of fire and explosion. Ask the Health, Safety and Environment Coordinator for advice, if required.
- Metal coming into contact with cryogenic substances may become brittle, so make sure that the metal used is suitable for application.
In general, the following regulations apply:
Contact the Health, Safety and Environment Coordinator when in doubt or when working with cryogenic fluids for the first time. Never perform this work alone.
- No transport in passenger lifts;
- An escort via the stairs or passenger list during transport in the goods lift;
- Dewar flasks in well-ventilated spaces;
- Do not carry around any loose flasks. Always use buckets with a handle or Dewar flasks with a wheeled base.
In case of any accidents with cryogenic fluids involving persons, the following rules apply:
- Leave the site of the accident and rinse the injured body part with water as soon as possible. The water may not be warmer than 25°C. Cold tap water will suffice;
- Call the BHV team (tel. 2222);
- Do not pull any frozen clothes loose;
- Touch the injured body part as little as possible and do not rub it.