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The Safe Handling of Cryogenic Substances
Cryogenic liquids can be handled easily and safely provided certain precautions are obeyed. The recommendations in this section are by no means exhaustive and when in doubt, the user is advised to consult the supplier.
They safe handling of cryogenic liquids requires a knowledge of the properties of these liquids, common sense, and sufficient understanding to predict the future behavior of such liquids under certain physical conditions.
The substances referred to in these recommendations are nitrogen, air, and helium.
GENERAL SAFETY RULES
Cryogenic liquids, even when kept in insulated storage vessels (dewars), remain at a constant temperature at their respective boiling points and will gradually evaporate. The very large increase in volume accompanying this vaporization is approximately 700:1 for helium and nitrogen and therefore:
CONTAINERS OF CRYOGENIC LIQUIDS MUST NOT BE COMPLETELY CLOSED AS THIS WOULD RESULT IN A LARGE BUILD UP IN PRESSURE AND THUS PRESENT AN EXPLOSION HAZARD. The nitrogen jackets is always fitted with a non-removable overpressure valve, the OVC is fitted with a combined overpressure / evacuation valve, and the helium bath must have the large black and red quench valve fitted. (This is normally supplied in the spares kit or left attached to the helium exit port).
In the event of a large spillage operate the fire alarm and evacuate the area.
HEALTH HAZARDS
Asphyxia of varying severity will occur if the magnet room is not properly ventilated. (Helium can displace air from the top of a room and cold nitrogen can displace air from lower levels).
Burns. Cryogenic substances in liquid or vapor form or as low temperature gases produce effects on the skin similar to burns (cold burns).
Exposed or insufficiently protected parts of the body coming into contact with uninsulated venting pipes or vessels (see ventilation section) will stick fast and the flesh will be torn if removed.
FIRST AID
If any of the cryogenic liquids come into contact with eyes or skin, immediately flood the affected area with large quantities of cold or lukewarm water and then apply cold compresses. NEVER use hot water or dry heat. MEDICAL ADVICE SHOULD BE SOUGHT IMMEDIATELY.
PROTECTIVE CLOTHING
Protective clothing must be worn mainly to avoid cold burns and dry leather or PVC gloves must be worn when handling or working with cryogenic liquids. Gloves must be loose fitting so that they can be removed easily in case of liquid spillage. Eyes must be protected by goggles. Do not wear any metallic objects (e.g. jewelry) on those parts of the body where they may come into contact with the liquid.
HANDLING
Cryogenic liquids must be handled and stored in well ventilated areas.
Do not allow cryogens to come into contact with the body.
Always handle the liquids carefully - boiling and splashing will always occur when filling a warm container or when inserting warm objects into the liquid. When inserting open ended pipes into the liquid, block off the warm end until the cold end has cooled down (otherwise cold liquid may spurt out of the open end under self-generated pressure). Never direct pipe/piping