CRYOGENICS HAZARD, RISKS AND DANGER BASIC INFORMATION

Cryogenics, or low-temperature technology, is the science of producing and maintaining very low temperatures usually below 120 K, as distinct from traditional refrigeration which covers the temperature range 120 to 273.1 K. At or below 120 K, the permanent gases including argon, helium, hydrogen, methane, oxygen and nitrogen can be liquefied at ambient pressure.

Any object may be cooled to low temperatures by placing it in thermal contact with a suitable liquefied gas held at constant pressure. Applications can be found in food processing, rocket propulsion, microbiology, electronics, medicine, metal working and general laboratory operations.

Cryogenic technology has also been used to produce low-cost, high-purity gases through fractional condensation and distillation. Cryogens are used to enhance the speed of computers and in magnetic resonance imaging to cool high conductivity magnets for non-intrusive body diagnostics. Low-temperature infrared detectors are used in astronomical telescopes.

Typical insulating materials include purged rockwool or perlite, rigid foam such as foam-glass or urethane, or vacuum. However, because perfect insulation is not possible heat leakage occurs and the liquefied gas eventually boils away. Uncontrolled release of a cryogen from storage or during handling must be carefully considered at the design stage. The main hazards with cryogens stem from:

• The low temperature which, if the materials come into contact with the body, can cause severe tissue burns. Flesh may stick fast to cold uninsulated pipes or vessels and tear on attempting to withdraw it. The low temperatures may also cause failure of service materials due to embrittlement; metals can become sensitive to fracture by shock.

• Asphyxiation (except with oxygen) if the cryogen evaporates in a confined space.

• The very large vapour-to-liquid ratios so that a large cloud, with fog, results from loss of liquid.

• Catastrophic failure of containers as cryogen evaporates to cause pressure build-up within the vessel beyond its safe working pressure (e.g. pressures ≤280 000 kPa or 40 600 psi can develop when liquid nitrogen is heated to ambient temperature in a confined space).

• Flammability (e.g. hydrogen, acetylene, methane), toxicity (e.g. carbon dioxide, fluorine), or chemical reactivity (fluorine, oxygen).

• Trace impurities in the feed streams can lead to combination of an oxidant with a flammable material (e.g. acetylene in liquid oxygen, solid oxygen in liquid hydrogen) and precautions must be taken to eliminate them.

• Several materials react with pure oxygen so care in selection of materials in contact with oxygen including cleaning agents is crucial.

CHEMICAL STORAGE GENERAL PRINCIPLES BASIC INFORMATION

• Store minimum quantities

• Control stock, i.e. first-in/first-out, move redundant stock

• Segregate chemicals, e.g. from water, air, incompatible chemicals, sources of heat, ignition sources

• Segregate ‘empties’, e.g. cylinders, sacks, drums, bottles

• Monitor stock, e.g. temperature, pressure, reaction, inhibitor content, degradation of substance, deterioration of packaging or containers/corrosion, leakages, condition of label, expiry date, undesirable by products (e.g. peroxides in ethers)

• Spillage control; bund, spray, blanket, containment. Drain to collection pit

• Decontamination and first-aid provisions, e.g. neutralize/destroy, fire-fighting

• Contain/vent pressure generated to a safe area

• Store in ‘safest’ form, e.g. as pre-polymers, as chemical for generation of requirements (e.g. hypochlorites for chlorine) in dilute form

• Handle solids as prills or pellets rather than powders to minimize the possibility of dust formation

• Split-up stocks into manageable lots, e.g. with reference to fire loading/spillage control. Limit stack heights; generally chemicals should be stored off the ground (e.g. to facilitate cleaning, to keep above any ingress of water in the event of flooding)

• Select correct materials of construction; allow for reduction in resistance due to dilution/concentration, presence of impurities, catalytic effects

• Transport infrequently to minimize stocks for both safety and to reduce costs and environmental hazards arising from the need to dispose of surplus or expired material

• Ensure appropriate levels of security, hazard warning notices, fences, patrols. Control access including vehicles

• Segregate/seal drains

• Appropriate gas/vapour/fume/pressure venting, e.g. flame arrestors, scrubbers, absorbers, stacks

• Ensure adequate natural or forced general ventilation of the storage area

• Provide adequate, safe lighting

• Label (name and number); identify loading/unloading/transfer couplings

• Facilitate sampling (for quality assurance and stock monitoring)

• Provide appropriate fire protection (sprinkler, dry powder, gas)

• Consider spacings from buildings, road, fence

• Ensure adequate access for both normal and emergency purposes with alternative routes

• Protect from vehicle impact, e.g. by bollards

• Assign responsibility for administration, maintenance, cleaning and general housekeeping