ࡱ> NPM d$bjbjΚΚ q> W$PB V L$R 4 U$W$W$W$W$W$W$,0&($ $! $!!!   U$! U$!!r#!$@ GX!v$A$$0$$x)!x)!$!!$ $$! $x)  :   * INTERPRETATION - "Department" means College/School/Department/Centre/Unit as relevant. 18.34.1 INTRODUCTION Cryogenics may be defined as the science of very low temperatures. To distinguish it from refrigeration, temperatures below -73.30C (-1000F) are considered being a broad definition of cryogenic technology. The most common application is the liquefaction of gases principally of helium, hydrogen, nitrogen, fluorine, argon, oxygen and methane. 18.34.2. HAZARDS Cryogenic fluids require special handling requirements to avoid the main hazards associated with their use. The principal hazards related to their usage re: fire, explosions, burns, toxicity, asphyxiation, high pressure, embrittlement of equipment of materials, oxidation and chemical reactivity. Hydrogen, methane are obvious flammability hazards, however, oxygen greatly increases the flammability of ordinary combustibles and can cause non-combustible material to burn readily. Liquefied inert gases (such as nitrogen and helium) or very cold metal surfaces can condense oxygen from the atmosphere, causing oxygen enrichment. The high-pressure gas hazard is always present when cryogenic fluids are used because of the large expansion ratio from liquid to gas on evaporation. Equipment must be carefully selected for cryogenic service because of the changes in their properties at very low temperatures - normally ductile materials may become extremely brittle. Methods of joining materials must also receive careful consideration, because of different rates of contraction and embrittlement of sealant. Chemical reactivity between the fluid and apparatus must be studied also. Personnel hazards exist in several areas. Exposure of personnel to the above hazards must be avoided, but of prime concern is bodily contact with the extremely low temperatures involved. Brief contact with cryogenic materials can cause burns similar to thermal burns from high temperature contact. Prolonged contact with these temperatures will cause embrittlement of the affected parts because of the high water content of the body. The eyes are especially vulnerable, so eye protection is mandatory. While a number of gases in the cryogenic range are not toxic, they are capable for causing asphyxiation by displacing oxygen. Even oxygen may have harmful physiological effects on prolonged breathing of the pure gas. 18.34.3. RISKS The risks associated with the aforementioned hazards are to be assessed by the Department (using the appropriate technical input where necessary). These assessments shall be carried out using: Check lists provided (where applicable) and Departmental Hazard Identification/Risk Assessment Work Sheets contained in Document No.3 i.e. Departmental Hazard Risk Assessment (D.H.R.A.). ARRANGEMENTS AND CONTROLS REQUIRED These hazards and risks will be minimised by the following arrangements and controls: Personnel must be thoroughly instructed and trained in the nature of the hazards and precautions against them, including emergency procedures, operating equipment, safety devices, the properties of the materials used and personal protective equipment required. If contact with a cryogenic fluid is possible, eye protection (or full-face protection is preferred), an impervious coat, trousers without turn-ups and high top shoes or boots must be worn. Watches and jewellery are not permitted, i.e. anything capable of trapping a cryogenic fluid close to the skin. Gloves may be worn as desired, but if they are necessary to handle containers or cold metal, they should be insulated, impervious and large enough to be tossed off the hand in case of a spill. Care is required in the transport and storage of cryogenic substances. Slow evaporation is bound to take place leading to contamination of the atmosphere, unless there is good ventilation. Cryogenic substances should not be carried in a passenger lift, with passengers present. Instructions for the storage of cryogens should comply with supplier's recommendations. Low boiling point gases are protected in their vacuum vessel by a guard jacket of liquid nitrogen which must be replenished regularly. If the supply of liquid nitrogen fails on a helium storage vessel, explosion may occur. Keep equipment and systems scrupulously clean and avoid contaminants creating hazardous conditions on contact with the cryogenic fluids. This is particularly important when working with oxygen. 19.34.4 ARRANGEMENTS AND CONTROLS REQUIRED (Cont.) If the boiling point of a gas is below that of liquid gas, care must be taken in transferring the liquid e.g. into Dewar-type vessels or cryostat. A vacuum-jacketed siphon must be used; if the gas is poured from the container, a plug of solid air may form in the outlet. These operations may only be undertaken after consultation with the supplier of the liquefied gas and the Departmental Safety Adviser. Liquid oxygen and nitrogen containers should not normally be emptied; occasionally allow them to warm to room temperature and purge with dry nitrogen. This avoids danger from accumulated hydrocarbon gases extracted from the atmosphere and the nuisance of water freezing out in the container. It may be convenient to transfer liquid oxygen or nitrogen from its container by pressurisation. This may be done safely if the appropriate dry gas is used and the container can withstand the pressure. Instructions for handling liquid nitrogen, helium, argon and methane should be sought from the supplier and the experimental work should proceed based on their advice with the full knowledge and agreement of the Departmental Safety Adviser. Following exposure to cold gas resulting in respiratory distress, obtain medical attention immediately. FIRST AID: Where the skin has been exposed to cryogenic fluids, obtain medical attention, (See Sect 18.28) and carry out the following Emergency First Aid: Remove any unfrozen clothing that may restrict the blood circulation to the burn area. THAW SLOWLY IN LUKEWARM WATER. Use a temperature between 420C and 450C. Do not use dry heat. Cover burn with a large sterile dressing. If frozen area is extensive or deeply frozen, take the casualty to hospital. Do not remove sticking clothing until completely thawed. Do not give alcohol or allow smoking. 18.34.5. ARRANGEMENTS AND CONTROLS The details of the Arrangements and Controls in place and those required in the short, medium and long term, shall be set out by the Department in the forms provided in Document No.4 i.e. Departmental Safety Action Plan (D.S.A.P.). These Arrangements and Controls shall be reviewed and updated on a yearly basis. 18.34.6. RESPONSIBILITIES The following personnel are responsible in the Department/Lab/Area for ensuring the implementation and ongoing compliance with the aforementioned arrangements and controls. AREA/LOCATIONPERSON RESPONSIBLE1.2.3.4.5.6.   DEPARTMENT SAFETY STATEMENT DOCUMENT NO. 2: Requirements for the Control of Hazards and Risks SECTION 18.34.0 - Cryogenic Technology Rev.2 PAGE   PAGE 1 of  NUMPAGES 2 AppSc\Doc 2\Sect 18.34 DOCUMENT NO. 2: Requirements for the Control of Hazards and Risks SECTION 18.34.0 - Cryogenic Technology (Cont.) 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