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Physics Division |
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5.1 Training of Cryogenic Personnel All personnel working with cryogenic fluids must be thoroughly familiar with the hazards involved. They must also be familiar with all emergency measures that might be required in the event of an accident. Employees who have not worked with cryogenic fluids and systems must be trained on the job by experienced employees until thoroughly familiar with safe methods of operation. The training will address: ● The physical, chemical and physiological hazards associated with cryogenic fluids ● The proper handling procedures for cryogens and cryogenic containers ● The emergency procedures required in case of an accident ● The reporting procedures in case of an accident Additionally, each employee will receive training by the responsible scientist on the specific cryogenic equipment or system he is expected to use. This will cover: ● Description of the equipment ● Operating procedures ● Maintenance schedule and procedures ● Specific hazards ● Reporting of incidents The training shall be documented. The documentation shall include: 1) content of training, 2) date, 3) name of trainer, 4) a dated training attendance list showing names of the trainees (typed or printed) and their signatures. The hazards associated with the handling of cryogenic fluids include: ● Cold contact burns and freezing (contact with cold liquid, gas or surface) The potential for freezing by contact with the extreme cold of cryogens necessitates varying degrees of eye, hand and body protection. When a cryogenic fluid is spilled on a person, a thin gaseous layer apparently forms next to the skin. This layer protects tissue from freezing, provided the contact with the cryogen involves small quantities of liquid and brief exposures to dry skin. However, having moist skin, exposure to moving cryogens, or extended periods of time, can freeze tissue. The most likely cause of frostbite to the hands and body is contact with cold metal surfaces. Since there is no protective layer of gas formed, frostbite will occur almost instantaneously, especially when the skin is moist. The damage from this freezing (frostbite) occurs as the tissue thaws. Intense hypothermia (abnormal accumulation of blood) usually takes place. Additionally, a blood clot may form along with the accumulation of body fluids, which decreases the local circulation of blood. Adequate protection and clothing is required at all times when handling, transferring or operating near cryogenic fluids (see 5.1.2). ● Asphyxiation (displacement of oxygen by inert gas) When liquid cryogens are expelled into the atmosphere at room temperature, they evaporate and expand on the order of 700 to 800 times their liquid volume. Even small amounts of liquid can displace large amounts of oxygen gas and decrease the oxygen content of the atmosphere below a safe level with a possibility of asphyxiation. Whenever possible, handling of cryogenic fluids where release into the atmosphere is possible should be done in open, well ventilated areas. When there is the possibility of an oxygen deficiency hazard (ODH) with a level of risk greater than Class 0, (see Appendix 3) oxygen monitors will be installed. If such a monitor triggers an ODH alarm, personnel are to leave the area immediately. ● Explosion (excessive buildup of pressure in container of cryogenic fluid) Heat flux into the cryogen is unavoidable regardless of the quality of the insulation provided. Since cryogenic fluids have small latent heats and expand 700 to 800 times to room temperature, even a small heat input can create large pressure increases. Dewars must be moved carefully. Sloshing liquid into warmer regions of the container can cause sharp pressure rises. Pressure relief devices must be provided on each and every part of a cryogenic system. Satisfactory operation of these devices must be checked periodically and may not be defeated or modified at any time. Vents must be protected against icing and plugging. When all vents are closed, enough gas can boil off in a short time to cause an explosion. Vents must be maintained open at all times. Liquid helium is cold enough to solidify atmospheric air. Only helium should be introduced or allowed to enter the helium volume of a liquid helium dewar. Precautions should be taken to prevent air from back-diffusing into the helium volume. Some materials may become brittle at low temperature and fail in the case of overpressure or mechanical shock. Only suitable materials may be used to store or transfer liquid cryogens. ● Fire/explosion (condensation of liquid oxygen) Liquid oxygen liquifies at a higher temperature than liquid helium or nitrogen. Consequently, liquid oxygen can condense on the exterior of cryogenic containers or transfer lines. An explosive situation may result if this oxygen-rich liquid is allowed to soak insulating or other materials which are not compatible with oxygen. Some oils can form an explosive mixture when combined with liquid oxygen. Surfaces where there exists a possibility of liquid oxygen condensation must be thoroughly cleaned and degreased. Whenever handling or transfer of cryogenic fluids might result in exposure to the cold liquid, boil-off gas, or surface, protective clothing shall be worn. This will include: ● face shield or safety goggles ● safety gloves ● long-sleeved shirts, lab coats, aprons. Eye protection is required at all times when working with cryogenic fluids. When pouring a cryogen, working with a wide mouth dewar or around the exhaust of cold boil-off gas, use of a full face shield is recommended. Hand protection is required to guard against the hazard of touching cold surfaces. Loose insulating gloves can be used. 5.2 Maintenance and Inspection Cryogenic systems and equipment must be inspected and maintained on a regular basis by qualified personnel to ensure safety. The schedule and nature of the maintenance must be included in the operating procedures manual. The inspection and maintenance shall be documented. Every cryogenic system or equipment shall be inspected by qualified personnel before being put into operation for the first time or after modification. Inspection by qualified personnel shall also take place after an unusual incident which might affect the integrity and safety of a piece of cryogenic equipment. One should note that these requirements for inspection, maintenance, calibration and documentation extend to the monitoring systems for oxygen deficiency. The Lockout/Tagout Policy establishes basic requirements involved in locking and/or tagging out equipment while installation, maintenance, testing, repair or construction operations are in progress. The primary purpose is to prevent hazardous exposure to personnel and possible equipment damage. The procedures shall apply to the shutdown of all potential energy sources associated with the equipment. These could include pressures, flows of fluids and gases, electrical power, and radiation. The formal lockout/tagout procedure for the Physics Division has been written and is the responsibility of the Physics Division Electrical Safety Committee. It is included as Appendix A of the Physics Division Electrical Safety Policy and Manual. The ANL-E lockout/tagout policy and procedure is included in the ESH Manual. The Physics Division procedure conforms to the ANL-E policy and procedure. All personnel who are involved in the installation, maintenance, testing repair, or construction of cryogenic equipment in which there are energy sources associated with the equipment must undergo documented training in the use of the Physics Lockout/Tagout procedure. In case of emergency, e.g. explosion of a dewar, leave the area immediately and dial 911.
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