Safety with cryogenics

Zabetakis, M. G., Safety with Cryogenic Fluids, London, Heywood, 1967... 

Other references on safety include the volume by Zabetakis, on Safety with Cryogenic Fluids, published in 1967 [2], and the volume by Edeskuty and Stewart on Safety in the Handling of Cryogenic Fluids, published in 1996 [3]. 

In spite of the outstanding safety record of the liquefied natural gas industry, two large-scale accidents have taken place. The Cleveland LNG plant accident of 1944 resulted in the loss of 128 lives. The cause of the accident was attributed to improper materials selection and basic design deficiencies of the storage tanks. In 1963, an LNG storage tank on Staten Island suffered an explosion that resulted in the loss of 40 lives. The tank had been warm, and under repair for more than a year, and should be considered as an industrial accident rather than directly associated with cryogenics. 

Several potential safety hazards exist when working with cryogens, but simple precautions are available to protect against all of them. 

ELdeskuty, F.J., Stewart, W.F. Safety with Handling of Cryogenic Fluids. Plenum, New York (1996)... 

Handling and Safety Factors. Oxygen difluoride can be handled easily and safely in glass and in common metals such as stainless steel, copper, aluminum. Monel, and nickel, from cryogenic temperatures to 200°C (4). At higher temperatures only nickel and Monel are recommended. The compatibihty of OF2 with process equipment depends largely on the cleanliness of the equipment contaminants such as dkt, moisture, oil, grease, scale... 

In contrast to other cryogenic fluids, liquid oxygen is slightly magnetic. It is also chemically reactive, particularly with hydrocarbon materials. Oxygen thus presents a safety problem and requires extra precautions in handling. 

It is obvious that the best designed facility is no better than the attention that is paid to safety. The latter is not considered once and forgotten. Rather, it is an ongoing activity that requires constant attention to every conceivable hazard that might be encountered. Because of its importance, safety, particularly at low temperatures, has received a large focus in the literature with its own safety manual prepared by NIST as well as by the British Cryogenics Council. 

There are many design features and styles of safety relief valves, such as flanged ends, screwed ends, valves fitted internally for corrosive service, high temperature service, cryogenic service/low temperatures, with bonnet or without, nozzle entrance or orifice entrance, and resistance to discharge piping strains on body. Yet most of these variations have little, if anything to do with the actual performance to relieve overpressure in a system/vessel. 

Different structural materials have different thermal contraction coefficients, meaning that accommodations should be made for their different dimensions at cryogenic temperatures. If not, problems associated with safety (e.g., leaks) may arise. Generally, the contraction of most metals from room temperature (300 K) to a temperature close to the liquefaction temperature of hydrogen (20 K) is <1%, whereas the contraction for most common structural plastics is from 1% to 2.5% [23]. 

All dewars of cryogenic liquids must be equipped with safety valves, so that pressure cannot raise to dangerous values in case of an accident. 

---