Precautions cryogens

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. 

An elementary introduction to chemistry is given in Chapter 3 this serves only to provide background and for more advanced consideration reference will be necessary to specific text books, e.g. as listed in the Bibliography. A brief discussion of the relevance of physicochemical principles to hazard identification is given in Chapter 4. Relevant toxic and flammable properties, and summaries of appropriate precautions to cater for them during handling, use and disposal, are provided in Chapters 5 and 6, respectively. Reactive hazards are discussed in Chapter 7. The special problems with cryogenic materials and chemicals under pressure, typified by compressed... 

Table 8.3 General precautions with cryogenic materials...

Liquefied gases. See also Liquefaction Cryogens and individual chemicals Liquefied Natural Gas (LNG), 263 physical properties, 295 precautions, 264, 292 vapour pressure, 294 Liquefied Petroleum Gas (LPG), 15, 287 hazards, 287 physical properties, 289 precautions, 292... 

The event that would cause the largest release of cryogens would be a catastrophic failure of the can. This would release the helium and the nitrogen very quickly. Fortunately, this is an unusual event and previously mentioned precautions should still work. 

Thermal burns result from the radiant heat emitted by a hydrogen fire and absorbed by a person, which is directly proportional to many factors including exposure time, burning rate, heat of combustion, size of the burning surface, and atmospheric conditions (mainly wind and humidity). For instance, thermal radiation flux exposure level of 0.95 W/cm2 may cause skin burns in 30 s. Cryogenic burns may result from contact with cold fluids or cold vessel surfaces. Exposure to large liquefied hydrogen spills could result in hypothermia, if proper precautions are not taken [17]. 

Recommended Safety Precautions for Handling Cryogenic Liquids, Crawley, Edwards High Vacuum, 1979... 

Cryogenic collection of true hydrocarbons as well as some oxygenated hydrocarbons works well if precautions are taken to remove ozone. 

The second technique for C02/methane separation is membrane permeation, now standard in industry. Cryogenic distillation may be applied for methane-enrichment purposes with some technical precautions because of C02 freezing. Equilibrium adsorption on activated carbon would give poor separation. Molecular sieving would permit only the removal of oxygen and nitrogen. 

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