It is well recognized that working in confined spaces involves significant risk to employees due to atmospheric hazards. One of the most common hazards is oxygen deficiency hazard (ODH) taking place due to undesirable release and displacement of air with compressed or cryogenic gases. The presence and use of pressure and cryogenic systems associated with storage, handling, and transfer of compressed and liquefied gases, and cryogenic and volatile liquids is commonplace at many industries and manufacturing areas, R&;D and test facilities. The uncontrolled introduction of these materials into the workplace environment presents a hazard and increases the risk of asphyxiation or fatality from exposure to reduced atmospheric oxygen. Humans cannot directly sense the presence of any of these gases, therefore monitoring instruments are critical to safety.
It is well documented that many injuries and fatalities are the result of employers not taking the proper measures to prevent these incidents by instituting proactive risk management and emergency preparedness programs.
This paper generalizes experience gained by developing and establishing a risk management program to attain compliance with OSHA Standard 29CFR 1910.146 "Permit-Required Confined Spaces" and with following the vertical standards taking precedence over the permit required confined space entry requirements for the specific hazards in specific operations that they address: 29CFR 1910.94 "Ventilation", Subpart M and Q; ANSI Z88.2 Standard for Respiratory Protection, and Compressed Gas Association Pamphlets CGA SB-2, "Oxygen Deficient Atmospheres" and CGA P-14, "Accident Prevention in Oxygen-Rich and Oxygen-Deficient Atmospheres". Recommended accident prevention strategies include the implementation of engineering and administrative controls, working in compliance with safety standards, establishing and implementing a written risk management program, wearing proper personal protective equipment, and providing appropriate worker training and medical surveillance.
Potential cryogenic and pressure hazards may be encountered at the cryogen unloading and storage operations, in the compressor and cryogenic refrigeration rooms, etc. There are four potential cryogenic hazards associated with the operations and testing in a closed loop cryogenic system: over-pressurization, thermal stress, freeze burns, and asphyxiation due to the cryogen displacing the oxygen in the air of an enclosed or confined work areas (ODH). ODH stems from or is a result of the release of cryogens by failures of pressurized systems such as: pressure vessels, piping, pressure relief valve, motor valves or associated control equipment, or an insulating vacuum jacket such as those encasing vessels.
According to the standard (CGA SB-2, 1987), oxygen deficiency begins when oxygen level is less than 19.5 percent volume by air, while oxygen enrichment starts when that level is greater than 23.5 percent. Only atmospheres containing oxygen levels within this (19.5 to 23.5) range are considered safe for confined space activities. Oxygen deficiency can be caused by displacement of oxygen by gases such as nitrogen (which is often used as a blanketing agent to prevent oxidation of a product stored in a container).
