Oxygen deficiency is a risk when handling gases such as nitrogen, helium, carbon dioxide, neon and argon. Best practices are essential here.
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Atmospheric gases are non-toxic. As they increase in concentration, however, they have an impact on life and combustion processes (especially in the case of oxygen).
Oxygen itself is not flammable, but it does support combustion. Nitrogen and argon, however, inhibit combustion
Any changes in the concentration of these gases cannot be detected by human senses. If they are not handled correctly, accidents may occur.
In order to be stored as liquids, these gases have to be cooled at extremely low temperatures (less than -180 0C at atmospheric pressure). In this state, they can rapidly cause cold burns and make certain materials brittle, which in turn may lead to structural failure.
Hazards from oxygen deficiency
Oxygen is essential to life. Although a healthy person may survive short exposure to oxygen content as low as around 16%, an adequate oxygen supply must be present in any atmosphere being breathed by humans. A drop in oxygen levels is not accompanied by any immediate signs, making deficiency impossible to detect by human senses.
| Oxygen volume % | Action and symptoms |
| 18 | Lowest limit for working without a fresh-air mask. |
| < 18 | Significant drop in physical and mental performance without noticing anything abnormal. |
| < 10 | Risk of unconsciousness without warning after a few minutes. |
| < 8 | Unconsciousness within a few minutes Recovery possible if carried outdoors immediately. |
| < 6 | Unconsciousness almost immediately. |
Causes and prevention of oxygen deficiency
Oxygen deficiency can be prevented by observing the following measures:
Leaks of gases other than oxygen automatically lead to oxygen deficiency. New equipment which uses inert or any other gas should be thoroughly checked for leaks using a timed gas pressure drop test plus a leak test with an approved leak detection fluid that is compatible with the equipment in question.
All equipment, including pipes and hose connections, should be properly fitted. Hoses and other equipment should be kept leak-tight and protected against damage. All maintenance and repair work should be carried out by experienced and fully qualified personnel.
When the work period is over, the cylinder valve or piped supply stop valve must be turned off in order to avoid leakage between two working periods. The valves on welding equipment should not be relied upon as shut-off valves for the gas supply. Gas cylinders in use should not be handled roughly, knocked or pulled over.
A small amount of liquefied gas can vaporise into a large amount of gas. Liquid spills can therefore rapidly cause oxygen deficiency in confined spaces. Tanks and equipment for storing and handling liquid gases should be inspected carefully and maintained in accordance with relevant regulations and recommendations.
Vented gases often have low oxygen content. Work should not be carried out in these atmospheres.
Oxygen deficiency arises when plant items such as vessels are purged with nitrogen or other inert gases in preparation for repairs.
Processes that involve the vaporisation of liquid nitrogen, such as food cooling, ground freezing, cryogenic surgery and blood plasma preservation, automatically lead to oxygen-deficient atmospheres. People should not enter these areas without adequate breathing equipment, even if the atmosphere is only slightly deficient in oxygen. Those kind of areas should be equipped with appropriate detectors and alarm systems.
All gas welding and heating processes extract oxygen from air. These processes can lead to oxygen deficiency if the workspace is too small and poorly ventilated.
Removing argon, carbon dioxide or any other cold gas from large vessels and deep pits can be difficult as these gases are denser than air. Air fed in to the bottom of these spaces tends to float up through the dense gas without displacing it. This means that purging can take much longer than expected.
Detecting oxygen enrichment or deficiency
Areas where the oxygen content can change to a dangerous extent must be continuously monitored using instruments that show increases and decreases in the concentration of oxygen in the ambient atmosphere.
In confined spaces, these instruments should be located as close to workers as possible. Ideally, workers should have a portable instrument attached to their work clothes.
Discontinuous measuring methods should only be used if the tendency for dangerous changes in oxygen content can be detected quickly in the time between any two measurements.
Other gases
Oxygen content is not the only factor that defines whether a space is safe or not. Atmospheres can be affected by other gases such as fuel gases and nitrogen oxides used with cutting or heating torches. These should be monitored wherever necessary.
Preventive measures
Apparatus used for the manufacture, distribution and utilisation of inert gases must be installed and identified in accordance with the recommendations of the industrial gas industry, and must comply with relevant regulations.
Any leaks must be dealt with by persons with adequate training and proper equipment.
Workers and first aiders should know what to do in the event of an incident.
Operating personnel must at all times obey site rules and regulations and wear protective equipment where necessary.
All persons working in spaces at risk from oxygen deficiency or enrichment should be adequately informed of the risks involved. Special attention should be drawn to the insidious nature of the risks and how rapidly they can develop without any indication to workers.
Linde offers trainings about risks involved in gas application as well as mitigating measures to take.