In our first Confined Space Atmospheric Hazards post, we discussed the basic principles of atmospheric monitoring in confined spaces and operating our four-gas detectors. In part two of our Confined Space Atmospheric Hazards series, we will be discussing hazards related to oxygen deficiency and oxygen enrichment.
The air you are breathing right now is comprised of approximately 20.8% oxygen. If the oxygen levels are reduced below that, you can begin to experience health effects. Oxygen is essential to sustain human life. All our vital organs rely on oxygen in order to properly function. In confined spaces, we use the range of 19.5% – 22% to define an acceptable oxygen concentration in the air. However, any oxygen concentration below 20.8% could indicate there is another hazard present.
This confined space killed a utility worker and firefighter, partly due to an oxygen deficient atmosphere. Source: NIOSH.
Oxygen deficiency can be caused several ways. Oxygen displacement occurs when there is another gas inside the confined space that is pushing the oxygen out. This can occur intentionally when a confined space is filled with an inert gas for a specific purpose, or due to an unexpected leak or chemical reaction that creates a gas that displaces the oxygen. The oxygen can also be consumed, for example by combustion, oxidation (i.e., rusting), or through workers’ respiratory systems consuming the oxygen.
Oxygen enrichment technically occurs when the oxygen concentration exceeds 21%. However, our acceptable entry conditions allow us to enter a confined space in concentrations up to 22%. When the atmosphere is oxygen enriched, there is an increased risk of fire. Furthermore, if a fire does occur, it will generally burn with more intensity than it would if there was a normal oxygen concentration in the air. Oxygen enrichment can occur when pipes or cylinders leak, liquefied gasses are improperly handled or disposed, and through mad-made processes such as welding.
In December 2011, a firefighter was killed when he entered a confined space to rescue an unconscious utility worker at the bottom of a sewer manhole. The confined space had both an oxygen deficient atmosphere as well as other toxic gases. The medical examiner reported that the firefighter’s cause of death was asphyxia and exposure to the toxic gases. For more information about this case, read the NIOSH LODD Report.
The next post in this series will discuss flammable atmospheres. Check back in a few days.
Owner / Lead Instructor
Elder Technical Rescue Services, LLC
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