Oxygen molecules moving through the blood stream
Posted in: Gas Detection

Oxygen Safety: Is 19.5 enough?

Oxygen is one of the most important gases in the world. Not only does it make a great deal of our technology work (including most gas sensors), but it also keeps us alive. Thankfully it is also quite plenteous. At sea level the effective oxygen percentage is 20.9%. At 2,000 feet it is 19.4%.

The alarm on most gas detectors is set to go off if oxygen levels go under 19.5 per cent. This is due to OSHA regulations which declare under 19.5 to be hazardous. But is this really the level at which a lack of oxygen becomes dangerous? Can you go lower, or is it even possible that amounts above this number can be deadly?

Oxygen Partial Pressure

It doesn’t matter to the body what the percentage of oxygen is. What matters is the actual amount, or partial pressure of oxygen. You can measure this in millimeters of mercury (mm Hg). At sea level, not accounting for humidity the air carries around 159 mm Hg. Most physiologists will generally agree that oxygen deficiency begins around 60 mm Hg. From that number it seems as though 10% oxygen should be plenty, right?

There are many problems with this outlook. The first problem is that oxygen mixes with moisture and carbon dioxide as it enters the body. This decreases the partial pressure as it enters your lungs. Under the above scenario by the time the oxygen is in the alveolar spaces it is already down to about 110 mm Hg. This is important because it is the here that it gets absorbed into the body.

The second problem is that this assumes sea level and no humidity. There are few if any places on earth which can provide these conditions. As you increase in altitude the air gets thinner and the amount of oxygen decreases. Additionally an increase in moisture vapor will take up space in the air, pushing out oxygen.

The final problem is acclimatization. Regardless of the amount of oxygen in the air the body will adapt itself to work with that amount. This is the reason why people climbing Mount Everest have to rest at the base camp before they can climb. This means that someone coming from a low altitude and working at a higher altitude will be sensitive to lower oxygen levels. But someone from a higher altitude will be less sensitive to oxygen loss while working at a low altitude. A regional native might be safe while a visitor from the coast would be skirting with disaster.

What else can the amount of oxygen tell us?

Besides telling you whether there is enough oxygen in the air to breathe the oxygen levels also hint at what else might be in the air. Because oxygen exists at a 1:4 ratio with nitrogen, any drop in oxygen levels also indicates a drop in nitrogen levels. A 1% drop in oxygen actually indicates 5% of the air is being filled by something else. This can be an indicator of toxic or combustible gases which were previously unknown. In these situations it might be a good idea to bring in a four-gas detector to verify what else is in the air.

There are many factors which need to be considered when looking at what levels are safe. OSHA and the various national, state, and provincial safety agencies lay out guidelines but these must be approached as the bare minimum and not applicable to all situations. At Concept Controls we have a team of trained sales specialists who can help you find the gas detector that is right for you, and our service team can help you configure and test it. For more details please call us at 1-888-207-2212

April 15, 2021
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