Minimum Oxygen Concentration for Human Breathing

By Mallory Malesky

Oxygen is essential to human life. The human body takes the oxygen breathed in from the lungs and transports to the other parts of the body on the red blood cells. Oxygen is used and required by each cell. Most of the time, the air in the atmosphere has the proper amount of oxygen for safe breathing. However, the level of oxygen can drop due to other toxic gases reacting with it. The minimum oxygen concentration for human breathing is 19.5 percent.

Normal Air Composition

Each time you take a breath, you inhale more than oxygen. The normal air in our environment is actually made up of a few different gases. Approximately 78 percent of the air is nitrogen gas while only about 20.9 percent is oxygen. The remaining fraction is made up of mainly argon gas, however trace amounts of carbon dioxide, neon and helium are also present.

Safe Oxygen Levels

For humans and many animals to sustain normal functions, the percentage of oxygen in the breathing environment must be within a small range. The Occupational Safety and Health Administration, OSHA, determined the optimal breathing range to be between 19.5 and 23.5 percent oxygen.

Side Effects of Unsafe Oxygen Percentages

Serious side effects will occur if the oxygen levels are outside of the safe zone. At levels at or below 17 percent, your mental abilities become impaired. When levels drop to 16 percent or below, noticeable changes to your beings while levels under 14 percent will cause extreme exhaustion from physical activity. Once levels drop below 10 percent, you may become very nauseous or lose consciousness. Humans won't survive with levels at 6 percent or lower. Higher-than-normal oxygen levels aren't as harmful to life, however there is an increased fire or explosion risk. With extremely high concentrations of oxygen in the breathing zone, humans can experience harmful side effects. Very high levels of oxygen causes oxidizing free radicals to form. These free radicals will attack the tissues and cells of the body and cause muscle twitching. The effects from short exposure can most likely be reversed, however lengthy exposure can cause death.

Altitude Sickness

The safe breathing levels are determined at sea level altitude. As you increase your altitude, such as driving or climbing up a mountain, there is less atmospheric pressure. Lower pressure allows air to expand more than it can at sea level. While the ratio of the oxygen and nitrogen in the air remains the same, there are less molecules within the same space. Therefore, each breath you take at a higher altitude contains less oxygen molecules than breathing at a lower altitude. This can cause an illness commonly referred to as altitude sickness. Most people afflicted with altitude sickness experience nausea, headache and fatigue. However, the condition can become more serious if not properly treated.