Compressed air is simply air stored at a pressure higher than the ambient atmospheric pressure. The short answer to whether a person can breathe this air is yes, but only under extremely controlled conditions. Normal atmospheric air is compressed and used for human respiration in various specialized applications, most famously in diving. Using compressed air requires strict adherence to two non-negotiable safety factors: the absolute purity of the air mixture and the management of physiological effects caused by the pressure difference. These considerations make breathing compressed air vastly different from breathing the air around us.
Air Purity and Compression Contaminants
The quality of compressed air is a major concern because compression introduces significant risks of contamination. Standard air compressors, particularly those used in workshops, often rely on oil for lubrication. This oil can vaporize under the high heat generated during compression, mixing with the air. This vaporized oil, which is a hydrocarbon, becomes highly toxic when inhaled, requiring specialized breathing air to meet stringent standards, such as the Compressed Gas Association (CGA) Grade D specifications.
A particularly deadly risk is the presence of carbon monoxide (CO). CO can be introduced if the compressor’s intake is near engine exhaust or if the compressor overheats, causing incomplete combustion of lubricating oil. Standards mandate that CO levels must not exceed 10 parts per million (ppm) to prevent poisoning. Specialized multi-stage filtration systems are required to remove water vapor, fine particulates, and oil mists, ensuring the air is safe. Without these filters and regular air quality testing, air from a typical industrial compressor is unsafe for breathing.
The Physical Risk of Pressure Changes
The most immediate danger when breathing compressed air relates to the mechanical effects of pressure changes on the body’s gas-filled spaces. This risk is explained by Boyle’s Law, which states that pressure and volume are inversely related for a fixed amount of gas. As pressure increases, volume decreases; conversely, as pressure decreases, volume expands.
The volume of air inside a person’s lungs, sinuses, or middle ear will expand dramatically upon ascent or pressure reduction. If a person breathes compressed air and holds their breath while ascending, the air in the lungs cannot escape and will over-expand. This phenomenon is known as Pulmonary Barotrauma, or lung overexpansion injury.
The expansion can rupture the delicate air sacs (alveoli) in the lungs, leading to a fatal condition called Arterial Gas Embolism (AGE). Even ascending just a few feet while breath-holding can cause this injury because the largest volume change occurs near the surface. The resulting air bubbles enter the bloodstream and can travel to the brain, causing a stroke or immediate loss of consciousness.
How High Pressure Affects Gas Physiology
Beyond the mechanical risks, breathing compressed air alters how gases interact with the body’s tissues, a principle governed by Henry’s Law. This law states that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas. As a person breathes air under high pressure, more inert gases, primarily nitrogen, dissolve into the blood and tissues.
This increased concentration of dissolved nitrogen leads to Nitrogen Narcosis, a reversible impairment of cognitive and motor function often described as feeling like alcohol intoxication. Known as the “rapture of the deep,” this effect typically becomes noticeable at depths around 100 feet (30 meters) and worsens with increasing pressure. The nitrogen molecules interfere with nerve cell membranes, leading to impaired judgment and delayed reaction times.
Another danger arises from the increased partial pressure of oxygen (PO2), which can lead to Central Nervous System (CNS) Oxygen Toxicity. While oxygen is necessary for life, breathing it at a high partial pressure causes oxidative damage to the nervous system. This can result in symptoms like twitching, visual changes, and sudden grand mal seizures, requiring dive professionals to carefully manage oxygen levels and exposure time.
A third major risk occurs when the pressure is reduced too quickly, causing the dissolved gases to come out of solution rapidly. If the ascent is too fast, the excess dissolved nitrogen forms bubbles in the blood and tissues, similar to opening a carbonated drink. This bubble formation is Decompression Sickness (DCS), commonly known as “the bends.” These nitrogen bubbles can lodge in joints, causing pain, or obstruct blood flow to the spinal cord and brain, leading to paralysis or death.