Oxygen enrichment is the general term for any gas or liquid that has more than 21% oxygen by volume in the air. In enclosed spaces, high levels of oxygen can be dangerous to humans.
Why 21% Oxygen?
The average oxygen level on earth is approximately 21% oxygen by volume. The oxygen level on the planet has stabilized at 21% because the amount of oxygen consumed is approximately equal to the amount of oxygen generated over time.
There is nothing “magic” about 21%. It is simply the volume of oxygen in our present day atmosphere. The same balances hold true for nitrogen (78% of air by volume) as well as the trace gases like argon, carbon dioxide and water vapor. If you go back far enough in geological time, these numbers will be different.
The earth formed over 4.5 billion years ago. At that time, there was virtually no free oxygen in the atmosphere. Fossil remains of oxygen-breathing mammals have been found that date back around 150 million years and human remains have been recorded over the last 200,000 years, so logic tells us that oxygen levels have risen to 21% over time. While there have been minor variations in the earth’s total oxygen level, over time humans and animals have become physically adapted to breathing air that contains approximately 21% oxygen.
Therefore, it makes sense that because humans and animals are adapted to breathing 21% oxygen in air, anything much different from 21% would be hazardous to our health. This is why OSHA considers any oxygen level below 19.5% as oxygen deficient or anything above 23.5% as oxygen enriched air. Both are potentially dangerous.
How much oxygen is too much?
While OSHA defines anything above 23.5% oxygen as dangerous, medical scientists have experimented with subjecting patients to hyperoxia, or breathing air at 100% oxygen levels for years. Hyperbaric oxygen therapy (HBOT) uses 100% oxygen at an ambient pressure higher than atmospheric pressure. Patients are placed in a sealed container with increased pressure and oxygen levels. For example, this is used to treat decompression sickness, to give supplemental oxygen to premature babies, and is used to treat a host of diseases under the general term of hyperbaric oxygen therapy.
The problem with breathing air at increased oxygen levels is that over time it can damage cell membranes, a collapse of the alveoli in the lungs, retinal detachment, and seizures. However, studies show that long term recovery is possible once oxygen levels are reduced.
Oxygen Enrichment Hazards
Leaking pipe, flange or manifold connections. This can be particularly hazardous in areas where there is not sufficient ventilation causing the oxygen concentration to increase.
Breaks in systems under oxygen pressure. A sudden release of oxygen under pressure can result in a relatively large jet of escaping oxygen. For example, a fork lift operator might rupture an oxygen pipe. Even a small volume of liquid oxygen can produce a large volume of oxygen gas.
Oxygen use in cutting and welding. In industrial processes where oxygen is used, oxygen may be allowed to freely escape during the process. Over time, the oxygen remains in the atmosphere and, if ventilation is inadequate, the air can become enriched with oxygen.
Liquid oxygen spill. A spill of liquid oxygen creates a dense cloud of oxygen enriched air when evaporating. In an open space, a hazardous oxygen concentration would only exist for a moment. In a closed space, this can result in a dangerous increase in the oxygen level.
Venting from cryogenic gas cylinders. As the temperature rises, liquid oxygen tank pressure can cause evaporation of the liquid oxygen. This is a normal occurrence. However, if the oxygen is not used for some time, the pressure relief valve can release oxygen into the surrounding atmosphere.
Desorption. Oxygen is released when cold materials which have absorbed oxygen, such as absorbents (molecular sieve, silica gel) or insulation materials are warmed to room temperature.
Ventilator Oxygen Enrichment Dangers
Ventilators are used in hospitals to both provide mechanical breathing assistance and supplemental oxygen to patients who have difficulty breathing. The oxygen used with a ventilator may be supplied by stand-alone pressurized tanks or by connection to a hospital-wide bulk oxygen source. In either case, the oxygen ventilator, tubing, and connections to the ventilator have the potential to leak oxygen into the room resulting in oxygen enriched air.
Because oxygen is required for fire, increased oxygen levels in an enclosed room means fire can start more quickly, spread faster and burn hotter than in rooms filled with fresh air.
Oxygen enriched air during ventilator use is the result of:
- Leaks from damaged hoses, pipes, connections and valves
- Valves left open either deliberately or unintentionally
- Poor ventilation where the oxygen is being used
Pressurized oxygen can raise the oxygen level in a room quickly. One liter of pressurized oxygen in a tank at 2,200 psi is the equivalent to 5 cubic feet of oxygen gas. If this were released into 12x12 foot room, it would immediately raise the oxygen level from 21% to 21.5%. During respiratory distress, oxygen flows from a patient's mask may reach 100 liters per minute or more.
Note that the same oxygen enrichment dangers apply to home supplemental oxygen tanks. Here are some additional tips for those who use oxygen at home:
- Don’t smoke near oxygen tanks. Most fires involving home-use oxygen are the result of smoking.
- Keep oxygen away from open flames. This includes gas stoves, grills, candles, fireplaces or any kind of fuel-burning space heaters.
- Avoid using electric razors, grinders, hair dryers or e-cigarettes. These are a source of sparks that can set off a fire in highly oxygenated air.
Oxygen Enrichment and Fire
While breathing moderately oxygen enriched air is not a problem, it does increase the risk of fire. To create fire you need heat, fuel and oxygen. By increasing any of these three elements you increase the risk of fire starting.
Firefighters have known for years that when the windows in a burning building break, the quick introduction of oxygen creates a backdraft, the rapid explosion of superheated gases in a fire with too little oxygen.
Another example of the dangers of oxygen enrichment are welding fires. According to the American Welding Society (AWS) Fact Sheet, Fire and Explosion Prevention:
- Sparks can travel up to 35 ft. (10 m) horizontally and even farther when falling. They can pass through or become lodged in cracks, clothing, pipe holes, and other small openings. Even at 35 ft., sparks can be hotter than 2,500 degrees F.
- Torch flames can ignite substances within several feet of the flame.
- Material in contact with the hot work piece, even away from the flame source and actual weld, can ignite.
- When this high heat and high levels of oxygen combine, wood, sawdust, rags, clothing or flammable vapors can become a potential fuel source for fire.
How Serious is the Risk?
While there are only a handful of cases each year of fires in hospitals intensified by oxygen enrichment, they do exist. According to the Federal Emergency Management Association (FEMA) between 2012 and 2014 there were 5,700 medical facility fires and 1,100 fires in hospitals in the US. While the majority of fires were related to cooking, between 1.6% of fires were the result of electrical equipment malfunctions.
For example, the Indian Journal of Anesthesia reported a near catastrophic ventilator fire leading to cardiac arrest in a patient during surgery. Sparks due to friction or an electrical short circuit within the oxygen ventilator may have acted as source of ignition leading to fire and explosion in the oxygen rich environment.
The ECRI Institute has published several cases over the years describing fires from defibrillation during oxygen administration when defibrillation produces an electric spark.
The increasing number of COVID-19 patients have resulted in some hospitals moving patients from private rooms to wards. The National Health System in the UK warned hospitals about “increased oxygen levels in the air” in wards repurposed to treat COVID-19 patients with ventilators. It went on to state that “the fire risk assessment for the area being converted should be reviewed in view of a higher life safety sleeping risk cohort and the additional issues of more oxygen being in use.”
In other words, even if all the oxygen ventilators are working properly, several of them in a single room could increase the oxygen level - and the potential file hazard.
Oxygen Enrichment Guidelines in the US
Oxygen storage systems in hospitals, institutions and industrial areas are covered under the United States Department of Labor Occupational Safety and Health Administration (OSHA) Guidelines 1910.104 Standard for Hazardous Materials – Oxygen. These general guidelines address the installation of bulk oxygen systems.
Oxygen Enrichment Guidelines Internationally
The European Industrial Gases Association (EIGA.eu) has published Fire Hazards of Oxygen and Oxygen-Enriched Atmospheres. This document is the most common international standard for bulk gas associations, covering the EU, Asia and Japan. It defines oxygen enriched atmospheres as exceeding 23.5% at sea level or whose partial pressure of oxygen exceeds 175 mmHg.
Regarding oxygen enrichment detection, the document states that:
“The method selected for oxygen detection shall offer a high degree of reliability of operation and be sufficiently sensitive to provide warning before a hazardous concentration of oxygen is reached. The usual method is to use an approved atmospheric monitoring instrument to confirm the effectiveness of the isolation and purging procedures before entry into the area and to periodically check during work to confirm that changes have not occurred.
If needed, oxygen measuring instruments should be used as warning devices only and should not be regarded as protection against the risks of oxygen enrichment. They should be seen as an addition to good practice of eliminating the causes of enrichment. Appropriate measuring instruments for the determination of oxygen content indicate an increase as well as a decrease of oxygen concentration in the ambient atmosphere.
Various measuring techniques and methods are used that give visible, audible, and/or tactile (vibration) warning, and they can be used for continuous or intermittent measurement. The manufacturer’s instructions for the use and maintenance of the measuring instruments shall be carefully followed.”
Oxygen Enrichment Safety: RACE
If an fire occurs in an oxygen-enriched environment, hospital personnel should follow the rescue, alert, contain and evacuate (RACE) procedure:
- Rescue patients in the immediate area of the fire. The person discovering the fire should perform the rescue if possible.
- Alert other personnel to the fire so that they can assist. The discoverer should also let others know of a fire by yelling "Fire in room 119!" while rescuing the occupants. Other personnel hearing the alert should relay the information to the facility switchboard or other alarm system.
- Contain the fire. Shut the door after rescuing the occupants to slow the spread of smoke and flame. Close fire doors. If oxygen and/or medical compressed air is in use in the room, shut off the zone valve controlling those gases to that room, and immediately assist all affected patients.
- Evacuate other patients and personnel in the areas around the fire. Facility personnel trained in fire emergency procedures should respond to the initial alarm to assist in evacuating patients to safe areas.
In addition to fire prevention, these additional tips are important in a potentially oxygen enriched atmosphere:
- Fire needs a spark/ignition, fuel and oxygen. Since anything non-metallic is a potential fuel and oxygen enrichment is potentially possible, pay attention to any source of sparks or ignition in the room like defibrillators, electrosurgical equipment, lasers, light sources or flames.
- Medical personnel using ventilators should be trained on proper operation of the device, especially in regards to connecting and disconnecting the machine from oxygen sources.
- Never force a tube connector into another connector. Make sure they are designed to mate properly for a proper seal.
- Know where the emergency oxygen shut-off valve is.
- Know where the nearest fire extinguisher, fire alarm, and fire escape is located as well as the proper procedure for contacting 911 in case of fire.
- Know how to cut off electrical power to the ventilator.
Oxygen Enrichment Safety
To protect workers and staff against high levels of oxygen, GasLab offers the RAD-0002-ZR-E Oxygen Enrichment Safety Alarm. This wall-mounted oxygen sensor continuously detects oxygen levels in an enclosed area and sounds an alarm if oxygen levels begin to rise or fall. It is used in industries that utilize bulk oxygen tanks like steel manufacturing, welding and cutting, cryogenics, for medical breathing gas, diving tanks, or in areas where bulk oxygen is produced.
Learn more about our line of wall-mounted indoor safety alarms.
Photo by Hush Naidoo on Unsplash