While oxygen deficiency in humans are often the result of a medical condition, an oxygen deficient atmosphere in a confined space is just as dangerous.
Except for drowning or being locked in a closet, most people don't worry about a lack of oxygen. But if you are in a hospital, a restaurant, a bar or any of a hundred businesses or factories there are stored tanks or cylinders of compressed gas nearby. A leak in any of these tanks or cylinders in an enclosed area has the potential to lower the oxygen level, resulting in a hazardous oxygen deficient atmosphere.
What is Oxygen Deficiency?
OSHA defines an oxygen deficient atmosphere as anything less than 19.5% oxygen by volume. At lower levels, different physical symptoms can occur.
Effects of Various Oxygen Levels
| Oxygen Level Percent | Effects |
| 20.9% | Normal - fresh air |
| 19.5-20.9% | Acceptable low oxygen (OSHA) |
| 10-19.5% | Increased breathing rate, accelerated heartbeat, impaired thinking and coordination |
| 6-10% | Nausea, vomiting, lethargy, leading to unconsciousness |
| < 6% | Convulsions, cessation of breathing, cardiac arrest. |
See the Occupational Safety and Health Administration's (OSHA) 29 CFR 1910.134 standard and ANSI/ASSE Z88.2-2015 (Z88.2) guidelines for more information. An employee who must enter a confined or potentially oxygen deficient space may require a low oxygen alarm, a respirator or personal protection equipment.
Oxygen Deficiency from Stored Gases
Stored gases used in businesses and industry include nitrogen, oxygen, carbon dioxide, argon, hydrogen, helium, acetylene, and other specialty gases.
With the exception of oxygen, all these other gases are asphyxiates. An asphyxiate gas is a nontoxic or minimally toxic gas which reduces or displaces the normal oxygen concentration in a confined space. Breathing oxygen-depleted air can lead to death by asphyxiation, or suffocation.
Where are Stored Gases Used?
Have you ever walked into a restaurant? That big aluminum tank on the side of the building is liquid carbon dioxide, or CO2. It is used to carbonate your beer or soft drinks. CO2 tanks are used in data centers for fire suppression systems. If you’ve ever taken a cruise, ships use them to fight fires too. In addition to oxygen, your local hospital has tanks of CO2 and medical liquid nitrogen installed on every floor.
Do you work in a factory? Welding is done using stored tanks of argon, CO2, hydrogen, nitrogen and helium.
Modern grocery stores are switching from ammonia (NH3) to CO2-based refrigerants to keep their meat, dairy and frozen food isles cold. NH3 is toxic and dangerous compared to CO2, but in either case, gallons of it are stored as a liquid in the store for refrigeration.
Need to get an MRI? That machine relies on liquid nitrogen and liquid helium to cool the magnets to -270°C, just above absolute zero temperature. Your dermatologist and local cryospa uses the same stored gases too.
How much stored gas is around you? The market for CO2 gas alone was 32,844 thousand tons of liquid CO2 produced in 2019. The industrial gas market for all stored gases is expected to grow by over 5% annually.
While you may not see them, when you go to work, to a store or to a restaurant a tank of stored gas is somewhere near you.
Stored Gas Tanks are Safe
The problem isn’t the tanks these gases are stored in. These are designed to strict government regulations and leaks are very unlikely. And small amounts of any pressurized gas are not harmful, especially when they can quickly mix with fresh air.
However, a leak in a pressurized gas line indoors can easily become dangerous. For example, one liter of liquid nitrogen vaporizes to 696.5 liters of nitrogen gas at room temperature. For most common gases the expansion ratio from liquid to gas is between 700 and 900. This means that even a small leak can quickly lower the oxygen level in an enclosed room or area.
The challenge is that people can make mistakes. No matter how much training they receive, eventually someone will turn the wrong valve, not tighten a fixture, or cut a hose.
Oxygen Deficiency Alarms
With the growing use of stored gases, state and local governments are developing new procedures to audit their use. Building inspectors across the country now require oxygen depletion alarms in rooms containing tanks of stored gases.
For example, an oxygen depletion safety alarm monitors the oxygen level in in a room in real time so that a leak will be noticed before it results in a dangerous situation. In addition, the alarm can control ventilation fans or can be connected to a facility’s HVAC and/or alarm system. In the case where CO2 is stored, a CO2 level safety alarm should be used.
The benefits of stored gases are numerous. From improved medical procedures to fire prevention to even the bubbles in the beer and soda we drink, we can all appreciate the benefits of stored gases. It’s also important to know that with the benefits comes a small risk that should not be ignored.