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 Preventing Injuries and Fatalities in
Low-Oxygen Atmospheres

Oxygen-deficient atmospheres may exist in any hazardous space regardless of whether it is subject to the Occupational Safety and Health Administration’s (OSHA) Grain Handling Standard 1910.272(g) or Permit Required Confined Space Standard 1910.146. This article discusses the symptoms and common causes of oxygen deficiency and the importance of atmospheric monitoring when entering hazardous spaces.


Oxygen Deficiency

The air we breathe contains approximately 20.9% oxygen, 78% nitrogen, and smaller quantities of gases such as argon and carbon dioxide.

 The immediate effects of low-oxygen environments can be traced to the body’s oxygen transport system. Blood absorbs oxygen from air in the lungs to fuel the cells in the body. The brain is the organ most sensitive to a lack of oxygen.

A person immediately will begin to feel the health effects associated with lack of oxygen with decreases of 1% to 2%. Healthy individuals are unable to work strenuously or lose coordination when oxygen levels are between 15% and 19%. When oxygen levels are between 10% and 12%, respiration increases, lips turn blue, and judgment is impaired. Fainting and unconsciousness occur when oxygen levels are between 8% and 10%. Death can occur within eight minutes, if the oxygen level is between 6% and 8%. These values may vary based on several factors including the person’s health, the level of physical activity, and the environment. 

The OSHA Respiratory Protection Standard 1910.134 defines oxygen deficiency as an atmosphere with an oxygen content below 19.5% by volume. OSHA’s Permit Required Confined Space Entry Standard 1910.146 and Grain Handling Standard 1910.272 also recognize that an atmosphere with less than 19.5% oxygen is hazardous.

 Many safety professionals agree that entry into any hazardous space or other area where oxygen deficiency may exist requires oxygen levels to be as close  as possible to normal. For instance, an atmospheric level of 20.5%, while still acceptable to OSHA, signals that there is issue that needs to be investigated.


The Cause

A number of factors cause oxygen deficiency. In general, oxygen deficiency occurs when another gas displaces oxygen in a poorly ventilated space.For example, decomposition of organic material or smoldering grain can consume oxygen within a space. 

Grain that is high in moisture or poor in quality can result in elevated levels of carbon dioxide. Carbon dioxide can displace the oxygen within storage spaces. Carbon dioxide is denser than air. Therefore, it can accumulate in low-lying areas adjacent to hazardous spaces.


Preventive Measures

A worker cannot see, taste, or even smell an oxygen-deficient atmosphere. The only way to identify oxygen deficiency is to test the air with a calibrated atmospheric monitor.

According to OSHA, calibration refers to an instrument’s measuring accuracy relative to a known traceable concentration of test gas. Atmospheric monitors must be calibrated according to the manufacturer. Keep in mind that calibration gases have an expiration date. Calibration gases that have expired should be replaced immediately.


Bump Tests

In addition to calibration, a bump test should be performed prior to each use. According to OSHA, a bump test is a qualitative function check, in which a challenge gas is passed over the sensor(s) at a concentration and exposure time sufficient to activate all alarm settings. 

The purpose of this check is to confirm that gas can get to the sensor(s) and that all of the instrument’s alarms are functional. The bump test does not provide a measure of the instrument’s accuracy.

Both the Permit Required Confined Space (1910.146) and Grain Handling (1910.272(g)) standards require atmospheric testing prior to entry into hazardous spaces. Safety professionals agree that performing a pre-entry test alone is not adequate. The atmosphere in an area where oxygen deficiency may exist should be monitored continually throughout the entry. Atmospheres within hazardous spaces can change rapidly. Therefore, monitoring the atmosphere continually during entry is a critical to ensure employee safety.



Both OSHA and safety professionals recognize that oxygen-deficient atmospheres may be present in hazardous spaces defined in OSHA’s Grain Handling and Permit Required Confined Space Standard. It can be easy to overlook the potential for oxygen deficiency based on past experience. 

 Safety leaders must be consistent in their approach and err on the side of caution. Implementing pre-entry and continuous atmospheric monitoring can be the difference between life and death. 

Source: Joe Mlynek is president of Progressive Safety Services LLC, Gates Mills, OH;; and content creation expert for Safety Made Simple Inc., Olathe, KS;


This Safety Tip of the Week is sponsored by: CCS Group.



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Safety Tip of the Week is edited by Managing Editor Tucker Scharfenberg and published each Monday by Grain Journal, Decatur, IL

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