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There are many hazards that can arise in confined spaces. Inarguably, the hazard that results in more fatalities in confined spaces are atmospheric in nature. In fact, at the time of writing this article, the last five recorded confined space deaths, according to OSHA Fatality Inspection Data, were caused by asphyxiation. This is because generally we can’t see, hear, taste, smell, or touch the atmosphere to determine its makeup. These tragedies serve as a sobering reminder that air monitoring isn't just a regulatory box to mark as checked – it's a matter of life and death.
Many fatal incidents have been documented by OSHA that were the result of changing atmospheric conditions after entry, underscoring the critical importance of on-going air quality monitoring.
"These fatalities highlight why continuous air monitoring must be integral to every confined space operation—it's non-negotiable for ensuring worker safety."
The Importance of Atmospheric Monitoring
Atmospheric hazards may be in the space prior to entry or could be introduced by workers based on the scope of work in the confined space. Typically, atmospheric hazards manifest in four main variations.
- Oxygen deficient environments – less than 19.5% oxygen
- Oxygen enriched environments – greater than 23.5% oxygen
- Toxic atmospheres – containing carbon monoxide, hydrogen sulfide, or other toxicants
- Flammable atmospheres – concentrations of gases between the LFL and UFL
Because of these potential risks, air monitoring is essential. Monitoring not only ensures compliance with OSHA standards (29 CFR 1910.146) but also provides real-time data to prevent accidents before they occur. Taking it a step further, continuous air monitoring can help to detect sudden changes in atmospheric conditions within confined spaces and give workers time to evacuate before negative health effects can set in.
What Should You Monitor For?
Looking at our list of atmospheric conditions from the previous section, it goes without saying that those specific conditions should be at the top of our list! OSHA requires testing of the following conditions, in this order.
- Oxygen Levels: Safe oxygen levels should be between 19.5% and 23.5%. If the levels drop below 19.5%, hypoxia and asphyxiation are possible. These levels can change quickly, especially when other gases are involved, and may not be recognized before it is too late.
- Flammable Gases and Vapors: The levels of flammable gases and vapors should be measured in percentage of Lower Explosive Limit (LEL) and remain below 10% of the LEL to avoid fire or explosion hazards.
- Toxic Gases: While there are too many toxic atmospheric conditions that may arise in confined spaces to list here, in general, carbon monoxide (CO) and hydrogen sulfide (H₂S) are the most commonly monitored conditions for standard confined space entries. It is critical to note that not all monitors detect all substances equally! Sensors must be calibrated specifically to detect the suspected condition. For example, a standard 4-gas monitor may not detect Benzene or other Volatile Organic Compounds (VOCs).
Types of Monitoring Devices
There are many different monitoring devices and configurations available for detecting hazardous atmospheric conditions in confined spaces. Being equipped with the appropriate tool for the job is a necessary step in ensuring safe entry.
- Single-Gas Detectors: These devices measure specific gases like oxygen, carbon-monoxide, or other specific gases. These may come in the form of digital direct-reading instruments with sampling pumps, personal monitoring devices, or, less commonly, gas detection colorimetric tubes.
- Multi-Gas Detectors: Ideal for confined spaces, these monitors detect several types of gases simultaneously, offering a more thorough view of atmospheric conditions. They are the most commonly used devices for monitoring atmospheric conditions before and during confined space entry. These devices may be an all-in-one unit with built in pump and wand used for monitoring the space or a personal monitoring device worn by the entrant.
NOTICE: Personal monitoring devices may be used to monitor atmospheric conditions in a confined space; however, they must be used in conjunction with a compatible external pump and wand which is usually sold as a kit from the manufacturer.
Calibrating Your Equipment
Using the right equipment is only effective if it’s properly maintained and calibrated. Gas detectors must be regularly bump-tested and calibrated according to manufacturer’s guidelines.
"Warning: These devices may give false readings without proper calibration, leaving workers unknowingly exposed to dangerous conditions."
As a general rule of thumb, devices should be bump-tested daily before use and calibrated every 90 days; however, you should always refer to and follow the manufacturer’s guidelines for your specific device.
OSHA Requirements for Confined Space Monitoring
OSHA’s Confined Space Standard (29 CFR 1910.146) mandates air monitoring as part of any confined space entry program. According to the regulation, employers must:
- Test conditions to determine if acceptable entry conditions exist before entry is authorized.
- Test or monitor the space as necessary to determine if acceptable entry conditions are being maintained during the entry.
- Evacuate the space immediately if unacceptable atmospheric conditions are detected.
Best Practices
To ensure adequate air monitoring, follow these best practices:
- Use the correct monitoring device equipped with appropriate sensors for the environment. Confined spaces vary, and the device must detect all relevant gases.
- Train your team to interpret air monitoring data correctly and respond to dangerous conditions.
- Test conditions at various zones (top, middle, and bottom) of the confined space as gases can stratify and may accumulate at different heights.
- Maintain your devices with regular checks, calibration, and servicing to ensure accurate readings.
Air Monitoring Saves Lives!
Atmospheric hazards in confined spaces are often invisible, yet they pose significant dangers, from oxygen deficiency to toxic gases. Continuous air monitoring is crucial because it provides real-time data, allowing workers to detect life-threatening changes in the atmosphere before harm occurs. Without monitoring, workers may unknowingly enter environments with unsafe oxygen levels, flammable gases, or toxic compounds. Proper air monitoring ensures compliance with OSHA standards and can prevent fatal accidents by giving workers the critical information needed to avoid hazardous conditions. Simply put, monitoring saves lives.
ONLINE REFERENCES:
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Brannon Aaron, ASP, NRP is an Associate Safety Professional through the Board of Certified Safety Professionals and a Nationally Registered Paramedic who works as a Safety Specialist and CSRT Crew Chief at Roco Rescue. Brannon has an extensive military background as well as years of experience in Pre-hospital Emergency Medical Services and emergency response settings.
