Statistically, atmospheric hazards are the most common cause of death in confined space accidents. It is important that first responders understand these atmospheric hazards and the basic principles of operating four-gas detectors. In Part 1 of this series, we will be discussing basic metering principles related to confined space incidents.
At confined space incidents, one of the first things we will do on-scene is air monitoring. Assuming your agency already follows the manufacturer recommendations on calibrating and bump testing your four-gas detector, the first thing you will need to do is turn your detector on. You must be 100% sure you are in a clean environment if you are going to do a fresh air setup or “zero out” your detector.
Remember, if we are on-scene as first responders, something has already gone wrong inside the confined space. If the patient inside the confined space is unconscious, then it is possible there is an atmospheric problem inside the space. We want to monitor around the opening to the confined space first, while being mindful of where we stick our noses. It is not a bad idea to wear an SCBA and breathe fresh air while performing your initial air monitoring of a confined space that could possibly have an atmospheric hazard. At the very least, approach it from upwind.
Remember to safely monitor the atmosphere around the opening to the confined space first!
After monitoring around the opening to the confined space, we will then direct our attention to conditions inside the space. To accomplish this, we typically use a four-gas detector with a pump and sampling hose. The pump will forcefully pull air into the detector to be tested, and the hose will extend our reach further into the confined space. Allow 2 seconds per foot of hose in use for the air to be pulled through the hose and hit the sensors. All irregular areas of the space where hazards may accumulate must be tested. Additionally, testing should be done at 4’ intervals vertically as well. Some gases are heavier than air, and there may be different hazards present at different levels in vertically oriented confined spaces.
Once the initial air monitoring is complete, first responders should begin ventilating the confined space if they have the appropriate equipment. Continuous air monitoring and ventilation will help prevent a hazardous atmosphere from forming during the rescue operation. It’s not a bad idea to have a backup detector available in case the first detector becomes inoperable for some reason. Initial and follow-up readings should be documented on the confined space rescue permit periodically based on your agency’s SOGs.
In Part 2 of this series of posts we will cover atmospheric hazards related to oxygen deficiency and oxygen enrichment. Check back in a few days.
Owner / Lead Instructor
Elder Technical Rescue Services, LLC
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