Confined Space Safety: Gas Detection Best Practices

Continuous gas monitoring with a calibrated and bump tested gas detector helps ensure the safety of workers.

Construction crews face multiple dangers when working in a confined space. The biggest risk is a hazardous atmosphere. Asphyxiation from oxygen deficiency or exposure to toxic gases is the leading cause of death in confined spaces. That’s why gas detection is a critical component of confined space safety.

The proper use of a gas monitor is essential to reduce worker exposure to harmful atmospheres that can be deadly. But all too often, companies don’t understand OSHA’s gas monitoring requirements, they become complacent about following them or they feel indifferent about the potential hazards and their impact.

Don’t put your workers at unnecessary risk. Follow these best practices for confined space gas detection to help keep them safe.

Best practices for pre-entry testing

Before entering a confined space, initial testing is required. Understanding the differences in portable gas monitors and the right method of sampling is critical. It’s also worth noting that proper pre-entry testing is done without applying any controls to the space (i.e. ventilation). The initial reading requires a baseline of the atmospheric condition in the space.

Pump-driven gas monitor vs. diffusion gas monitor

Using a pump-driven gas monitor gives the competent person visibility to the instrument readings while drawing air samples from within the space across the sensors.

Don’t use a diffusion gas detector for pre-entry gas detection unless it is configured with the manufacturer’s supplemental pump and functions properly to draw a sampling of the atmosphere across the sensors while the competent person remains outside the space. Without a supplemental pump, a diffusion gas detector tests only the surrounding air that the sensors are exposed to through normal air movement.

Testing at multiple levels

The key to effective pre-entry testing is drawing air from multiple levels within the space. Why? Gases contain different molecular weights, and pockets of toxins may settle at lower levels within the space.

OSHA’s general standard for confined space pre-entry testing requires sampling at every 4 feet. The construction standard doesn’t address this, but the 4-foot standard remains a good, minimal one to follow and is consistent with the recommendations of most gas detector manufacturers.

Why to use continuous gas monitoring

A designated competent person with the proper training has to test the atmosphere before anyone enters a confined space. But that one-time test isn’t enough. Construction activities such as welding, cutting, scraping or applying a coating inside or even directly outside the space, for example, can quickly create a toxic atmosphere.

That’s why continuous gas monitoring is a best practice. When the concentration of a gas reaches unsafe levels, or when there’s too much or too little oxygen in the air, the gas detector will alarm, usually with an audible and a visual alert, indicating that immediate evacuation is required.

Even before the gas detector alarms, it will indicate a change in the concentration of a gas. It’s important to know if there are significant swings, which could indicate that something unusual is happening that may need to be addressed.

Continuous vs. periodic monitoring

OSHA regulation 1926.1203(e)(2)(vi)) calls for continuous monitoring of confined spaces for construction projects “unless periodic monitoring is sufficient,” but OSHA hasn’t defined periodic in the context of gas monitoring. In other contexts, periodic means often enough that there’s a good likelihood that problems will be found before they pose a hazard. But it can be hard to know if you’re in compliance, so continuous monitoring is a better and safer choice.

If you use periodic monitoring, be sure to keep written records about what atmospheric tests were done and their results to show OSHA if necessary.

How to implement continuous gas monitoring

Once crews are working in the space, you can use a pump-driven gas detector or a diffusion gas detector for continuous gas monitoring. Gas detectors that workers wear are an acceptable type of diffusion gas monitor that should be worn near the worker’s breathing area.

Remember that one monitor can perform both pre-entry testing and continuous monitoring. You don’t need multiple monitors to do the job. A diffusion gas detector with a fitted external pump, tube and probe assembly will do the pre-entry test. Pop off the pump, and the same monitor will do the continuous monitoring.

Perform bump testing and calibration at required intervals

Bump test the gas monitor before using it each day. What is a bump test, exactly? It’s a qualitative function test to confirm that gases get to the sensors and that the alarms are operating properly. It usually takes less than a minute.

Calibration is also necessary. It puts the gas monitor through a full cycle of tests and resets the sensors as needed to ensure they are working, accurate and set to the proper range for detecting gases. You can perform a calibration test in the field with the proper equipment, or have the monitor tested by an approved product support specialist, such as a representative from United Rentals Trench Safety. It’s a best practice to do a calibration at least once a month, but follow the manufacturer’s guidelines if more frequent calibrations are recommended.

When you bump test and calibrate your gas detectors regularly, their sensors should last longer.

Bump test and calibration kits

Make sure you’re using the bump test gas and calibration kit designed for your equipment, since different types and brands of gas detectors are designed to detect different concentrations of gases.

Don’t take chances

Most confined space accidents result in a fatality, and 60% of those who die are would-be rescuers. Follow the best practices for confined space gas monitoring, including using the right gas detectors and testing the equipment as required, to mitigate the risk of harm from hazardous atmospheres and help ensure your workers come out of the confined space as healthy as they went in. You should always consult with an expert regarding the specific circumstances, applicable rules and regulations related to your site and to your situation.

To rent a gas monitoring system or get help with bump testing and monitor calibration, call us at 833.456.3179 or visit your local United Rentals branch.

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