Workplace Solutions Confined spaces Construction safety

Gas detection in confined spaces

OSHA requires a direct-reading portable gas detector to test the atmosphere in a confined space before my workers enter. Why is a direct-reading monitor needed instead of an alarm-only monitor?


Responding is Dante Moore, senior applications engineer, Industrial Scientific Corp., Pittsburgh.

Answer: Confined spaces are defined by OSHA as spaces large enough for workers to enter yet not intended for continuous use.

Confined spaces have limited or restricted entry and exit points. These characteristics mean that gas levels can change rapidly, rendering the atmosphere hazardous with little warning. For this reason, it’s important for confined space entrants and hole watchers to not only know – at any given moment – whether the space is safe or not, but also whether conditions are trending toward danger so they have time to make informed decisions about their safety.

So, how can you protect your workers in confined spaces? Supply them with direct-reading monitors. In fact, OSHA requires the use of direct-reading monitors when testing the atmosphere of a confined space before entering.

You might be tempted to use alarm-only gas monitors because of their promises of simplicity – your workers only have to know whether the device is in alarm mode and, when it is, they evacuate the space.

However, alarm-only monitors don’t give workers the information or time they need to prepare for risky situations.

Let’s say that a worker takes a reading of the confined space with an alarm-only detector before entering and the alarm doesn’t activate. The oxygen level is above the minimum safe level of 19.5%, but only barely.

The worker then assumes the space is safe and enters. It might only take a few minutes for the oxygen level to drop below the safe amount, giving the worker no notice that they need to leave the confined space. This can lead to a rushed exit if the worker is lucky and a tragedy if they’re not.

On the other hand, if the worker had used a direct-reading monitor, they would have known that the space had a nearly unsafe oxygen level before entering and been able to ventilate the space or delay the entry.

Direct-reading monitors show workers how safe the atmosphere is as well as give them a chance to recognize patterns and respond to shifting gas levels.

In addition to testing the atmosphere with a direct-reading monitor before entering a confined space, it’s a best practice to continuously monitor atmospheric conditions.

Gas levels can be unpredictable and change quickly even between periodic checks. A personal gas monitor with a slide-on sampling pump allows workers to use their device for pre-entry sampling, then remove the pump and wear it on a lapel for continuous monitoring while within the confined space.

Workers inside confined spaces aren’t the only ones who can benefit from using direct-reading monitors – 60% of confined-space deaths are would-be rescuers.

There are personal and area monitors that can wirelessly connect to share gas concentrations and alarms in real time.

This gives all workers onsite the information they might need to execute a safe rescue. This connectivity keeps your workers visible to attendants even when they can’t be seen or heard.

Confined spaces are dangerous, but you can reduce the risk by following OSHA guidelines and best practices. Providing your workers direct-reading monitors – especially those that monitor the atmosphere continuously and wirelessly connect – is the best way to help them return home safely at the end of the day.

Editor's note: This article represents the independent views of the author and should not be construed as a National Safety Council endorsement.

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