How to Remote Test Atmospheric Conditions of a Confined Space

We find that some entering confined spaces are not fully aware of both the requirements to test the space before entry is made (a remote test) and the ways to perform such a test. In this short article, we hope to clear up any confusion on how to best remote test a confined space.

Pre-Entry or Remote Test Requirement

OSHA 1910.146(c)(5)(ii)(C) states the following: "Before an employee enters the space, the internal atmosphere shall be tested, with a calibrated direct-reading instrument, for oxygen content, for flammable gases and vapors, and for potential toxic air contaminants, in that order."

The simple translation is this--before any entry can be made into a confined space,  a gas monitor must be used to test for the presence of a hazardous atmosphere. A hazardous atmosphere includes not only the presence of explosive gases, carbon monoxide, and hydrogen sulfide, but also too much or not enough oxygen.

The space must be tested before entry is made. A confined space entry should never be made until this requirement is met. This is often called pre-entry testing or remote testing.

Methods for Remote Testing

There are typically three methods to remote test a confined space before entry is made. (1) Lower the gas monitor down on a rope; (2) Attach an external sample pump to the monitor and lower the pump's sample tube into the space; (3) Use the monitor's (if it has one) internal pump and lower the pump's sample tube into the space.

There are pros and cons to each method. We prefer Method 1.

Method 1 - Rope Method

Most, if not all, gas monitors have a belt clip and/or metal d-ring. It's quite easy to attach some sort of line or rope to this to perform a pre-entry remote test. One simply lowers the monitor into the space by feeding out the rope.

Pros: This method makes it very easy and more likely that multiple "layers" of the atmosphere are tested. As long as the monitor is lowered slowly, it will have enough time (a few seconds at each layer) to detect these various layers. The air does not have to travel up a sampling tube. The sensors themselves are being exposed to the air in the space.

Cons: There is the risk of dropping your monitor or lowering it into water. Caution should be taken to accommodate these risks.

Concerns: It is suggested that this method makes it difficult to know what readings the monitor obtained during the remote test. This is incorrect. All monitors keep track of peak readings. Once the monitor is brought back up, all one need do is scroll though the peak readings. 

Method 2 - Attached Pump Method

Most monitors have a detachable pump option available to purchase. The pump can either be a battery operated sample draw pump or a hand squeezed pump. 

Pros: If the pump breaks, you still have a working gas monitor. You can resort to Method 1 above to do a remote sample. There is also less risk of dropping your monitor into the space you are testing. The monitor is in your hand so the readings can be seen in real time. There is no need to scroll through the peaks readout.

Cons: With respect to a hand squeezed sample draw pump, accurate testing is very difficult. To accurately test the various layers of a space using, say a ten foot hose, one has to stop at each layer and squeeze 20-30 times to draw up the correct amount of air. Nobody does this.

With respect to a battery powered detachable pump, accurate testing is easier. It requires that the end of the sample tube be left at each layer for many seconds to get a correct sample. This still requires patience.

With respect to both types, it is possible that if the filters are not used properly water can be sucked up into the monitor. Also, remember, pumps draw air from the point of least resistance. If the tubing or filters are clogged, your pump may be drawing air from a point at the monitor itself and not the end of your sample tubing. In other words, you may not be testing the atmosphere of the confined space at all.

Concerns: Pumps require additional maintenance. The particulate and water filters need to be changed and looked after. The battery powered pumps need charging or replacement batteries. Pumps can break or fail in some capacity.

Method 3 - Internal Pump Method

Some gas monitors can be purchased with a built-in internal pump.

Pros: Like Method 2, there is less risk of dropping your monitor into the space you are testing. The monitor is in your hand so the readings can be seen in real time. There is no need to scroll through the peaks readout.

Cons: In addition to Method 2's cons, there is also one very significant other con. Depending on the monitor, if the pump fails, it is likely that you will not be able to use your monitor at all. In other words, it will not work as a diffusion monitor.

In some cases, even if you can still use the monitor in diffusion mode, it is likely you may not be able to calibrate it. A monitor that can't be/hasn't been calibrated is not fit for use.

Concerns: Method 3 has the same concerns as Method 2.


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Posted by Corby Amos on

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About the Author

Corby has over 25 years of experience in the safety industry. His area of specialization is confined space, gas detection, and fall protection equipment and applications. He's advised hundreds of contractors, cities, manufacturing plants, and government agencies on what equipment best suits their applications.



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