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Using a sample drawing pump with confined space monitors

July 1, 2007

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When choosing a confined space monitor, how important is the sample drawing pump?

Answered by Steve Peluffo, technical services manager, RKI Instruments Inc., Union City, CA.


By definition, a confined space is any space that:

  • Is large enough and so configured that an employee can bodily enter and perform assigned work
  • Has limited or restricted means for entry or exit
  • Is not designed for continuous employee occupancy
These spaces may include, but are not limited to: underground vaults, tanks, storage bins, pits and diked areas, vessels, sewers, and silos. In addition, this space may not have adequate ventilation or air movement, allowing gases to form pockets or stratify within the confined space. This adds to the danger.

When testing confined spaces prior to entry, it is necessary to test at all levels for dangerous gases. This may include gases that are lighter than air and may collect at the top of a confined space, such as methane; heavier-than-air gases that may settle at the bottom of a confined space, such as hydrogen sulfide; and carbon monoxide, which has about the same density as air and oxygen content. Using a sample drawing portable gas monitor for this application makes this task extremely easy to perform. Confined space monitors can be provided with an internal motorized sample pump or an attachable sample pump (either motorized or hand-aspirated) that can turn a personal portable diffusion monitor into a sample drawing instrument, allowing for greater versatility.

For example, if a worker is required to enter a confined space such as a manhole, this individual would need to test the atmosphere around the top of the manhole cover before removing the lid. A confined space safety gas monitor with sample pump would allow the user to easily "sniff" around the lid for gas; if the lid has pick-hole openings, the sample probe can be used to test under the lid for explosive, toxic gas and oxygen content.

Once the lid is removed, the sample probe can be lowered into the confined space – starting at the top and sampling all levels until the probe reaches the bottom. With a non-sample drawing instrument, the sensor block or the monitor itself is lowered into the confined space. The danger of using a monitor in this fashion is that it can be dropped into liquids, destroying the sensors or the instrument. Also, if the monitor is lowered into the confined space, the user would be unable to see the actual gas readings at the various levels. Monitors provided with sample pumps include hoses that can be purchased in various lengths to accommodate a variety of confined spaces. In addition, each monitor would include a probe with a water-blocking filter to prevent damage to the instrument in the event that the probe is dropped into liquids.

In summary, choosing either a monitor with an internal motorized pump or a diffusion monitor with attachable pump will allow the instrument to be used in a variety of different applications, including confined space entry where accurate sampling of the atmosphere is essential to worker safety.



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