How to Test All Depths of a Confined Space

Atmospheric testing is a cornerstone of safety in confined space entry operations. The National Institute for Occupational Safety and Health (NIOSH) reinforced the importance of this step in a 2004 fatality investigation where an Oregon tank mechanic lost his life after he entered a confined space without first testing the atmosphere. In its recommendations NIOSH states the critical importance of not only testing the confined space for atmospheric hazards but also ensuring that all levels of the space -- top, middle and bottom -- are evaluated by a qualified person.

Things You'll Need

• Confined space entry permit
• 3 gas detector
• Calibration gas cylinder
• Forced air ventilation system

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Instructions

• 1

  Bump test the gas monitor to be used for confined space testing. A bump test is a quick exposure of the gas monitor sensors to a known quantity of test gas. According to the Occupational Safety and Health Administration (OSHA), a bump test is essential prior to each use to ensure that the gas monitor is properly calibrated and ready for use. 3M warns that bump tests must be completed according to manufacturer's instructions and using the appropriately matched calibration gas cylinder for the sensors utilized in the gas monitor.

• 2

  Insert the gas monitor into the top or entrance of the confined space. The person completing the testing must take care to not bodily enter the confined space at any time during initial atmospheric testing because of the risk of hazardous atmospheric conditions. Generally acceptable entrance conditions are oxygen levels of 19.5 to 23.5 percent by volume, concentrations of flammable or explosive gasses to less than 10 percent of the specific lower explosive limit for the gas, and all other toxic gases under OSHA established permissible exposure limits, according to the Canadian Center for Occupational Health and Safety and RAE Systems Inc. Carbon monoxide and hydrogen sulfide are two of the most common toxic gases monitored for in confined spaces. If readings from the gas monitor do not stay within established safe tolerances, forced air ventilation may be used to ventilate the space until safe atmospheric levels are reached and can be maintained.

• 3

  Move the gas monitor into the middle section of the confined space. In a vertical confined space such as a manhole this can be done by physically lowering the monitor itself lower into the space. In horizontally configured, confined spaces, this technique will not work, so it is important to attach a probe or sample line to the monitor and extend it into the confined space without physically entering the space. All specifications previously mentioned must still be met.

• 4

  Move the gas monitor or gas monitor probe to the bottom or furthest part of the confined space from the entrance. All previously mentioned specifications must still be met. Some toxic gases that are heavier than air, such as hydrogen sulfide, may have readings that are higher in this region of the confined space and therefore create a greater hazard.