Confined Space Safety
A confined space isn’t fully assessed, without a completed gas test!
What are some potential confined space gas testing errors?
Testing the atmosphere inside a confined space is a critical step for any entry. There are three atmospheric hazards to consider 1) combustibles and flammables, 2) oxygen content, and 3) toxics. The results of gas testing are critical for verifying that the space has been properly isolated and cleaned.
The SWP requires the involvement of the unit/area supervisor in determining potential air contaminants when a confined space is initially being set up for entry. When all contaminants have been identified and measured, the supervisor signs off on the initial permit verifying that gas testing has occurred and that proper handling and respiratory precautions are identified. Gas testing requirements are documented in the Initial Confined Space Entry Pre-Plan.
When conducting air monitoring, there are a few things to be aware of to ensure a proper gas test.
- Be sure the gas meter has a current calibration – gas meters drift over time and the results may not be accurate if a meter is used past its calibration due date.
- The samples need to be representative. For example, if the ventilation system is drawing air into the space, the probe must be placed far enough into the space to avoid measuring air intruding from outside the space.
- Select the correct device to measure contaminants. An LEL meter provides results as a “percent”. Toxics are measured as parts per million or “ppm”. Don’t assume that a zero LEL reading means there are no toxics.
- Initial tests may not reflect changes that occur after work begins, such as from work inside the space (e.g., welding). Continuous monitoring is required during confined space entry to check for changing conditions as work progresses.