Gas monitoring instruments are designed to check environmental gas concentrations at regular intervals.
These battery-powered, direct-reading instruments are available as single gas instruments or multiple gas instruments, typically monitoring one or a combination of atmospheric conditions for reliable gas detection.
Depending on the capabilities of the instrument, monitoring can be conducted simultaneously for oxygen and combustible gas, or for oxygen, combustible gas and toxic gases. These devices are commonly referred to as 2-in-1, 3-in-1, 4-in-1 or 5-in-1 gas alarms.
Regular monitoring is required to be performed to check environmental gas concentrations because a contaminant’s level of combustibility or toxicity might increase even if it initially appears to be low or non-existent. Additionally, oxygen deficiency can occur without warning.
Reliable instruments should be used to draw air samples to determine the composition of atmosphere in a confined space. Ideally, the entrance to the confined space should not be opened before completing this step.
Sudden changes in atmospheric composition within the confined space could cause violent reactions, or dilute the contaminants in the confined space, giving a false low initial gas concentration.
When testing permit-required spaces for acceptable entry conditions, testing must be performed in the following order:
- Oxygen content
- Flammable gases and vapours
- Potential toxic air contaminants
Comprehensive testing should be conducted in various locations within the work area. Some gases are heavier than air, and tend to collect at the bottom of a confined space. Others are lighter, and are usually in higher concentrations near the top of the confined space. Gases with the same molecular weight as air can be found in varying concentrations throughout the space.
Test samples are recommended to be drawn at the top, middle and bottom of the space to pinpoint varying concentrations of gases or vapours.
The results of the atmospheric testing will have a direct impact on the selection of protective equipment necessary for the tasks in the area. It may also dictate the duration of worker exposure to the environment of the space, or whether an entry will be made at all. Substance-specific gas detectors should be used whenever actual contaminants have been identified.
MSA (Aust.) Pty. Limited supplies a range of gas detection systems.