Gas Monitor Function/Bump Tests

Portable gas monitors and detection units play a vital part in maintaining the safety and security of personnel working in atmospheres which are potentially contaminated, contain too much or too little oxygen or could be toxic or explosive.

There are a number of manufacturers of suitable and reliable equipment for use in these locations. These units provide early warning of changes in the atmosphere with some units also providing short and long term monitoring of exposures to toxic gases (STEL/TWA). But how do you know if the equipment is working as designed and will in fact provide a warning should there be a sudden change?

Most manufacturers and relevant Australian Standards recommend regular calibration with certified test gases, in most cases at least every six months or more often if the gases are particularly aggressive or in the case of exposure to consistently very high concentrations. In addition, environmental factors including air pressure, temperature and humidity can affect the accuracy of the unit. Completing a daily 'Fresh Air' or 'Zero Sensors' calibration 'tunes in' the sensors to todays conditions and ensures the units daily accuracy.

There have been cases where a fault has prevented the atmosphere from interacting with the sensors, leading to the unit not detecting the change and one particular case, a worker was overcome by lack of oxygen in a heavily nitrogen contaminated atmosphere. Fortunately, there was a rescue plan in place and after being resuscitated, the worker lived to work another day.

So how can we be sure that the unit will in fact alarm in the presence of high or low levels of gas? Gas detection manufacturers and standards documents (AS/NZS2865/61779) recommend that all instruments are function or bump tested using a certified gas mixture prior to operation to ensure that sensors will react correctly in the contaminated atmosphere and, in turn, cause the instrument to alarm.

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