Electricity and Control May 2020

PLANT MAINTENANCE, TEST + MEASUREMENT

Safer gas monitors

This white paper from Industrial Scientific is presented here in abridged form.

Personal gas monitors are essential in keeping people safe in environments where there is a risk of exposure to harmful gases. Given this, gas monitors need to be regularly maintained if they are to perform their lifesaving function. Periodic calibration and bump (or functional) tests are industry standard practice: calibration is done to ensure the continual accuracy of the gas monitor; a bump test verifies that the monitor is working properly by checking that the sensors are responding to gas and the monitor is alarming appropriately.

C alibration and bump tests are performed by exposing the monitor to a measured concentration of gas and verifying the response. Both tests can be done manually or using automated test equipment such as docking stations. In practice, users of gas monitors are more concerned with detection and alarming than reading the exact concentration of gas. This is not surprising given that the primary use of many gas monitors is as personal protection equipment (PPE). Most manufacturers recommend more frequent bump tests than calibrations. Typically, it is recommended that gas monitors be bump tested prior to each day’s use and calibrated at least monthly. Questioning how realistic these recommendations are, whether or not they are followed in the field, and what levels of risk result from this, Industrial Scientific conducted two extensive studies. Bump test practices in the field Looking at more than 25 000 gas monitors used in the field over a period of two years (2008-2009), it found that: - about 20% of users bump tested their monitors prior to each day’s use; - 15% never bump tested; - the rest of the users bump tested on average once a month (see Figure 1 ).

Several factors contribute to this low level of compliance with manufacturers’ recommendations: education/training to some extent; and more significantly the practicality of performing a bump test before use each day – particularly for users working in remote environments, and costs in time and money. Risks of not bump testing In another study, looking at the results of more than 2 million bump tests conducted in the field, it found that: - users that bump test their instrument(s) every day experience an average of one failure per 1 253 instrument use days. In other words, if a user performs a bump test every day and uses the instrument for 1 253 days (about 3.5 years), on average the user will experience one day where the instrument does not function properly. - users that bump test once a month experience on average, one failure per 286 instrument use days. This means a high number of users today are over four times less safe than they can be if they bump test prior to each day’s use. It is important to note that bump testing every month will not necessarily result in an injury or fatality every 286 days – the user would need to be exposed to harmful levels of gas as well. Nevertheless, it is clear that a monthly bump test schedule is an unmitigated risk factor.

Figure 1: Percentage of fleet bump tested before use.

Figure 2: The risk was measured by determining the average number of instrument use days before a failure for a given bump test schedule.

Figure 3: Failure rate comparison – Monitor with DualSense Technology versus traditional monitor.

24 Electricity + Control MAY 2020