Understanding gas detection limits - an opinion piece from Industrial Design

Gas detection UKWhen we look at gas detection systems the most important thing is to understand what the detection limits are and what they actually mean. For instance, the lower explosive limit (LEL) is defined by any concentration of gas (calculated as air volume) which can potentially ignite and support the flame. As a consequence, anything below the LEL threshold will not support the flame and thus will not present imminent danger. 

In the gas detection industry, knowing the LEL levels is crucial, as you don’t want the gas concentration to exceed them. For example, over 50% LEL means a high flammable gas concentration that may well ignite. It is important to bear in mind the fact that the actual concentration of gas in the air depends on the type of gas detected; concentrations of over 4.4-5% by volume are at high risk of ignition.

When dealing with toxic and flammable gases, even a percentage of less than 50% gas in air (which would mean a 2.5% concentration) needs to be acted upon, although it does not present an immediate ignition danger.  For this reason, whenever making a gas detection plan, events are rated on different risk levels. 50% would be our upper alarm level and, depending on the application, we normally have two alarm levels. A concentration of 15-20% gas in air would be common for a lower alarm level.

This is mainly because even the lower level of gas leaks should be taken seriously and considered a first warning sign. This allows the safety representative to evacuate the area and investigate the cause of the alarm. If things go even further, let’s say to 50% LEL, machinery and equipment needs to be shut down so that all potential ignition sources are excluded. 

Gas detection UKIn the above scenario we are using gas detection in a safety capacity. Gas concentration is being measured for the safety of people, the plant and the products stored onsite.

Calibration is an important part of a successful fire prevention strategy. It enables better and accurate readings and it can make the difference between life and death in some cases. This is why we use two types of calibration systems: fixed systems (which can be mounted on the wall, on site) and portable devices (which are usually handheld and can be moved from location to location).

In terms of the actual calibration process, one must always make sure the detector is working to optimum standards. The best way to guarantee this is by exposing the gas detector to the various gas concentrations.

There are various factors that determine the frequency of calibration: operating processes, the frequency with which gas is exposed to the detector or the stability of the detector. Different manufacturers will give you different indications on how to calibrate your detector. For instance, we choose to calibrate our equipment four times a year, corresponding to the changing of the seasons and inherent temperature modifications. 

A quick and easy way of testing that your device is working is bump testing. This is traditionally done on portable devices and it basically means exposing the detector to gas to make sure it’s working. Bump testing is not to be confused with calibration, as the latter is a more in depth analysis that checks the accuracy of the readings taken by the detector.