A gas detector is a vital part of PPE and if used correctly it may save your life if you find yourself in a hazardous environment. Many people with gas detectors don’t understand how they work and the hazards associated with incorrect use. Just because it was calibrated last week, doesn’t mean it is working properly today.

The toxic sensors are usually electro-chemical cells which means they contain a chemical that will react with the gas to be detected and generate an electrical signal to indicate the level of gas detected. However when the chemical in the sensor is consumed by the sensor, it stops measuring gas and doesn’t generate a fault alarm. So in this circumstance the user is not protected by the gas detector because it will display no gas present even when there is.

The flammable sensor is usually a semi-conductor, and these sensors are prone to being poisoned. Silicon is the biggest problem and commonly present in paint fumes and a vast array of chemicals. If a chemical sticks to the semi-conductor sensor probes and coats them, the sensor can no-longer measure the flammability of the environment the detector is in and will continue to display zero or a very low %LEL even when the actual LEL rate is dangerously high.

So now understanding the way a gas detector works we can adopt strategies to keep the workforce safe. We know that just because your detector worked yesterday it doesn’t mean it is working properly today, so the best way to check it is working properly is to apply gas, this process is known as response testing or bump testing. With multi-gas mixtures available now with 4 or 5 gases in one cylinder, it can be a very quick process to simultaneously check all sensors. The typical time it takes a detector to respond to all gases is about 20 seconds. To be truly safe, a gas detector should be response tested every time before use. In reality companies and authorities set their own guidelines and often agree on once per day.

The consumable cost of the gas might be somewhere in the region $1.50 per response test but if that saves one life, it has to be worth it, especially if it is yours!

With docking stations available for gas detectors that charge the battery in the detector and response test it over-night this process is automated.

People often confuse response testing with calibration, they are not the same thing. A calibration is the process to accurately set the levels of the sensor and must be done in a controlled environment. It takes time for the sensors to settle to an accurate level so typical duration of a calibration is 60 to 90 seconds. A response test is just a quick check the detector is working with a typical duration of 20 seconds. When a response test gas mix is applied If you applied all you really want to see is all gases go into alarm mode, it doesn’t matter about the value they are showing.

A readily available response test gas mixture contains 25PPM H2S, 100PPM CO, 50% LEL and 18% O2.