The don’ts and don’ts of zeroing your CO2 detector

Unlike other toxic gases, carbon dioxide (CO2) is all around us, albeit at levels too low to cause health issues under normal circumstances. It raises the question, how do you zero a CO2 gas detector in an atmosphere where CO2 is present?

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Life Offshore

Many of you may have wondered what life is really like offshore? To fly in a helicopter to work in the middle of the sea? To work 12-hour shifts for 14 days straight, surrounded by dangerous equipment and hazardous materials?

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The risky side of default alarm settings

Logically, people assume the lower the gas detection alarm level, the safer the working environment, as the body will be exposed to less poisonous gas. However, this is not always the best option! If set too low, they can cause spurious alarms and unnecessary disruption. Worse still, these wolf cries have led to many incidents of detectors being ignored or switched off; with terrible results1.

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Successful aspirations

Good confined space entry procedure requires the use of a pumped portable detector to check the space is safety to enter. But some detectors don’t have pumps built in, in which case, an aspirator should be used. An aspirator is a manual system for drawing the air through a tube to the sensor, and it can work well. However, it is something that requires practice to give confidence that you are doing it right.

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Planning for shutdown season

Maintenance performed during a site shutdown often takes in gas detection systems, including checking expiry dates and calibration. For some, shutdowns also increase the use of portable and transportable monitors, as fixed systems are being maintained and extra personnel come on site to work.  Every year, around this time, we get a significant increase in calls about problems arising during site shutdown. Many of these could have been avoided with a little planning and forethought.

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Pellistor sensors – how they work

Pellistor gas sensors (or catalytic bead gas sensors) have been the primary technology for detecting flammable gases since the ‘60s. Despite having discussed a number of issues relating to the detection of flammable gases and VOC, we have not yet looked at how pellistors work. To make up for this, we are including a video explanation, which we hope you will download and use as part of any training you are conducting

A pellistor is based on a Wheatstone bridge circuit, and includes two “beads”, both of which encase platinum coils.  One of the beads (the ‘active’ bead) is treated with a catalyst, which lowers the temperature at which the gas around it ignites. This bead becomes hot from the combustion, resulting in a temperature difference between this active and the other ‘reference’ bead.  This causes a difference in resistance, which is measured; the amount of gas present is directly proportional to it, so gas concentration as a percentage of its lower explosive limit (%LEL*) can be accurately determined.

The hot bead and electrical circuitry are contained in flameproof sensor housing, behind the sintered metal flame arrestor (or sinter) through which the gas passes. Confined within this sensor housing, which maintains an internal temperature of 500°C, controlled combustion can occur, isolated from the outside environment. In high gas concentrations, the combustion process can be incomplete, resulting in a layer of soot on the active bead. This will partially or completely impair performance. Care needs to be taken in environments where gas levels over 70% LEL may be encountered.

For more information about gas sensor technology for flammable gases, read our comparison article on pellistors vs Infrared gas sensor technology: Are silicone implants degrading your gas detection?.

*Lower Explosive Limit – Learn more

Click in the top right hand corner of the video, to access a file that can be downloaded.

Training – the vital ingredient

Gas detection is a critical safety function in many industries, to protect people from harm and avoid costly plant disruption or damage. Not only must you use a suitable instrument for the task and the environment, but it must be used correctly and maintained properly if it is to fully serve its purpose.

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