What You Need to Know About CO Sensors - Part 3 of 4
Welcome back to part 3 of our series on what you should know about CO sensors! Today, we will be discussing CO sensor behaviors that are often misinterpreted. Last week, we talked about false positive alerts. Today, we will discuss the more egregious version, the false negative, as well as sensor baseline drift.
False negative
The terrifying brother of the false positive, the false negative is a scenario that safety companies like ours do everything in their power to mitigate in all products. A false negative is when an alarm should have gone off due to the presence of gas, but failed to do so, either because the sensor was obstructed, the sensor has physically failed, or the sensitivity of the sensor is so low that it cannot even reach alarm level with more than enough of the target gas present. The only way to ensure that false negatives never occur is to regularly test and calibrate your device to prove that the sensor is performing optimally.
Drifting baseline
A baseline is the “zero” point, where a sensor reading stabilizes in clean air, free of the gas the sensor is meant to target. Just like with false positives, rapid changes in temperature and humidity can temporarily cause the baseline of the sensor to increase. Users may report seeing 10-20 PPM on the display even when another meter is present showing zero. This is a normal reaction for EC sensors, and usually, they just need time to acclimate. Many detection devices offer the ability to “zero” the device in clean air, which will reset the baseline and allow the meter to show zero PPM on the display again.
Problem: Chemical exposure. Metal oxide and electrochemical sensors alike, along with many other types of sensors, can be greatly affected or even damaged beyond repair by exposure to certain types of gases. This is an effect known as poisoning. For carbon monoxide EC sensors, this can happen with gases like hydrogen sulfide (H2S), ethylene, and ethylene oxide. Exposure to high amounts of poisoning gases can cause the sensitivity of the sensor to drop significantly, making it no longer able to safely detect gases at the alarm levels. This can also cause significant baseline drift.
Solution: Keep your sensor away from known sources of non-target gases and only use it for clean air operations where the target gas may be present. For example, when using a personal carbon monoxide detector, only operate in environments known to be free of other gases, but where the possibility of the presence of carbon monoxide exists.
Stay tuned for part 4 next week where we discuss how lack of training can have major impacts on not only device usage, but also the selection of the proper tool for the job when it comes to purchasing. Stay safe, and know your environment!"