How a CO2 sensor can help to improve personal safety

The stuffy feeling that you get in a crowded room is not lack of oxygen but your body reacting to high levels of CO2. The normal level of CO2 is around 400 parts per million (ppm) but as people breath out, CO2 levels can rapidly rise to 2,000 ppm. You breath out a hundred times more CO2 than you breath in and even more if you are exerting yourself. As the concentration of CO2 rises so does the stuffy, drowsy feeling and it becomes harder to concentrate; at even higher levels, it has a narcotic effect and then causes unconsciousness.

There are many workplaces where levels of CO2 can be high enough to cause health issues but it is often overlooked as it can’t be seen or smelt. For example, CO2 is used in the food industry to keep food fresher for longer. CO2 puts the fizz in drinks and the CO2 cylinders are often stored in pub and restaurant basements where a CO2 leak can build up as it is heavier than air. This raises the possibility of pockets of higher concentration CO2 and so the best solution is to monitor the exposure of the individual personnel themselves rather than the general atmosphere in a room.

What needed is a small portable CO2 monitor/alarm that can be worn for long periods of time. However, almost all CO2 sensors need a lot of power and time to achieve stability so they have to be mains powered and therefore are not suitable for a wearable solution. The power is needed to heat up a source of infrared (IR) that is passed through the sample gas. CO2 molecules have a distinctive absorption in the 4.2 to 4.4 micron range so the more that is absorbed, the greater the concentration of CO2. This measuring technique is called Non-Dispersive Infra Red (NDIR).

There is one exception to this. Gas Sensing Solutions (GSS) is unique in that the company uses proprietary LEDs that it makes itself as the IR source. Being LEDs means that they use very little power when on and are almost instantly on and off further cutting down power consumption. As a result, its CO2 sensors can be powered by a battery for up to ten years. A further benefit of LEDs is that they are solid state and very rugged, enabling them to be used in challenging environments.

An example of this technology is use in wearable, battery-powered CO2 monitors is on the International Space Station. CO2 build up has to be carefully monitored as NASA has already established that high levels of CO2 can compromise the astronauts’ ability to work. Also, the poor circulation of the air due to lack of gravity can easily result in pockets of high CO2 concentration. The solution would be to provide each astronaut with a wearable CO2 monitor. Supported by GSS distributor, SST Sensing, NASA designed and made personal CO2 monitors using GSS sensors, which were used on the ISS to gather data.

Photograph provided of inside the International Space Station (ISS), courtesy of NASA.

NASA has found that crewmembers develop CO2 related symptoms at lower CO2 levels than would be expected terrestrially. Since 2010, operational limits have been controlled to an average of 4.0 mmHg or below as driven by crew symptomatology. However, crewmembers have reported symptoms starting as low as 2.3 mmHg that are due to CO2. Between 2.3-2.7 mmHg, fatigue and full headedness were reported. Between 2.7 and 3.0 mmHg, errors occurred in procedures. And above 3.0-3.4 mmHg, headaches were reported. It was also noted that crewmembers varied in their sensitivity to CO2 levels. This evidence indicated to NASA that an operational level of between 0.5 and 2.0 mmHg may maintain health and performance, which they want to research further:

Many industries require their workers to enter enclosed spaces such as bulk food stores, mines, submarines and tunnels, where environmental monitoring is critical to safety and so the use of a personal CO2 monitor with an alarm could save lives.

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