Posts

co2 sensors to measure co2 levels in a car

GSS Analyse CO2 In Car Journeys

Ever wondered why long car journeys make you feel tired and sleepy? Is it the boredom of endless, never changing motorways or perhaps something else? Carbon Dioxide sensor specialists, Gas Sensing Solutions, wondered if it could be a build-up of CO2 gas, because at levels of 1000 ppm and above people can become drowsy and lethargic. So they took a CO2 datalogger from their gas sensor range on a road trip to find out how CO2 levels changed throughout the journey.

co2 sensors to measure co2 levels in a car

Why can car journeys make you feel sleepy?

Dr David Moodie, Technical Manager at GSS, explained, “This follows on from our trip to Asia where we used our CO2 datalogger to measure CO2 gas levels on planes, trains and taxis. We were surprised that levels were the worst in taxis – peaking at an astonishing 10000 ppm on one journey – so we decided to check the levels on our own road trip in the UK.”

datalogger to measure co2 in a car

Measure CO2, temperature & humidity in a car

Before the datalogger took to the road, it was first used to test CO2 levels in a stationary car. This would show the impact on CO2 levels with a group of 4 people in a confined space. The engine was switched off and the windows kept closed to avoid any flow of fresh air inside the vehicle. The datalogger showed that when the passengers got inside the car, the CO2 level was 1000 ppm. It then rocketed to almost 4000 ppm in just 15 minutes. At that stage, the atmosphere inside the cabin had become extremely stuffy and unpleasant.

Graph showing CO2 levels in a stationary car

Graph showing CO2 levels in a stationary car

Next came the road trip. The first car journey involved two people travelling to the supermarket. The CO2 from their exhaled breath increased the concentration of CO2 in the car cabin to around 1400 ppm. Surprisingly, it only took about forty-five minutes to reach this level, which shows how quickly CO2 levels can rise. The datalogger was then left in the car overnight with the windows closed. The graph shows just how long it takes for the CO2 to disperse from a closed car, taking until around 9am the next day to drop down to nearer ambient levels of CO2.

graph showing CO2 levels in car recorded with a datalogger

CO2 levels recorded with a datalogger

The second car journey recorded four people travelling non-stop from Wales to Scotland. With four people, the level of CO2 shot up even faster, reaching 2000 ppm in about twenty minutes. This is the level where CO2 symptoms can start to cause loss of concentration, headaches and sleepiness for example. Fortunately, they opened the windows to bring in fresh air from outside, which reduced the CO2 to more acceptable, ambient levels within an hour.

Dr David Moodie, added, “Our real-world datalogger measurements show how CO2 levels can rapidly build up in an enclosed space with several occupants – and in a relatively short space of time too.  The results on both journeys exceeded The World Health Organisation* guideline that CO2 levels should be below 1000 ppm.” 

Datalogger details

The datalogger used in the experiment measures CO2 concentration, air pressure and temperature, along with relative humidity every few minutes. This unit was designed and built by GSS and it uses one of its low power, ambient air, CozIR®-A sensors. GSS’s unique LED technology at the heart of its sensors means that it has a very low power consumption, unlike many other CO2 sensors that need mains power. This enables battery-powered CO2 monitoring products to be created, such as this datalogger, that is able to record over a 2-week period without needing a change of battery.

co2 datalogger for measuring co2 levels

GSS CO2 datalogger with a CozIR sensor inside

Dr David Moodie, concluded, “This ability to be battery powered for long periods has opened up a whole new range of design possibilities for CO2 monitors. Now it’s possible to have handheld breath monitors with high speed sensing for people with respiratory conditions, portable leak detection instruments, handheld MAP analysers, and wireless air quality monitors for IoT applications. These are just a few examples of what is achievable, the possibilities really are endless.”

Drowsy driving facts and stats

According to a 2005 poll by the American National Sleep Foundation, 60% of adult US drivers – about 168 million people – said that they have driven a vehicle while feeling drowsy in the past year. More than one-third, (37% or 103 million people), have actually fallen asleep at the wheel. Of those who have nodded off, 13% say they have done so at least once a month. According to data from Australia, England, Finland, and other European nations, drowsy driving represents 10 to 30 percent of all crashes. More details at http://drowsydriving.org/about/facts-and-stats/ and https://www.sleepfoundation.org/sleep-topics/drowsy-driving

A paper on ‘Modelling CO2 concentrations in vehicle cabins’, which focusses on the build-up of CO2, can be found at: https://www.engr.ucr.edu/~heejung/publications/2013-CO2-model.pdf

In an article entitled ‘The Drowsy Driving Off Switch’, Air Quality Consultant Dale Walsh found that recycling the air in a car cabin causes CO2 levels to rise rapidly. In his experiment, it took an hour for a level of 2500 ppm to be reached when recycling the air with only one occupant in the car. The article is available at: https://www.americanasafety.com/associates/docs/publications/The%20Drowsy%20Driving%20Off%20Switch.pdf

CO2 Sensors 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:
https://www.nasa.gov/mission_pages/station/research/experiments/2101.html

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.