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EXTECH indoor air quality monitor model CO100 from Farnell is a great thing to have!
I tested the device during a lecture with ca 20 people. CO2 concentration raised to 2200 ppm after 50 minutes. During the next lecture one window was open to have a ca 10 cm gap and the CO2 concentration stabilized at 1500 ppm. This shows the importance of reasonable ventilation. After the lecture there were questions from attendants who asked what the device is doing and what it costs.
This triggered me to search for information what are acceptable CO2 levels?
- In Earth atmosphere CO2 content has increased from 300 to 400 ppm=0.04% during the last 60 years. It is a greenhouse gas responsible for global warming. Less in sommers when plants absorb it. I think there is some global warming taking place because of diminishing glaciers and polar ice. Melting is an integral effect over years, while just measuring temperature is not precise enough because of large scatter.
- 2000...5000 ppm sleepyness, headaches, loss of concentration, increased heart rate.
- maximum allowed concentration within a 8 hour working period: 5000 ppm = 0.5%
- slightly intoxicating, breathing and pulse rate increase, nausea: 30,000 ppm = 3%
- above plus headaches and sight impairment: 50,000 ppm = 5%
- unconscious, further exposure death: 100,000 ppm = 10%
Breath contains almoust stable amount of 3.8% CO2 (38000 ppm). In other words, exaled air contains about 100 times the concentration of carbon dioxide that inhaled air does. If a healthy person were to voluntarily stop breathing (i.e. hold his or her breath) for a long enough amount of time, he or she would loose consiousness, and the body would resume breathing on its own. If one does not inhale, the level of carbon dioxide builds up in the blood. Is monitored while performing artificial lung ventilation in hospitals during surgeries.
Accidents have happened inside beer cellars, garages with car motor running, or while sleeping in a car and running engine against cold. In such extreme environments as submarines and space ships caustic soda or limewater can be used to absorb CO2 from air.
The ability to measure carbon dioxide (CO2) in the breath of a patient or capnometry, is one of the fundamental technological advances of modern medicine
By blowing into the Extech analyser I easily reached the maximum reading of 9999 ppm and the device became saturated.
Found a great overview article about CO2 measurement history:
M. B. Jaffe, Infrared Measurement of Carbon Dioxide in the Human Breath: “Breathe-Through” Devices from Tyndall to the Present Day , 2008.
There seems to be some contraversy in values from different sources. Seems that CO2 is not very toxic. We exhale it so much 38000 ppm in breath!
When you use CO2 sensing, energy savings can result because ventilation is based on actual occupancy of the rooms. One can estimate if the rooms are overventilated or not enought ventilated.
Recommended levels
- 250 ‐ 350 ppm – background (normal) outdoor air level
- 350‐ 1,000 ppm ‐ typical level found in occupied spaces with good air exchange.
- 1,000 – 2,000 ppm ‐ level associated with complaints of drowsiness and poor air.
- 2,000 – 5,000 ppm – level associated with headaches, sleepiness, and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present.
- >5,000 ppm – Exposure may lead to serious oxygen deprivation resulting in permanent brain damage, coma and even death.
Regulatory limits in different countries
- ASHRAE 62‐1989: CO2 concentration in occupied building should not exceed 1000ppm.
- Building bulletin 101 (Bb101). UK standards for schools say that CO2 averaged over the entire day (i.e. 9am to 3.30 pm) should not exceed 1500ppm.
- OSHA, Germany, Japan, Australia, UK: 8 hours weighted average occupational exposure limit is 5000ppm.
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