Carbon Dioxide Meter

The chemical formula CO₂, also written CO2 in simplified form, stands for carbon dioxide. Carbon dioxide is a natural component of the atmosphere but is also produced by human and animal metabolism, fermentation and combustion processes. Many soft drinks contain carbon dioxide dissolved in water only a small proportion of which reacts with the water to form carbonic acid. When the pressurised bottle is opened, bubbles rise and the carbon dioxide is released from the liquid into the ambient air. Besides water and sunlight, plants need the carbon dioxide for photosynthesis during which glucose is produced in the plant and oxygen is released into the environment.

Carbon dioxide is non-flammable and chemically inert - in other words, non-reactive. The carbon dioxide itself is not toxic but as it prevents the absorption of oxygen when its concentrated is too high, it is life-threatening for humans and animals. Since carbon dioxide is heavier than air, it can collect in pits. In a normal outdoor climate, air movements due to temperature differences usually ensure sufficient mixing with the other components of the air.

Carbon dioxide meter at workplaces with increased carbon dioxide concentration
In work rooms where carbon dioxide is used for technical purposes or is released during processes on a large scale, the concentration should be permanently monitored with a carbon dioxide meter. This concerns, for example:

- in wine cellars, breweries during fermentation and brewing processes
- in food production by fermentation
- in greenhouses, stables
- in cold storage rooms with CO2 enrichment
- in packaging of foodstuffs in a protective atmosphere with CO2 enrichment.

In these areas, the carbon dioxide meter can be used not only to protect the employees but also to monitor the processes. For example, the shelf life of food packaged in a CO2 enriched atmosphere is directly related to the CO2 concentration. The carbon dioxide enrichment of the ambient air during fermentation processes allows conclusions to be drawn about the progress of the process.
However, employees at plants for energy generation or waste water treatment and in workshops in which carbon dioxide escapes through combustion or decomposition processes must also be protected against increased concentrations. Particularly when working in wells, pits, silos and tanks or underground pipes, there is an increased risk because the carbon dioxide produced collects near the ground and is not carried along and diluted by ambient air flowing past. These danger areas should be checked with a mobile carbon dioxide meter before entering. Even leaning into a fermentation tank can lead to unconsciousness and subsequent choking as the unconscious person is no longer capable of self-rescue! Persons staying in endangered areas should carry a carbon dioxide meter with an acoustic alarm. If the carbon dioxide concentration rises while working in the danger zone, the alarm is triggered and the person can leave the danger zone in time.

Carbon dioxide meter in homes, offices, schools, restaurants, sports facilities and meeting venues
In normal common rooms, carbon dioxide is mainly produced by the respiration of the people present. The more people present in the room, the faster the carbon dioxide concentration increases. A simple carbon dioxide meter with a traffic light signal enables users to ventilate as required. If sufficient air exchange rates cannot be achieved using the existing ventilation options, the indoor air quality can be improved by making structural changes or changing the number of users. A carbon dioxide meter for common rooms should be set up or installed at breathing height and in such a way that it is easily reached by the room air and can be easily seen by the users. Indicator lights on the carbon dioxide meter with green-yellow-red evaluations of the measurement result in addition to the numerical display are easily visible even from a distance and facilitate monitoring of indoor air quality. The room should be ventilated as soon as the indicator light changes from green to yellow. When the indicator light is red, adequate cross-ventilation should be provided quickly.

Smoke and exhaust gas testing with a carbon dioxide meter
In flue and exhaust gases, the carbon dioxide content is an indicator of the efficiency of combustion. If too much or too little air is supplied to the combustion process, the fuel is not used to its full potential. A carbon dioxide meter for the exhaust gas analysis of heating systems or motor vehicles has special probes that have to be positioned at defined points in the exhaust gas flow.

Carbon dioxide meter after firefighting with CO2 as extinguishing agent
Carbon dioxide is used for firefighting both in permanently installed extinguishing systems and in mobile fire extinguishers as an extinguishing agent. It is especially suitable for electrical operating rooms, server systems and laboratories as carbon dioxide does not form any residues. However, the release of carbon dioxide can lead to life-threatening increases in concentration. If rooms where extinguishing was done with carbon dioxide are to be entered without a breathing apparatus, it is recommended to check the concentration of carbon dioxide in the room air beforehand with a carbon dioxide meter.

The carbon dioxide content in the air is usually expressed either in ppm or in volume per cent. Ppm stands for parts per million. In terms of weight, the unit ppm corresponds to one milligramme per kilogramme and in terms of volume to one millilitre per cubic metre.

1 ppm = 1 mg/kg = 1 ml/m³

Occupational exposure limit values and recommendations for guidance values for indoor CO2 content are usually provided in ppm. The measurement range can be limited to the values required for alerting users or for controlling equipment. In many technical applications, higher carbon dioxide concentrations are measured than in regular indoor spaces. The carbon dioxide meter must be adapted to the application both in terms of the measurement range and of the design of the sensor.

Control of Substances Hazardous to Health (COSHH) - EH40/2005 Workplace Exposure Limits
The carbon dioxide content in outdoor air not contaminated by exhaust gases is about 0.038 vol% and in the air exhaled by humans about 4 vol%. At hazardous workplaces, the concentration must not exceed 0.5 vol% or 5,000 ppm for a maximum of 8 hours per day. For short exposure times (15-minute average), a maximum value of 15,000 ppm applies. An average value of 1.5 vol% of carbon dioxide in more than 15 minutes, measured with a carbon dioxide meter, is therefore permissible if the exposure then falls back below the workplace limit value.

Health hygienic guide values for CO2 in indoor rooms
As early as 1858, Max von Pettenkofer defined the carbon dioxide content as a guide value for monitoring the air quality in common rooms as it was already objectively measurable at that time. Pettenkofer's recommendation at that time to ventilate when carbon dioxide contents were above 0.1 vol% was also confirmed in more recent environmental medical studies.

Recommendation for rooms with natural ventilation
Based on comprehensive studies, the ad hoc working group on indoor air quality guidelines of the German Environment Agency recommended the following hygienic reference values in 2008:
• <1,000 ppm CO2 - hygienically harmless - no measures required
• 1.000 ... 2,000 ppm CO2 - hygienically conspicuous - check and improve ventilation behaviour, increase air exchange
• >2,000 ppm CO2 - hygienically unacceptable - check the room for ventilation and initiate measures for improvement

Classification of indoor air quality for rooms with air-conditioning systems in DIN EN 13779
• Up to 800 ppm CO2 - indoor air category IDA 1 - high indoor air quality
• >800 ... 1,000 ppm CO2 - indoor air category IDA 2 - medium indoor air quality
• >1,000 ... 1,400 ppm CO2 - Indoor air category IDA 3 - moderate indoor air quality
• >1,400 ppm CO2 - indoor air category IDA 4 - poor indoor air quality

Effect of the CO2 content in the air we breathe
0.038 vol%, 380 ppm - current carbon dioxide concentration in the atmosphere, i. e. in unaffected fresh air
0.1 vol%, 1,000 ppm - Pettenkofer number, recommended hygienic reference value for indoor areas such as offices, classrooms
0.2 vol%, 2,000 ppm - reference value as of which indoor air quality measures must be implemented
0.5 vol%, 5,000 ppm - with limited exposure time, generally no particular impairment of basic body functions, defined occupational exposure limit for max. 8 hours per day
1 vol%, 10,000 ppm - for only short-term exposure (15-minute average), permissible as a workplace limit value according to the German Technical Rule for Hazardous Substances (TRGS). During this time, the pH value of the blood changes by 0.04 units and the lower standard limit 7.35 is not reached.
1.5 vol%, 15,000 ppm - for only short-term exposure (15-minute average), permissible as a workplace limit value according to COSHH - EH40/2005. The respiratory time volume increases by more than 40 %.
2 ... 3 vol%, 20,000 ... 30.000 ppm - increasing irritation of the respiratory centre with increase in respiration and pulse rate
4 vol%, 40.000 ppm - normal CO2 content of the exhaled air. If the CO2 content in the inhaled air is more than 4 vol%, CO2 from the blood can no longer be exchanged for oxygen and accumulates in the bloodstream
5 vol%, 50,000 ppm - circulatory problems in the brain, headache, dizziness, nausea, ear noises, risk of permanent impairment of health
8 vol%, 80.000 ... 100.000 ppm - unconsciousness and death within 30 to 60 minutes
>10 vol%, > 100.000 ppm - death occurs within a short time

The chemical formula CO stands for carbon monoxide. High levels of carbon monoxide are produced by the incomplete combustion of fossil fuels and biomass, in forest and bush fires and by the oxidation of methane and other volatile organic compounds. Apart from energy production, motor vehicle traffic is one of the main sources of CO pollution in industrially developed areas. Carbon monoxide is a powerful respiratory poison that inhibits oxygen uptake by humans and animals and has effects on the central nervous system. Carbon monoxide is not only colourless, odourless and tasteless, it also does not cause irritation typical of other respiratory toxins, such as coughing or shortness of breath. Carbon monoxide burns to carbon dioxide. At concentrations between 12.5 and 75 vol% in air, explosive mixtures are formed.

A cable fire, a defective gas boiler or a fire in an underground car park can put the occupants of an entire building at risk due to the carbon monoxide emissions. Even rooms far away from the source of carbon monoxide can be polluted as the gas penetrates even massive ceilings and walls. A carbon monoxide meter with an alarm function warns in time so that the danger zone can be left when concentrations rise.

Carbon monoxide meter at workplaces with increased carbon monoxide concentration
Carbon monoxide can occur in hazardous concentrations, especially in indoor areas and in the vicinity of combustion or oxidation processes. Humans cannot perceive this gas with any of their senses. Miners used to take advantage of the fact that canaries react much more sensitively to carbon monoxide. If the bird taken into the pit stopped breathing, there was often enough time for the miners to leave the endangered area. Now, the carbon monoxide meter, which is either carried to the workplace or permanently installed there, provides timely warning. When the carbon monoxide values measured are recorded and evaluated, in some cases measures can also be taken to avoid high CO pollution in the future. The use of diesel or petrol-powered floor-level conveyors or construction machinery or gas-powered radiant heaters in a closed hall can already lead to life-threatening concentrations of carbon monoxide.

Carbon monoxide meter in residential rooms and other common rooms
Time and again, headlines are made about deaths from carbon monoxide poisoning in arbours and homes. Although the chimney sweep checks the function of the heating systems at regular intervals, he cannot take special weather conditions or other deteriorations of the situation into account. For example, during extraordinary heat, the exhaust fumes from gas-fired boilers are able to spread into living areas. This inadequate extraction of the exhaust gases to the outside can be intensified by air conditioning systems and extractor hoods with air exchange to the outside. In all heated buildings where rooms are equipped with gas boilers, gas flow heaters or wood-burning stoves, the carbon monoxide content of the room air should be constantly monitored with a carbon monoxide meter. A carbon monoxide meter also helps to detect the dangers of excessive CO concentrations in arbours and other rooms that are only heated occasionally or in which other combustion devices such as electricity generators or propane gas heaters are used before it is too late. Especially for rooms where people sleep, the carbon monoxide meter should have an acoustic alarm, just like smoke detectors which are already mandatory by law.

Smoking tobacco and water pipes also produces carbon monoxide. In shisha bars where several water pipes are used at the same time, carbon monoxide poisoning is becoming increasingly common. The carbon monoxide is produced by the glowing coal.

Smoke and exhaust gas monitoring with a carbon monoxide meter
The carbon monoxide content in smoke and exhaust gases is a sign of incomplete combustion. There are specified maximum emission values for the carbon monoxide content in exhaust gas for heaters, motor vehicles, machines with combustion engines and small appliances powered by liquid fuels such as chain saws, lawnmowers and leaf blowers. Compliance with these limits can be checked with a special carbon monoxide meter. They do not only serve to keep the air clean but also provide information on poor fuel utilisation and necessary maintenance measures.

Carbon monoxide meter during and after rescue operations
Firefighters and rescue services should avoid self-endangerment during operations in indoor areas and poorly ventilated areas where carbon monoxide is likely to be present by carrying a portable carbon monoxide meter. Such a carbon monoxide meter for rescue services often not only warns acoustically but also vibrates so that the warning also works in case of noise and distraction.

A carbon monoxide meter for personal protection should definitely have sufficient sensitivity in the lower range and one or two alarm thresholds. In order to be able to classify the available measurement ranges of a carbon monoxide meter and the measured values, see the following list of important carbon monoxide values:

Carbon monoxide concentration in the air we breathe and its effects
1.8 … 4.6 mg/m³ / 1 … 4 ppm - average CO concentrations in UK properties without indoor sources
10 mg/m³ / 8.6 ppm - highest 8 h mean value of a day outdoors according to WHO; if this value is exceeded, countermeasures must be taken to prevent air pollution
23 mg/m³ / 20 ppm - 8-hour limit value according to EU Directive 2017/164, measured as mean value
40 mg/m³ / 35 ppm - CO max. exposure for 8 hour work day (OSHA)
75 mg/m³ / 60 ppm - workplace limit value as 15-minute short time value, ventilate area, alert fire brigade, limit stay of rescue workers to max. 15 minutes
117 mg/m³ / 100 ppm - 15-minute limit value according to EU Directive 2017/164, measured as mean value
250 mg/m³ / 200 ppm - peak CO level for employees engaged in roll-on roll-off operations during cargo loading and unloading (OSHA), already after 30 minutes slight symptoms of poisoning, headache after 2 to 3 hours; arrange cross ventilation, leave area, alert fire brigade
375 mg/m³ / 300 ppm - pronounced symptoms of poisoning such as slowing of the pulse, increase in blood pressure, trembling
500 mg/m³ / 400 ppm - pronounced symptoms of poisoning after 2 to 3 hours of inhalation
625 mg/m³ / 500 ppm - often produced in garage when a cold car is started in an open garage and warmed-up for 2 minutes, after 10 minutes mild and after 20 to 30 minutes moderate symptoms of poisoning and hallucinations; leave danger area, alert fire brigade
1,250 mg/m³ / 1,000 ppm - moderate symptoms and movement restrictions after a few minutes, potentially fatal after 2 hours
1,875 mg/m³ / 1,500 ppm - death after one hour of inhalation
3,750 mg/m³ / 3,000 ppm - severe symptoms of poisoning after a few minutes, potentially fatal after 30 minutes
10,000 mg/m³ / 8,000 ppm - immediate death