It may be tempting for users of CO2 (R744) refrigeration to use oxygen (O2) gas detectors to monitor for high levels of CO2 in a confined space instead of a CO2 detector. But U.K. manufacturer International Gas Detectors (IGD), advises against it in an article on its website.
IGD points out that CO2 is present in the atmosphere at around 450ppm (0.04%). However, at higher concentrations in enclosed spaces, CO2 becomes problematic, generating occupational exposure alarms: the “first alarm” takes place at 0.5% (5000ppm) concentration, which is the long-term exposure limit (over an 8-hour period); the “second alarm” occurs at 1.5% (15,000ppm) concentration, the short-term exposure limit (15 minutes).
Given this data, “at first glance it seems that it would be feasible to set a 0.5% depletion alarm on an O2 gas detector to monitor for CO2,” noted IGD. “However, this would be dangerous, misguided and potentially fatal.”
The reason for this, explains IGD, stems from the fact that oxygen accounts for 20.9% of air by volume, while nitrogen makes up most of the balance at 78% (with 1% as argon and a mix of other trace gases, including CO2).
First-alarm levels on an O2 gas detector are usually set to 19.5%, IGD says. The oxygen level will be depleting either because another gas is leaking into the area, causing dilution/displacement of the oxygen, or because something is consuming the oxygen (like a fire).
Since 78% of the atmosphere is nitrogen, in the event of a CO2 leak, most of the gas displaced is nitrogen. A much smaller percentage of the oxygen is displaced. “The increase in CO2 is therefore not matched by a correlating decrease in oxygen levels,” IGD notes.
For example, if CO2 is present at 4% in the atmosphere, the corresponding oxygen level would still only be 20%. “Therefore, you would have exceeded both the long-term and short-term exposure limits for CO2 by a factor of eight and still not trigger an alarm,” the company explains. Thus the need for a CO2 detector.
Risk of excess CO2
IGD also explains why excess levels of CO2 in the environment are harmful. People normally exhale air that contains 4–5% CO2 produced by cellular metabolic processes. This metabolic function balances the acidity of the bloodstream, ensuring it is kept at a neutral level. However, areas with elevated levels of CO2 make it difficult for the body to disperse CO2, making blood more acidic, a condition called acidosis, which can harm organs if left unchecked.
This, rather than asphyxiation (displacement of oxygen), is why excess CO2 is harmful, says IGD.
Established in 1917, IGD has been manufacturing CO2 detectors since before the Second World War. In 2021the company introduced a personal CO2 monitor designed to keep staff and technicians safe from the dangers of elevated carbon dioxide levels in confined spaces.
Last year, IGD secured a contract to supply Stockport, U.K.-based Robinsons Brewery with an iGAS CO2 portable gas detector.
“At first glance it seems that it would be feasible to set a 0.5% depletion alarm on an O2 gas detector to monitor for CO2. However, this would be dangerous, misguided and potentially fatal.”International Gas Detectors