Carbon dioxide is a component of normal air, at around 0.037%. However, it can be produced by the burning of fossil fuels and other chemical reactions, and is a common component in the manufacture of many consumer products, notably beer and other fizzy drinks. Working in these environments risks exposure to levels elevated over the norm. At high levels, CO2 is a suffocation risk, and it can pose a significant toxic threat as well.
A common error is to think that CO2 can be detected by smell or taste; this is not the case. Another misconception is that monitoring oxygen (O2) levels provides effective protection against CO2. Reliance on monitoring levels of O2 to protect against carbon dioxide has led to fatalities. It is not possible to monitor levels of CO2 other than by use of the appropriate detection equipment.
Exposure to as little as 0.5% by volume CO2 represents a toxic health hazard, while concentrations greater than 10% by volume can lead to death, regardless of the oxygen levels present. Because CO2 is completely odourless and colourless, there may well be no indication of danger until it is too late.
Fixed systems can be used to monitor an at-risk area for CO2 build-up. Such systems typically comprise one or more detector “heads” connected to a separate control panel. If a detector reads a dangerous CO2 level, extractor fans can be automatically triggered and sirens or visual beacons can also be activated to warn workers to vacate the area. This is not sufficient to guarantee protection individuals against toxic exposure, however. For this, on-going worker exposure must be individually monitored.
This on-going exposure is generally defined in two ways:
- Short Term Exposure Limit (STEL) –
maximum allowable concentration over a shorter time period, usually 15 minutes
- Long Term Exposure Limit (LTEL) –
calculated as an 8-hour time weighted average (TWA)
I discussed TWA in my previous blog, but in short, the concept is based on a simple average of worker exposure during an 8-hour day. It permits periods of exposure above the TWA limit, but only as long as the STEL is not exceeded and there is equivalent under-exposure to compensate. In the UK, the TWA for CO2 is set at 0.5%, and the STEL at 1.5%, and these levels are enforced by statute. While regulatory levels may vary a little, similar limits are enforced in other jurisdictions.
In order to guarantee workers exposure stays under the statutory exposure limits, it is necessary to monitor the levels of CO2 each worker is exposed to, individually, using a suitable personal monitor.