Carbon Monoxide (CO) is an odourless, colourless and tasteless gas that is also highly toxic and potentially flammable (at higher levels: 10.9% Volume or 109,000ppm). It is produced by the incomplete combustion of fossil fuels such as wood, oil, coal, paraffin, LPG, petrol and natural gas. Many HVAC systems and units burn fossil fuels, so it’s not hard to see why HVAC professionals may be exposed to CO in their work. Perhaps you have, in the past, felt dizzy or nauseous, or had a headache during or after a job? In this blog post, we’ll look at CO and its effects, and consider how the risks can be managed.
How is CO generated?
As we have seen, CO is produced by incomplete combustion of fossil fuels. This generally happens where there is a general lack of maintenance, insufficient air – or the air is of insufficient quality – to allow complete combustion.
For example, the efficient combustion of natural gas generates carbon dioxide and water vapour. But if there is inadequate air where that combustion takes place, or if the air used for combustion becomes vitiated, combustion fails and produces soot and CO. If there is water vapour in the atmosphere, this can reduce the oxygen level still further and speed up CO production.
What are the dangers of CO?
Normally, the human body uses haemoglobin to transport oxygen via the bloodstream. However, it is easier for the haemoglobin to absorb and circulate CO than oxygen. Consequently, when there is CO around, danger arises because the body’s haemoglobin ‘prefers’ CO over oxygen. When the haemoglobin absorbs CO in this way, it becomes saturated with CO, which is promptly and efficiently transported to all parts of the body in the form of carboxyhaemoglobin.
This can cause a range of physical problems, depending on how much CO is in the air. For example:
- 200 parts per million (ppm) can cause headache in 2–3 hours.
- 400 ppm can cause headache and nausea in 1–2 hours, life threatening within 3 hours.
- 800 ppm can cause seizures, severe headaches and vomiting in under an hour, unconsciousness within 2 hours.
- 1,500 ppm can cause dizziness, nausea, and unconsciousness in under 20 minutes; death within 1 hour.
- 6,400 ppm can cause unconsciousness after two to three breaths; death within 15 minutes.
Why are HVAC workers at risk?
Some of the most common events in HVAC settings may lead to CO exposure, for example:
- Working in confined spaces, such as basements or lofts.
- Working on heating appliances that are malfunctioning, in a poor state of repair, and/or have broken or worn seals; blocked, cracked or collapsed flues and chimneys; allowing products of combustion to enter the working area.
- Working on open-flued appliances, especially if the flue is spilling, ventilation is poor and/or the chimney is blocked.
- Working on flue-less gas fires and/or cookers, especially where the room volume is of inadequate size and/or the ventilation is otherwise poor.
How much is too much?
The Health and Safety Executive (HSE) publishes a list of workplace exposure limits for many toxic substances, including CO. You can download the latest version free of charge from their website at www.hse.gov.uk/pubns/books/eh40.htm but at time of writing (August 2021) the limits for CO are:
| Workplace Exposure Limit | ||||
| Gas | Formula | CAS Number | Long Term Exposure Limit (8-hr TWA Reference Period) | Short Term Exposure Limit (15-min Reference period) |
| Carbon monoxide | CO | 630-08-0 | 20ppm (parts per million) | 100ppm (parts per million) |
How can I stay safe and prove compliance?
The best way to protect yourself from the hazards of CO is be wearing a high quality, portable CO gas detector. Crowcon’s Clip for CO is a lightweight 93g personal gas detector that sounds at 90db alarm whenever the wearing is being exposed to 30 and 100 ppm CO. The Clip CO is a disposable portable gas detector that has a 2-year lifespan or a maximum of 2900 alarm minutes; whichever is sooner.