When you’re thinking mood lighting, candles might be one of the first things that spring to mind. But are they entirely safe? The answer is yes, but only when used correctly.

That’s why at ADSL we test candles for a variety of noxious gases, one of which is carbon monoxide, something that is commonly associated with flames. And something that is particularly dangerous to human health, not least because it can’t be seen or smelt

How do candles produce carbon monoxide?

As a candle burns, the carbon and the hydrogen in the wax react with oxygen in the air to produce carbon dioxide and water vapour. This happens whenever something burns, the process is not specific to candles. 

The problem comes when the reaction doesn’t complete. In some cases, usually where oxygen is limited, the candle will fail to produce carbon dioxide and instead produce carbon monoxide. It will likely only be a small amount, but any measurable amount can cause issues. The amount of carbon monoxide produced will be the same whether the candle is scented or unscented.

How does carbon monoxide affect us?

From a scientific point of view, carbon monoxide binds with haemoglobin to form carboxyhaemoglobin which affects gas exchange and cellular respiration. Put simply, a build up of carbon monoxide can cause symptoms such as headaches, dizziness and nausea. And when it reaches higher concentrations can ultimately can be fatal.

Carbon monoxide is difficult to spot because it can’t be detected by any of our senses. 

What levels of carbon monoxide can cause a problem?

When present in the atmosphere at levels as low as 35 ppm the symptoms of carbon monoxide poisoning can begin to show. That’s why the World Health Organization (WHO) makes suggestions for maximum carbon monoxide levels. They look at different environments. For indoor environments, most relevant to candles, the WHO recommended limits are:

  • 9-10 ppm for no more than 8 hours
  • 25-35 ppm for no more than 1 hour
  • 90-100 ppm for no more than 15 minutes

Important considerations when burning candles

Candles should never be left burning in an unventilated room. If a candle is left burning in a small room with no ventilation it will eventually build up enough carbon monoxide to pose a serious risk to health. Making sure there is enough air in the room to help the carbon monoxide dissipate is key.

Can we test for carbon monoxide levels in candles?

Candles can produce quantifiable levels of carbon monoxide. This means that ADSL can offer carbon monoxide testing for candles, monitoring concentration of the gas over a certain time period. This allows us to see whether a significant amount of carbon monoxide is released and to determine whether the candle can be considered safe. 

This test has been designed to semi-quantitatively assess the amount of carbon monoxide produced by a candle burning under normal conditions in order to compare various products and assess whether extra safety guidance may be required. 

Stay up-to-date on regulations

If you would like to know more about our carbon monoxide testing in candles then get in touch with Tierney King, Analytical Chemist, working in our Analytical Laboratory +44 (0) 1803 520 048

Find out more about ADSL’s cosmetic development and testing work at In-Cosmetics 28-30 March, Stand AA11. 


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