Carbon monoxide (CO) poisoning – what are the signs of trouble - follow the clues!

Silent, Unseen Poisoner

CO is a highly toxic gas that affects people at low doses and kills quickly in higher concentrations.

Stove flue gases have very high levels of CO. They can be 100 times higher than the levels of CO from a gas burner.

CO cannot be seen or smelt so you need to follow clues to check if you are at risk.

If you suspect a problem, the first step is to ask 'do I feel ill on my boat, but not ashore?'

Early symptoms

Early symptoms of CO poisoning are easy to mistake for other problems;  headaches, mood swings, feeling sick, dizzy, tired or confused or having stomach pains and being sick.

These are often taken for signs of colds and flu, or feeling run down.

While you may feel OK, for medical or lifestyle reasons, other crew members can be affected by CO before you?

If you think you are being poisoned, don't delay, see a doctor and say you may have suffered carbon monoxide poisoning.

If it is confirmed you are being affected, get a properly qualified person to find the source and fix the problem before the appliance is used again.

Even if you feel fine, don't ignore signs of early problems: -

  • is the stove difficult to keep burning properly;
  • are the flames lazy and weak?
  • do you have a strong smell of smoke when it's on?

If there's something not right, check, is it the appliance or is it how you're running it:-

  • Most stoves are not made to be run with the loading door open, so keep it closed.
  • Using a fuel not recommended by the stove supplier could give a poor burn and more
  • Even with the right fuel, if it's not dry you can still get 'lazy' flames and poor burning and that means there could be a CO risk.
  • For example, wood must be both dry, and well-seasoned to help keep the flue clear.
  • Have you blocked up or close some ventilation - stoves need lots of oxygen to run efficiently


In the BSi Code of Practice BS8511 which came out in 2010, revised calculations were published to take account of the amount of air stoves are now known to need to run

We have published the calculations on the New Stove, New Chimney page.

If you're concerned about carbon monoxide affecting your family, why not check your boat's ventilation for yourself?

For more information about CO poisoning and how to avoid it visit the BSS website CO page or read the Carbon Monoxide Safety on Boats leaflet.