Four people were taken to hospital after carbon monoxide levels high enough to kill were detected on their Broads cruiser.
Emergency services were called after all six passengers on the 21ft boat began to feel unwell simultaneously.
The boat users initially thought that they might have suffered food poisoning after sharing soup on board.
But firefighters with testing equipment found that carbon monoxide had reached dangerous levels on the boat at Somerleyton marina near Lowestoft, Suffolk.
Four adults who were said to be close to passing out were taken by ambulance to the James Page University Hospital, Gorleston, Norfolk.
The other two adults decided they were well enough not to go to hospital. It is believed that they inhaled deadly fumes from the engine of the privately-owned cruiser which had wafted into its cabin space.
The Government’s Marine Accident Investigation Branch has begun an investigation into the incident.
Know the symptoms
David Burwood, a rescue officer with HM Coastguard Lowestoft and Southwold, said: “The symptoms of carbon monoxide poisoning are very similar to food poisoning. You feel sick, light-headed and dizzy.
“The people on the boat initially thought they had food poisoning from soup they had eaten earlier, but thought it was strange to all have it at the same time.
“At first carbon monoxide levels were recorded at 25 parts per million, which is higher than normal. This then rose to 240 parts per million. To be blunt that is high enough to kill somebody.
“Four people were taken off to hospital while the other two felt okay to stay with us. And once the area was deemed safe, we were stood down.”
Boat Safety Scheme
The RYA endorses the advice on CO provided to boaters by the Boat Safety Scheme. The Boat Safety Scheme warns that CO build-up in boat cabins can occur with one or a mix of these factors:
• faulty, badly maintained or misused appliances
• exhaust fumes from a boat’s engine or generator
• escaped flue gases from solid fuel stoves
• blocked ventilation or short supply of air-fuels need the right amount of oxygen to burn safely
Mr Burwood added: “The message from us and the fire service is very much the same. Make sure you have a carbon monoxide alarm on your boat; if not you are putting your life at risk it is the silent killer. These boaters did the right thing and called for help when they knew they were in trouble.”
Image courtesy of East Anglia News Service.