What is carbon monoxide poisoning and how does it happen?

By Jake Evans

In most cases of death from carbon monoxide poisoning, the first responder will not recognise the risk and also die trying to rescue the victim, an expert says.

Carbon monoxide poisoning is suspected to be the cause of death of at Gunning in the Southern Tablelands of NSW.

Andrew, Anne and Richard Basnett all died after they each entered the tank late on Thursday.

Professor Anthony Brown from the School of Rural Health at the University of Sydney said people often did not recognise the silent danger of the situation.

“The tragic thing that happens in these sorts of confined space accidents is somebody’s in an area, they lose consciousness, they collapse, and somebody finds them and, quite understandably thinks, ‘Oh crikey, I’ve got to get this person out’,” he said.

In fact, Professor Brown said in over 60 per cent of cases, not only did the victim die, but the first rescuer as well.

At Gunning, it is believed the petrol-fuelled water pump being used to clean the tank emitted carbon monoxide fumes, which quickly built up inside the tank.

Professor Brown said even with a roofless tank fumes could quickly build up, and, because carbon monoxide is invisible and odourless, people did not realise until it was too late.

He said while a person may smell petrol fumes, because they might be used to smelling car exhaust or lawnmower fumes, they often did not consider how it might be building up in a confined space.

What happens inside the body?

Confined space fatality expert Dr Ciaran MacCarron said inside the body, blood cells would immediately begin reacting to the gas build-up.

He said carbon monoxide molecules began attaching themselves to the haemoglobin, in turn preventing the body from getting enough oxygen.

But unlike oxygen, which attaches itself at the lungs and then gets off when it reaches the tissue, carbon monoxide sticks to the haemoglobin, acting as a barrier.

Dr MacCarron said while sometimes people noticed they were feeling woozy or even recognised what was happening, usually by that time it was too late.

Safe Work Australia said there were 13 worker fatalities between 2003 and 2015 due to being overcome by fumes in a confined space, but that number did not include deaths outside the workplace.

Professor Brown said while industries were highly regulated and had safety protocols in place for entering confined spaces, farmers often did not.

“Because farms are your home, they don’t feel like a workplace in quite the same way,” Professor Brown said.

How long does the gas build-up take to affect you?

Dr MacCarron said during one case in Canada, five people from the same family all followed each other into a manure pit on a farm.

“The victim, his two sons, his grandson and his nephew. One after another was killed in that manner,” he said.

Dr MacCarron said people did not realise how quickly gas poisoning could affect them.

“Between four to six minutes turns a rescue into a recovery,” he said.

“A person has got that amount of time in an oxygen deficient atmosphere to breathe before they die.”

He said one person could not safely rescue someone suffering from carbon monoxide poisoning by themselves.

“It would be impossible to initiate a rescue, other than having emergency services on hand,” Dr MacCarron said.

This post originally appeared on ABC News.