Carbon monoxide is sometimes referred to as a "silent killer". Difficult to detect without an alarm, this colourless and odourless gas is both toxic and asphyxiating. In extreme cases it can kill within minutes. Video: AFPWoman dies after gas seeps into shower.Source:istockA South Australian woman died from carbon monoxide poisoning, the lethal gas given off by a dodgy water heater installed in a bathroom, an inquest has heard. Heather Diane Pearce, 47, was about to start shearing sheep with her husband and two sons at their farming property at Reedy Creek, southeast of Adelaide, when she was found unconscious.She was on the floor of a makeshift and freestanding bathroom, fashioned from a converted concrete tank, after taking a shower.An inquest has been held into the death of Heather Diane Pearce, who died from carbon monoxide poisoning after taking a shower on her farming property near Adelaide. Picture: AAPSource:SuppliedThe lethal gas given off by a dodgy water heater installed in a bathroom. Picture: AAPSource:SuppliedAn inquiry on Mrs Pearce's death revealed at first she was believed to have died from health issues, but a post-mortem revealed carbon monoxide toxicity.In his opening address, counsel assisting the coroner Ahura Kalali said a hot water heater had been installed inside the bathroom 22 years prior and had never been serviced.Tests on the water heater found it was not compliant with regulations and in his evidence, senior gas inspector Ron Jessen from the Office of the Technical Regulator told the inquest the hot water heater never should have been installed - adding it was so old the brand and model were no longer manufactured."There were several issues with the ventilation and a metal plate had been left on the heater inside and the rotary ventilator on the roof had ceased," Mr Kalali told the inquest on Wednesday."The combination caused a lethal build-up of carbon monoxide inside the bathroom."Tests on the water heater subsequently found it was not compliant with regulations. Picture: AAPSource:SuppliedMr Jessen told the coroner that because of the metal plate, the build-up of combustion gases would have been "virtually instantaneous".He said a 10-second test he performed on the water heater returned a carbon monoxide reading of 960 parts per million.A normal reading would be between 40 and 150 parts per million.Mr Jessen said a second test had to be stopped because it was exceeding the levels his instruments could take."It certainly showed in a very short time this heater was becoming a CO (carbon monoxide) generator," he said."It should have been isolated and tagged off as too dangerous to operate."Mr Jessen warned gas hot water systems should be serviced at least every two years.Deputy state coroner David Whittle was urged to issue a public warning about the dangers of non-compliant water heaters.He will hand down his findings on a date to be fixed.WHAT IS CARBON MONOXIDECarbon monoxide is a colourless, odourless gas emitted from combustion processes and if incorrectly installed can cause poisoning.According to SafeWork South Australia, this occurs frequently in domestic settings."If ventilation is reduced, or the rate or duration of CO production increases, a normally safe environment can suddenly become extremely hazardous," the site states.A 10-second test on the water heater returned a carbon monoxide reading of 960 parts per million. A normal reading would be between 40 and 150 parts per million. Picture: AAPSource:AAPChris Barnes, heating expert and product category manager household at Choice, emphasised that both gas water systems and gas room heaters need to be fitted by listened gas fitters."They need to be checked every couple of years by a professional to ensure they're performing as they should," Ms Barnes told news.com.au"Once gas heaters start malfunctioning, you're not going to notice it. That's when you get incomplete combustion and carbon monoxide as a bi-product starts coming into the room - you don't smell carbon monoxide, taste it or see it."It will at first make you feel sick and can be fatal."He said it needs to be a flued model - with a chimney or a pipe that vents to the outside.HOW CARBON MONOXIDE AFFECTS HEALTHAccording to the Department of the Environment and Energy, increased levels of carbon monoxide reduce the amount of oxygen carried by haemoglobin around the body in red blood cells.When this happens, it prevents vital organs, such as the brain, nervous tissues and the heart, to stop receiving oxygen to function properly."At very high concentrations of carbon monoxide, up to 40 per cent of the haemoglobin can be bound to carbon monoxide in this way. This level will almost certainly kill humans," states the Departments Air Quality fact sheet.The lethal gas is known to affect people irrespective of their health. If you're healthy and have been impacted by a small increase in the level of carbon monoxide it can affect concentrations.However those with heart problems are likely to suffer from more frequent and longer angina attacks, and they would be at greater risk of heart attack, according to the report."Children and unborn babies are particularly at risk because they are smaller and their bodies are still growing and developing."