The onset of autumn and cooler weather traditionally heralds the start of another season in the northern hemisphere—the peak incidence of unintentional deaths from carbon monoxide. Each year around 50 people in the United Kingdom die from carbon monoxide poisoning, and a year ago the chief medical officer warned again of the dangers.1 As yet there is no evidence that the population is at any lesser risk. Humans have been poisoned by carbon monoxide since they first discovered hydrocarbon fuels, incomplete combustion of which is the usual cause of poisoning. Napoleon's surgeon, Larrey, saw soldiers with carbon monoxide induced myonecrosis when billeted in huts heated by woodburning stoves. And over 60 years ago American physicians were warned that chronic carbon monoxide exposure could mimic many neurological conditions, such as “cerebral haemorrhage, encephalitis, multiple sclerosis, spastic paraplegia, chorea and tetany.”2 Throughout the world people continue to die unnecessarily from carbon monoxide exposure or to survive their encounter with disabling symptoms whose cause is misdiagnosed. Carbon monoxide famously binds to haemoglobin over 200 times more strongly than oxygen, a strange evolutionary quirk explained by the tiny amounts of carbon monoxide produced naturally in the body by haem oxygenase and the need to have an efficient scavenging system for such a …