"Back a couple of weeks you were discussing the real canaries in the coalmines. They were an early warning of carbon monoxide gas which was a silent killer being odourless. Miners who died from this exhibited the characteristic cherry red coloured skin caused by the CO forming a strong bond to the haemoglobin in the blood & thus leaving it unable to carry the oxygen necessary for life. At school in a mining valley in Wales in the sixties, our chemistry teacher, who had worked underground, told us haunting details like these which have stayed with me much longer than the chemistry has. The methane in the mines, known as 'fire damp' was an explosion risk and it was these explosions that caused most large scale mine disasters up until the National Coal Board was formed and started spending money on mine safety."

David Fuller's view Thanks for these interesting facts. Unfortunately, coalmine explosions are still a problem today, although largely confined to poorer developing counties.

Chemistry was a more dangerous class than I realised at the time. I remember playing with liquid mercury, including rolling it around in my hands. That may explain a lot.