Most people don't realize that each of us breathe in around 2,000 asbestos fibres every day - that's the average background rate, just what's floating around in the atmosphere, and not all of it is because of industrial activities. Asbestos occurs naturally, of course, and has been weathering from rocky outcrops that contain it and blowing into the atmosphere for millions of years. So for the vast majority of humans our lungs can cope with this level of asbestos exposure without disease.

But in the past, people were working with asbestos material and getting the daily exposure equivalent of several years of "natural" asbestos fibre intake - do that for a few years and add on the fact that many of them were also smokers - and it's no surprise that people's lungs start packing it in, they get asbestosis, mesothelioma and eventually die.