In many areas of the East African country of Uganda, schools are roofed with sheets of asbestos, a material banned in the developed world. It is a leftover of colonial rule, put in place by white men as the material was in vogue during the days of European imperialism.
Asbestos itself is an interesting rock, formed from six minerals; the serpentine variant chrysotile and the amosite, tremolite, anthophyllite, actinolite and crocidolite members of the amphibole solid solution series. A solid solution is a range of chemical forms of a mineral, where the relative proportions of cations such as sodium, iron and calcium change. The rocks most recognisable feature is the well known fibrous crystal habit of the minerals; fine crystal strands that have high enough tensile strength and flexibility to be woven as cloth.
Although the rock has been mined for thousands of years, large-scale extraction only began in the 19th Century, which in hindsight is a blessing, as the dangerous properties of the rock may not have been identified in more primitive societies. The rocks properties make it a tempting poison apple. As a building material, it is excellent; featuring not only the high tensile strength and flexibility previously mention, but also resistance to fire, heat, electrical and chemical damage, affordability and sound absorption. Small wonder then that it was used so extensively throughout Africa.
The mechanism by which asbestos is dangerous to humans is perhaps not what you would expect. The current, most widely recognised hypothesis is that the finest fibres of around 60 nanometres in size (around one millionth of a centimeter) cause physical damage to the chromosomes within a cell's nuclei. This genetic disruption can trigger unrestrained mitosis, or division of the cells; replicating them beyond normal levels. Which in turn, forms a tumour and thus cancer. As these fibres enter the body through the breathing process, the lungs are the most likely affected area and the more fibres that are breathed in, the higher the chance a chromosome will be damaged in such a way as to have this effect.
It is thus of great concern that the future generations of Ugandans are being exposed to these fibres at such an early age and for extended periods of time; over the course of years. This leaves a large scope for cancer to be triggered and the roofs should be removed as soon as possible. Recent 2012 guidelines on asbestos roofing from the UK government can be found here.