Exposure to Asbestos
Mesothelioma is caused by asbestos exposure. There are other risk factors, but exposure to asbestos is the most important factor. A latency period of 20 to 50 years between initial exposure and development of mesothelioma is observed in most patients with the average being around 35 to 40 years. However, there have been rare instances where the latent interval has been much less than 20 years. (Tumors and Pseudotumors of the Serous Membranes, by McCaughey, Kannerstein & Churg, pg. 21 & 22). The incidence of mesothelioma rises with increasing intensity and duration of exposure to asbestos. However, there are numerous cases of mesothelioma among household members or people with very little occupational exposure. There are cases of people who had a summer job working construction in high school and cases of a housewife or children getting exposed from asbestos dust on their father’s clothes.
A study published in the journal Environmental Health Perspectives in 2008 found that the "asbestos fiber burden" (number of asbestos bodies per gram of lung) correlated strongly with risk of death. Those with a high burden has a 4.8-fold elevated risk of death compared with those with a moderate burden. More on the time between exposure and when symptoms show up.
Materials
Most insulation materials before the mid-1970s contained asbestos. Many other construction materials also contained asbestos.
Some of the most common products were pipe covering insulation which came in two premolded halves; block insulation for external insulation of boilers and many other high temperature vessels; insulating cements, plasters, and joint compounds which came in powder form and created a lot of dust before being completely mixed with water, fireproofing spray insulation, refractory products such as firebrick and gunnite used for internal insulation of furnaces, boilers, and other vessels, floor and ceiling tiles and transite siding; and many many more. Materials containing hazardous materials should have material safety data sheets available in the workplace.
Trades
There are numerous trades where workers were exposed to asbestos. These include insulators (also known as asbestos workers) who actually installed insulation; boilermakers who constructed boilers which were often several stories high and filled with insulation; plumbers, pipefitters, and steamfitters who fitted and welded the pipes together and often worked in small unventilated compartments in ships where large quantities of insulation were used; plasters who worked with fireproofing spray on steel beams, electricians, bricklayers, millwrights, carpenters, steel workers, refinery and other industrial workers, maintenance workers, laborers, and many others. Although asbestos has been removed from many work environments, it still exists in some. For example, auto mechanics are still exposed to asbestos when working on car brakes. Similarly, construction workers may be exposed to asbestos when working on buildings, especially those built before 1980.
Sites
Industrial sites typically had the heaviest exposure. These include shipyards where ships are built, power plants, refineries, steel mills, manufacturing plants, where numerous boilers, pipes, turbines, furnaces, and other high temperature vessels are located. There was also high exposure at commercial sites such as high rise buildings, hospitals, universities and schools, shopping centers etc. High exposure also occurred in residential construction and places where auto repairs take place.