Asbestosis has always been regarded as a disease of heavy exposure. The first cases were seem amongst people who spent their whole working day exposed to large amounts of dust and continued to work in these conditions for periods of years.
However, despite some dust control measures were introduced in the asbestos factories as a result of the Asbestos Industry Regulations 1931, cases of asbestosis still stubbornly appeared.
It was then appreciated that lower or less concentrated exposure over a longer period could still cause the disease.
It also became apparent that taking the worker away from further exposure would not necessarily prevent the disease from developing or, if it was already present, from becoming progressively worse.
Studies of cases of asbestosis have almost always focussed on workers in asbestos factories or on thermal insulation engineers, known as "laggers".
These types of worker will inevitably have experienced longer and more concentrated exposure. The effects of long term light exposure or of intermittent exposure in other occupations are less well studied and understood.
However, research published between the 1960's and the mid 1980's has led to an acceptance of a 5-6-fold reduction in the amount of total exposure which would create a risk of asbestosis developing.
Experts still generally agree that asbestosis needs heavier and more prolonged exposure to develop than other asbestos related diseases, such as mesothelioma, pleural plaques and diffuse pleural thickening.