Similar problems arise in relation to the hazards underlying occupational disease. Here, the problems are so pervasive that it is often difficult to know where to begin dealing with them.
It is estimated that industry at present creates and uses over 63,000 chemicals, perhaps 25,000 of which would be classified as toxic. Many of these are new, and their long-term effects are unknown. The effects of their interaction are impossible to predict in a comprehensive manner because of the number of possible permutations. In the view of some safety experts, the approach commonly adopted is a kind of trial and error using people in the workplace as human guinea pigs until concrete risks are identified.