Although these studies were designed with the intent of clarifying the quantitative relationship between diesel exhaust and cancer, grounds for scientific debate will still remain. Given the large number of previous diesel exhaust studies, it is unclear whether any single new study will significantly alter our position on this issue. Furthermore, we must ask whether it is ethical to wait another 5 to 10 years for the results from these studies before making any decisions about protecting workers and the public from the potential hazards of diesel exhaust exposure. Finally, we must recognize that risk assessment has become a battleground for powerful interests that are potentially affected by regulation. Organizations with ample resources have discovered that debates about the uncertainty of risk assessments can be a powerful tool for impeding regulations.
All scientific work is liable to be upset or modified by advancing knowledge.
That does not confer upon us a freedom to ignore the knowledge we already have, or to postpone the action that it appears to demand at a given time. 22 Scientists clearly recognize that all risk assessments are inherently uncertain and subject to change when new data are obtained. Regulators and other decision makers in our society must accept this as an inevitable consequence of the scientific process and not allow the acknowledgment of uncertainty to be used as an excuse for delay in developing policies to protect workers and the public from exposure to diesel exhaust and other hazards. Making decisions when the risks are uncertain will inevitably lead to errors. It is to be hoped that risk managers will continue to use conservative assumptions, with the result that any errors will be in favor of protecting workers and the general public from environmental hazards.