Doug Daniels, US National Institute for Occupational Safety and Health (NIOSH), has investigated the overall excess cancer incidence in firefighters, including oesophagal, intestinal, lung and kidney cancers.
He identified the exposure to PAHs, formaldehyde, benzene, asbestos, diesel exhausts and shift work as increasing cancer risk, and suggested that dermal exposure, rather than inhalation, may be the main route. He went on to explain the difficulties of proving links to increased susceptibility of firefighters, who were healthier than the general population. For example, only mesothelioma and oral cavity cancer showed as proven firefighter occupational diseases in pooled studies, based on large numbers of smaller studies, compared with the larger number of occupational cancers in the International Agency for Research on Cancer (IARC) findings.