series studies do not consider pre-existing conditions and report on acute outcomes rather than long-term health effects. For relevance to Gulf War veterans, the committee focused on long-term respiratory effects that persist after exposure ceases (see Chapter 2).
The first section of this chapter will discuss respiratory outcomes related to exposure to fuels, and the next section will discuss outcomes related to exposure to combustion products. The section on combustion products has the benefit of several large epidemiologic studies of Gulf War veterans who had objectively confirmed exposure to smoke from oil-well fires.
Most studies of fuel exposure reviewed by the committee were cohort-mortality studies. They included Australian petroleum-industry workers (Christie et al. 1987), Chevron petroleum-refinery workers (Dagg et al. 1992), Exxon refinery and chemical-plant workers (Hanis et al. 1985), US petroleum-refinery workers (Kaplan 1986), UK oil-refinery workers (Rushton and Alderson 1981), and petroleum-refinery workers in Beaumont, Texas (Wong et al. 2001a) and Torrance, California (Wong et al. 2001b). The occupational-cohort studies, which had multiple outcomes apart from respiratory disease, are described briefly in Appendix D.
All the occupational studies examined mortality due to noncancer respiratory outcomes among petroleum workers. Generally, the studies failed to indicate specific respiratory outcomes, although some do examine asthma, bronchitis, emphysema, and pneumonia or influenza separately. Most studies group all respiratory outcomes under the broad heading of “diseases of the respiratory system or tract” or “non-malignant respiratory disease”.
The studies that examined nonmalignant respiratory disease (Christie et al. 1987; Dagg et al. 1992; Hanis et al. 1985; Kaplan 1986; Wong et al. 2001a, 2001b) included all respiratory disorders, such as acute infections, diseases of the upper respiratory tract, pneumonia and influenza, asthma, bronchitis, emphysema, COPD, pneumoconiosis and other diseases due to external agents (such as asbestos), and other respiratory diseases. In all of those studies, the standardized mortality ratios (SMRs) were below 1.0 when compared with the general population or those not employed in the petroleum industry; this indicates that persons involved in the petroleum industry are not at greater risk for dying from respiratory diseases than the general population. However, selection bias is a limitation of the studies cited above because of the “healthy-worker” effect.
In addition to the retrospective mortality studies identified above, the committee reviewed a cross-sectional study of Norwegian cable-plant workers exposed to oil mist or kerosene vapors (Skyberg et al. 1986). Seven cases of pulmonary fibrosis were found in 25 workers compared with one case in the control group. In a followup study of those workers (Skyberg et al. 1992), the authors examined whether the progression of pulmonary fibrosis continued after exposure to oil mist and vapors ceased and found that 10 of the 25 workers had pulmonary fibrosis compared with one in the control group. Smoking and exposure to asbestos were possible confounders in both studies.