Indirect exposures occur frequently at worksites where different operations are carried out in close proximity. This form of indirect exposure is commonly referred to as bystander exposure. Grandjean and Bach (1986) reviewed the literature on bystander exposures, including asbestos, and concluded, “Indirect exposures may occur at work when adjacent workers are exposed to hazards originating from fellow workers’ activities” (Grandjean & Bach, 1986).
As stated by Selikoff et al. (1964), “Asbestos exposure in industry is not limited to the particular craft that uses the material. The floating fibers do not respect job classifications. Thus, for example, insulation workers undoubtedly share their exposure with their workmates in other trades; intimate contact with asbestos is possible for electricians, plumbers, sheet-metal workers, steamfitters, laborers, carpenters, boilermakers, and foremen; perhaps even the supervising architect should be included” (Selikoff, Churg, & Hammond, 1964).
In his 1971 testimony before Congress, Selikoff noted, “Asbestos diseases were found not only in men directly working with the material, but also in other people in the same industries as, for example, not only the insulation worker in a shipyard, but the electrician in the shipyard, the steamfitter, the shipfitter, the plumber, etc. because they were in the same atmosphere, on the same ship with the men actually using the material” (Donovan, Donovan, Sahmel, Scott, & Paustenbauch, 2010).
The shipyard industry was among the first in which increased awareness existed regarding the potential for exposure to asbestos of workers in close proximity to insulation work (Harries, 1971; Donovan, Donovan, Sahmel, Scott, & Paustenbauch, 2010). Harries (1968) noted that cases of asbestosis seen at the Naval Dockyards in the United Kingdom frequently occurred in men not officially recognized as asbestos workers (Harries, 1968). He listed 12 non-asbestos occupations of asbestosis patients seen during the previous year.
Additional studies showed that malignant mesothelioma occurred frequently in occupations without direct asbestos exposures (Grandjean & Bach, 1986; Newhouse & Thompson, 1965).
Asbestos diseases were found not only in people working directly with the material, but also in others not officially recognized as asbestos workers.
In the late 1960s, several studies in British shipyards reported that significant airborne concentrations (up to 200 f/cc) could occur during the application of sprayed-on crocidolite asbestos insulation. These airborne concentrations were higher than what had been reported for non-shipyard settings or for shipyards in the United States, which also differed with respect to the asbestos fiber type present in the insulation and the method of application (Harries, 1971; Donovan, Donovan, Sahmel, Scott, & Paustenbauch, 2010).
The duration and extent of bystander exposures can vary considerably, usually due to the magnitude of the exposure of the primary worker and the bystander’s distance from that person. Industrial hygiene measurements have shown that asbestos fibers may be carried far from the source by air currents (Grandjean & Bach, 1986; Donovan, Donovan, Sahmel, Scott, & Paustenbauch, 2010).
Based on an indoor air eddy diffusion model for particulate emissions, Donovan et al. (2010) proposed the following guidelines for estimating airborne asbestos concentrations at various distances from a point source:
1–5 feet from source = 50–100% source concentration*
>5–10 feet from source = 35% source concentration
>10–30 feet from source = 10% source concentration
>30 feet from source = 1% source concentration
(Donovan, Donovan, Sahmel, Scott, & Paustenbauch, 2010)
*Based on a comparison of direct and bystander air sampling data, bystander exposure levels may be comparable to direct exposure levels, and in some cases higher, when within five feet of the source; therefore, this guideline has been modified accordingly. Because airborne asbestos concentrations can reach significant levels and even bystanders may experience substantial exposure, it’s important to apply practical control measures to reduce these risks to acceptable levels.
Control
From the determinations and analysis performed in the recognition and evaluation components of industrial hygiene, control recommendations are made to reduce exposures determined to have an unacceptable risk. Using a hierarchy of controls from most effective to least effective, control mechanisms can be implemented to protect subjects from exposure to hazardous agents.
Hierarchy of Controls
- Eliminate Hazardous Agent
- Substitute for Less Hazardous Agent
- Implement Feasible Engineering Controls: Closed Enclosures, Ventilation, Etc.
- Provide Administrative Controls: Training & Surveillance
- Require Use of Personal Protective Equipment (PPE)
The most effective controls at the top of the hierarchy can also be the hardest to implement in an existing process. Likewise, the least effective (PPE) may be the easiest to implement. Having a comprehensive understanding of the hazardous agents, exposure risk, and effects of exposure both in the short and long term plays a key role in control recommendations.
References
Donovan, E. P., Donovan, B. L., Sahmel, J., Scott, P. K., & Paustenbauch, J. (2010). Evaluation of Bystander Exposures to Asbestos in Occupational Settings: A Review of the Literature and Application of a Simple Eddy Diffusion Model. Critical Reviews in Toxicology, 1–23.
Grandjean, P., & Bach, E. (1986, December). Indirect Exposures: The Significance of Bystanders at Work and at Home. American Industrial Hygiene Association Journal, 47(12), 818–824.
Harries, P. G. (1968). Asbestos Hazards in Naval Dockyards. Annals of Occupational Hygiene, 11, 140.
Harries, P. G. (1971). Asbestos Dust Concentrations in Ship Repairing: A Practical Approach to Improving Asbestos Hygiene in Naval Shipyards. Annals of Occupational Hygiene, Vol. 14, 241–254.
Newhouse, M., & Thompson, H. (1965). Epidemiology of Mesothelial Tumors in the London Area. Annals of the New York Academy of Science, 132, 579–588.
Selikoff, I. J., Churg, J., & Hammond, E. C. (1964, April 6). Asbestos Exposure and Neoplasia. JAMA, 22–26.
By investing in industrial hygiene programs, employers can protect workers, improve productivity, reduce injury-related costs, and maintain compliance with regulatory requirements.