Health hazard evaluation report: HETA-96-0252-2763, San Francisco Recreation and Parks Department, San Francisco, California.
In August 1996, the National Institute for Occupational Safety and Health (NIOSH) received a management request for a health hazard evaluation (HHE) from the San Francisco Recreation and Parks Department, San Francisco, California to evaluate the Parks Departmentís composting operation. Their request indicated that one of the three employees assigned to the composting site had experienced respiratory problems, nausea, shortness of breath, and muscle soreness. In addition, NIOSH was also asked to evaluate the effectiveness of the enclosed cabs on the heavy equipment used at the compost site. On September 4, 1996, two NIOSH Industrial Hygienists conducted a site visit to the composting site and conducted limited air samples during simulated turning operations. The San Francisco Recreation and Parks Department operates a small composting operation which is located adjacent to the San Francisco Zoo. The material which is composted at this site consists of leaf, and green waste which is mixed with manure from the zoo. The green waste is collected at the cityís parks and is trucked to the composting site. The zoo manure (zoo-doo) from herbivores is collected and also trucked to the site for mixing with green waste. During the surveys conducted at these composting sites, work area air samples were collected for total dusts and bioaerosols. Samples were collected during simulated operations at the compost site. Total sampling times for the samples collected were approximately two hours, and therefore, do not reflect an eight-hour time weighted concentration. Air samples were collected at locations upwind and downwind of the site, and inside and outside of the cabs of the chipper and front-end loader. Total bacteria concentrations measured inside and outside the chipper cab were 9250 and 6.06 x106 colony forming units per cubic meter of air (CFU/m3 ), respectively. Fungi concentrations were 9.7 x 103 CFU/m3 inside the cab and 6.8x 105 CFU/m3 outside the cab. The total dust concentration inside the cab of the loader was 0.68 milligram per cubic meter of air (mg/m3) compared to 6.69 mg/m3 outside the cab. Bacteria concentrations inside and outside the loader cab were 2.6 x 104 and 3.5 x 106 CFU/m3, respectively. Fungi concentration were lower inside the loader cab as compared to outside the cab, but not as pronounced as that seen for total dust and bacteria. Fungal concentrations inside and outside were 3.2 x 104 CFU/m3 and 4.6 x 104 CFU/m3, respectively. The results from this health hazard evaluation have shown that the enclosed machinery cabs can reduce exposures. However, these controls will be ineffective if the cab windows or doors are opened during operation. Acceptable levels of airborne microorganisms have not been established. Lack of standardized exposure assessment techniques, inability to quantitate non-viable organisms, and inter-individual variability in response have confounded efforts to set such standards. To reduce this potential hazard it is important to reduce worker exposures using either engineering controls or a combination of engineering controls and respiratory protection. The results from this health hazard evaluation indicate that enclosed machinery cabs on the equipment at the San Francisco Recreation and Parks Department sites reduce exposures to airborne fungi and bacteria. Microorganisms play such an important role in composting. Acceptable levels of airborne microorganisms have not been established. Lack of standardized exposure assessment techniques, inability to measure non-viable organisms, and inter-individual variability in response have confounded efforts to set such standards. To reduce this potential hazard it is important to minimize worker exposures using either engineering controls or a combination of engineering controls and respiratory protection.