On March 28, 1995, the National Institute for Occupational Safety and Health (NIOSH) received a management request for a health hazard evaluation from the Maui County Council, Maui, Hawaii. The Council asked NIOSH to evaluate their composting operation since they recently began receiving complaints of poor working conditions from former employees, as well as complaints from neighboring business (Kahului Airport) about odors emitting from the composting site. There was no indication that any current employees have or had any health problems associated with the compost operation. This request was also prompted by the NIOSH Alert pertaining to Organic Dust Toxic Syndrome (ODTS). On May 11, 1995, NIOSH investigators conducted an initial site visit to the composting facility. During that site visit, the composting operation was toured, and area air samples were collected for total dusts, bacteria, fungi, and endotoxin. Bulk samples were collected of the various compost products for microbiological analysis. The purpose for collecting theses samples was to determine the microbial activity of the compost. The contractor operating the site was in the process of ending his contract with the County, so very little work was being accomplished at that time. On September 11-13, 1995, a return visit was made to the composting facility to conduct a comprehensive industrial hygiene survey. During that survey, the old contractor was still in the process of leaving and the new contractor preparing to take over operations. During that transition, the old contractor was loading and removing product, while the new contractor was focusing on reducing the stock-pile of accumulated green waste and sewage sludge by mixing one static windrow of compost. A final survey was conducted during June 24-26, 1996. During that survey, the composting site was fully operational under the new management. Many positive changes to the site were obvious, including the reduced stock pile of sewage sludge and green waste, a new office trailer, and most importantly, new front-end loaders equipped with air conditioned enclosed cabs. Other equipment used consisted of a compost mixing truck, a screener, and a new chipper/grinder. Water was also now available from the nearby quarry to spray on the compost and the roads to keep dust down. Total dust concentrations from the samples collected upwind ranged from 0.2 to 21.5 mg/m3, with the highest level measured on the outside of the loader working the greens. Other samples of note were the total and respirable samples collected inside and outside of the cab of a front end loader loading in the greens area. Total dust concentrations inside the cab were 0.69 mg/m3, while concentrations measured outside were 21.5 mg/m3. Respirable dust concentrations inside and outside the cab were 0.3 ands 0.72 mg/m3, respectively with the highest level measured on the access road to the landfill. Bacteria concentrations ranged from none detected (ND) to 8.0 x 107 colony forming units per cubic meter of air (CFU/m3), with the highest levels also measured on the loader at the greens. The primary bacteria identified was Bacillus. Thermophilic bacteria was only detected on the sample collected near the workshop. Fungi concentrations ranged from ND to 2.8 x 106 CFU/m3, with the highest levels measured near chipper/grinder. The primary fungi identified from the samples were Aspergillus and Penicillium. Endotoxin concentrations ranged from none detected (ND) to 3.0 x 105 endotoxin units per cubic meter of air (EU/m3), with the highest concentration measured near the greens chipper/grinder. To reduce this potential hazard it is important to reduce worker exposures by means of either engineering controls (e.g., enclosed cabs), respiratory protection, or a combination of engineering controls and respiratory protection. Samples collected showed that the enclosed cabs, when used properly such as keeping the windows closed, can reduce worker exposures. However, these controls are relatively ineffective if the cab windows are opened during compost handling operations. Also, these results show that individuals in the general area of the composting pads or those not operating enclosed equipment, should either wear respiratory protection or stay upwind during turning operations. The results from this health hazard evaluation has shown that the enclosed machinery cabs on the equipment can reduce exposures. Also, these results show that individuals in the general area of the chipper/grinder should wear respiratory protection during operation. 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. Just as individuals vary in their resistance to disease, a few individuals may be particularly sensitive to some of the organisms in compost.