In August 1998 the National Institute for Occupational Safety and Health (NIOSH) received a confidential health hazard evaluation (HHE) request from the American Postal Workers Union, AFL-CIO (APWU) to conduct a health hazard evaluation at the Tampa Mail Processing and Distribution Center (TMPDC), Tampa, Florida. The request listed exposures to paper dust, bathroom cleaning chemicals, and rust / dust in the ventilation system as potential health hazards by inhalation, skin exposure, and ingestion. Health effects resulting from these exposures were listed as chronic respiratory conditions and skin conditions including rashes and hives. On October 6 - 7, 1998, NIOSH investigators performed a walkthrough survey of the worksite and met with APWU and US Postal Service representatives to discuss worker exposure to dusts including paper dust and dusts associated with the operation of heating, ventilating, and air conditioning (HVAC) systems. NIOSH investigators monitored real-time aerosol concentrations before and after "blowout" of paper dust from a mail sorting machine (delivery point bar code sorter) and collected 10 particle size selective area air samples. The investigators inspected 27 HVAC systems. Workers were notified by public address that NIOSH investigators were available to discuss respiratory symptoms. On November 11 - 13, 1998, NIOSH investigators returned to obtain three personal respirable dust samples from maintenance workers performing "blowout" of paper dust. A total of 12 airborne spore samples were collected and analyzed for fungal structure counts and fungal identification among plant (10), office (1) and outdoor (1) areas. Four area air samples were collected in the center of both the first (2) and third (2) floors for mite and roach antigen. Three bulk floor dust samples were collected for roach antigen in the first (2) and third (1) floors. Bulk dust samples were collected from each of 12 HVAC systems which service the first (7) and third (3) floors and the office area (2). The bulk samples were analyzed for viable fungi and mite antigen. Bulk drain pan water was collected from the same 12 HVAC systems for endotoxin analysis. A total of 12 airborne dust samples were collected and analyzed for endotoxin among plant (10), office (1) and outdoor areas (1). Of the 56 workers who discussed respiratory symptoms with NIOSH investigators during the walkthrough in October, 38 workers were contacted by telephone for follow-up interviews with a questionnaire in December 1998. Respiratory symptoms and worker job descriptions were obtained during the interviews. Nearly all interviewed workers reported that they experienced nasal symptoms: irritated, stuffy, or runny nose (97%); and sinus fullness or postnasal drip (89%). Seventy-nine percent (79%) reported eye problems; 74% reported irritated throat; 66% had headaches, and about 60% reported cough. Sixty-eight percent (68%) reported flu-like symptoms [fevers, aches, tiredness]; 34% reported wheezing, 39% were bothered by tightness in the chest, and 35% reported that they were short of breath more than once a week while at work. Of the 27 HVAC systems inspected, 21 had internal components that were in need of cleaning or adjustment to address problems ranging from dusty coils, slime within drain pans and coils, poor drain pan drainage, filter blow-by, dusty surfaces, and accumulation of dust in drain pans. Bulk dust was collected from each of 12 HVAC units for mite antigen analysis. Ten units were free from dust mite antigen, two which service the first floor were positive for antigen at a concentration associated with mite sensitization. Bulk floor dust collected in the areas adjacent to the cafeteria and lunchrooms on the first and third floors were negative for roach antigen. Mite antigen was not detected in airborne dust from the first floor but was detected in airborne dust from the third floor. The concentration of mite antigen in the airborne dust exceeded the level associated with an allergic response in mite-sensitized individuals. No roach antigen was detected in the airborne dust samples. The average concentration of viable fungi per gram of bulk dust collected from 3 air handlers servicing the 3rd floor was 15 times greater than average concentrations of fungi in bulk dust collected from air handlers that service the office and 1st floor areas. Bulk dust samples from three air handlers that service the third floor were dominated by Tritirachium (80 - 86%) and Acremonium (69 - 93%). Of the bulk dust samples collected from seven air handlers that service the first floor, one was dominated by Exophalia (92 - 93%), five by Cladosporium (30 - 99%) and Penicillium (10 - 43%), and one by Aspergillus niger (21 - 29%) and Penicillium (49 - 53%). Counts of fungal spores in third floor and office samples ranged from 386 to 1157 spores per cubic meter of air (spores/m3); first floor counts ranged from 771 to 3470 spores/m3. These indoor spore counts were below the outdoor concentration of 6169 spores/m3. Respirable paper dust concentrations measured during five hours of blowout activity by maintenance workers ranged from 0.052 to 0.056 milligrams of dust per cubic meter of air (mg/m3). No exposure limits as enforced by the Occupational Safety and Health Administration (OSHA) or recommended by NIOSH or the American Conference of Governmental Industrial Hygienists (ACGIH) were exceeded for paper dust concentrations in air. Endotoxin in bulk fluid samples from 12 air handler drain pans ranged from 0.3 to 2312 endotoxin units per milliliter of water (EU/ml). The drain pan fluid in air handler 37 (which services the third floor) was 2312 EU/ml, about 5.6 times the next highest concentration. Endotoxin concentrations in airborne dust samples in third floor, first floor, and office areas averaged 4.4, 6.5, and 5.6 endotoxin units per cubic meter of air (EU/m3) respectively. These endotoxin concentrations were below the outdoor concentration of 8.8 EU/m3. On the basis of environmental data and information gathered from employee interviews, NIOSH investigators did not find clear evidence that employee symptoms were caused by exposure to microbial contaminants or paper dust. Recommendations are made to control the accumulation of paper dust, improve the operation and cleaning of HVAC systems, and provide respiratory protection from paper and non-specific dusts if exposures initiate or aggravate respiratory conditions. Recommendations for respirator selection are presented in this report. In addition, the presence of airborne mite antigen indicates that dust containing this antigen was aerosolized. The concentration of the mite antigen in the airborne dust was high enough that it should be considered as a potential factor for triggering symptoms in employees with dust mite sensitivity.