From September 6 through September 9, 2005, investigators from the National Institute for Occupational Safety and Health (NIOSH), Division of Respiratory Disease Studies, performed a site visit at the Environmental Protection Agency facility at Research Triangle Park in Durham, North Carolina. This evaluation was conducted in response to a request from EPA management for a NIOSH health hazard evaluation regarding a history of particulate exposure and staff health effects in the laboratory areas of the facility. Laboratory staff became aware of excessive indoor particulate levels starting in 2003. Some EPA researchers measured PM2.5 (particulate smaller than 2.5 microns) levels and noted instances where indoor concentrations were higher than outdoor concentrations. Staff in many laboratories started to note a rapid buildup of white dust on surfaces which would quickly recur after cleaning. High efficiency particulate filters in bio-safety cabinets in many laboratories had to be changed out after several months use when normally they would be expected to last several years. Electrical components of several laboratory devices were found to be damaged and to have evidence of corrosion and accumulated particulate. Investigations by EPA/RTP facilities staff revealed that the humidification system in the heating, ventilation, and air conditioning (HVAC) units was causing a buildup of sodium and chloride deposits on the cooling coils and was a potential source of the laboratory particulate. An additional issue contributing to the particulate problem was periodic malfunctioning of ventilation-system controls which would cause transient increased airflows in laboratory areas. Such malfunctions were associated with increased deposition of visible particulate matter on surfaces. These events were referred to as "dumps" by EPA staff. In 2004, a number of laboratory staff in Buildings A and B developed acute health symptoms in laboratories where a dump had just occurred. The symptoms reported by these individuals included cough, shortness of breath, chest pain with inhalation, chest tightness, sore throat, and eye irritation. Some individuals had persistent symptoms for many days prior to eventual resolution, and some had symptoms recur when they tried to return to their usual laboratories. One individual reported receiving a diagnosis of asthma due to the particulate exposure. Despite attempts by EPA/RTP facilities staff to address the particulate problem, employees continued to detect excess particulate in laboratory areas and to experience respiratory symptoms. Results of limited air sampling and observations by NIOSH staff during the site visit suggest that particulate accumulation in the ventilation system air handling units, coupled with periodic loss of control of laboratory airflows by the system, is a likely source of excess particulate in laboratory areas. Other sources of laboratory particulate may include ceiling tiles, floor cleaning activities, and soil and construction activities outside the facility. The ongoing replacement of the cooling coils in the HVAC units, along with utilization of reverse osmosis and a water softener to treat the water for the humidification system, may correct the ventilation system particulate problem. However, the fact that the humidifier atomizer heads will still be relatively close to the cooling coils may cause particulate buildup on the coils to recur. In confidential interviews with 17 employees who requested interviews with NIOSH staff, employees reported health effects they experienced in, or attributed to, the EPA/RTP facility (mostly laboratory areas). The most common reports were of upper and lower respiratory symptoms and eye irritation. These symptoms may represent primarily irritant responses. Whether or not particulate exposures in the laboratories caused or exacerbated asthma in some employees could not be determined from the information available. Particulate accumulation on, and corrosion of, the cooling coils in the HVAC units has likely led to increased amount of visible particulate and PM2.5 in the laboratory areas of the EPA/RTP facility. The particulate may be responsible for the irritant-type symptoms that some employees have experienced while in their laboratories and/or adjacent offices. Symptoms were severe in instances where employees were exposed in relation to a particulate "dump" that resulted from a ventilation-system airflow malfunction. The ongoing replacement of the cooling coils reportedly will take several months to complete. This should decrease the amount of particulate that enters the laboratory areas from the ventilation system and may lead to resolution of employee symptoms. This report contains recommendations for steps that EPA/RTP facilities and health and safety staff should follow to prevent and minimize particulate from the ventilation system and other sources, and to protect employees that may continue to be adversely affected until the particulate problem is eliminated.