High temperatures and the presence of combustible dust presented potential fire hazards at a wastewater treatment plant where NIOSH staff recently conducted a health hazard evaluation. Employees at the plant requested the evaluation due to concerns about odors, upper airway irritation, and dust exposures related to a newly installed thermal dryer. The plant used the thermal dryer during the last step of the treatment process to evaporate water from sludge and significantly reduce its volume.  According to the NIOSH report, heat drying is an EPA-approved method for treating biosolids, but the process can create a combustible dust hazard. Agency staff noticed that some parts of the plant, including areas near the entrance to the thermal dryer room, were very dusty. NIOSH’s report notes that excess dust build-up can increase the risk of fires and explosions from combustible dust and urges the employer to ensure that these hazards are eliminated. Another focus of NIOSH’s visit to the plant was to evaluate employees’ exposures to endotoxins and silica. Levels of both endotoxins and silica in the air were below occupational exposure limits, according to the agency’s sampling results. During its evaluation, NIOSH staff observed some issues with the facility’s respiratory protection program. “Management representatives reported to us that employee respirator use was voluntary; however, we noted that the standard operating procedures for removal of dryer blockages required employees to use disposable P99 filtering facepiece respirators,” the agency’s report explains. “The company written respiratory protection program included the procedures for voluntary respirator use, but did not have procedures, such as medical evaluation and fit-testing, for mandatory respirator use.” NIOSH staff also noticed that respirators were not properly worn, maintained, or stored. The report urges the employer to institute a respiratory protection program for all employees who are required to wear respirators and to conduct in-person training that includes demonstrations of proper donning and doffing of respirators. The full report is available as a PDF from the NIOSH .