NIOSH recently responded to a union’s request for assistance regarding persistent symptoms experienced by firefighters following a response to a chemical fire. The fire occurred in January 2018 at a chemical manufacturer and distributor. When firefighters entered the building, they found an active fire burning in a chemical disposal vat. According to NIOSH’s health hazard evaluation report on the incident, it was unclear what was in the vat due to missing or incomplete labeling and inventory documentation. Some of the firefighters who responded to the incident reported becoming ill inside the building, while others became ill after leaving. Several firefighters reported a metallic taste in their mouths. Sixteen of the 65 firefighters who participated in the response were transported to local emergency departments from the scene of the fire. One developed shortness of breath, chest pain, and cough, and was treated by standby emergency medical services units. An additional firefighter serving as an emergency medical provider became ill during transport of a fellow firefighter to an emergency department. The day after the fire, a firefighter who had not been on the scene reported onset of symptoms while performing routine cleaning and maintenance on equipment used in the response. NIOSH’s response included confidential medical interviews with 46 firefighters. Agency staff also reviewed firefighter medical records, departmental incident reports, the fire department’s hazardous material and decontamination protocols, chemical inventory records of the company, and laboratory analysis of solid and liquid samples collected from the location of the fire.  NIOSH’s investigation found that many firefighters who responded to the chemical fire reported symptoms during or shortly after the response. The most common immediate symptoms they reported included dry cough, shortness of breath, fatigue, and throat irritation. Thirteen of the 26 firefighters who reported immediate symptoms told NIOSH staff that they had ongoing symptoms about one month after the fire. When agency investigators conducted a second round of interviews about four months after the incident, seven firefighters reported persistent respiratory symptoms such as cough, trouble breathing, wheeze, chest tightness, or being awoken by cough or shortness of breath. The fire department determined that an alkaline substance was present at the chemical manufacturer, but NIOSH could not determine the exact exposures to firefighters participating in this response. The agency explains that the unpredictable mixtures and unknown products of combustion present during chemical fires make exposure reconstruction challenging. “[The company’s] incomplete documentation and labeling practices, the nature of these types of fires, along with the minimal sampling conducted after the fire contributed to these unquantifiable and unidentifiable exposures,” NIOSH’s report concludes. “Due to these factors, the exact chemicals encountered by responding firefighters will likely remain unknown.” NIOSH urges the fire department to audit its practices and procedures for chemical fire responses and HAZMAT situations. Further recommendations from the agency are available in the PDF report.