Abstract: During batch production of bifenthrin, gases are normally released in the reactor vessel and are delivered by a closed system to an acid gas scrubber for neutralization with sodium hydroxide. This scrubber failed because the sodium hydroxide feed line clogged, releasing a plume that was probably a mixture of hydrochloric acid and sulfur dioxide gases. The plume was blown across the facility, including the chemical laboratory where technicians and supervisors were working. The chem lab's own HVAC system pulled some of the plume into the building, driving out the five technicians and one supervisor, who were choking, coughing, and having difficulty breathing. Two employees had been walking to a job site and had encountered the same plume. The plant nurse had been alerted and administered oxygen until the ambulances arrived and took Employees #1 through #8 to local hospitals. The employer had extensive written emergency response and evacuation procedures that are practiced six times a year, and designated employees are given emergency response training (emergency respirator use, confined space entry, acid spill containment) weekly. No violations were noted with procedures or responses.