Abstract: At approximately 10:15 a.m. on May 30, 2012, Employee #1, a 46-year-old truck driver with Univar USA was making a routine delivery of sanitation chemicals to Darigold. This Darigold facility is a milk packaging plant, Darigold purchases their sanitation chemicals through Ecolab. The chemicals are delivery by Univar USA which is a local chemical trucking company. Employee #1 delivered the chemicals to Darigold's milk-loading dock #2 where the chemicals are pumped through receiving pipes located on the south wall the loading dock. The pipes lead to three large tanks located in the Clean In- Place (CIP) room located adjacent to the dock. The multi-compartment tanker truck was loaded with two different chemicals; AC-55-5 (nitric and phosphoric acid blend) and AC-103 (sodium hydroxide). The sodium hydroxide was pumped first, without any problems. When the truck driver hooked up the hose to pump the second delivery, which was the nitric and phosphoric acid blend, he selected the wrong intake pipe. Employee #1 started pumping the acid into the "CIP Exelerate" sanitizer tank which contained sodium hypochlorite. The mixture started a reaction that generated chlorine gas. Employee #1 could not see the tank in the CIP room, thus there was a delay in recognizing a problem. By the time the mix-up was identified, approximately 325 gallons of acid was mixed with approximately 1,150 gallons of sodium hypochlorite. The Darigold Dock attendant evacuated the area to safety. Employee #1 donned a full face APR and shut-off the acid tanker. He then evacuated to safety. The entire milk plant was evacuated. Employee #1 was most severely injured and was hospitalized overnight due to inhalation burns. The receiving dock attendant and nine other adjacently exposed workers were sent to emergency rooms for evaluation and were released with only minor injuries. All others employees were unharmed. The chemical reaction continued to generate chlorine until approximately 8:00 p.m. that evening. The building and perimeter remained evacuated all evening and the chlorine was controlled by fans blowing into the room until the reaction was stopped and the tank was pumped out. Related Factors, Negative -A chlorine concentration above the IDLH (10 ppm) was formed. The fire department's chlorine meter was pegged out (about measuring range). Chemical truck deliveries tie up one of the two milk delivery docks. There was an emphasis on limiting milk delivery interruptions, thus the truck driver was in a hurry to get the delivery done. The milk receiving attendant at the Darigold Dock was too busy to verify and watch the delivery. The Bulk Delivery Release Form (BDRF) was not signed by Darigold. The locks were under the control of the truck driver and the lock combinations on the acid and hypochlorite locks were very similar. The Ecolab safety procedure was being used as the standard for this operation. The "two sets of eyes" unloading concept discussed multiple times in the Ecolab training was not being followed. The truck driver could not see both this truck and the receiving tank during the delivery and the milk receiving attendant was not present (per the Ecolab procedure, both must be watched.) Positives, the tanker truck was properly labeled. The pipe hook-ups in the wall of the load dock were properly labeled and color coded. The pipe hook-ups were locked. However the lock combinations were given to the truck driver. The emergency evacuation was successful. The CIP was unmanned at the time of the incident. Site had previously reduced their ammonia usage to not be a PSM covered process.