Abstract: On April 7, 2008, Employee #1, a chemical technician was filling chemical orders in the West Chemical Storage Room for use in other parts of the facility. He mistakenly mixed hydrogen peroxide and hydrochloric acid. He then capped the container containing the inadvertent mixture; stepped away from the cart to rinse his funnel in a sink; and, upon returning, noticed a discoloration of the liquid in the container. He recognized his error, realized that a chemical reaction was underway in the capped container, and attempted to transfer the offending container to another area using a cart. Upon rounding a corner at a hallway intersection referred to as the crossroads, the container rolled off of the cart, split along one side from top to bottom, and spilled the majority of its contents. Employee #1 immediately started to clean up the spill using absorbent pads. The location where the container split was immediately outside of a room that contained a Zellweger System 16 gas detection system. At the time of the spill, the room's door was open and a portion of the spilled material entered the room. Gas from the event caused staining of the system tape and triggered a Chlorine alarm in several remote basement locations. There was no sampling port in the room containing the system because a chlorine spill was not expected at that location. The Chlorine alarm triggered an evacuation of the basement and a call for the hazmat team to report to the crossroads. Upon reporting to the crossroads, the team discovered that the crossroads was the location of the incident and that a cleanup was already in progress. Team members left for a nearby storage area, donned SCBAs, and returned to check the area for victims. Employees #1, #2, #3, #4 and #5 were transported to the Hutchinson Hospital for observation, but were treated and released.