Abstract: On September 17, 2003, Employee #1 was part of a crew of plasterers working at a school construction site in Irvine, CA. He was helping the foreman apply the first batch of a cement and stucco mixture to a building. They were using a 250 ft to 300 ft long rubber hose with a 3 in. diameter to dispense the coating, which had been mixed together in a tank. The distance from the hose nozzle to the pump was 144 ft. When the mixture didn't flow out, Employee #1 and the foreman checked the hose and found a cement blockage near the hose joint. The foreman called out, "Turn the switch off at the pump!" A coworker did so and then approached to see what the problem was. He noticed that the hose was packed with plaster near the joint, so he hit the pressure relief valve and returned to the area of the blockage. He also saw Employee #1 striking the hose with a hammer to unpack the cement. The coworker then overheard someone say that the cement was cleared and ready to go, so he ran back to the pump and hit the ON switch. Employee #1 was still using the hammer on the hose. The resulting pressure rise within the hose caused the backed-up cement/plaster slurry to spew out at both the hose-pump connection and the hose dispensing end. At the same time, the dispensing end of the hose lashed out, striking Employee #1 and the foreman. Employee #1 sustained multiple fractures to his sternum, his left arm, and his left leg, and he suffered trauma to other parts of his body. The foreman was thrown back 10 ft and sustained minor injuries. The pressure was above 600 psi at the delivery area.