An employee was preparing to load catalyst from a trailer into a catalyst hopper. They used nitrogen to build up pressure to move the catalyst. Something wasn't working, so the employee climbed onto a 9-foot high platform on the truck to check a valve. When the employee was climbing down, the cap of the trailer shot out and hit the employee in the chest, knocking the employee down to the ground. The employee was hospitalized with a fractured skull and eight broken ribs.