Abstract: Employee #1 had completed service on a large stainless steel swimming pool filter. When the filter was turned on, he noted that the water pressure was 35 psi at the top of the filter. Apparently, the backwash valve was blocking both the backwash escape line and the filter return line to the pool. The pool's electric water pump was pushing water into the filter with no method of discharge. The pressure continued to build to the point of metal fatigue, until the two-part filter housing flew apart. The upper half of the housing struck Employee #1 in the head. He was killed. The backwash valve blockage was not detectable when the system was in operation.