Employee injured by exploding pump

Employee #1, the derrick man on a land oil drilling rig, was operating an auxiliary mud pump during the rigging-up phase of drilling in order to operate the cellar jet. The jet became clogged with rocks and debris, and the pressure relief valve on the pump did not operate. The high-pressure header on the pump came apart, and pieces of it struck employee #1 in the head. The pressure relief valve was found to have been set with a nail instead of a manufacturer's specified shear pin. The nail and valve had both corroded, rendering the valve inoperable. The high-pressure header was found to have suffered erosion around a fitting, which failed under pressure. No routine maintenance or inspection of the pump was conducted by the company.
Source:OSHA.GOV