Second degree heat (thermal) burns

Two maintenance employees received second degree burns on their torso, legs and arms while troubleshooting a pump that moves ambient air, water and paper stock through a sewer/pipe system. The line/pump was plugged and the pump was shut down. After a period of time where the pump was running (not moving water and paper stock) and plugged, the ambient water and paper stock heated up. The maintenance personnel did not realize that the water had heated (temp unknown at time) and proceeded to open the inspection port. As the inspection port was opened, a sudden release of hot water/paper stock sprayed the two maintenance personnel.