The injured person (IP) was pumping fluid waste contents from the hazardous drain tank to the tote tank on deck. Approximately 40 seconds after the fluid had been flowing, the IP called the Engine Room Operator (ERO) and asked him to stop the pump; at this time the ERO noticed that the Motorman’s breathing sounded labored over the radio. Communication was broken off, and the ERO pushed the E-Stop and tried to re- contact the IP to see if he was all right. When there was no response he proceeded to personally check on him. Arriving at the scene, the ERO found the IP lying face down on the Deck, with obvious signs of a head injury.