A vessel was underway in bad weather and was pitching and rolling. An engineer was tasked with a routine check of an A/C compressor. He removed the safety guard of the still-running compressor, but the motion of the ship caused him to lose balance. He instinctively reached forward to steady himself, but his left hand came into contact with the moving belt of the compressor, resulting in a serious injury. The next day he was evacuated to shore facilities for expert attention. Lessons Learned Before any intervention, machinery should be fully stopped and isolated (Lock out/tag out). Effective risk assessment, work planning meetings, and toolbox talks are essential. They should include specific consideration of vessel motion, weather conditions, and human factors. Crew members shall be encouraged and empowered to exercise Stop Work Authority whenever unsafe conditions are identified.