Confined spaces can be deadly when combined with hydrogen sulfide.
You may have missed the news story about three crew members dying while repairing a waste line aboard the Royal Caribbean ship “Monarch of the Seas.” The ship was docked at the Port of Los Angeles.
The accident report indicated the crew members were replacing a section of pipe connected to the ship's sewage system. The broken line released about 5 gallons of sewage, as well as sewer gas into the starboard propeller shaft tunnel.