Much easier than most people realize... I went to a number of people who died from carbon monoxide poisoning during my career as a firefighter. The saddest was a little girl who was sleeping in her friend's parents new cabin cruiser boat. They were coming home from a long day out on the water and had a tailwind that caused the exhaust from the engine to get sucked into the sleeping quarters. No one noticed the odor of exhaust and didn't realize that the kids had CO poisoning until they tried to wake them up. We were unable to revive the one little girl. It was very sad.
Oh wow, that is something I can imagine will never leave your brain, that is as horrific as it gets when it involves a kid, I’m so sorry, I can’t even imagine it. My cousin was a cop in New York city and actually a good friend of mine was for 2 years who went on to join the secret service. He was a combat vet for operation Desert storm and all it took was for him to witness one subway accident victim and he resigned and went to the secret service.
Would a CO detector with a loud alarm have helped there? Every enclosed or semi-enclosed living space on a vessel should have one.