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Carbon Monoxide, the Silent Killer On-Board

August 29, 2019

You can’t smell it and you can’t taste, and you probably will be unconscious before you ever suspect that you're breathing a deadly gas. Unfortunately, I have had firsthand experience with seeing the dangers of Carbon Monoxide (CO) having been directly involved with two CO related deaths, one on a boat and the other in a car. Frankly, I shudder when I think of how easy it is for people to be exposed to CO and how common it is to people to ignore the potential risk and even deny the risk exists.
CO is created whenever there is a flame. Even those vent less gas heaters create some CO. Obviously running any engine creates CO. And, unless you are bent on ending your life, you should avoid breathing air contaminated with exhaust and the CO it contains. The interesting thing is that CO can build up in a boat even when it is mechanically 100%. Drop curtains can actually cause higher than safe accumulations of CO. I think I had my boat for five years before I came across the warning in the owner’s manual to never run the boat with the drop curtains down.
I know of a live aboard boater in New York City who kept his boat tied to a bulkhead all year. He had a portable gasoline generator on top of the bulkhead to provide electricity for heaters on cold days. One cold winter morning when he did not show up for his job at a marina fuel dock, a fellow worker went to his boat and discovered he and his spouse dead of CO poisoning. Somehow, the exhaust gas from the generator had silently floated down into the boat causing the death of the couple who were asleep when they died.
There is good reason for the warning about drop curtains. There have been lots of cases where a boat moving slowly in a following sea developed dangerously high levels of CO. In fact, one story I know of is about a fellow who was running for hours with a downwind in a following sea with the curtains down while he ran the boat from the fly bridge. Then when he was approaching his berth, he called for his crew to come up and help him dock the boat, there was no response. It turns out that two people were unconscious in the forward V bunk. CO had drifted back from the stern exhaust and trapped behind the closed curtains then down to the bunks. CO works in funny ways. On report tells about a man shoveling snow around his running car. Even though he was in the open air, the CO accumulated to the point where he collapsed. There have been countless incidents where someone running a car in enclosed spaced caused their accidental death.
The dangers of CO are not limited to the engine exhaust.
Stoves, heaters and generators produce CO. If it has a flame CO is produced. It is always vital to ventilate any device that produces heat from a flame. Oddly enough, CO can accumulate in your deck area from the exhaust of other boats. And, probably more surprising is that fact that CO can accumulate under and around your swim deck. Never have the engine running when the swim deck is in use. And never allow anyone to “Teak Surf “by hanging onto the swim deck while the boat moves forward.
Caution is your best defense. Always make sure your engine room is properly ventilated. Exhaust hoses and even cast-iron metal engine parts can leak. Just a few months ago I started up my diesel 110 generator which is encased in a metal housing to reduce noise. I soon discovered a water-cooled elbow on the exhaust manifold had cracked and was leaking exhaust gas into the bilge. Fortunately, I did not simply start the generator from the pilot house and let it run unaware that the engine room was filling with deadly CO.
 The US Coast Guard recommends that all exhaust hoses and clamps be checked once a month. It is especially important to make sure the raw water-cooled mufflers are in good shape. Often, they are hidden under bunks or hidden in under the rear deck. Look for black streaking, water leaks and corrosion. Never tie up to a bulkhead where the generator discharge side of your boat is facing the bulkhead. Avoid rafting with the generator exhaust from another boat blowing toward your boat.

One of the most important things you can do to avoid being a CO victim is to install an approved CO detector in all enclosed living spaces.
When you are buying a CO detector for your boat you should be aware that starting in the year 2010 CO detectors must meet the ANSI/UL 2034-2005 standard, and it should compute the time-weighted average of the CO concentration in the air. The time-weighted average measurement process constantly monitors all CO levels, eliminating most false alarms. It is ideal to have a CO detector that provides multi-channel monitoring. This the level of CO in different cabins to be constantly measured and when one alarm goes off, they all go off. It is recommended that sensors be mounted at eye level safely away from hatches. The chart below shows how exposure to concentrations of CO affects humans.

100 ppm................01%
Slight headache in two to three hours
200 ppm................02%
Slight headache within two to three hours;
loss of judgement
400 ppm................04%
Frontal headache within one to two hours
800 ppm................08%
Dizziness, nausea and convulsions within
 45 minutes. Insensible in two hours.
1,600 ppm...............16%
Headache, dizziness and nausea within
20 minutes. Death in less than two hours.
3,200 ppm................32%
Headache, dizziness and nausea in five to ten minutes. Death within 30 minutes.
6,400 ppm.................64%
Headache and dizziness in one to two minutes. Death in less than 20 minutes.
12,800 pp.................1.28%
Death in less than three minutes.

 

 

The way CO works is that it when a person inhales air contaminated with CO the CO is more easily absorbed by the hemoglobin in the blood. In fact, CO is absorbed 200 times more easily than oxygen. In effect, the CO pushes out the oxygen and the victim is suffocated from within their own respiratory system in what is called hypoxia. As is shown in the above chart, the percentage of CO in the blood can result in from a simple headache to death in less than three minutes.
A CO accumulation can develop at any time without warning. Your best insurance against a tragedy is to invest in a carbon monoxide detector for your boat. It is an investment that could save your life.

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