Skip to main content

An Invisible Killer: What You Should Know About Carbon Monoxide

Even owners of open boats, like this center console, should be carbon monoxide aware. 

Even owners of open boats, like this center console, should be carbon monoxide aware. 

Many of us have been too close to the rail when backing our boats down or have had a gust of wind push exhaust fumes into our face. Spend any time fishing offshore, and that time at idle while you pull in your catch can be enough to make you choke when the air is otherwise calm. Engine exhaust fumes smell and taste bad, so avoiding them is almost automatic. The problem is that the part that smells bad and tastes awful isn’t the immediately dangerous part — carbon monoxide (CO) is.

Carbon monoxide is odorless and colorless, and while it is always present in smelly exhaust fumes, it can also stealthily build up and creep into the air you breathe without warning. Just a few breaths of CO in high concentration can make you sick. Worse yet, you can go to sleep in your boat thinking everything is fine, and then simply not wake up.

This is an area where regulations require inspections for commercial vessels. But that used cabin cruiser you just bought may be leaking CO from a number of hose connections. Even if you have a newer vessel, breathing exhaust fumes is harmful to you or your passengers. Besides regular (at least annual) inspections by a certified marine mechanic, boaters should know the signs of CO poisoning and how to prevent it.

The aft cockpit is a common place for carbon monoxide to accumulate.

The aft cockpit is a common place for carbon monoxide to accumulate.

Signs And Symptoms

When a person inhales CO, no matter the concentration, the gas passes into the bloodstream through the lungs and attaches itself to red blood cells. It’s actually more readily absorbed into the bloodstream than oxygen is. 

Besides displacing the oxygen around it, CO also renders your blood cells unable to absorb oxygen. Simply put, CO makes oxygen transfer impossible. So, the signs and symptoms of CO poisoning are a lot like those of altitude sickness. Nausea is just one. When someone feels seasick who doesn’t usually get seasick, the cause may be CO. Other signs include, headache, confusion, fatigue, dizziness or even seizures.

What To Do

If you notice these symptoms in yourself or others, step one is to get to fresh air immediately and make at least a pan-pan call, if not a request for medical assistance. No, I’m not suggesting a distress call for obvious seasickness, but I am suggesting you at least consider that it may be more than just seasickness, particularly if there are obvious exhaust gasses present.

The CO in the bloodstream will, eventually, let go and be expelled from the lungs the same way it came in, but only if the air coming into the lungs is free of CO. Pure oxygen is best to breathe during recovery, but few of us have that in our medical kits. Shutting the engines down or heading into the wind can help provide clean air to breathe. If the poisoning is bad enough, hospital treatment may be necessary and can involve spending time in a pressurized oxygen chamber.

Avoiding the CO is a Better Plan

The first and best thing you can do to avoid CO buildup on your vessel is regular exhaust system inspections and maintenance. Lack of maintenance is almost always the cause of CO inside vessel spaces, so regularly inspect exhaust hoses and hose clamps for leaks, cracking, charring, looseness or any visible deterioration. Replace any problematic hoses and hose clamps you find.

Even on a well-maintained vessel, CO buildup in the cabin spaces can occur while at idle, or when operating at speed with a high bow angle. Back-drafting also can happen, and CO sometimes finds its way in through other hull openings.

After one incident along the Gulf Coast last year, the Coast Guard released Marine Safety Alert 10-17, which describes how the design of the subject vessel’s swim platform and transom created a condition where an otherwise perfectly maintained vessel would build up high concentrations of CO on the back deck, flybridge and even into the cabin spaces. During one trip, multiple passengers had to be hospitalized.

A $99 carbon monoxide detector. 

A $99 carbon monoxide detector. 

$99 Can Save Your Life
So, besides keeping up with engine maintenance and being aware of the situations that cause CO to accumulate, how are you supposed to defend yourself against this colorless, odorless gas? There’s a $99 solution: a carbon monoxide detector. Generally inexpensive and very effective, they’re available at most marine supply shops. There should be one or more on every boat with enclosed living spaces. Most CO detectors wire right into your existing direct-current system and they all sound an alert when potentially dangerous levels of CO are present. They’re easy for just about any boat owner to install, so there’s no excuse not to have one.

Once you’ve installed a CO detector or two, take some time to read through the Coast Guard’s CO recommendations to learn about the conditions that can cause CO to accumulate in your boat. The life you save could be your own. 



5 Things You Should Know About Flares

Only once in my career as a USCG helicopter rescue swimmer did I ever launch on a flare sighting that turned into an actual rescue. Three commercial fishermen were at anchor, sleeping, when their shrimp boat caught fire. By the time they got on deck, the wheelhouse was ablaze, and the only thing on the boat not on fire was these three guys, the Type 2 PFDs they were wearing and the one flare they grabbed out of the flare locker.


DSC Is An Amazing Tool. Do You Know How To Use It?

At a meeting with 250 boaters last year, I asked for a show of hands: “How many of you have registered your DSC radio and have an MMSI number?


Can You Tell When a Person is Drowning?

Mention drowning and we all tend to envision a person in the water waving his hands, splashing and screaming for help. That’s not even remotely close to what a drowning person looks like, writes Mario Vittone in this week’s Lifelines: Safety And Rescue At Sea blog.


If You Had to Pick One: EPIRB vs. AIS vs. Satellite Devices

What’s the one man overboard device you should pack in your life jacket? The answer is, “Yes,” writes Mario Vittone in this week’s Lifelines: Safety And Rescue At Sea blog.


The Truth About Cold Water Recovery

Victims of cold-water immersion aren't out of trouble after being rescued. In his latest installment of Lifelines: Safety And Rescue At Sea, Mario Vittone discusses what to do — and what not to do — when treating someone with hypothermia.


The Air You Breathe

Every boat owner should recognize the signs of carbon monoxide poisoning and how to prevent it.


More Myths About Drowning

Last week in Lifelines, Mario Vittone dispelled a massive myth in his post Drowning Doesn't Look Like Drowning, which went viral and will save lives. This week, Vittone tackles the fallacy that untrained, but otherwise competent swimmers, can't make an attempt to save someone who's drowning and tells us how to (safely) do it.