Fatal Fumes

Tips for avoiding carbon monoxide poisoning.

November 1, 2001

First published in 2001, these 12 tips are just as relevant today

One minute, the two boys were swimming beside their family’s anchored boat. The next minute, they were dead, poisoned by an accumulation of carbon monoxide that had built up beneath the swim platform. This tragedy happened last fall on Lake Powell in Utah. And it can happen to you wherever you boat. Coast Guard studies reveal that at least five boaters die every year as a result of carbon monoxide (CO) poisoning.

Thousands more receive medical attention due to the deadly gas, which is odorless, tasteless, and mixes well with air. The deadly vapor is produced any time your engine or generator is running and can affect those both in and out of the boat. Effects run the gamut from simple nausea to brain damage, coma, or death.


How much CO does a boat produce? How does CO kill? Is your boat safe? We took a handheld Gas Baron CO detector ($495; CEA Instruments, 201/967-5660, on the water to find out. Then we asked the experts what you can do to prevent CO poisoning aboard your boat.

IT’S NO CHOKE. CO attaches itself to hemoglobin-red blood cells-preventing your body from absorbing oxygen. Breathing is unaffected while you’re being poisoned, so there usually aren’t any telltale warning signs.

THE CHAMELEON. The nausea, headache, drowsiness, and dizziness associated with CO poisoning may be confused with seasickness. Move the person from the immediate area, provide him or her with fresh air, and check for a source of CO. Remember: Evacuate. Ventilate. Investigate.


THE TIME FACTOR. Lengthy exposure to small quantities of CO is as deadly as brief exposure to large concentrations. At 400 parts per million (ppm), it takes an hour for a slight headache to occur. At two hours, brain damage and coma are likely.

GAS VS. DIESEL. When burned, gasoline produces 10 times more CO than diesel. We measured 186 ppm at the exhaust outlet of a 480-bhp diesel-powered boat. A 500-hp gas-powered boat’s exhaust registered 1,743 ppm.

RUN FOR SAFETY. Excessive bowrise exacerbates the “station wagon effect,” causing more exhaust to backdraft into the boat, particularly when full canvas is erected. Maintaining a flatter running angle is more fuel efficient and safer. Keep companionway hatches closed underway. Windshields with opening vents minimize backdrafting.


DUCK DOCKSIDE DISASTERS. Engine or genset exhaust can concentrate between your boat and a sea wall, bulkhead, or even another boat’s hull, where it can be sucked in through open ports or hatches. Position yourself accordingly, and be aware of your neighbor’s exhaust location.

OUT IN THE COLD. More CO is produced by a cold engine. So be aware of that fact as you prepare to get underway.

IN THE DRINK. Swimming near your anchored boat? Good. You don’t need the a/c. Turn off the genset.


MAINTENANCE. Inspect exhaust hoses along their complete run, paying particular attention to clamps and chafe where the hose runs through bulkheads. Check that machinery spaces are completely sealed from living spaces. Cracks and pass-throughs should be treated with foam, sealant, or a skirt. Inefficient operation increases CO, so fouled bottoms, dinged props, and poorly tuned engines are no-no’s.

DETECTION. Install and test monthly a UL-approved CO detector such as a Fireboy-Xintex ($50 to $85; in every living space aboard your boat. Soon, boats seeking NMMA certification must have them standard in living spaces.

PASS OR FAIL? With engines running and the genset on, none of the 27 new boats we “sniffed” registered the presence of CO in the living spaces.

AVERT TRAGEDY. Don’t teak surf. That’s a warning courtesy of Captain Scott Evans, chief of the Coast Guard’s Office of Boating Safety, regarding a new and dangerous boating game. It works like this: The so-called teak surfer holds onto the swim platform while the boat creates a wake. When it’s large enough, the surfer lets go of the platform and body surfs on the wake.

“People don’t think about the danger until the surfer passes out because of exposure to the carbon monoxide in the engine’s exhaust,” explains Evans. “Serious injury and fatalities can easily occur.”

If direct exposure to carbon monoxide isn’t enough to deter you from teak surfing, what about this? Hanging from the swim platform puts you in extremely close proximity to a whirling prop. What happens if the driver of the boat zigs when you’re expecting a zag? Not a pretty picture.


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