Carbon monoxide poisoning: Recognizing, preventing the invisible killer

Gino Bottino, MD


Whether you own a powerboat or sailboat or just drive a car, you should be aware of the dangers of carbon monoxide poisoning and know how to detect and treat it.

Silent, odorless, invisible and deadly

Difficult to detect, carbon monoxide is a colorless, odorless, tasteless gas that’s heavier than air. It’s made whenever carbon-based fuels are burned, such as in internal combustion engines like gasoline-powered generators and car and boat engines. Although diesel-fueled engines produce CO in smaller concentrations than gasoline engines, they still produce enough to be dangerous.

Heavier than air, CO tends to collect in closed areas with poor to no ventilation. It can even enter your boat from a nearby vessel. Boaters need to be aware that exhaust from their engines and generators can enter any adjacent opening on their boat or their neighbor’s. The real danger with CO production is not just the rate (or amount) the source produces, but the space it’s in (or can get in) and how well-ventilated that space is. Not long after propane instant water heaters came out, numerous carbon monoxide exposures and deaths were attributed to CO accumulation in showers with these units. Shortly thereafter, the water heater designs were changed to account for the CO generated. The station wagon effect occurs when CO enters a station wagon’s rear window due to the low pressure area immediately behind the car as it moves. This also happens on boats, even open-transom designs, as the low pressure draws the CO in.

CO poisoning signs and symptoms

Most CO exposures cause only mild headaches and lightheadedness because they are transient and the CO level is low. The higher the exposure level or the longer the exposure time, the more symptoms you experience, and the more dangerous it gets. Common symptoms start as a slight frontal headache with possible dizziness. As the headache worsens, a lack of coordination and judgment occur, compounding the problem. As exposure grows, you start experiencing dizziness, nausea, vomiting and lethargy. Your mucous membranes (lips, gums, etc.) turn cherry-red, and eventually your skin reddens. Ultimately, convulsions and coma ensue. When this happens, death is imminent. Although the process usually develops slowly, if the concentration is high, it can progress rapidly. At concentrations greater than 6,000 parts per million, death can be sudden and immediate. A person’s size and general health can influence and vary the signs and symptoms caused by CO poisoning. Often, these symptoms are initially attributed to other causes, such as heat stroke, dehydration, seasickness and even food poisoning. Sometimes the frontal headache and dizziness can be interpreted as a sinus headache or allergies. If you aren’t aware of and on guard for the possibility of CO exposure, you may not recognize it till it’s too late.

CO poisoning treatment

Carbon monoxide is so chemically similar to oxygen that our bodies absorb it, and it combines with the blood (hemoglobin), forming carboxyhemoglobin in place of oxygen. CO has a stronger affinity for hemoglobin than oxygen, thus displacing the life-sustaining oxygen we need to breathe. Carbon monoxide victims suffocate due to the lack of oxygen in their systems. As the exposure and chemical reaction continue, the blood loses its ability to carry oxygen to the body’s tissues and organs. The first step in treatment is to remove the victim from the area with high levels of CO. Next, administer oxygen in the highest concentration available, and encourage deep breathing. At 10 percent carboxyhemoglobin levels, most individuals are pretty sick, and it takes five hours to reduce the carboxyhemoglobin level to 5 percent using 100 percent oxygen. Transfused blood can be life-saving for very sick patients, but time is critical.

Preventing CO poisoning

Prevention is the best treatment. Carbon monoxide detectors are small, cheap, readily available and easy to use. Install them wherever CO may accumulate: in the bilge, engine room, basement, furnace room and especially where you sleep—at home and on the boat. CO detectors can save your life!

  • Be aware and vigilant of areas and situations where CO levels could rise above normal using the CO prevention checklist:
  • Open forward hatches, portholes, bridge windshield openings in boats and front windows in cars to stop the station wagon effect.
  • Use extreme caution when using generators and diesel or propane heaters. Keep areas well ventilated, and use CO detectors that you check each month.
  • Be aware of nearby boats running engines or generators. CO can enter your space from a nearby or adjacent boat’s engine or running generator.
  • Inspect the exhaust system of all motors on board for leaks at the beginning and end of each season. This includes stoves and heaters.
  • Keep aft portholes and openings closed.
  • When in a slip or at anchor, look around for operating engines and sources of CO before settling in for the night.
  • Never swim near the rear of a boat unless the engines and generators have been off for a reasonable period.
  • Use carbon monoxide detectors with loud audible alarms for all living spaces and sleeping quarters.
  • Install CO detectors in any space containing a unit that burns carbon-based fuel or carries exhaust conduits.

For more information from the U.S. Coast Guard on carbon monoxide exposures while boating, visit

Gino Bottino, M.D., has had wide experience in medical practice and emergency medical matters. A member of United States Power Squadrons First Aid Support Team (FAST) and the Safety Committee, Gino also has a background in competitive sail racing and is familiar with health-related problems afloat.

United States Power Squadrons, America's Boating Club logo

The Ensign magazine is an official channel of United States Power Squadrons, America’s Boating Club, a volunteer organization whose members teach boating skills and best practices to help improve the safety of our nation’s waterways. Learn more.