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Carbon Monoxide Inspection Guide
Your Inspection Guide
Carbon Monoxide - The Silent Killer Aboard Your BoatIs your boat emitting
toxic levels of CO?

Does Your boat trap
hazardous CO levels?

Follow this step-by-step guide as you perform a safety inspection of your boat's propulsion system and its aerodynamics. By identifying potential trouble spots in your boat's mechanical systems and cabin configuration, and correcting potential problems before they occur, you can enjoy many hours of safe boating.

Periodic inspections of mechanical systems and total operating systems will maintain your boat's value as well as it's safety.

If you detect potential problems, consider hiring a mechanic or marine surveyor for an evaluation.

Carbon Monoxide Facts
  • Carbon Monoxide is a colorless, odorless, tasteless gas.  It is produced when a carbon-based fuel such as gasoline, wood, coal, or charcoal is burned.
  • Carbon monoxide freely disperses through the air, and will readily travel throughout a boat.
  • The most common source of carbon monoxide is exhaust from gasoline or diesel engines. Cooking ranges, heaters, and charcoal grills also produce carbon monoxide.
  • Carbon monoxide is a cumulative poison. Relatively low concentrations in the atmosphere may accumulate in the victim's blood over a period of time with serious or fatal results. It is absorbed by the lungs and attaches itself to the red blood cells, much like oxygen. However, blood will bond with carbon monoxide 200 times faster than oxygen.
  • Carbon monoxide discharged as engine, generator, or appliance exhaust may re-enter your boat through any opening.

Parts Per Million Concentrations
Here is what the "parts per million" concentrations of carbon monoxide mean to your health:

100 ppm.01%Slight headache in two to three hours
200 ppm.02%Slight headache within two to three hours
400 ppm.04%Frontal headache within one to two hours
800 ppm.08%Dizziness, nausea, and convulsions within 45 minutes. Insensible within 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 ppm1.28%Death in less than three minutes.

Carbon Monoxide: Cause and Treatment
Do you know what carbon monoxide is?
  • It is a chemical formed when one atom of carbon links with one atom of oxygen. When carbon monoxide is absorbed through the lungs, it reacts with blood hemoglobin to form carboxyhemoglobin, which in turn dramatically reduces the ability of your blood to carry oxygen. The end result, if sufficient carbon monoxide is present, is asphyxiation. Blood has 200 times the affinity for carbon monoxide as it does for oxygen.

Do you know what creates carbon monoxide?
  • Carbon monoxide is a colorless, odorless, invisible, and very toxic gas. It is the product of incomplete combustion. If a carbon-based fuel - such as gasoline, wood, coal, of charcoal briquettes - is burned in an atmosphere with insufficient oxygen, the carbon in fuel is not completely oxidized into carbon dioxide and carbon monoxide results.
  • Every year, according to national statistics, hundreds of deaths are recorded from carbon monoxide produced by malfunctioning or improperly vented heating appliances. Many more people suffer chronic illness brought on by less than lethal carbon monoxide levels that go undetected.

Do you know the symptoms of carbon monoxide poisoning?
  • Carbon monoxide poisoning symptoms may be easily overlooked because of their similarity to other health-related problems aboard boats - including sea sickness, colds, flu, overindulgence of alcohol and even the normal stressors of a day spent on the water (fatigue, eye strain, and the effects of sun and motion). One or more of the following symptoms may signify the adverse effects of carbon monoxide accumulations: water and itchy eyes, flushed appearance, throbbing temples, inattentiveness or lack of concentration, inability to think coherently, ringing in the ears, tightness across the chest, headache, drowsiness, nausea, dizziness, fatigue, vomiting, collapse, and convulsions.
  • These are generally but not always the sequence of symptoms. They may change for different people or different conditions.  People who smoke or who are exposed to high concentrations of cigarette smoke, consume alcohol, or have lung disorders or heart problems are particularly susceptible to an increase in the effects of carbon monoxide. 

Do you know how to treat suspected carbon monoxide poisoning?
  • Evacuate, Ventilate, Investigate, Take Corrective Action - Those are the basic steps. Move the affected person to fresh air. Administer oxygen if available. Contact medical help. If the person is not breathing, perform artificial respiration as taught in Cardiopulmonary Resuscitation Training until medical help arrives. Ventilate the area.  Investigate the source of carbon monoxide and make repairs. 

Do you know what factors affect carbon monoxide accumulation?
  • Carbon monoxide accumulation is affected by virtually every component and operation of your boat. Among the principle factors affecting how and where carbon monoxide may accumulate are: Vessel geometry (shape); hatch, window, and door openings; ventilation openings; canvas and dodgers; wind direction; and the mechanical condition of your boat.

In Your Engine Room
Do you inspect the exhaust systems of all the propulsion and auxiliary engines aboard your boat?
  • Gasoline engine exhaust is the most common, but far from the only source of carbon monoxide. Follow these four steps when inspecting every exhaust system: (1) Look and listen for leaks in the exhaust system, including a visual check at each joint for discoloration, water leaks, carbon, stains, etc.; (2) Check that all exhaust clamps are free of corrosion, in good repair, and are properly tightened; (3) Make sure all ventilation systems are in good repair and are not obstructed, restricted, or punctured; and (4) Make sure gaps around engine room and exhaust system doors, hatches, and access panels are minimized to reduce the opportunity for carbon monoxide to enter the cabin.

Can you inspect the full run of your exhaust system?
  • In many boats, especially double cabin vessels, the exhaust lines pass through the aft cabin on their way to the transom.  You must be able to inspect every joint and every flexible component for wear, cracking or loosened clamps. If the exhaust lines run behind cabinetry, install inspection ports or removable panels in the cabinetry.

Other Sources Of Carbon Monoxide
Never install a portable electric generator below deck. At the time of this writing, no portable generator meets Coast Guard Electrical and Fuel System Standards. With the fuel tank above the generator directly above electrical components that are not ignition-protected, a potentially serious fire hazard exists. Also, exhaust systems are rarely constructed of marine alloys and may rust through after brief exposure to a marine environment. Do not use any flame-producing device in a non-ventilated area. Alcohol heaters and stoves, propane heaters and stoves, catalytic heaters, oil or gasoline lamps, and charcoal stoves and grills consume oxygen. As oxygen levels in an enclosed space fall, fuel is incompletely burned and carbon monoxide is produced.  A clue this is happening is that a normal blue flame becomes yellow and smoky.

In Your Engine
Are the main propulsion and auxiliary engines aboard your boat operating properly?
  • A properly engine is essential to eliminate carbon monoxide hazards. Carbon monoxide is most often produced in the following areas:
Fuel system: Fuel that is contaminated, stale, or of the wrong octane number for the engine.

Carburetors/injectors: Dirty or clogged flame arrester, malfunctioning automatic choke or faulty adjustment of manual choke plate, worn flat needle valve and seat, high float level, incorrect idle mixture adjustment, and dirty or worn injectors.

Ignition System: Fouled or worn spark plugs, worn points or improperly gapped points, shorted or opened circuit high tension spark plug cables, and incorrect timing.

General Items: Worn piston rings and valves, low engine operating temperatures (cold-running engines increase carbon monoxide production, while engine operating at a higher end of the manufacturer's temperature range produce less), exhaust back-pressure caused by modifications to the exhaust system, and restricted engine compartment ventilation.

Carbon Monoxide Detectors
There are three major types of carbon monoxide detectors:
Single point detectors sound an alarm whenever the detector senses that a single pre-set level (usually in parts per million) of carbon monoxide is present.
Multi-point detectors sound an alarm at a number of pre-selected carbon monoxide levels, and may include several different measuring time periods with correspondingly different parts per million level alarm settings.
Fully-integrated detectors will sound an alarm to any combination of carbon monoxide concentrations and exposure time that is hazardous to health.
Most alarm system combine both light and sound.  More sophisticated combine different colored lights with different alarm sounds.  For example, one system responds with an amber warning light and an intermittent horn when unsafe levels of carbon monoxide accumulate, and a red light and continuous horn at dangerous levels of carbon monoxide.
Some simple chemical carbon monoxide detectors respond with a color change of a sensor chemical in the presence of unsafe levels of carbon monoxide. These are not recommended in sleeping compartments.
Boaters are unlikely to detect the presence of unsafe levels of carbon monoxide until there is a dangerous health hazard. The United State Coast Guard recommends that recreational boaters consider installing a carbon monoxide detector in living and sleeping areas.
Carbon monoxide detectors must be recalibrated as prescribed by the manufacturer and no less often than annually. Don't rely on them as your only source of warning.

Operating Your Boat Safely
If all boat engines produce carbon monoxide, can I operate safely?
  • Yes, you can! If you keep a steady flow of fresh air moving through your boat you will eliminate much if not all of the hazard. The danger comes when there are pockets of stagnant air loaded with carbon monoxide that are not flushed from your boat.

Can I stop the "station wagon" effect and make my boat safer?
  • Backdrafting, or the "station wagon" effect occurs as air moves around a boat and forms a low pressure area immediately behind the broad, flat transom. Carbon monoxide from the exhaust system entering this low pressure area is fed back into the cockpit and into cabin. A similar low pressure area may be created behind a windshield or even the boat's cabin or wheelhouse. If you open a foredeck hatch and let the fresh air flow through the boat this could be eliminated. Opening a wind screen or vent in the fore part of the pilot house also will purge the stagnant air in the area of the cabin.

Are there other ways for carbon monoxide to get aboard my moving boat?
  • Unfortunately, yes. If you alter the configuration of your boat, even doing something as minor as adding a canvas dodger around the cockpit, you change the potential airflow and the ability of the boat to purge itself of carbon monoxide. While your guests might think it more comfortable to be out of the wind, a safe skipper realizes that an alternate source of air is a vital safely measure. If you can feel a flow of air coming through the cockpit and cabin from an open forward hatch and/or port in the windscreen, you probably have little to be worried about.

If I shut down the engines on my boat, have I eliminated the risks?
  • Not if you are moored near another craft.  Carbon monoxide from an adjacent boat can invade your boat through hatches, doors, or even drains. While you may believe that opening your boat to a flow of air is enough of a safety practice, reality is that the incoming air may bring a deadly cargo.

Do you minimize the time between engine start-up and getting underway?
  • Carbon monoxide production is greater while combustion chamber surfaces and gas passages are cool. To minimize carbon monoxide production, skippers should ventilate their boats, orient their boats so that they will permit the maximum dissipation of carbon monoxide, and minimize the time spent getting underway.

This guide is based on the experiences of large numbers of boaters as well as accepted safety standards and practices, and is intended to help you identify and prevent problems involving your gasoline fuel system. It does not take the place of a professional marine survey and is not intended to identify any or all the fuel systems that may arise. The Washington State Parks and Recreation Commission makes no warranties, expressed or implied, by any statements contained herein. For more information about safe boating in the State of Washington, contact: Boating Programs, Washington State Parks and Recreation Commission, P.O. Box 42650, 7150 Cleanwater Lane, Olympia, WA 98504-2650, telephone (360) 902-8515, TDD (360) 664-3133.