Hazards of Carbon Monoxide on Fishing Vessels

Carbon monoxide (CO) is a silent killer that can attack when you are awake or asleep. Its victims do not realize they are being slowly poisoned just by breathing. They cannot see or smell this gas so they don't realize they are in danger. The only symptoms they may recognize are dizziness, drowsiness, headache, or nausea. Eventually they can become unconscious and die.

CO is a hazard in any enclosed space on a boat where the gas can build up and asphyxiate crew. Most fatalities have been crew who were sleeping on board.

What is carbon monoxide?

CO is a colourless, odourless, tasteless gas that is produced during the combustion of fuels such as gasoline, diesel, and propane. Because CO is about the same density as air, it doesn't rise or fall in an enclosed space, but spreads evenly throughout it.

If CO is in the air, it enters the lungs when someone breathes. CO combines with hemoglobin in the red blood cells, taking the place of oxygen. Even though oxygen is still available in the air, hemoglobin is about 200 times more likely to combine with CO than with oxygen. As a result, CO prevents oxygen from getting into the blood and being carried throughout the body.

Symptoms of carbon monoxide poisoning

CO poisoning can make you seriously ill, cause heart and brain damage, or kill you. Because CO is colourless, odourless, and tasteless, you may not even be aware that you are breathing it in. It reduces the oxygen carried in your blood, and the following symptoms begin to appear:

• Headache
• Watery or itchy eyes
• Nausea
• Weakness
• Dizziness

Sometimes these early symptoms are mistaken for sea sickness, flu, or drunkenness. As the level of CO in your blood increases, further symptoms can appear:

• Fatigue
• Dulled senses
• Incoherent thinking and speaking
• Convulsions

If you are rescued, you could still suffer mild to severe heart and brain damage. If no action is taken, CO poisoning can result in death. This can come quickly if you are exposed to high levels of CO. However, even low levels can lead to death if you are exposed for several hours.

Exposure limits for carbon monoxide

WorkSafeBC sets the following exposure limits for CO:

• 25 parts per million as an 8-hour exposure limit
• 100 parts per million as a short-term exposure limit

Detection

If a CO monitor is installed, the monitor will sound the alarm if the gas is building up to a dangerous concentration. This advance warning allows the crew to ventilate the space and stop the build-up of gas. Most marine grade CO monitors use "time weighted averaging" to determine CO levels within the vessel's crew spaces. Averaging allows the monitor to assess the CO levels over various time periods and at various levels to reduce the number of nuisance alarms.

Causes of carbon monoxide build-up

CO can build up in any poorly ventilated space where the gases produced by combustion can collect. This involves areas with engines, heaters, and stoves if they do not have adequate ventilation. In addition, CO may seep into nearby areas - for example, into the sleeping quarters from a poorly sealed engine compartment.

Possible sources of CO include:

• The engine of your boat: At low rpms, exhaust gases are not pushed very far out of the exhaust. If the vessel is not moving, the gas can enter the crew spaces and begin to build up. Leaks in the exhaust system may also allow CO to enter crew spaces. Be aware that CO can be building up even if you don't smell exhaust fumes. Gasoline engines, during normal operation, produce significantly more CO than diesel engines. Diesel engines are still a source of CO, but operators of vessels with gasoline engines are potentially at risk of higher exposures in a shorter period of time.
• Oil-lubricated compressors: Under some conditions, such as overheating, oil-lubricated compressors can produce CO.
• Fuel-burning devices such as heaters, stoves, and lanterns: In an enclosed, poorly ventilated space, the flames from these devices can reduce the oxygen supply. This causes incomplete combustion, which produces CO.

Even properly vented exhaust can result in the buildup of CO within a boat. Mooring too close to another boat, a seawall, or a dock can result in the exhaust entering your boat, as shown in the illustrations below.

Exhaust can also enter your boat and cause a buildup of CO as a result of back drafting. This can occur because of a combination of boat speed and wind direction. As the boat moves forward, areas of lower air pressure are created behind the wheelhouse. If there is no forward ventilation in the wheelhouse, low pressure will develop there as well. This draws in exhaust gases, including CO, which can build up in the wheelhouse and crew spaces. The illustration shows how this happens.

Improperly sealed engine compartments and poor maintenance can allow CO to build up. For example, a diver died on board a vessel when CO and other engine gases leaked into the cabin area where he was sleeping. The gases seeped in through an access panel and through holes in the cowling that the exhaust flowed through.

How to assist someone with carbon monoxide poisoning

If you suspect that someone is suffering from CO poisoning, take action immediately. Quick action can mean the difference between life and death. Move the person to fresh air.

1. Give the person oxygen, if available.
2. Call for medical help.
3. If the person is not breathing, perform artificial respiration or CPR until medical help arrives.
4. Ventilate the area thoroughly.
5. Determine the source of the CO and eliminate it.

Be very careful when you enter a space that may contain a high level of CO to rescue someone. Remember that you can be overcome too. Before searching for the source of contamination, ventilate the area well.

Prevention

Protect everyone on the boat from CO poisoning by following these safe work practices:

• Install a marine grade CO detector. Follow the manufacturer's instructions for installation, use, and maintenance.
• Configure, inspect, and maintain the engine exhaust system, and seal engine compartments to ensure that exhaust gases cannot enter crew spaces.
• Maintain the engine. A well-maintained and tuned engine will produce less CO.
• Don't use flame-producing devices in poorly ventilated or unventilated areas. These devices include propane and diesel stoves and heaters, gasoline or oil lanterns, alcohol heaters and stoves, catalytic heaters, and charcoal stoves.
• Equip oil-lubricated compressors with a high-temperature auto shut-off and CO alarm to warn of possible contamination.
• Ensure that all crewmembers know the hazard of CO buildup and can recognize the signs and symptoms of CO poisoning.
• Ensure that all crew spaces have an adequate supply of fresh air.
• Check on the well-being of the crew at regular intervals. Watch for symptoms such as headaches, dizziness, nausea, or mental confusion or dullness.
• Take action immediately if you suspect CO poisoning.

Marine grade carbon monoxide detectors

Make sure that you buy a CO detector designed for use on boats. Do not install CO detectors sold for use in homes. These are calibrated too low for boats and will result in false alarms.