Carbon Monoxide

In 2004 the US coast guard reported 31 cases of Carbon Monoxide (CO) poisoning resulting in 3 deaths. Now this may no seem like anything to worry about, however many non fatal cases go unreported as they are often misdiagnosed as seasickness or flu.

Yachts and motorboats have relatively small spaces in which cooking, heating or refrigeration appliances all burn fuel. A combination of poor ventilation, poor maintenance or adverse weather conditions can easily produce high concentrations of CO. In addition, poorly maintained engines or exhaust systems can lead to CO poisoning whose early symptoms’ are so to misdiagnosed seasickness.

The Silent killer

Carbon Monoxide is colourless, tasteless, odourless, non-irritating poisonous gas. Often referred to as the silent killer, it removes the victims will to ability to help themselves by starving the body of oxygen. The CO forms a very stable bond with the haemoglobin in the blood system thus preventing it from transporting oxygen. As the poison affects the respiratory system it poses greater risk to infants, the elderly and those with existing ailments such as heart problems or lung disease. The poison is cumulative, so a small concentration of CO over a long period can prove fatal. The early signs of CO poisoning include drowsiness, nausea, dizziness and headaches. It will also interfere with cognitive functions leading to bad decision making, which is not good at sea. Unfortunately for sailors, these symptoms are only to commonly diagnosed as seasickness and so often go un-reported.

Effects of Carbon Monoxide

Formation of Carbon Monoxide

Complete combustion of a hydrocarbon fuel will produce water vapour and Carbon Dioxide, both are harmless. However, air is required to allow complete combustion, a shortage of air or a poor mixing of air and the fuel will result in incomplete combustion and the formation of CO. In extreme conditions, soot may also be formed.

Sources of Carbon Monoxide

Carbon Monoxide can be produced by burning any hydrocarbon fuel. On board, the most obvious source is the exhaust from an engine. Even a small leak will allow CO to contaminate the air in the cabin. Generators and other such systems should not be overlooked. Exhaust gases can also enter the cabin as the superstructure can create a low pressure area and suck in exhaust gases over the transom. Sailboats can also be at risk when motor sailing. When you moor up next to a quayside or in a marina, CO can also drift in from other boats.

Less obvious sources of CO can be just as fatal. Your cooker has the potential to produce CO. Incorrect adjustment or poor maintenance present well known risks, however every time a flame is allowed to impinge against a cold surface such a kettle of cold water, a grill fret or the inside a cold oven, CO will be generated. The use of the cooker as a cabin heater could prove to be very dangerous. The codes of practice changed in 1999 prohibiting the installation of non room sealed gas appliances, cookers excepted, but for older installations there may well be cabin heaters or water heaters that either vent directly into the cabin space or have open flues. All these appliances have the potential to produce CO, open flued water heaters in particular, if there is inadequate ventilation.

For live aboard’s the use of a solid fuel cabin heater should be treated with caution as all wood smoke contains carbon monoxide. This can enter the cabin by diffusion. Human nature will make you close outside vents when it is cold and windy, this prove to be fatal as substantial ventilation is required to prevent to build up of CO.

When the alarm sounds

• Don’t panic – the alarms are designed to operate well in advance of a dangerous or life threatening situation.
• Ventilate the effected cabin thoroughly
• If safe to do so, turn off all fuelled appliances and engines
• Move everyone into fresh air on-deck or near an open hatch
• Do not re enter cabin until the alarm stops sounding
• Seek medical help immediately for anyone suffering the effects of CO poisoning – ask for a Carboxyhaemoglobin Test
• Do not use the fuel burning appliance or engine until checked by a competent person.

Carbon Monoxide Detection

CO detectors are not designed to sound as soon as they detect CO. This instant response would create frequent nuisance alarms that would detract from a potentially dangerous situation. The current standards provide a “dose monitor” that only triggers the alarm when the concentration persists for sufficient time to create a real danger. The alarms will have a stepped response, allowing very low levels to persist for a long time whereas high levels will trigger the vitally instantly.

Where to install your Carbon Monoxide Alarm

Unlike LPG, CO is the same weight as air so they should not be fitted at low level. They need to be fitted in a central location, about a couple of metres from potential sources, but close to you and your crew. They should not be fitted;

• In areas of dead air
• Next to hatches or windows
• Directly above a sink or cooker
• Where it is likely to get knocked or damaged

 Carbon Monoxide Detecting Standards

The CO alarms currently available in the UK may be made to one of three standards. They do not all require the alarms to sound at the same levels. Alarms manufactured for the North American market use the American Standard - UL2034 . For the UK market there are two standards, BS7860:1996 and EN50291:2001. The BS7860:1996 is due to be made obsolete and after April 2006 all new CO alarms should be manufactured using EN50291:2001. The kite mark means the product has been independently tested and proves that it meets the standard. The CE mark usual means the alarm has been test for electrical safety and radio frequency interference. It does not mean it has been tested for performance in detecting CO.

Buy the SF Detection Portable Carbon Monoxide Detector from the Marine Shop

Read the recent Practical Boat Owner group test report on CO Alarms - 800Kb