Boating carbon monoxide poisoning

Boating carbon monoxide poisoning is a big problem because high performance engine exhaust is not vented away from where people breathe.

This week we will focus on a topic which has achieved the status of a fast-rising epidemic in regard to carbon monoxide; boating carbon monoxide poisoning. For many years the concern has been raised over this particular hazard in houseboats. However, now we are beginning to realize that these concerns reach farther, encompassing ski boats, cabin cruisers and even personal watercraft. We have discussed previously that the danger of carbon monoxide poisoning goes hand in hand with any fuel burning engine or equipment, but it is now becoming apparent that these dangers can exist in areas that we might not consider due to the false sense of security we feel in the open air.

boating comes with great risk of carbon monoxide poisoning

Boating carbon monoxide poisoning is far more common than expected because high performance engines don’t have same efficiency and exhaust protections that cars do. Boat engines are high performance without the efficiency and emission controls of modern cars. 

When you hear Boating carbon monoxide poisoning, you probably assume that the danger would be restricted to being in a closed cabin or area aboard a boat. But let’s examine some of the lesser known dangers which have impacted the public because they were unaware of the dynamics involved. Both the US Coast Guard and the National Institute of Occupational Safety and Health have been investigating the dangers of CO poisoning and it is truly shocking how many fatalities and injuries have occurred in a very short period of time. The findings have dispelled beliefs the CO poisonings only occur indoors.

We have to first understand that typically, boats with gasoline engines vent near the rear of the boat or the stern,  logically keeping the cabin areas or living areas free from any fumes. Safely vented from the stern area, we feel secure that those fumes are dispersed and pose no danger to boaters.

I want to pause for one moment to stress that carbon monoxide poisoning can occur inside the cabin or living areas as well due to several factors. First and foremost, lack of maintenance of the exhaust system can contribute to the presence of carbon monoxide. All boaters are encouraged to do proper maintenance prior to taking their boats out for the first trip of the season. Another risk is purely physics when certain air pressure and air flow conditions arise to create backdrafts which may draw toxic fumes from the stern back into the cabin area. This largely depends on the motion of the boat, existing wind conditions and certain structural aspects which may create a vacuum effect. For that reason, all boats should be equipped with adequate CO detectors placed properly. As CO is lighter than air, positioning the detectors in higher locations would be recommended. Please note that carbon monoxide poisonings have occurred when detectors have been disconnected to stop the alarm from sounding in a percentage of in-cabin poisonings.

Other causes of in-cabin poisoning are an actual blockage of exhaust vents resulting in fumes entering even when the cabin is secured. Moving at a slow speed can cause an accumulation in the cabin, especially in conjunction with tailwinds – back drafting because the boat is too heavily loaded and the bow is riding too high can result in high levels of CO.  And simply mooring next to another vessel that is running can result in dangerous levels of CO. It is important to observe the 20-foot rule when mooring next to another boat which is running a gasoline powered engine.

But let’s talk about a phenomena which has claimed the lives of many boaters and which may come as a surprise to many of you: The dangers associated with rear swim decks and how they can become deadly traps. I want to start this off with stressing that teak surfing, dragging or waterskiing within 20 feet of a moving boat can be fatal. Teak surfing or dragging is when the occupants hang onto the swim platform while the boat is in motion. Since the exhaust exits through the stern of the boat, carbon monoxide can build up to a fatal level in seconds underneath a swim platform. Often swim platforms are lowered to produce bigger wake and the dynamics create an air pocket where CO gas can accumulate and create a lethal bubble around the person in the water.

Swimming near boats with idling engines is very dangerous, but the most dangerous situations are swimming under swim platforms, which is in essence like being trapped in a small room with an operating portable electric generator. 

The possibility of CO poisoning from rear ventilation systems came to light in around 2000 when boating deaths occurred on Lake Powell in the Glen Canyon National Recreation Area were examined. One incident involved two brothers (aged 8 and 11 years) who had been swimming in the airspace underneath the swim platform. One brother lost consciousness and the other had convulsions and they both drowned. Another incident involved three boys who were using a rear mounted slide. One boy became very dizzy and fell into the water and drowned. And one incident involved an 18-year-old teak surfing or hanging onto the boat’s swim platform while the boat was in motion. Several CO poisonings were associated with people doing maintenance or clearing propellers.  This brought the attention of several agencies after initial concerns by the National Park Service and the US Department of the Interior.

The National Institute for Occupational Safety and Health (NIOSH)  and US Coast Guard issued warnings and studies were undertaken to determine what factors were responsible. Their research found that levels of carbon monoxide were so high that death could occur very quickly and even more disturbingly, that because unconsciousness was a factor, that many drowning deaths were most likely related to the presence of CO so the number of fatalities might be much higher than documented. Even sitting on a swim platform while a boat is in motion can be fatal. A thorough examination of the incidents at Lake Powell revealed that between the years 1990-2000, 111 cases of carbon monoxide poisoning could be absolutely verified. Nine of these cases were fatal. 67% of the poisonings occurred on houseboats and 50% of those were outdoor poisonings. It is also difficult to determine how many other incidents occurred because the symptoms of carbon monoxide poisoning can be mistaken for so many other things. And training of EMS and first responders to the possibility of carbon monoxide poisoning in these instances is also an important component.

All types of boats from many manufacturers were examined and it was determined that this is a problem that exists across the board, regardless of design or engine type. And the dangers rose sharply in boats running in a stationary position or at a slow speed. They discovered concentrations so high that they exceeded CO sensors. The main difference in CO levels factored in many of the things I have discussed; the particular environmental conditions, exhaust systems, engine types, wind conditions, and speed. The consensus was that the only solution would be to require boat manufacturers to use cleaner burning engines. Boat manufacturers and lawmakers have been reluctant to work towards stricter standards for the boating industry despite the findings. We would be right to surmise that new technology for cleaner engines is easier on outboard motors so the prospect of retrofitting inboard motors, very common in ski boats, is meeting the most resistance.

Houseboats, on the other hand, can be retrofitted easily and inexpensively with vertical exhaust systems which carry fumes above and away from the boat’s occupants. In 2001, the US Coast Guard recalled the rear venting houseboats produced by six manufacturers to be refitted with side venting systems, but this was not a complete fix of the problem.

Part of the solution to boating carbon monoxide poisoning has to be to clean up the engines. We don’t have actual statistics, but from what we know about gas engines in other applications, if you are working off of 1960’s engine technology, an engine will be will exhaust as 1,000 times the CO as a modern car. Portable generators using lawn mower sized engines, emit nearly 100,000 ppm in the exhaust. The two big components to reducing CO emissions from gasoline engines are the electronic fuel injection (EFI) and catalytic converters. EFI alone can reduce CO emissions by 90%. That should be required on all marine uses, for the reasons stated herein. If EFI isn’t workable, then some other method needs to be utilized to make sure that all the fuel in an engine is burned at the time of ignition. We are hearing that most marine engines are meeting current California EPA requirements. The irony of this whole issue is that the Clean Air Act requirements are there to improve atmospheric levels of air pollution, not reduce CO poisoning. But the net effect of reducing pollutants in engine exhaust is to insure complete combustion of the fuel. Incomplete combustion equals on boats equals boating carbon monoxide poisoning.

For our treatment of carbon monoxide poisoning from portable electric generators, click here.

CO Detectors not enough to stop  Carbon Monoxide poisoning

Boat builders have readily agreed to the installation of CO detectors in boats but this hardly addresses the problem associated with the rear swim platform. The Center for Disease Control (CDC) states that the presence of CO above a swim platform is dangerous but the concentration below a swim platform can be deadly in  matter of seconds.

“(H)ouseboats with a rear swim deck and a water-level swim platform are an imminent danger to persons who enter the air space beneath the deck or spend time near the rear deck. The presence of features … that attract occupancy of that airspace enhances the risk for severe injury and death. To prevent (boat carbon monoxide poisoning) and deaths, boat manufacturers should immediately devise engineering changes to new and existing boats to prevent the collection of CO in airspaces around the stern deck.”

And like CO poisoning in other scenarios this is especially hazardous for children. The only way to ensure a safer boating environment is through public awareness, education and ultimately through regulation of the boating industry. The US Coast Guard has undertaken a program for public awareness but there are still many hurdles to overcome on the regulatory level. Research is also essential in finding ways to create cleaner burning engines and alternate venting solutions as well as changes in the formulation of fuels. Some of these solutions are very much tied into current EPA standards which are threatened at this point in time. Stricter regulations are called for at a time when we are loosening the regulations needed to solve this problem.

So, in the interim, much more public awareness needs to surround the dangers of carbon monoxide poisoning in all arenas. Whether it’s a weekend stay at a hotel, or a day out enjoying the water. Our safety is directly connected to the regulations that are put in place by our lawmakers. Education and awareness is only one part of an equation, and legal actions are very much required to push lawmakers to act. We have known about the dangers associated with swim platforms for well over a decade and it really is time for some accountability.

Engine Exhaust Equals CO

Never forget that when you are around a fuel burning engine, that unless there is adequate engineering to assure complete combustion (like in a modern car) that CO emissions will be almost unimaginably high. Use a concrete saw indoors, and you are at high risk of death. Portable electric generators have been the subject of attempted regulation by the U.S. CPSC for a generation, because of the known risk. Boats contain more powerful engines by many magnitudes than either of these but may never have been forced to clean up by EPA regulations.  If you can smell fumes, you are undoubtedly inhaling CO. Keep that in mind when you are onboard, and remember that even if outside, you can be poisoned by carbon monoxide fumes. But CO can be there in concentrations above 10,000 ppm, before you can smell it.

Rebecca Martin contributed to this blog.


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  1. […] capitalized ownership. Over the past couple of months, we have blogged about two main topics, carbon monoxide poisoning in boating and carbon monoxide poisoning in hotels. This week we want to revisit the hotel topic with some […]

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