Carbon Monoxide Poisoning and Boats

Carbon monoxide poisoning from houseboats, cabin cruisers and ski boats is a rapidly rising problem, fueled by boat design characteristics and boaters’ ignorance of the hazards. Over the last several years, the U.S. Coast Guard (USCG) and the National Institute for Occupational Safety and Health (NIOSH) have been working together to investigate, find solutions to, and raise awareness of this epidemic.

CO is a potentially deadly gas that is odorless, colorless and tasteless and is found as a byproduct of internal combustion engines.  On boats, this gas is found in the exhaust emitted by the pleasure craft’s electric generator and drive engine. Federal officials have known for some time that carbon monoxide can reach lethal concentrations from generator exhaust that gathers at the stern of houseboats, but only in the last few years have they found evidence that carbon monoxide can gather in deadly concentrations behind ski boats, cabin cruisers and even personal watercraft.  The highest concentrations of CO are often around swim decks, an area where occupants frequently sit while a boat idles or is traveling at low-speed and where the exhaust ports are located.

A report detailing recent investigations at Lake Powell, Utah, from 1990 to 2000 found 111 CO poisonings, 74 on houseboats, 37 occurred on other types of recreational boats.  A NIOSH report, “Boat-Related Carbon Monoxide (CO) Poisonings” cited 93 fatalities and 377 non-fatal CO related poisonings identified on or around boats through March 19, 2003.  NIOSH and Coast Guard believe, however, that the incidence rate is much higher, because many emergency personnel the cause of these fatalities as simply drowning.

On ski boats, a popular activity known as “teak surfing” or “dragging,” in which occupants hold onto the swim deck as the boat pulls them through the water, has claimed the lives at least 11 and injured another 10.  “Teak surfers” hang off the swim platform and when the wake gets large enough, they release their hold and body surf on the wake.  Surfers forego life vests because they interfere with the ability to surf the wake.  Many boaters think teak surfing is safe, because the propellers are located under the middle of the boat, a significant distance from the rear swim deck.

But this pastime exposes “surfers” to dangerous levels of carbon monoxide. Swim decks, which often are weighted to sink them lower in the water and create bigger wakes, are located where deadly exhaust fumes accumulate.  The surfer’s head is inside a “burble,” a spot where the air stream behind the boat breaks up and CO accumulates in a pocket.  Victims can be overcome by carbon monoxide in a matter of minutes and even when monitored by other boat occupants can slip under water and drown. In 2001, prompted by the death of an 18-year old teak surfer on Lake Powell, NIOSH released its first nationwide warning about the activity and began conducting a study of the CO poisoning hazard related to ski boats.

Researchers once thought that CO poisoning was not possible outdoors.  But recent studies of CO concentrations outside houseboats have shown readings that well exceed the 1,200 parts per million (ppm) that is immediately dangerous to life. A NIOSH report found that CO concentrations outside a houseboat in open air at the stern swim platform were as high as 10,000 ppm while transom-exhausted generators were running.  Concentrations up to 30,000 ppm were found in the cavity under the swim platform.

NIOSH’s study included an evaluation of approximately 25 recreational boats from several manufacturers.  The engine types included gasoline-powered, two-stroke, four stroke, outboard, stern-drive, inboard, and generator sets.  The study examined CO concentrations at various locations on each boat while the boat was moving and while it was stationary.  The results showed that most boat drive engines and generators produced hazardous CO concentrations near the stern, and that even sitting on a ski boat swim deck while an engine is running could be fatal.  The concentrations were particularly hazardous for boats operating at low speed or in a stationary mode while boaters were near the emission source.  Factors that influenced exposure included CO generation rate, boat design and shape, boat speed, wind conditions, and distance between exhaust terminus and occupant.  Some concentrations were so high that they exceeded the limits of the CO sensors.  In general, NIOSH researchers found that cleaner burning engines produced less CO exhaust, two-stroke engines were dirtier than four-stroke engines, and airflow ratio was a big concern because restricting the airflow increased the CO output dramatically.  Two engines, one a direct fuel injected 2-stroke outboard, the other a 4-stroke outboard, were noted to have dramatically lower CO concentrations than any of the other boats evaluated.

While the problem of CO poisoning on boats has come into sharper focus, the solutions have been more elusive. The Coast Guard, NIOSH and the boating industry have met to discuss current research, education, and solutions to the CO risks associated with recreational vessels. To date, manufacturers have been slow design this hazard out of their products and regulators have been reluctant to establish new regulations that would force a change.

Boating design solutions include engines that employ clean-burning technologies and meet new EPA regulations for outboard marine engines.  (Ski boats present a greater challenge because they use inboard engines, which, according the manufacturers, will not use the newer clean burn technology for several years and there are no known retrofits available.)

Another way to reduce CO hazards on houseboats is to employ a “dry stack” or vertical exhaust system that routes the exhaust away from occupants. NIOSH has evaluated the “dry stack” exhaust system and found that the stack exhaust system is extremely effective at removing CO from the occupant environment.  The data showed that the vertical stack exhaust was a simple and effective control that performed well during all the evaluations.  No high CO concentrations were measured under any test conditions.  NIOSH have researchers called for a retrofit of these devices and inclusion on new production and stressed the need for a standard and compliance protocols for stack exhaust systems.
The “dry stack,” which can be retrofitted in a couple hours and costs about $500, has been installed on the fleets of several Lake Powell houseboat rental companies. However, houseboat manufacturers oppose including the design on future production and are leaving it to the owners to retrofit houseboats currently in use.

On the regulatory front, the USCG recalled six manufacturers’ houseboats with rear-venting exhausts in February 2001, to reroute the generator exhaust to the side rather than through the transom.  Six other houseboat makers voluntarily recalled their boats to retrofit them with side exhaust.  The agency noted, however, that this is not a complete “fix” for the houseboat problem.

The USCG is also moving forward with an education campaign and warning label requirement to bring attention to the problem of CO poisonings outside of pleasure craft and the hazards of dragging or teak surfing. Regulators are waiting for results from an ongoing study being conducted by Southwest Research Institute (SRI) on catalysts and cleaner burning engines, as well as finalization of new EPA regulations before initiating rulemaking.

Some changes do appear to be underway.  Manufacturers are likely to begin installing the “dry stack” exhaust system.  In a recent edition of Water Ski magazine, boat manufacturer Ski Centurion advertised a side vented exhaust system on its boats that can help reduce CO accumulations around occupants.

Boat builders seeking National Marine Manufacturers Association certification for their boats now have to install carbon monoxide detectors inside the cabin (at a cost of $50 to $100) if the craft has living accommodations below.  These devices don’t function well in outside environments.  The requirement was added to the NMMA’s certification standards in March 2001 to for model year 2002.