Safety Alert
Danger in the Air

Boating and Carbon Monoxide Exposure


Danger is in the air – and you can’t see or smell it.

Many boaters already are aware of the importance of life jackets in avoiding tragedy, as well as how even small amounts of alcohol contribute to accidents on the water. But there’s also an invisible danger that can turn a boat outing deadly.

Gasoline-powered engines on boats, including onboard generators, produce carbon monoxide (CO), a colorless and odorless gas, which can cause an array of health problems —even death.

Of increasing concern are CO-related poisonings and fatalities associated with recreational watercraft. From 2005 to 2018 alone, there were 78 known deaths due to CO poisoning following use of recreational watercraft in the United States. But this number could be even higher, as some deaths may have been inaccurately attributed to drowning instead of CO poisoning.

The University of Cincinnati’s Thomas Gerding and his colleagues wanted to examine the significance of this public health hazard.


Using handheld analyzers, the scientist monitored carbon monoxide levels on and around four boats, including the always popular back passenger seat — the closest seat to a boat’s engine. The team took measurements at engine idle, as well as in motion at engine speeds that mimicked recreational activities. The four study boats — with different engines, hours in operation, and exhaust systems — provided an opportunity to investigate a range of CO exposure scenarios and represented a cross-section of boats in use on many U.S. waterways.

The researchers also noted air temperature, relative humidity, and wind direction and speed to see how these conditions affected CO readings.


The results suggest CO exposures can occur at concentrations that exceed thresholds established by government agencies for boats running and boats at engine idle. As suspected, at engine idle the scientists discovered the highest CO concentrations closest to the engine for all four boats, with concentrations decreasing farther away from the back of the boat.

As a point of reference, the National Institute for Occupational Safety and Health, the agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness, designates occupational exposures to CO concentrations that are at or above 1,200 parts per million (ppm) as immediately dangerous to life or health. Specific levels of the four boats at idle were as follows: 42,600 ppm, 6,100 ppm, 3,700 ppm, and 2,550 ppm.

The differences in these levels reflected different engine types, engine performance, and wind variability.

One boat started and stopped several times, mimicking typical recreational skiing or surfing. The air current during this time was dragged into the back of the boat and increased CO concentrations by upwards of 300 ppm inside the boat.


For all four boats, the study showed that persons using the swim ladder or hanging from the back of the boat or swim platform could be exposed to CO levels that exceed government recommendations. Improper fuel mixtures, engine malfunctions, exhaust system damage, and other factors could create conditions that would be of even greater concern than the results observed in the study.

Overall, the study results validate the potential for poisonings and fatalities that the U.S. Coast Guard has documented.

the full study


Sara Mirabilio is a fisheries extension specialist with North Carolina Sea Grant and co-curator with Sea Grant’s Scott Baker of the award-winning Hook, Line & Science series, which originally published this story:

lead photo credit: NC State University.

from the Spring 2023 issue of Coastwatch magazine