In response to a request from the Houseboat Industry Association (HIA) and working under an interagency agreement with the United States Coast Guard, National Institute for Occupational Safety and Health (NIOSH) researchers continued to evaluate carbon monoxide (CO) exposures and engineering controls for gasoline-powered generator exhaust on houseboats. The current evaluatIon is part of a series of studies conducted by NIOSH investigators during the past several years to identify and recommend effective engineering controls to prevent CO poisonings on houseboats and other recreational marine vessels. Performance of exhaust stacks on two Sumerset houseboats was evaluated in August 2003 at Lake Cumberland, Kentucky. In the Spring of 2003, the HIA sent a letter to NIOSH and the Coast Guard Office of Boating Safety requesting further testing of houseboats having generator exhaust stacks. HIA indicated that their members would provide the necessary houseboats and testing sites. The request was made because HIA members were concerned that previous NIOSH evaluations of houseboat generator exhaust stacks failed to include all of the appropriate environmental and operational conditions. Therefore, the HIA requested that additional testing be performed under the following conditions: 1) after dark, 2) in high temperaturelhigh humidity environments, and 3) during temperatnre inversions. Following further discussion, the HIA also requested additional exhaust stack testing under various generator loading conditions and at different houseboat trim angles. For comparison purposes, side exhaust was also evaluated on the houseboats provided by HIA. During subsequent discussions between the HIA and NIOSH researchers, it was decided that NIOSH would conduct two field evaluations in August 2003. One evaluation at Lake Cumberland, Kentucky described in the current report, and another evaluation at Table Rock Lake, Missouri described separately. For the evaluations at Lake Cumberland, Sumerset Houseboats provided two model 2003 privately owned houseboats. Exhaust stacks have been installed on the majority of Sumerset houseboats manufactured during the past several years. In addition, Fun Country Marine Industries is the other houseboat manufacturer that has installed a large number of exhaust stacks on houseboats. The evaluated Sumerset exhaust stacks were constructed from aluminum pipes and had two different designs. One stack was straight having a 1.75 inch inside diameter and extended approximately 8'3" above the houseboat's upper deck. The second stack (referred to as the flagpole design) initially had a 1.75 inch inside diameter with numerous elbows and extended approximately 7 feet above the upper deck off of the stem of the boat at approximately a 75 degree angle. Initial testing was performed on the flagpole exhaust stack, and it was found to be improperly installed causing exhaust gases to be forced out of the water outlet on the starboard side of the boat. Therefore, a temporary retrofit consisting of larger diameter, black high temperature hose was used for the evaluation. Prior to this field evaluation, most of the generator exhaust stacks evaluated by NIOSH had a larger inside diameter, fewer elbows, and typically extended 9 feet above the upper deck. Results of this study were consistent with those of previous NIOSH exhaust stack evaluations. Both exhaust stacks performed dramatically better than side exhaust (even on the upper deck of the houseboat). The highest mean CO concentrations on the upper and lower decks of the houseboat with a straight stack were 27 ppm and 17 ppm. The highest mean CO concentrations on the upper and lower decks of the houseboat having the modified flagpole stack were 5 ppm and 2 ppm. This compares with 67 ppm and 341 ppm for the highest mean CO concentrations on the upper and lower decks for the side exhausted configuration. This survey also showed that high temperature/high humidity environments, temperature inversions, generator loading, and houseboat trim angles had relatively small effects on exhaust stack performance. It also demonstrated the importance of ensuring that all exhaust stacks are properly installed to ensure that performance is consistent with design intent. Based upon the results of NIOSH exhaust stack studies, NIOSH investigators recommend that houseboats using gasoline-powered generators be evaluated for potential CO exposures and poisonings, especially near the lower stem deck. Houseboat manufacturers, rental companies, and owners should consider retrofitting their gasoline-powered generators with engineering controls to reduce the potential hazard of CO poisoning and death to individuals on or near the houseboat. Properly installed exhaust stacks have performed well during all NIOSH evaluations, and they are successfully being used to prevent CO poisonings on hundreds of houseboats across the U.S. Other engineering control options such as cleaner burning engines and after treatment devices are being developed, and these options could also play an important role in preventing future poisonings.
National Institute for Occupational Safety and Health, Division of Applied Research and Technology, Mail Stop R-5, 4676 Columbia Parkway, Cincinnati, OH 45226