Carbon monoxide poisonings from small, gasoline-powered, internal combustion engines: just what is a "well-ventilated area"?
A modeling study to estimate the time for carbon-monoxide (630080) produced by a small gasoline (8006619) powered internal combustion engine to exceed NIOSH exposure limits was performed. A model was developed to calculate time for a gasoline powered five horsepower four cycle engine to produce carbon-monoxide (CO) concentrations exceeding NIOSH recommended peak concentration (RPC) of 200 parts per million (ppm) and immediately dangerous to life and health (IDLH) concentration of 1,200ppm in rooms of various sizes with various ventilation rates. Modeling was performed by applying a simple material balance to CO levels in the room utilizing an equation that related CO accumulation rate to generation and removal rates. The model was first used with field data collected at a site in Colorado where workers were exposed to CO generated by a five horse power concrete saw during a remodeling project in a 2,332 cubic foot (ft3) bathroom at a municipal zoo to compute the room's ventilation rate and CO generation rate. The ventilation rate was calculated as 836ft3 per minute (ft3/min), or 21.5 air changes per hour (ACH). The CO generation rate was 0.818ft3/min. These values were used to compute the time for CO concentrations to reach the NIOSH RPC and IDLH in room sizes of 1,000, 10,000, and 100,000ft3 and ventilation rates of 1 to 20ACH. In the 1,000ft3 room, RPC was reached in 0.1 minute and the IDLH was reached in less than 1 minute at all airflow rates. In the 10,000ft3 room, IDLH was reached in 7 minutes at an airflow of 1ACH and in 10 minutes at an airflow of 5ACH. Ventilation rates required to keep CO concentrations from reaching the RPC in the 2,332ft3 room where exposure occurred was then calculated. A ventilation rate of nearly 5,000ft3/min, or 120ACH, was required to prevent CO concentrations from exceeding 200ppm RPC. The authors conclude that small gasoline powered engines should not be operated inside buildings or in enclosed spaces. They recommend tool manufacturers improve warnings about CO hazards and develop engineering controls for better user protection.