New CO Study Shows that Home Generators Can Emit Dangerously High CO Levels

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A new study simulating carbon monoxide levels in detached and manufactured homes commissioned by the U.S. Consumer Product Safety Commission shows that that operating a generator for 18 hours is likely to result in high CO exposures whether the generator is in the house or the garage; and that generators that have been modified to limit CO emissions using a shut-off mechanism or other technology can significantly reduce exposure compared to generators without emissions controls.

Last September, our blog Home Use Generators: Dangerous and Behind the Curve documented the rising incidence rate of CO poisonings linked to the use of home generators as extreme weather events and an aging power grid result in more and more prolonged outages. The agency’s response has been to closely track the data and promulgate a stronger warnings rule. Heightened hazard language has done little to dissuade homeowners from putting portable generators in locations that can create significant health risks for home occupants.

The simulation study authors noted that CPSC has recorded 755 deaths from CO poisoning associated with home generators, from 1999 through 2011, with nearly three-quarters of those occurring between 2005 and 2011, and many of which occurred during power outages.

The CPSC has been working on a technology-based solution. A previously published report on a low-CO emitting generator technology demonstration project showed that an engine with a substantially reduced CO emission rate could reduce the risk of fatal and severe CO poisoning in an indoor location, by reducing CO emissions enough to delay the onset of poisoning symptoms and slow their worsening, giving occupants time to recognize the danger and exit the building.  

The results of this simulation study, Residential Carbon Monoxide Exposure due to Indoor Generator Operation: Effects of Source Location and Emission Rate, are likely to be used as foundational research in any CPSC rulemaking regarding home generator safety. Conducted by the U.S. Department of Commerce and the National Institute of Standards and Technology, it evaluated indoor CO exposures by generator source location and CO emission rate to “support life-safety based analyses of potential CO emission limits for generators.”

The computer simulations used CONTAM, a multizone airflow and contaminant transport model, applied to 87 single-family, detached dwellings for a total of nearly one-hundred thousand individual 24-hour simulations in different house layouts and sizes, airtightness levels, weather conditions, generator locations and CO source strengths. The locations include attached garages and basements, and a first floor interior room in all of the houses. (Researchers didn’t use attached and apartment models because it was too difficult to account for airflow between units and the lack of air leakage data for the partitions between units. The 87 homes represented about 60 percent of U.S. dwellings.) These simulations presented the results in terms of the maximum levels of percent carboxyhemoglobin (COHb) that occupants would experience as a function of CO emission rate for different indoor source locations  

The researchers noted that their task was complex: house layout, source location, outdoor temperature and wind speed and direction can all have significant impacts on airflow and CO transport, so considering only one or a small number of buildings under limited conditions would not be enough to fully understand the levels of CO exposure in residences as a function of generator location and CO emission rate.

This study adds new weight to the CPSC’s goal of supporting a standard to reduce CO exposure from home generators. While a mandatory standard appears to be far off, the CPSC staff, as a non-voting member of Underwriters Laboratory’s Standards Technical Panel (STP) for UL 2201 Portable Engine-Generator Assemblies, (issued in March 2009), has recommended that requirements be developed to address consumer exposure to unsafe CO emissions and for safe outdoor use of generators in wet conditions to reduce the risk of shock or electrocution and to help reduce the numbers of consumers improperly using generators indoors.