Pellet industry addresses carbon monoxide issue in storage spaces

By Sue Retka Schill | July 24, 2013

The U.S. pellet industry is learning from its European counterparts as well as conducting research here in response to the deaths of two individuals in Europe from carbon monoxide poisoning associated with offgassing of stored pellets. The Biomass Thermal Energy Council held the third in a series of webinars July 23 to bring its members and the public up to date on the initiative begun to address the issue. The informational webinar was funded in part by the New York State Energy Research and Development Authority.

Joseph Seymour, executive director, said although a pellet storage survey had a limited response, it did reveal some trends that will be helpful in understanding the pellet storage systems in use. “The first thing we found was the types of wood pellets sold are 39 percent softwood, 22 percent described their fuels as hardwood and 44 percent said they sell a blend of soft and hardwood.”  The most common size of pellet storage was a 3-ton bulk container reported by 46 percent of the respondents with indoor storage comprising three-fourths of the facilities in use.  

Ray Albrecht, technical consultant, described the work being done in Europe where new standards are being introduced on the delivery and storage of bulk pellets. “We’re looking to the Austrians to help with U.S. standards,” he explained.  Bioenergy 2020, an Austrian nongovernmental agency, has issued three reports looking at carbon monoxide formation and mitigation. In monitoring fresh pellets, the organization found most samples show acceptable peak CO offgassing rates of less than 1 milligrams per kilogram. “But they’ve seen a regular number of outlying data points at a 3 mg rate,” explained. The standards are being written to mitigate the hazards posed by those higher levels.

The Europeans recommend a maximum CO concentration of 30 parts per million (ppm) which can be achieved with a ventilation airflow of 4 cubic feet per minute (cfm). The Austrian work found that a 1 mile per hour cross ventilation airflow through a 4-inch opening provides 30 ppm CO level in a 5-ton storage system filled with pellets offgassing at the worst-case scenario of  3 mg/kg CO per 24 hours. “It’s not a whole lot, but it’s commercially important,” he said. A number of U.S. organizations are recommending 9 cfm which requires a 7 inch diameter opening, he added, and wind speeds in the Northeast are 1 mph or higher 90 percent of the time. Bioenery 2020 has also examined the effectiveness of ventilated caps, finding that when the temperature differential is sufficient, there can be adequate air exchange, and that relatively small passive openings help when there is no temperature difference.

Albrecht is working on summary of the newly introduced European standards on pellet delivery and storage as well the Bioenergy 2020 studies. He added that an international pellet safety project is planning its second workshop for next May or June to continue work on developing international standards.

Philip Hopke, direct of the Center for Air Resources Engineering and Science at Clarkson University, described the new research project to examine carbon monoxide offgassing. “We were contacted by NYSERDA as they became aware of [the CO poisoning] issue in Europe,” he explained. The research include a series of laboratory studies following up on the work done in Europe in the University of British Columbia to determine the kinetics of offgassing of carbon dioxide and other volatile organic compounds. “The experiments are trying to determine what’s generating the carbon monoxide,” he said. “Once we understand the mechanism better, we’ll have a better opportunity to provide recommendations to the pellet industry.”

The research also involves the monitoring of several types of pellet storage facilities both on campus, and in nearby schools and residences. In the residential storage, there was an initial rise of CO levels to 70 ppm in the basement storage area that quickly fell to below 5 ppm for weeks until rising again to a level under the maximum set by the Occupational Safety and Health Administration but above the lower levels recommended in other standards. “We’re not sure why,” he said. In contrast, a middle school storage space with active ventilation has shown consistently low levels. A third, sealed system, showed several values above the OSHA limit, but being closed and outdoors it would not present a hazard. “It would need to be ventilated well, however, if anybody needed to enter into the confined space,” he said.

Tim Cullina, senior consulting engineer with Fauske & Associates LLC, closed out the webinar by reviewing the OSHA standards that would apply to the carbon monoxide exposure issue for employers. “Identify where your confined spaced are and comply with OSHA standards. For nonconfined spaces, treat all storage spaces as hazardous until proven otherwise,” he recommended.