Tree work incident report 18MA022: carbon monoxide in a wood chip fuel hopper, Massachusetts

This page reports what the official source says. It is not legal advice: ask the office named here. This page restates one official fatality report in our own words: case 18MA022 from the Massachusetts Department of Public Health FACE program, dated August 13, 2021. It covers a company owner found unresponsive inside the chip hopper that fed a boiler heating his own yard. No one is named here or in the report. OSHA lists the report under "Other" on its tree care page. The table of every report we read is in the official case library for tree work incidents.

The employer and the boiler

The company cleared land, took in trees from other firms and made bark mulch and chips, with 20 employees that included tree cutters, an arborist, machine operators and office staff. It had a written safety and health program covering chain saws, ladders, rigging, mobile equipment, line clearance and noise. The report says the program did not cover confined spaces, hazards at the yard, or job hazard analyses, and no written records of training were kept. The boiler was a solid fuel unit made abroad, which the owner installed himself 18 months earlier despite the manual's call for a professional installer. Its fuel hopper held five cubic yards, stood 7 feet 9 inches tall and was sealed tight against fire. The boiler was built for pellets, briquettes or chips of 10 to 30 mm, and the company fed it chips it made on site. The report says it needed ash cleared twice a day instead of weekly and jams cleared from inside the hopper every two to three days, and that the unit was too small for the space it heated.

What happened

On Sunday, March 25, 2018, the owner drove in just before 9:00 a.m. to check the boiler and told his wife he would be back in an hour. Camera footage showed he arrived and never left. His wife and co-workers searched through the afternoon. A co-worker saw a step ladder at the hopper and found him unconscious on the bottom with a grain shovel. Emergency services were called just before 5:00 p.m. His wife had climbed in by the time paramedics came, and he was pronounced dead at the scene. Responders first thought a heart attack. The autopsy found acute carbon monoxide poisoning with a carboxyhemoglobin level of 88 percent.

The hazard was not recognised until April 8, 2018, when another worker was poisoned after about 10 minutes servicing the unit. His level was 40 percent and he was taken to hospital. The report puts back-calculated concentrations at more than 5,000 parts per million in the hopper on March 25 and 5,900 in the second case, against the OSHA limit of 50 as an 8 hour average and the NIOSH immediately dangerous level of 1,200. The fire department later measured 48 ppm in the room with the boiler off. The unit was taken out of service and the hopper was demolished.

Contributing factors the report lists

Five: no adequate ventilation for the boiler, no carbon monoxide monitoring where fuel burning equipment ran, an unidentified confined space, unclear and poorly visible warning labels with little training on carbon monoxide, and no comprehensive safety and health program covering confined space entry and lockout. The report adds that the shed lacked the compensation air opening the install specifications called for, and that wood chips stored in a closed hopper give off carbon monoxide and carbon dioxide on their own. It counts at least nine carbon monoxide deaths after entry into wood pellet stores from 2002 to 2016 in the scientific literature.

What the report recommends

Five recommendations. Employers follow the maker's guidance on installing and maintaining wood boilers and exhausts, and survey for places carbon monoxide can collect. Employers identify confined spaces and write, train on and enforce entry procedures. The report explains that the hopper met OSHA's permit-required definition in 29 CFR 1910.146 because it held a material that can engulf, had a ladder entry and could hold a hazardous atmosphere, and it lists the program parts OSHA requires, including an attendant outside the space and rescue arrangements. Training and labels cover carbon monoxide. A full safety and health program rests on hazard analysis of each task. Equipment makers apply Prevention through Design, for example built-in ventilation or a detector. For chip piles and mulch as a product see the guide to wood chips and mulch, and for other health hazards in the trade the guide to health hazards.

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