The widow of a Utah firefighter who was killed when a supertanker dropped nearly 20,000 gallons of fire retardant near his position fighting a Northern California fire has filed a lawsuit against Cal Fire and the aircraft company for alleged negligence.

State investigators found 42-year-old battalion chief Matthew Burchett, of Draper, died last August when fire retardant was dropped from an aircraft flying barely above the treetops because spotters mistakenly sent it on a route too close to the ground.

The retardant, dropped from a Boeing 747 mistakenly flying only 100 feet overhead, struck with such force it uprooted an 87-foot tree that fell on Burchett. The pilots had failed to recognize that there was a hill in the flight path, according to a report by The Associated Press detailing the findings of the Green Sheet report by the state’s firefighting agency.

Burchett, who was one of one of about 40 Utah firefighters from seven agencies deployed to help a state facing the most intense wildfires in the nation, died later at Ukiah Valley Medical Center.

The Draper resident had years of experience with wildfires, beginning to work seasonally with the Unified Fire Authority’s wildland division in 1995 after he graduated from Judge Memorial High School the year before.

He eventually became a full-time firefighter with Unified Fire and reached the rank of captain. He responded to house fires and medical emergencies like every city firefighter but also continued battling wildfires. He’d traveled to blazes in California twice before, in 2009 and 2016.

The lawsuit, filed Wednesday by Heather Burchett, the firefighter’s widow, and Griffin Burchett, his son, says Burchett was in a “safe zone” when the retardant was dropped.

The defendants failed to properly warn or protect ground forces, including Burchett, from the “unreasonably hazardous conditions,” the lawsuit alleges, and improperly executed the retardant drop, thereby breaching their owed “duties of care.”

The plane and its pilot “had not performed drops in the area and was not familiar with the heavy vegetation and elevation changes along the flight path,” the lawsuit alleges. And the height from which the drop was performed was at “a much lower elevation than the required heights for such retardant drops.”

The plaintiffs are seeking non-economic damages in an amount to be determined at trial, for “the loss of Matthew Burchett’s love, companionship, care, assistance, protection, affection, society, moral support, training, guidance and intimate relations.”

They are also seeking an as-yet undetermined amount in economic damages, including for funeral, burial and litigation expenses as well as a loss of financial support and inheritance.

Cal Fire did not immediately comment on the lawsuit.

The Associated Press contributed to this report.