[related_gallery align=”right”]ANNAPOLIS, Md. (AP) _ Fire investigators are scheduled to hold controlled burns of Christmas trees as part of a continuing investigation into a fire that killed six people in January near Annapolis.

The burns on three trees will be done at a federal Bureau of Alcohol, Tobacco, Firearms and Explosives laboratory in Beltsville on Thursday.

Investigators say the blaze started as an electrical fire that spread to a 15-foot Christmas tree.

Special Agent Dave Cheplak, a spokesman for the ATF, says the burns are being done to gain a better understanding of how much heat a tree of that size can generate. He says the results will end up in a report in a matter of weeks or months.

The Jan. 19 fire killed Don and Sandra Pyle and their four grandchildren.