CONCORD, N.H. (AP) — New Hampshire’s fire marshal says the fireworks explosion at a Pelham home last summer that seriously injured a 2-year-old boy was accidental.

WBZ NewsRadio 1030′s Bernice Corpuz reports

Fire Marshal J. William Degnan said that 344 reloadable mortar shells on the back deck of the home were set off by an aerial spinner firework.

Degnan says all 13 people — including eight adults and five children — injured were on the deck or in an adjacent, three-season porch.

One of the most seriously injured was 2-year-old Ben Bertini, who was kept in a medically-induced coma for a week at Shriners Hospital in Boston.

Degnan says the investigation by his office, the Pelham police and the Hillsborough County Attorney’s Office is ongoing. He said there were 900 injuries nationwide from mortar shell fireworks in 2011.

Copyright 2013 The Associated Press.