LIVERMORE FALLS — Four teenage boys are accused of setting fires at a Hammond Lumber yard and detonating homemade explosives in unrelated incidents over the weekend, the state fire marshal’s office said.

Investigators believe two 15-year-old boys from Rumford started two fires Sunday at the lumber yard at 80 Prospect St. Firefighters extinguished the fires before they caused much damage, according to Joseph Thomas, acting state fire marshal. The two boys were charged with arson.

In Livermore Falls, two other boys, ages 14 and 15, face criminal charges after being accused of detonating six homemade bombs. The remnants of the devices, which consist of volatile chemicals contained in plastic soda bottles, were found by law enforcement over the weekend in roadways and parking lots near Green and Baldwin streets, Thomas said.

No one was injured in the two incidents, which joined a series of other house and mobile home fires since Friday in other communities statewide that investigators have deemed arson, he said.

Thomas on Monday said the four teenagers’ charges are being handled by law enforcement and prosecutors in their respective communities.

Thomas described both incidents as troubling, saying they showed a disregard for the dangers posed to emergency responders and community members alike.

The homemade bombs are known as overpressure devices because they rely on pressure to cause the chemicals to explode, Thomas said. He added that some of those found in Livermore Falls also contained BBs that became shrapnel, making the devices even more dangerous.

Investigators don’t believe the bombs were targeting any specific property or people. The incident remains under investigation by the state fire marshals office and the federal Bureau of Alcohol, Tobacco and Firearms, Thomas said.

The two teenagers are charged with criminal use of explosives, according to a Department of Public Safety release.

In general, when a homemade explosive is designed to produce shrapnel, the person is breaking federal explosive laws, which typically carry more severe penalties than state laws, Thomas said. He would not discuss details of the case because of the ongoing investigation.

Earlier this year, a homemade explosive device was detonated alongside a remote road in Farmington. Thomas believes that incident in January, which has yet to result in an arrest, is unrelated to the one in Rumford.

Thomas did not know details about the lumber yard fires, saying an emergency 911 call reported the fires. The town fire department did not return a call Monday.

According to the public safety department release, three other arsons from this past weekend remain under investigation.

In Detroit, a fire that started late Friday night destroyed a camper trailer being used to store antiques off Troy Road.

In Milo on Saturday, a fire that started in a basement badly damaged a farmhouse on Highland Avenue.

In Boothbay Harbor, a fire that started on Sunday heavily damaged a house under construction on Middle Road.

Investigators with the state fire marshals office believe all three fires were arson, none of which resulted in injuries, Thomas said.

Thomas said investigators do not believe any of the incidents over the weekend are related.

David Robinson — 861-9287

drobinson@centralmaine.com