BOSTON -- Four teens have been charged with making and exploding so-called “Drano bombs,” Concord, N.H. police said.

The explosive devices, which are made from household drain cleaner, are extremely dangerous, according to police.

Instructions for making the bombs are readily available in videos on the Internet.

Concord police said they investigated more than four incidents involving the explosion of the bombs. The incidents occurred on Heartwood Lane, Millstream Lane, Modena Drive, Community Drive and Rolfe Street in Concord.

Marshall Talley, 19, Alex Temple, 17, both of Concord, N.H., Ryan Lee, 18, of Boscawen, N.H., and Jorge Barrientos, 19, of Webster, N.H. were charged by police and released on bail.

No one was injured, but damage was estimated at $2,000. Police said a “Drano bomb” is a class A felony.