CHARLOTTE, N.C. — Three firefighters were injured Monday night as they helped search a home in northwest Charlotte for explosives during their investigation of a pen that blew up in a classroom and injured a student.

The exploding pen sent a 15-year-old Turning Point Academy student to the hospital and forced authorities to evacuate the school.

A 16-year-old Turning Point student was arrested at the scene and his 15-year-old brother was arrested hours later when authorities searched the teens’ house.

Officials said the three firefighters suffered minor injuries during an explosion at the house.

The first explosion happened in a classroom at the school. LaTarzja Henry, a spokeswoman for Charlotte-Mecklenburg Schools, said a student reached into his desk to get a pen. “When he took the top off the ink pen, it exploded,” Henry said.

The force of the explosion sent fragments of the pen into the boy’s arm and chest and burned his hand.

The student was taken to Presbyterian Hospital-Huntersville with injuries that are described as “not life-threatening.”

Local and federal authorities swarmed the house of the teen suspected of rigging the pen to explode.

Three of the Charlotte Fire Department firefighters who accompanied police to the house were performing a field test on a substance found at the scene.

The firefighters were taken to area hospitals for treatment of non-life threatening injuries.

A dozen nearby families were evacuated while bomb squads meticulously combed the single-family home for further explosive devices.

Late Monday, they had found one device and performed a “render-safe procedure,” which usually refers to a controlled detonation.

Earlier, bomb-sniffing dogs were sent through the school at least three times, without finding any other explosives. Students initially were taken to a nearby gymnasium, then were sent home for the day.

One possibility being investigated was that the student was a victim of a prank that has become a viral video on YouTube. A small amount of explosive material is inserted in a pen, and it explodes when someone pulls the cap off.

Police didn’t release any of the teen’s names on Monday.