Story highlights 2 possible suspects are in custody, a Memphis police sergeant says

There was a loud noise after a bomb threat was made, according to police

An assistant principal suffers smoke inhalation and is taken to hospital

It appears to be a prank, a school spokeswoman says

A pair of makeshift bombs blew up Thursday inside a Memphis, Tennessee, high school, sending one person to a hospital and two into police custody, officials said.

The "pressurized" devices, which incorporated Drano clog remover, were placed in different hallways -- one on the second floor, the other on the third floor -- of Craigmont High School, Memphis Fire Department Lt. Wayne Cook said.

"What it appears is that we had a student or two do a prank," said Staci Franklin, a spokeswoman for Memphis schools, describing each device as a "mailbox bomb."

Police received a call around 11:20 a.m. CT to inform them that someone had called the school warning of a bomb, Memphis police Sgt. Karen Rudolph said.

After the bomb threat, school staff heard a loud noise and saw fumes, Rudolph added.

An assistant principal sought medical treatment after inhaling smoke from one of the bombs while evacuating students, according to Franklin. The injured person was taken to Methodist North Hospital in Memphis, Cook said.

Franklin said the school staff member was believed to be OK. Rudolph said that no other injuries were reported.

By that time, two possible suspects had been tracked down and taken into custody, Rudolph said.

In addition to firefighters, Memphis police and members of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were on site Thursday afternoon, the fire department lieutenant said. Rudolph said members of the police department's bomb unit were inside the school to clear out damage.

Craigmont High School is on 50 acres in northeastern Memphis, a few miles from Interstate 40. The school has about 1,300 enrolled students, Cook said.