South Carolina officials on Wednesday renewed their call for federal help in dealing with the dangers of cellphones behind prison walls, telling Federal Communications Commission officials they need permission to block cell signals altogether to keep both prison employees and the public at large safe.

"Every day and every night, I hold my breath," Gov. Nikki Haley said during a hearing in Columbia with officials from the FCC and cellphone industry, saying she dreads getting a call that a cellphone-orchestrated prison riot has occurred.

At Haley's invitation, FCC Commissioner Ajit Pai spent the day in the state, gathering information in what Pai has said he hopes will be an effort to rejuvenate agency action on cellphones.

Haley and South Carolina prisons officials have long spoken of the dangers of cellphones, which are smuggled by the thousands into the state's institutions. Officials say they're thrown over fences inside hollowed out footballs, whisked in by corrupt employees or sometimes even dropped by drone.

Corrections Director Bryan Stirling and his predecessor, Jon Ozmint, have sought permission to jam cell signals at the state's prisons, but a 1934 law says the FCC can grant permission to jam public airwaves only to federal agencies, not state or local ones.

In 2008, the state got FCC permission for a one-time test of a jamming system at Lieber Correctional Institution, home to the state's death row. Officials flipped a switch on a briefcase-sized device, which emitted a frequency that immediately shut down cellphones around the auditorium, while outside, cell service was uninterrupted.

Five FCC commissioners voted in 2013 on a proposal to kick-start a conversation about what the agency could do to combat the problem, but that effort never advanced.

"The status quo is not acceptable," said Pai, who in October visited a Georgia prison to learn about issues there. "We owe it to all Americans ... to get the job done."

The cellphone industry says jamming can interfere with emergency communications and legitimate cellphone use nearby. They advocate other, potentially more expensive technology they say can be more precise but has seen only limited use.

"When we consider these proposals, we have to also consider the negative consequences of them," said Gerard Keegan of CTIA, a wireless industry trade association, reading an article about people living near a Honduran prison who can't use their own cellphones because of jamming. "We want to work cooperatively."

Central to Wednesday's hearing was testimony of Robert Johnson, who in 2010 was shot six times outside his Sumter home. Johnson, who then oversaw anti-contraband efforts at Lee Correctional Institution, a maximum-security prison, survived, has endured more than a dozen surgeries and is now retired.

Authorities have said Johnson was the first U.S. corrections officer harmed by a hit ordered from an inmate's illegal cellphone. He has become an advocate for pushing authorities to allow prisons to use jamming technology.

"If the South Carolina Department of Corrections had been able to block cellphone signals, my ordeal would not have happened," Johnson said Wednesday. "Why are we allowing inmates to continue to hurt people?"

Earlier Wednesday, Stirling led Pai on a tour of Lee, which officials say is among the state's most dangerous prisons. In recent years, there have been two large insurrections, including one in which an inmate overpowered a guard and used his keys to free others from their cells in a six-hour standoff. Two officers were stabbed during a fight last year.

Walking the facility's halls with Stirling, Pai met wardens and officers who told him of threats they've experienced because of inmates' ability to have unfettered, unmonitored cellphone conversations. One associate warden said he intentionally took different routes home, more than an hour away, after an inmate using a cellphone threatened his family. Another said one of his children had moved out of state because of fear after an inmate used a phone to look up his family details and track him down.

"It's just a constant battle," Stirling told Pai, as they examined a display of hundreds of cellphones and other contraband seized in a single raid. "We are desperate."