Nine months ago, a tremendous controversy began with a simple e-mail:

"Gentlemen, The BART Police require the M-Line wireless from the Trans Bay Tube Portal to the Balboa Park Station, to be shut down today between 4 pm & 8," wrote Bay Area Rapid Transit (BART) construction supervisor Dirk Peter on August 11, 2011. (The Transbay Tube runs beneath the Bay, moving people to and from San Francisco; Balboa Park is a residential city neighborhood.) "Steve," the note continued, "please help to notify all carriers."

The message was addressed to Steve Dutto of Forzatelecom, a wireless project management company situated across the Bay in Oakland. BART requested the wireless network shutdown in response to an expected station demonstration that day to protest the killings of Oscar Grant and Charles Hill by BART officers a few days earlier.

Two hours and fifteen minutes after sending the e-mail, BART had its answer. "We have been told that we must shut down the DAS system from the Oakland portal to the Balboa St. Station [in San Francisco] from 4-8 pm," Dutto wrote back, referring to BART's radio system for amplifying mobile signals through tunnels. "We do not believe that any of the carriers need to do anything, the nodes will be turned down from the Civic Center Headend [near San Francisco City Hall] and then turned back up when given the ok from the BART police."

Design specifications for BART's Distributed Amplifier Radiating Cable System (a type of distributed amplifier system, or DAS) indicate that it operates in the 800MHz public safety band. The DAS provides below-ground radio coverage through the rail network's subway stations and tunnel areas, and it's built to be redundant—amplifiers can "feed" the wireless signal into tunnels from both ends. The nodes link to each other via fiber optic cable. In addition to providing cell phone access to passengers, the system also serves BART's Mutual Aid Radio System for police, fire, and medical responders.

"The system shall be provided with a Network Management System that permits remote interrogation and control of the equipment for the purposes of adjustment, diagnostics, and alarms," the specifications note. Also—for shutting it down when people protest.

And so it was done. While protesters occupied a BART station with their placards and chants, BART security shut the network down for four hours. "The BART DAS is now back up and functioning normally," Dutto reported at 8pm.

Critics of the action regarded it as anything but normal. Here was a regional government agency blocking wireless access in response to a public protest. Groups like the American Civil Liberties Union (ACLU) and the Electronic Frontier Foundation (EFF) filed complaints. Oakland and San Francisco residents responded to the move with outrage—filling a downtown BART station with even more demonstrators.

The move was "unacceptable," one activist told us when we covered the protest. "That's the kind of stuff that happens in places like Egypt, where Mubarak did it to put down the protests, and Tunisia, where the dictator did it to put down protests. That should not be happening here in the United States."

In December, the Federal Communications Commission (FCC) announced that it would launch a probe of the BART move. Central to the agency's request for comments on the matter was one simple question: "Under what circumstances, if any, is it appropriate for a public agency to interrupt wireless service?"

Reading through the many responses that the FCC received last week to this question, especially from the telcos and their representatives, it's clear that the big wireless companies are willing to shut down service—but they want the government to offer some direction. "Verizon Wireless understands that there may be some cases where shutting down wireless service to an area is necessary," the company wrote to the FCC on May 1. "In such cases, wireless carriers need a process for ensuring that the decision to shut down the network has been appropriately vetted and that the request comes from a single, reliable source."

Similarly, the wireless industry trade association CTIA wrote that it "has significant concerns about any interruption of wireless service, but recognizes that in certain emergency situations a service interruption may be necessary to prevent or stop a life-threatening emergency."

Bottom line: even if this conversation doesn't lead to an FCC proceeding and formal order, it has the potential to influence wireless interruption policy for years to come. Here's how the conversation has gone so far.

Terrorists use wireless networks

In response to public concerns, BART outlined a new cell phone interruption policies in December 2011. It shall be the policy of BART to implement "a temporary interruption of operation" of its System Cellular Equipment only when:

It determines that there is strong evidence of imminent unlawful activity that threatens the safety of District passengers, employees and other members of the public, the destruction of District property, or the substantial disruption of public transit services;

That the interruption will substantially reduce the likelihood of such unlawful activity; that such interruption is essential to protect the safety of District passengers, employees and other members of the public, to protect District property or to avoid substantial disruption of public transit services;

And that such interruption is narrowly tailored to those areas and time periods necessary to protect against the unlawful activity.

BART defended these new rules in its filing with the FCC. "A temporary interruption of cell phone service, under extreme circumstances where harm and destruction are imminent, is a necessary tool to protect passengers and respond to potential acts of terrorism or other acts of violence," wrote the transit agency.

Wireless devices could be used "to detonate explosives," the statement continued. "Such an explosion in a system like BART, with much of its approximately 100 miles of track located under either metropolitan downtown areas or the San Francisco Bay itself, would be devastating, not just for the passengers, but for the public at large located around the devastation or affected by flooding that could be caused by damage to the Transbay tube."

These arguments draw strong sympathy from other public safety agencies around the country. The American Association of State Highway and Transportation Officials' Special Committee on Wireless Communications Technology (yes, SCOWCoT) also invokes terrorism to support BART's comments.

"Transportation infrastructure is particularly vulnerable," SCOWCoT warns.

Terrorist attacks on mass transit and commuter rail facilities in Moscow, Madrid, London, and Mumbai, and the death, injury and disruption caused, highlight the susceptibility of transport facilities. In each of the Madrid, London, Moscow and Mumbai incidents, wireless telecommunications assisted the terrorists. Information indicates that cell phones were used to coordinate and detonate the 2004 Madrid bombings. The bombs detonated onboard London Underground trains went off within fifty seconds of each other. The Mumbai terrorists located targets using GPS; their wireless devices coordinated their resistance to Indian security services. Each of these circumstances rose to become a national incident, yet local agencies were the first to respond.

And so the filing contends that that "balance" must "resonate" in any wireless communications shutdown policy. The Commission should understand that certain situations could present a "credible threat," says the group, and thus, "Interrupting wireless service, when balanced against the disruption to the public, may be a reasoned alternative to consider."