Mimi Hall
USA Today 
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All Rights Reserved

WASHINGTON — Homeland Security officials seeking to counter terrorist bombs in subway and highway tunnels are hoping to use inflatable balloons, giant plugs and blast-resistant liners that could protect the nation's transit systems from underground fires and floods.

The new program, dubbed "Resilient Tunnel," aims to address post-9/11 concerns that terrorists will target vulnerable tunnels, trapping and killing countless commuters, flooding cities and causing billions of dollars of damage.

"The mass transit system is a very ripe target," says John Fortune of Homeland Security's Science and Technology division. The vulnerability of the nation's tunnels, many of which are more than 100 years old and narrow to work in, "is not a problem we're going to solve overnight," Fortune said.

Terrorists have set off bombs in transit systems in Europe and India in recent years, and the Homeland Security Department considers mass-transit systems a major vulnerability in the USA.

That's why the government has begun researching technologies that could one day help shore up tunnels in New York City and elsewhere. One goal, according to Homeland Security, is to "prevent flooding of subway tunnels from IED (improvised explosive device) bomber(s)."

The first phase of the government's research, a $1 million project in fiscal year 2007, has scientists looking into "inflatable structure technology" that can limit the damage from floods and fires.

Fortune says a British company, Lindstrand Technologies, has developed a fireproof inflatable device that can be built into tunnel walls at intervals of about 1,000 feet or so and used to limit fires.

The company's website says the tunnel plugs, which cut off the flow of oxygen to the fire, can resist temperatures of up to 450 degrees Celsius, or 842 degrees Fahrenheit.

It would work this way: If a fire broke out in a rail car, balloons could inflate on either side of it, trapping the fire and smoke, so it wouldn't spread through the entire tunnel. The balloons have zippers to allow rescuers to pass through.

In New York City, where the Metropolitan Transit Authority is responsible for more than 600 miles of subway track and 14 underwater tunnels, work is underway to harden the tunnels, says the MTA's Lewis Schiliro, a 26-year FBI veteran and expert on terrorist bombings. Tunnel security isn't easy, he said. "We don't have one magic bullet."