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Giant plug for sealing off subway tunnels in a hurry

By

March 27, 2012

The giant plug inflates to roughly 32 feet (9.7 m) long and with a diameter of 16 feet (4....

The giant plug inflates to roughly 32 feet (9.7 m) long and with a diameter of 16 feet (4.9 m) to seal off a section of tunnel (Photo: ILC Dover)

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What’s the best way to plug a giant hole? Why with a giant plug, of course. That’s the thinking of the Department of Homeland Security’s (DHS) Science and Technology Directorate (S&T), which has created just such a giant plug to contain flooding or dangerous gases in mass transit tunnels. Measuring roughly 32 feet (9.7 m) long and with a diameter of 16 feet (4.9 m), the giant plug is an enormous inflatable cylinder that can be filled with air or water in minutes to quickly seal off a section of tunnel in the event of an accident, natural disaster or terrorist attack.

Developed through S&T’s Resilient Tunnel Project in partnership with Pacific Northwest National Laboratory, West Virginia University (WVU) and ILC Dover, the plug is tunnel-shaped with rounded capsule-like ends and holds 35,000 gallons (132,489 liters). When deflated, the plug is designed to pack into a small storage space in the tunnel where it can be remotely triggered for immediate inflation by the tunnel’s command center.

The giant plug in tests using a specially-built test tunnel (Photo: E.M.Sosa, WVU)

The plug’s circumference is sufficiently larger than that of the tunnel to ensure a tight seal even when dealing with the various pipes, vents, lights, and subway tracks that line transit tunnels. The material used to make the plug needed to be pliable enough to conform to the irregular shape of a tunnel, while still being strong enough to hold back a full tunnel’s worth of water. An initial full scale prototype with a single-layer design failed during pressurized testing, with the team ultimately settling on a plug with three separate layers.

The outer layer that gives the plug its shape and strength is made up of a thick webbing of a liquid-crystal polymer called Vectran. A second layer of non-webbed Vectran and final layer of polyurethane seal the inflation medium – be it water or air – inside. The plug's designers say relying on commercially available materials for the plug’s construction helped keep development costs down and make them more affordable for mass transit operators.

Dave Cadogan, Director of Engineering at ILC Dover, which is the longtime maker of NASA space suits, said, “"We used the same design and manufacturing techniques we use in space suits and inflatable space habitats. The webbings and underlying layers form a tough barrier that is strong and resilient to damage."

The giant plug being tested at WVU (Photo: ILC Dover)

In January 2012, the giant plug was successfully tested in Morgantown, West Virginia, in a specially-built test tunnel that was configured like a tunnel in a major metropolitan city. The plug was initially inflated with low-pressure air – which could be enough to restrain explosive or dangerous gases in real world applications – before the air was replaced with water to achieve the plug’s design pressure. When the closed end of the test tunnel was then flooded to mimic the pressure of an actual tunnel flood occurring well below sea-level, the seal held.

While there’s no word of when they’ll be packed into actual subway walls, the designers say the simplicity of the giant plug makes it much less expensive and disruptive than retrofitting a transit system with retractable, watertight doors.

Source: US DHS, ILC Dover

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick
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8 Comments

Hacker triggers plug. Train hits plug. Plugs removed. :(

Von Meerman
28th March, 2012 @ 12:37 am PDT

needs to have walkthrough airlock ports and sealed pipe connections to allow cleanout etc. double walled construction with self sealing properties would be desirable

Brad Needham
28th March, 2012 @ 04:38 am PDT

Oddly enough, these plugs would seem to stop people trying to move through the tunnels, too. They would be chalked up to collateral damage by Homeland Security, I suppose.

Gene Jordan
28th March, 2012 @ 02:13 pm PDT

Yay! One more thing for terrorists to target!

Ed
28th March, 2012 @ 04:49 pm PDT

"While there’s no word of when they’ll be packed into actual subway walls, the designers say the simplicity of the giant plug makes it much less expensive and disruptive than retrofitting a transit system with retractable, watertight doors."

An old trick. Justify a ridiculous solution to a possibly never occurring problem by saying that it's cheaper and better than an even more ridiculous approach. I'm surprised that they didn't say that it can be more quickly deployed than stuffing blue whales at either end of the problem area...

Marcus Carr
28th March, 2012 @ 06:40 pm PDT

These plugs could save NYNY a lot of money in the event of a massive storm tide, but they would also have to plug all the air vents.

Slowburn
30th March, 2012 @ 08:42 am PDT

re; Gene Jordan

There are ten people and a bomb (a hand grenade with a timer and anti tamper detonator) in a welded shut vault. It will take you and hour to cut your way in and the timer has two minutes left. How do you limit the casualties?

Slowburn
31st March, 2012 @ 01:00 am PDT

With the benefit of hindsight, all of the naysayers here, including Marcus Carr and his "possibly never occurring problem," have lots of egg on their faces after Hurricane Sandy flooded entire NYC subway tunnels from floors to ceilings only a few months after they ridiculed the idea.

Gadgeteer
14th December, 2013 @ 11:40 am PST
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