From inflatable wings to … a subway plug???

Readers may recall my Weekend Wings article about “Inflatable Aircraft“. After summarizing the development of inflatable aircraft over the years, I mentioned that inflatable wings (as opposed to entire aircraft) were becoming a factor in the design of unmanned aerial vehicles, and might even be used for the aerial exploration of other planets. I discussed the work of a company called ILC Dover in that regard.

Given that background, you can imagine that I was intrigued to find the company mentioned in connection with a new project for the Department of Homeland Security. Popular Mechanics reports:

A giant plug for a giant tunnel. That sounds straightforward, but it’s taken more than five years and nearly half a million dollars for researchers to develop a 32-feet-long, 16-feet-wide tube that can inflate to up to 35,000 gallons of volume to close off tunnels and block fire, gas leaks, or flooding water from getting in. We asked John Fortune of the Department of Homeland Security’s (DHS) Science and Technology Directorate (S&T), the project leader, how this thing really works.

Q: What is the Resilient Tunnel Project?

A: The project started in 2007. The idea behind the tunnel plug was to be able to section off regions in a subway system so you can contain flooding and prevent a widespread event. Flooding is the most difficult, but there are also concerns about fires and toxic gas releases, all of which could be addressed by a plug.

. . .

Q: Why did you choose the “inflatable plug” design?

A: The concept of a plug was something less costly and quickly deployable. We could put it in a soft bag container, like a huge parachute, and mount it to the tunnel walls. We also wanted to use what we knew—one of our partners, ILC Dover, had done a lot of work for NASA and had a lot of experience in high tech textile design and manufacturing. The technology we’re using in the tunnel plug is actually tech they’ve used in space habitats and space suits; the Mars Rover landing bags were made from the same fabric as the tunnel plug. So even though the design and the application are novel, working with high strength textiles was something we had a lot of experience in.

Letting the plug fall into place is also a very important part of the design. If you fold this thing up compactly and then deploy it, it probably won’t go into tunnel the right way and there will be gaps. The packaging is very important, so our project team is coming up with different ways to fold it and put zip ties in place (like a fishing rag) so when a certain pressure is reached, the zip ties pop and different portions of the bag will inflate. This makes for a staged inflation and ensures that you fill the entire tunnel.

There’s more at the link, as well as at the Science & Technology Directorate of the Department of Homeland Security, which issued this press release about the project.

I must admit, I hadn’t thought of the possible need to block a large tunnel against the passage of water (e.g. during a flood), or gas (e.g. during a terrorist attack), or anything like that. I don’t know how effective this would be if debris were being swept along by a flood, as fast-moving sharp objects might puncture it: but it’s presumably been designed to resist such damage. It’s certainly a fascinating idea. I hope it never has to be used ‘the hard way’, but as a ‘just-in-case’ tool, it certainly appears to have its place.



  1. It was also designed to seal off subways and tunnels to stop the spread of a WMD attack.

    The late Dr. Bill Dunn was the person who should get credit as he thought of it when he worked on the PROTECT program tha pre-dates DHS.


  2. And given DHS' speed and efficiency, they should be able to get one of these to where it's needed only a few days after it's moot, anyway. 🙁

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