The US Department of Homeland Security (DHS) has developed a ten-by-five-metre inflatable structure that could be quickly deployed to isolate sections of transit or rail tunnels in the event of flooding or the release of chemical agents.

The cylindrical "resilient tunnel plug" is made out of a flexible material that can be rapidly inflated and then filled with water to make it sturdier. It was developed by the DHS's Science and Technology Directorate in collaboration with Pacific Northwest National Laboratory, West Virginia University and ILC Dover

When the plug is not in use, it can be packed into a small storage space in the tunnel, a little like an airbag. The system has been designed to avoid situations like the one that took place in Chicago in 1992 when a leak in an unused freight tunnel caused £1.26 billion in damages and took six weeks to clear.


The plug is made out of three separate layers of strong material: a thick webbing made out of a liquid-crystal polymer called Vectran, a second non-webbed layer of Vectran and a third polyurethane layer. The design draws inspiration from manufacturing techniques used by ILC Dover to make space suits and inflatable space habitats

The plug was tested earlier this year in a dummy steel tunnel.

It was then inflated and tested with pressurised liquid and gases to see whether it would keep them isolated. It succeeded in doing so.

The team hopes to test the system further over the course of 2012, with a view to commercialising the product.