Can space-suit science keep New York’s subways dry?

In October 2012, I moved to the US from Newcastle, England, to lead Arup’s New York civil engineering team. Two weeks later, Hurricane Sandy hit. My building flooded, and I was evacuated into a shelter — an all-too-personal reminder of the importance of resilient urban infrastructure.

Over the past few years, I’ve been fortunate to be involved in a project that’s a major step in the right direction to help to protect large cities from future flooding.

Transit troubles

Sandy devastated New York’s transportation system, shutting down subway and bus service for days and causing billions of dollars in damage.

Soon after the storm subsided, New York City Transit (NYCT) set up meetings with infrastructure consultants to determine how to prevent similar problems during future storms.

subway station new york

Sandbag flood barriers at Bowling Green subway station before the onset of Hurricane Sandy

Arup was tasked with various pieces of this work. One involved preventing floodwater from entering subway stations through common portals like passenger entrances and ventilation grates.

Sidewalk ventilation grate

Sidewalk ventilation grate

Stairs, logs, and doors

After studying a given problem, engineers look for existing resources or tools that they can apply or adapt to solve it. In this case, our team quickly realized that off-the-shelf tools simply wouldn’t work.

This was particularly true for subway entrances, which typically consist of surface-level stairways — big holes in the ground, effectively.

Canal St. Subway station entrance

A traditional flood management approach would be to place flood logs or marine doors at the bottom of the stairwell entrances. However, these solutions create additional problems before, during, and after floods. For instance, flood-log systems consist of many components, and lost or misplaced pieces can complicate storm preparation.

Another common challenge: during flood surges, the weight of water building up in the stairwell exerts a significant amount of pressure on the station’s structure. These pressures create forces greater than the structure was originally designed for and can necessitate costly reinforcement.

Water and debris also remain in the stairwell after the storm subsides, requiring extensive pumping and cleanup.

From outer space to Canal Street

When Sandy hit, NYCT was aware that ILC Dover, an innovative Delaware-based company that makes NASA space suits, was working on an inflatable tunnel plug. NYCT introduced Arup to ILC’s material scientists to see whether a similar technology could be used to floodproof subway entrances.

Just six months later, I stood at Manhattan’s Canal Street Station as NYCT officials pumped water over a prototype of a product called Flex-Gate. The test: could it withstand a level of flooding associated with a Category 2 hurricane plus an additional 3 feet of water?

Canal Street Flex-Gate test

Canal Street Flex-Gate test

A simple, straightforward system comprising just three parts — a box that stores a spool of thin material, a pair of guide rails to stretch the fabric across the opening, and a clamping mechanism securing the assembly to the top of the stairwell — Flex-Gate is designed to be permanently installed at the top of the entrance.

Flex-Gate rendering

Flex-Gate rendering

The system has none of the drawbacks associated with marine doors and flood logs. It does not necessitate any structural reinforcement. Water and debris never enter the staircase, eliminating the need for post-storm cleanup. Deployment can be completed in less than 10 minutes. There are no removable parts to misplace.

Testing conducted at the ILC facility in Dover, Delaware

A subway success story

Having exceeded expectations during the Canal Street test and others, Flex-Gate is now being installed at vulnerable stairwells throughout New York’s subway system.

Flex-Gate deployment

Flex-Gate deployment

ILC has further developed the product for use in a vertical plane, turning it into a Flex-Wall.

Flex-Wall measuring 12 feet tall by 16 feet wide being tested against 10 feet of water at ILC Dover

Together, the two systems offer an excellent example of how technology can help protect society from the elements.


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