NEW ORLEANS – The Superdome has long been billed as virtually hurricane proof, with a roof touted in promotional materials to stand up to 200-mph winds.

Katrina stuck two large leaky holes into that claim, sending rain cascading down on some 10,000 people huddled in the 30-year-old landmark to seek shelter from the storm.

Winds, estimated around 100 mph by the National Hurricane Center, shredded a new roofing system installed five years ago that some critics at the time warned could make the 10-acre dome more vulnerable to both leaks and wind.

While no one was hurt and the dome’s underlying steel structural framework remained intact, the outer covering was “severely damaged,” said Doug Thornton, regional vice president of SMG, the company that manages the famed stadium for the state.

There were at least two holes, each about 15 to 20 feet long and 4 to 5 feet wide, where loose steel decking rattled high in the 19-story dome.

Thornton said he believed winds apparently penetrated an exhaust system, then ripped thick rubber covering the dome’s metal decking. The company that installed the roof and a roofing researcher speculate debris also could have pierced the outer material.

Either way, the rupture would allow the twin forces of wind and pressure to peel the rubber sheeting like a paring knife slices away orange skin.

“My guess is that once it starts to go into a peel mode and the wind gets under it, there is no real way to stop that sucker,” said Dick Fricklas, technical director emeritus at the Roofing Industry Educational Institute.

The Superdome, with its massive dome supported by a network of steel girders arranged in overlapping triangles, was considered an engineering landmark when it opened in 1975. The original roof consisted of a corrugated steel deck, covered with a thick polyurethane foam, not unlike the material sprayed on the space shuttle’s giant fuel tank, and a thinner silicon layer.

While the roof held up for 25 years, Fricklas stressed that the initial “200 mph” wind resistance claim was almost certainly an estimate not verified by engineering studies.

Even early on, the roof suffered problems: a freak hail storm punctured the outer covering and saturated some of the sprayed-on foam, according to a 1982 story in the Engineering News-Record.

There were manmade problems as well, said Fricklas, including bullets.

“Any big target like that, you get everything you can imagine,” he said. “Guys with rifles, you have mechanics up there with tools.”

According to a series of articles by Bruce Eggler of the New Orleans Time-Picayune, there were so many small holes and leaks that the Superdome Commission, which oversees the stadium, ordered it reroofed in 2000, in time for the 2002 Super Bowl.

Originally the plan was to spray on a similar foam roof.

That idea was shelved for newer technology. The new plan: scrape away much of the old foam, spray in a thin layer of new foam to hold 1.5-inch-thick insulation boards. Then thick rubber sheets, 10 feet wide and 100 feet long, would be glued down, material that manufacturer Firestone guaranteed for 120-mph winds, Eggler reported.

That installation was altered a bit when the old roof proved in worse shape than believed. Instead, designers decided to scrape away all the old foam, clean the rust, screw insulation boards to the metal decking and then glue down the rubber strips. That approach also raised concerns about leaks from “millions of screw holes,” Eggler reported.

Steven Wightman, general manager of Horizon Group of New England, an Albany, N.Y.-based construction firm that installed the new Superdome roof, said the screws may actually have helped hold the roof together.

“We think the black rubber membrane has peeled off the insulation and what you’re seeing is the insulation,” he said. “If it weren’t for the (screws), I think you’d have all the insulation blown off, too.”

Even though a natural disaster like a hurricane would likely void any warranty, Wightman said his company planned to dispatch a team Wednesday to New Orleans.

Wightman said while the rubber covering was rated by an insurance industry lab for 120-mph winds, resistance might be considerably less in real world applications on the 280-foot high dome.

“When you take into account everything, how high the building is, what the angle of the roof is, whether anything hits it, that rapidly reduces the wind rating,” he said. “That 120 mph is not absolute.”

Fricklas likened the rubber strips to a piece of duct tape. If you try to pull the tape up in the middle, it’s resists strongly. But peel away at any edge and it comes up much easier. One a rip formed in the rubber, wind and pressure “create forces which are way beyond what the manufacturers design or test for.”

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