Unlike the first three times the roof went down, its age and the extent of damage mean it could take months to complete repairs.
Repairing the Metrodome roof, damaged in the December blizzard, has been slow going. At least five panels were damaged in the 30-year-old roof; the number could rise when evaluations are complete. It is possible a new roof will be needed, with a decision expected by the end of the month.
The first time the Metrodome's roof came down after a snowstorm, in November 1981, it took four days to fix it.
The second time it fell, in 1982: three days. The third time, in 1983: 16 hours.
Now? A month, and counting.
It could take until April if only the five ruptured panels need replacing. Or could be until August if it's decided that a new roof is necessary.
The big differences from the early '80s episodes are twofold. Much more of the air-supported roof was torn up in the Dec. 11-12 blizzard than in earlier snowstorms, said Steve Maki, Dome facilities and engineering director. And the once state-of-the-art roof is 30 years older and showing its age.
"We've had much more damage, so we're being more cautious and prudent," said Maki, who has overseen the Dome's operations since the mid-1980s. "And given the age of the roof, we're trying to determine if there is any damage to other panels."
Nearly five weeks after the roof burst open in a dumping of snow and ice captured on video, Maki and other officials with the Metropolitan Sports Facilities Commission are sending six 5-by-5-foot samples taken from various points on the roof's outer membrane to a testing lab in Buffalo, N.Y.
The strength-assessment results will go to consulting engineers, who will recommend a fix by the end of January. That could range from replacing the five panels to installing a new roof, Maki said.
"We don't know if we'll need more [panels] beyond the five,'' he said. "We might."
Four panels were damaged by weather. A fifth was deliberately opened with a shotgun slug to relieve pressure from snow and ice. Birdair Inc., which makes the panels, has enough material for nine panels, Maki said.
Whole new look in the middle
The Dome is already getting one big change: a large swath of the inner liner is being stripped from the central portion of the roof to let heat inside the stadium reach the roof faster and melt snow better, Maki said.
The roof consists of two super-thin woven fiberglass fabrics, the outside one coated with Teflon. The inner liner is designed to absorb noise and improve sound quality in the stadium. To make up for its partial loss, acoustical batting will be hung from roof cables, Maki said.
But the main focus is on the roof's durability. Last year an inspection showed that fabric strength was comparable to original specs. Maki said the inspection by Birdair "raised no red flags."
Now a more intensive, safety-minded inspection is called for, he said. "We have to have a safe building for people to attend. This is the appropriate time to take those steps."
Each fall involved weather
Each of the first three times it fell in, the Dome roof lost only one panel. And there were no questions then about stress on other parts of the roof.
• On the night of Nov. 19, 1981, a small metal piece poked a hole through the fabric as the new roof, inflated barely a month earlier, pitched under the weight of a fresh 10-inch snowfall.
The hole developed into a 30-foot tear in a triangular panel over left-center field.
A new panel was quickly made by Birdair, which provided and installed the roof, and flown in four days later. That same day it was bolted into place and the roof was reinflated. The stadium opened for baseball the following April.
• In the early morning of Dec. 30, 1982, the roof was ripped open by a crane bucket used to remove 16 inches of snow that had fallen a few days before.
Three shovelers narrowly avoided being hurt in a snow avalanche, and the rip developed into a 150-foot gash.
With a Viking game just four days later, Birdair called in workers on overtime to fabricate a new rectangular panel, which was flown in less than 48 hours after the accident. The Dome was reinflated in time for the Monday night game.
• The roof came down late on the night of April 14, 1983, after one of the Twin Cities' biggest spring snowstorms. The storm had already resulted in cancellation of a Twins baseball game because their opponents were grounded by the storm. As workers cleared off snow and ice, a bolt on a ring beam punctured the fabric. The resulting 38-foot tear would have been worse had not a quick-thinking superintendent intentionally deflated the dome to limit the damage.
Snow removal strategy
With the Twins scheduled to play the next night, Dome workers patched the hole with spare material and reinflated the roof just in time. Two weeks later, a permanent replacement panel was installed.
Since then Maki and others devised a snow removal strategy that shoots hot air between the roof layers and turns up the interior stadium thermostat to melt the snow. If that doesn't do the job, workers go out on the roof with hoses to wash it off with hot water.
The Dome remained aloft for 27 years until the Dec. 11 storm. That day, after six hours on the roof, Maki concluded that the combination of snow, high winds and plunging temperatures endangered his crew of six trying to clear snow. He called them off the roof.
Eleven hours later, three roof panels gave way before a bank of watchful Fox news cameras, sending the image around the world.
Kevin Duchschere• 612-673-4455