|
Blasts more successful than first thought
More of Embrey Dam went boom than first glance indicated
By ELIZABETH PEZZULLO
Date published: 2/25/2004
Some 130 feet of Embrey Dam was breached after the second of two blasts went off Monday afternoon.
"Everyone thinks that 100 feet was blown up, but it was actually 130 feet," said 1st Lt. Scott Stroiney, a member of the Army's dive team responsible for rigging the dam.
"It came off better than predicted," said Brian Rheinhart, project manager for the U.S. Army Corps of Engineers in Norfolk.
"Our number one concern was public safety and safety to nearby structures."
Stroiney said further investigation of problems with the initial blast at 12:05 p.m. indicated that a piece of concrete or debris knocked out two underwater timers placed between first charges and the rest of them. As a result, 90 percent of the explosives didn't go off at first.
"It was very flukeish and very rare," Stroiney said. "Because of all the redundancies in place, we don't normally worry about it, because the secondary system will kick in."
The timing devices between the detonators were set at 25 milliseconds. The delay would be imperceptible to the crowd, but would provide a sequential order to the explosion that would ensure safety.
"That reduces the amount of fragments and shock waves you get coming off the dam," Rheinhart said. "It's also the most effective and safest way to breach it."
After the first blast, divers reconnected the detonator to the remaining charges for the megaboom that went off an hour and 14 minutes later at 1:21 p.m. It blew holes in the side of the dam, but left the cap on the 22-foot high concrete behemoth.
Blowing up a dam isn't easy.
City, state and federal officials have been working for the last year on the best way to breach the 94-year-old concrete structure.
The corps and Army dive teams were responsible for all facets of the explosion. The operation even got the green light from the Department of Defense's Explosive Safety Board.
Arranging the charges at the downstream base of the dam was another safety precaution, Rheinhart said.
"The charges were put there so the water had a dampening effect on the sound and vibration of the blast," he said. "It also helped in containing any fragments."
Still, logs and debris floated downstream soon after the breach. Among them was a wooden box that once held explosives attached to the dam.
On instinct, Lt. Chris Hurst, executive officer for the Army Dive Company, jumped into the Rappahannock near Riverside Drive to retrieve the box and make sure it was empty.
What likely happened was instead of breaking apart, the box blew off the dam and floated downstream, Stroiney said.
City workers may not have played a role in the actual breach, but their plates were full nonetheless.
A stage and platform was set up for a ceremony featuring Virginia's senior U.S. Sen. John Warner and other notables. City staff also managed to keep hordes of media--many in big, white satellite trucks--traffic, and a crowd of about 4,000 under control.
To reach ELIZABETH PEZZULLO: 540/374-5421 epezzullo@freelancestar.com
Date published: 2/25/2004
|
Star Directory
