TAMPA — The Secret Service plans to ring the Republican National Convention with miles of steel and concrete, including fences 8 feet tall and vehicle barriers that can stop a 7-ton truck barrelling in at 30 mph.

The agency has yet to release information saying where it will put its secure perimeter. But the Secret Service has begun telling private contractors what it needs to create lines of defense in both Tampa and St. Petersburg, where Tropicana Field will host the RNC's official welcome party.

The barriers will have to stop everything from a water balloon to a car bomb. According to a request for proposals issued this week, the 8-foot fences must be all-steel, difficult to climb and have a 1/8th-inch steel mesh to disperse any liquid thrown at them.

The portable vehicle barriers will consist of 32-inch-high retractable steel plates. Their stopping power is measured against a set of standards created by the U.S. Department of State for protecting embassies from runaway trucks weighing up to 15,000 pounds.

At the GOP convention in 2008, these sorts of intense security measures surprised some people in St. Paul, Minn., who said it hurt business.

Tampa Mayor Bob Buckhorn does not expect the same shock.

"I think, initially, people will be curious, but I think they also recognize the potential risk and that the Secret Service is doing what they're charged to do, which is to mitigate the risk," he said. "If an impenetrable fence is what's required, that's what's required."

In Tampa, the Secret Service is seeking 33 portable vehicle barriers, more than 10,000 linear feet of concrete barriers, 7,500 feet of anti-scale fencing, nearly 13,000 feet of other fencing and 4,500 feet of "bike rack" barricades.

In St. Petersburg, it expects to use 13 portable vehicle barriers, 5,000 feet of anti-scale fencing and 21,300 linear feet of concrete barriers with fencing.

The agency's request for proposals says the winning contractor must be able to work from about Aug. 16 through Sept. 3.

What this means for baseball fans was not clear Thursday. The Tampa Bay Rays have six home games the week before the Aug. 26 welcome party at the Trop.

The Secret Service's invitation to bidders does not say what the installation timeline will be, but both sides say they'll work to minimize inconvenience to fans.

"We are working with the city and everybody there to lessen the impact on the community as much as we can," Secret Service spokesman George Ogilvie said.

"At this point we are not aware of the details of their security plan, but we will work diligently with the RNC to make sure our fans are not inconvenienced," Rays spokesman Rick Vaughn said in an email.

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The perimeter's location is arguably the biggest logistical decision of the convention. Where it goes will affect businesses, commuters, protesters and residents on Harbour Island.

The Secret Service is looking at releasing information about its security plans four to six weeks in advance of the RNC, now slightly more than six weeks away.

Speaking to a group in downtown Tampa this spring, Buckhorn said the perimeter could go as far north as Brorein Street.

Tampa officials also have said they assume it will circle the Tampa Bay Times Forum, the Tampa Convention Center, Embassy Suites Hotel, Tampa Marriott Waterside Hotel & Marina and maybe the Tampa Bay History Center.

The Platt Street bridge, which sends 34,000 cars and trucks a day into a tunnel under the convention center, will be closed. Other closures could include the Lee Roy Selmon Expressway, which carries about 50,000 vehicles on a typical August weekday, and the bridge from the convention center to Harbour Island.

The Secret Service will pay for the secure perimeter and will control everything inside it.

Typically, the agency brings in bomb-sniffing dogs, counter-assault and counter-sniper teams, plus its own uniformed officers to work metal detectors at the entrances.

Beyond the perimeter, the responsibility for handling crowds belongs to Tampa police and about 3,000 more officers from around Florida.

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For a national political convention, security planning entails everything from issuing credentials to what officials have called "bomb blast analysis."

In other words, how far away do potential threats need to be kept to protect convention facilities?

There are standards for these decisions. The federal Bureau of Alcohol, Tobacco, Fireworks and Explosives has calculated "lethal blast ranges" for car and truck bombs. For a sedan with 1,000 pounds of explosives packed in the trunk, anyone within 125 feet of the blast could be killed. The range at which life-threatening injuries could be minimized from such a blast is 1,750 feet.

Blast analyses at previous conventions led to the closure of an interstate next to the 2004 Democratic convention in Boston and a new route for a protest march outside the St. Paul RNC in 2008.

In Tampa, the same kind of analyses apply to the Selmon Expressway, which overlooks the forum and passes next to the convention center, the working hub for 15,000 RNC journalists.

In May, a convention official told visiting journalists the outermost perimeter would include a vehicle checkpoint. There, drivers will need a placard issued by the Secret Service and will go through a security sweep before driving on.

Closer in, there will be a second perimeter and a second check of credentials to get into the convention campus.

Getting inside the forum or convention center will mean going through a metal detector at a third checkpoint.

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So far, the companies lining up for perimeter work are from outside the Tampa Bay area.

As of Thursday, three companies from North Carolina, Texas and Maryland had put their names on a list of vendors interested in the barriers contract. Another four companies from New York, North Carolina, Colorado and Washington were interested in providing the Secret Service with generators and other equipment.