There was a large police presence, following Monday's sectarian clashes, and two water canon vehicles arrived.
Another worker told France's Le Figaro newspaper that the captors had mined the facility and demanded food, water and vehicles.
The Police Service of Northern Ireland (PSNI) has six water cannon vehicles, which are sent out in pairs to tackle public disorder.
As Nelson and Hick were toiling, firefighter and diver Shanna Hanson arrived on the north side, where, with just a rope tied around her waist, she dove repeatedly into the water, searching vehicles for possible survivors.
CNN: Officers sprang into action to help victims of bridge collapse
Armoured vehicles with water cannons and dogs were deployed.
Cheshire Police said water was up to 4ft (1.2m) high and some vehicles became stuck in water.
Technologies on display ranged from solar powered water purification units to military vehicles using next generation materials and energy sources to light weight batteries that can give better range and endurance.
Two other vehicles went into the water about 25 feet below as the structure crumbled.
In Devon and Somerset, the fire service was called to 18 rescues of people in vehicles caught in flood water.
At least 17 of the drowning victims were in vehicles driving into the water or swept away by rising water, the U.S. Commerce Department report said.
People can still water their gardens with a watering can and wash their vehicles using a bucket and sponge, which use a fraction of the amount of water that a hosepipe or sprinkler does.
The same physics apply to vehicles immersed in air and water, allowing for different values of mass and viscosity.
More than 600, 000 vehicles had some level of water damage after Hurricane Katrina struck the Gulf region in 2005.
They outfit their three technicians' vehicles with five-gallon water jugs and check that the air-conditioning units are always functioning properly.
The council said surface water made existing potholes worse because the water washed away loose particles of road surface whenever vehicles passed over them.
In America, where the price of a gallon of petrol can be less than the price of a gallon of bottled water, large fuel-guzzling trucks and sport utility vehicles (urban assault vehicles) make up more than half of the market.
"This is a really significant event and we need to learn from it, not just in Washington but around the country, " Hersman said after taking a boat ride on the Skagit River below the dramatic scene where a truck bumped against the steel framework, collapsing the bridge and sending two vehicles and three people falling into the chilly water.
Of the world's automakers, General Motors is the most resolute champion of a future filled with vehicles powered by hydrogen fuel cells that emit only water as exhaust.
Fuel cell electric vehicles generate their power from hydrogen and oxygen, and emit only water.
BBC: Nissan FCEV on display at a car show in Brussels in January
The vehicles are a popular tourist attraction and take in city sights from land and water.
Recreational vehicles even build cabinets now with pullout drawers that contain built-in food and water bowl trays.
Among the energy-saving options, two promising technology switches are the electrification of transportation (electric vehicles can be about four times as energy-efficient as standard fossil-fuel vehicles) and the use of electric-powered heat pumps to deliver winter heating and hot water (heat pumps can be four times as energy-efficient as standard heaters).
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