"You don't want to go crushing anything with hydraulic tools," said Samuel Caroluzzi, an assistant chief with the Norristown Fire Department outside Philadelphia. "It's enough to kill you from what they're telling us in training."
Hybrids draw power from two sources, typically a gas or diesel engine combined with an electric motor. The battery powering the electric motor carries as much as 500 volts, more than 40 times the strength of a standard battery.
That worries those who must cut into cars to rescue people inside.
"If you can't shut it down, you don't know where the high voltage is," said David Dalrymple, an emergency medical technician in New Brunswick, N.J.
Manufacturers have put in place a laundry list of safety checks that the car's computer must go through for the electrical system to run. They've published guides showing where the electric components are on their models; on the Toyota Prius and other hybrids, the high-power cables are colored bright orange to catch the eye of a rescue worker or a mechanic.
But there are concerns over what happens if something goes wrong and the battery, ignition and other points are inaccessible.
"It's the 'what-if' that worries me," said David Castiaux, an instructor for Mid-Del Technology Center in Del City, Okla., who teaches rescue workers about hybrids.
Chris Peterson, a service training instructor for Toyota, said the Prius' electric system should shut down if anything goes wrong. "There should not be high voltage in those cables, but I'm not going to stand up and say there isn't," he said.
First responders are taught to disconnect the battery and turn off the key immediately before cutting into a car, but that's not always possible.
"Years ago you could just cut with your extrication tools through a post, but now you have to look before you cut," said Ken Nelsen, chief of the Iselin Fire Department District 11 in Woodbridge Township, N.J. "It's just another thing you need to worry about."
The worries are not confined to hybrid cars; other alternative-fuel vehicles — like those using liquefied or compressed natural gas, methanol or ethanol — also pose special risks for rescuers.
When air bags started becoming more common in the 1980s, rescue workers became aware of their potential to seriously injure or kill when inflated. Those concerns have been heightened now that the safety devices are being installed in side panels, seats and other areas.
Complicating the concerns about hybrids and other alternative fuel vehicles, the NHTSA says, is that unlike commercial trucks or railroad cars carrying dangerous materials, alternative-fuel cars are not covered by a standard system of labels to indicate what's inside.
Concerns about hybrids are increasing in large part because of their growing popularity. Sales have risen at an average annual rate of 88.6 percent since 2000 and recent figures show the number of Americans driving them jumped more than 25 percent from 2002 to 2003.
The Honda Insight and the Toyota Prius are common now and more are on the way: hybrid versions of the Ford Escape, Honda Accord and Lexus SUV this year, and a Toyota Highlander in 2005.
The Alachua County Fire Rescue in Gainesville, Fla., even has two hybrids of its own. Although its crews haven't had to deal with a hybrid crash, they've been getting versed on what to do when it happens, said Cliff Chapman, assistant chief.
They know not to cut into a hybrid's doors — that's where many of the cables are — and to peel off the roof instead. They also now operate under the assumption that a car is energized, wearing rubber gloves and boots.
The NHTSA safety manual also advises rescuers to beware of toxic fumes from electric vehicles, which may be borne by smoke or steam.
Manufacturers say they will continue to keep rescue personnel up to date on their hybrids. But they also contend that hybrids can be seen as safer than regular cars.
"Everybody's concerned about the electrical side, but could you imagine if we tried to bring gasoline out today as a motor fuel?" Peterson said.