Inside, two scientists explained to an audience of more than 400 how the hydrogen-powered car works.

Using helium balloons, blocks of aluminum, toy rockets and gallons of liquid nitrogen, the two researchers demonstrated three ways a tank of such highly-pressurized, extremely-cold liquid gas could work. It needs to be vacuum-insulated, reflective and separated from anything too conductive.

Or else it could explode.

Those three requisites, though, make condensed hydrogen gas safe enough for everyday drivers, said Gene Berry, a researcher from Lawrence Livermore National Laboratories.

Berry played video clips of lab tests in which tanks like the one outside were heated over a 1,000-degree fire and dropped from 30 feet onto concrete — without breaking.

“If the car is intact, the tank will be intact. It should be pretty safe,” Berry said, adding that manufacturers are still working out where to place the tank on the car.

The Prius outside the theater carried its tank in the trunk, but for mainstream use, it would more likely be built under the car, Berry said.

Clad in a lab coat and rubber gloves, Tracy High School science teacher Dean Reese intermittently demonstrated Berry’s points with little experiments, at one point shooting off a mini rocket fueled by bubbling hydrogen and nitrogen inside the theater.

The visual aids sparked avid cheers, claps and whistles from the crowd.

Up on the screen, Berry showed the mostly student audience how one would fill up the tank of a hydrogen-powered car using a lock-tight nozzle at the hydrogen gas station of the future.

He switched the slide to a map of Gov. Arnold Schwarzenegger’s proposed “Hydrogen Highway,” a string of alternative fuel stations along California’s major roadways.

The U.S. could transition from fossil to hydrogen fuel in about four or five decades, predicted Berry.

Hydrogen “is clean, sustainable and you can manufacture it wherever you have water and electricity,” he said.

Already, Berry explained, companies like BMW and Honda are putting hydrogen cars on the market. Within a few years, he predicted, they should be a common sight.

“Hopefully, when you guys get out of college, you can ask for a hydrogen car as a present,” he suggested.

“I would definitely buy one,” said Victoria Cardoza, 15, a Tracy High School sophomore who attended the lecture. “The lecture was really fun in showing how it’s a practical switch from regular cars.”

Students from Manteca, Livermore and Tracy schools hovered around the model car after the science session, getting an up-close look at the tank in its intended context.

“I thought they did a good job, between the physical demonstrations and the video and lecture,” said Manteca resident Greg Nix, who went with his son to the event. “But I would like to see how they adapt the hydrogen fuel to power the engine.”

At a glance WHAT: “Energy Crisis: Will Technology Save Us?”

WHEN: 9:30 a.m. Saturday

WHERE: Grand Theatre Center for the Arts, 715 Central Ave.

INFO: http://education.llnl.gov/sos or farnsworth1@lnl.gov