Toyota released two videos this week showing what happens when tanks used in hydrogen cars are subjected to severe abuse—from a high-speed crash and a shot from a high-caliber rifle. Thrill-seeking viewers expecting to see a car fire—there are about 150,000 of them a year on US roads—might be disappointed with the videos. Movie-goers accustomed to dramatic car rescue scenes will consider them un-cinematic. That’s because the fundamental nature of hydrogen, the sturdy construction of the tanks, and the careful design of the systems make the gaseous fuel much safer than people realize.
Mirai’s carbon-fiber hydrogen tanks undergo a test using a high-powered 50-caliber gunshot from point blank range. The high-caliber bullet pierces the tank, but the structure remains intact and the tank does not burst. The gas merely escapes through the hole and disperses into the atmosphere with no catastrophic rupture. A special high-speed camera slows down the action to showcase the strength of this innovative tech at work. We subject these tanks to such extreme testing to help ensure durability in the event of a crash. Just one more way to help you drive change with complete peace of mind.
“When you see what happens when you penetrate a hydrogen tank with a bullet, it’s not some great event,” said Jackie Birdsall, senior engineer in the fuel cell hybrid vehicle group of Toyota Motor Engineering and Manufacturing North America. “It’s actually anticlimactic.”
Birdsall, who works on codes, standards and regulations related to high-pressure gaseous systems, is eager to dispel myths held by consumers. “We want to show people what we do—the testing, engineering and fundamental safety design that makes these systems so reliable,” she said.
If the systems in a high-pressure gas system detect a dangerous condition, like high temperature, the hydrogen gas is released into the air. “Hydrogen only goes in one direction, which is straight up, and it goes away very quickly,” said Tim Lipman, a researcher in environmental technology at U.C. Berkeley and co-director of its Transportation Sustainability Research Center.
“Whereas gasoline forms a pool on the ground, the hydrogen is gone in seconds,” Lipman explained. He said the efficiency of fuel cells means that less energy is stored in the tanks—never more than the equivalent of about five gallons of gasoline. In addition, the “battleship strength” of the tank, as he described it, makes it simultaneously able to hold gas under high pressure and resistant to penetration from materials it might encounter on the road.
After ruling out a wide range of theoretical risks posed by fuel cell cars, engineers working on high-pressure gas systems—for carmakers and testing companies—have resorted to draconian tests. “We've put that system trough extreme conditions in the field and they've all passed with flying colors,” said Birdsall.
Powertech Labs in Vancouver, Canada, has been testing high-pressure gas systems for more than 30 years. Philip Horacek, senior manager for gas systems engineering at Powertech, looks for every possible way a hydrogen vehicle system could fail. “The gun fire test is not meant to simulate someone actually shooting the tank,” he said. The idea is to evaluate if stresses from that one particular spot are not transferred to the areas around it.
After looking at the video, UC Berkeley’s Lipman said the integrity of the tank was not damaged beyond the bullet hole. “The hydrogen vented out, which is exactly what we expect to happen.” He said that it takes about 15 to 30 seconds for the tank to discharge. “As long it doesn’t ignite in those 30 seconds, which is very unlikely, it’s gone as a hazard.”
Lipman said that only a .50-caliber bullet was powerful enough to penetrate today’s tanks, which are made from a polymer that’s reinforced with ultra-strong carbon-fiber. “A .45 would probably just dent it,” he said.
Haracek cited a long list of tests that Powertech conducts, including: cycling through a lifetime of filling and dispensing high-pressure gas; exposing it to severe temperatures; soaking it in chemicals that might be found on roads; and even conducting a bonfire test.
“We blow the tanks up with water to determine if the ultimate strength of the tank is where it needs to be,” said Horacek. “I’ve dropped a two-and-a-half-ton metric weight on tanks from a height of two meters on a fully pressurized tank,” said Horacek. “The weight just bounces off the tank. That’s how strong they are.”
Despite the high degree of safety, Lipman said that more work needs to be done to train first responders in handling incidents involving a hydrogen fuel cell vehicle—for example, how to listen for the sound of a high-pressure release. “We need to have local officials understand what’s supposed to happen and what’s not. They’re not there yet.”
This is a simulation to show the effects of a 40-mph crash on Mirai’s carbon-fiber-wrapped hydrogen tanks. Two separate slow motion camera angles show how the vehicle’s body structure is designed to absorb and distribute crash forces efficiently throughout the vehicle. This helps protect you and reduces body deformity around the fuel cell stack and hydrogen tanks. With Mirai you can drive the alternate fuel movement with confidence.
Even though the tanks are extremely strong, auto engineers use best practices to keep it away from crash impacts and crumple zones. System regulators, valves and lines that would be more vulnerable than tanks in a crash are low-pressure components. In the video of a fuel cell car in a crash, the high-pressure tanks are pushed aside but not penetrated.
Toyota’s Birdsall believes it will be difficult to find a scenario in which the hydrogen tanks and systems can be beaten. “The baseline of the standard is what we expect the vehicle to go through. Then we take it to the next level,” she said. “I’m so impressed with the design engineers, the materials engineers and structural engineers. It's remarkable what they've done with these tanks.”