It was just before 3 p.m. on a Thursday afternoon and traffic was moving smoothly on the Pomona Freeway, about 20 miles outside downtown Los Angeles. Suddenly, a truck carrying compressed hydrogen caught fire, and by the time the local fire department had arrived on the scene, two of the hydrogen tanks had begun venting gas, and flames had engulfed the truck’s cab.

It took almost seven hours for firefighters, working with a mix of chemicals and water, to end the threat.

“It had the full spectrum of colors,” Captain Will Pryor of the Los Angeles County Fire Department recalled of the fire on Nov. 14, 2013. “It’s like a log in a fire. You’d have blue parts of it. Orange parts of it.

“There is a school nearby, there are multiple residences nearby, apartment buildings, office buildings,” Pryor said. “They were all in a half-mile blast radius, what was reported would be the blast radius of hydrogen.”

In the end, there were no casualties, and the worst-case scenario was avoided. But as California expands its use of hydrogen-fueled cars and builds out its infrastructure for servicing those cars, more hydrogen is going to be trucked around.

Later this year, 1,000 of Hyundai’s hydrogen-fueled cars will go on sale in California, and Toyota has announced plans for a commercial model to go on sale in 2015. Ford, Daimler, Nissan, General Motors and Honda have also announced plans for partnerships on hydrogen fuel cell technologies. The California Air Resources Board has projected that there will be over 50,000 electric and hydrogen cars in California by 2018.

California Gov. Jerry Brown last year agreed to devote $20 million every year over the next decade to build 100 additional hydrogen fueling stations. The state currently has 23 active stations.

Hydrogen as a fuel source is an attractive proposition mainly because it doesn’t emit toxic, heat-trapping pollutants the way gasoline does. An analysis conducted by the U.S. Department of Energy shows that for a mid-size SUV, the total greenhouse gas emissions from using hydrogen as a fuel is at worst half that for gasoline.

However, hydrogen poses several other risks that gasoline does not. It is highly flammable, and can ignite more easily than other fuels. Hydrogen is also colorless and odorless, making it difficult to readily detect leaks.

Environmental and regulatory experts have long worried about the threat posed by the vast array of dangerous materials daily being moved across the country, from nuclear waste to pesticides and compressed gases.

“As far as the aggregate risk that is presented to the American public, I don’t think it’s going to change significantly,” said Carl Southwell, a risk analyst who studies infrastructure and chemical risks. “But there will be slightly more risk to first responders and people near the hydrogen fire.”

A ProPublica review of voluntarily submitted data collected by the Department of Energy does show there have been some problems with hydrogen infrastructure nationally.

There have been 37 recorded “events” in recent years involving hydrogen trucks or fueling stations. Of the 22 events recorded at fueling stations, hydrogen was released in a dozen of them, and twice the releases resulted in fires. Fires occurred in five of the 15 recorded events involving hydrogen trucks.

At the moment, the transport of hydrogen is monitored by both state and federal agencies. The federal agency, the Pipeline and Hazardous Materials Safety Administration (PHMSA), says it requires various types of documentation and labeling for shipments of hydrogen and training for employees involved in its transport.

However, there have been recent reports —one by an inspector general with the federal Department of Transportation — asserting that the agency has been chronically understaffed and underfunded. A senior agency official recently conceded as much, saying funding from Congress had dried up and that the regulatory process he oversees was “kind of dying.”

Gordon Delcambre Jr., a PHMSA spokesman, told ProPublica that the agency ensures compliance of hazardous materials shippers and carriers by conducting unannounced inspections. But he acknowledged that federal regulations do not actually require such inspections or mandate how often they should occur.

ProPublica determined that the agency’s western office, which is responsible for 12 states, has just seven inspectors.

Warnings about the transport and use of dangerous materials of all kinds have been sounded for years. In 2007, the Federal Motor Carrier Safety Administration (FMCSA), which is in charge of enforcing regulations for cargo trucks and interstate buses, called for changes in its operations to meet the rise in vehicles that used hydrogen.

“The current regulations do not consider safety systems and equipment required for commercial vehicles using hydrogen as an alternative fuel,” the authors of the report said. But to date, the FMCSA has not made changes to include separate inspection procedures and regulations for hydrogen-powered vehicles.

Quon Kwan, who helped compile the report at the FMCSA, said he was hopeful that more action would be taken in spite of the fact that the number of hydrogen-powered vehicles on the roads today are a “drop in the bucket” when set against the millions of diesel-powered trucks the agency is responsible for regulating.

Chief Jan Dunbar at the California Office of Emergency Services downplayed the challenge any increase in hydrogen transport and use might present to first responders.

“There’s nothing special about hydrogen that sets it apart from any other flammable gas,” he said.

California’s Office of the State Fire Marshal does have a 16-hour emergency response training program for alternative fuels vehicles. The curriculum allocates one hour to the discussion of hydrogen. But fire departments aren’t required to provide the course to their firefighters. Since the program was started in 2009, four classroom sessions have been conducted, each with 44 students. The manual for the program is also available for download on the State Fire Marshal’s website.

We have it available to departments. It’s whether or not they choose to access that,” said one instructor at the State Fire Marshal’s office.

Jennifer Hamilton, an education specialist at the California Fuel Cell Partnership, said she has been delivering hundreds of workshops on hydrogen fuel cells to firefighters. Currently, the California Fuel Cell Partnership and the Department of Energy are the two main organizations with outreach programs to educate firefighters on the properties of hydrogen and the working of hydrogen cars.

Hamilton estimates that her workshops have reached more than 5000 firefighters so far, but is quick to clarify that they do not qualify as true training.

“Training implies that there is some sort of certificate or credits and an approved curriculum,” she said. “We don’t give anything like that. Our program is at the information or awareness level.”