Al Qaeda's bizarre plan to attack America by using an "ember bomb" to ignite wildfires is so impractical that the terror group would be better off armed with a cigarette lighter, according to California fire officials who recently tested an al Qaeda-prescribed incendiary device.

In early May, the California Department of Forestry and Fire Protection and the state's threat assessment center conducted a "practical evaluation" of a home-made "ember bomb," a complex device described in detail in a recent edition of the al Qaeda-produced Inspire magazine under the title "It Is of Your Freedom to Ignite a Firebomb."

"In America, there are more houses built in the [countryside] than in the cities," the Inspire article's author says under the pseudonym The AQ Chef. "It is difficult to choose a better place [than] in the valleys of Montana."

In response, California officials went about building and testing a sophisticated version of the device, complete with time-delay ignition, according to a "For Official Use Only" document published online today by the anti-secrecy website Public Intelligence.

During the test, which was conducted on the concrete floor of a training facility, the device lit a fire that burned on its own fuel for just under 12 minutes. While the testers said the fire could have potentially spread to any nearby brush, the device itself did not produce any embers and all the heat was concentrated in one location - meaning it would not start other fires on its own - and left behind a large, black, "obsidian-like substance" where the device had burned.

"The 'Ember Bomb' device is an effective heat source and will ignite vegetation; however, we judge it is highly impractical based on the amount of energy and time it takes to construct the device, and the amount of physical evidence that will likely remain following its use," the document said. "…[T]here appears to be little practicality associated with employing this method versus other that would likely leave far less physical evidence, such as manually starting a burn with a cigarette lighter."

Capt. Ryan Stonebraker, head of the California State Threat Assessment Center and trooper with the California Highway Patrol, told ABC News he has not seen any indication anyone has attempted to start a fire with such a device, but said that regardless of how a blaze starts, the "threat is still on my mind."

"It's very difficult to stop fires," he said. "I think what's important is that first responders are aware of the methodology… The threat isn't just from al Qaeda [abroad], but homegrown extremists as well."

Stonebraker said the test was the first-ever collaboration between the threat assessment center and the California Department of Forestry and Fire Protection and the results were sent to law enforcement agencies across the country.

"We thought this was kind of obviously something different, so we did the tests so that first responders could see how it worked… and what to look for," he said.

The firebomb device was described in the ninth edition of Inspire, a magazine produced by al Qaeda's Yemen affiliate, AQAP. Earlier editions of the sleek magazine were believed to be crafted by U.S.-born radical Samir Khan before he was killed in a U.S. drone strike in Yemen in September 2011.