Fighting Fire With Electricity

6 April 2011—Researchers at Harvard University have found a new way to snuff out flames: zapping them with electricity. If they could turn their method into a practical device, it could give firefighters a way to control the direction and the spread of fires. It could also prevent the damage caused by water from sprinkler systems or fire-extinguishing foam.

The researchers, led by chemistry professor George Whitesides, have been able to put out 45-centimeter-high flames of burning methane using an electrified wire. They presented their results at the American Chemical Society meeting in Anaheim, Calif., last week.

The first report on the electrical nature of flames dates back 200 years, says Ludovico Cademartiri, a chemist in Whitesides’s group, who performed the experiments. Scientists who study this effect have mostly used static electric fields, and their effects on flames have been small, Cademartiri says.

The Harvard researchers used fields generated by alternating current instead. The equipment was simple. They connected the output of a 600-watt commercial power amplifier to a thin 10-centimeter-long insulated metal wire. "In order to put out the flame, the strategy is to get very close to the flame, right in front of it, and point the wire at the flame," Cademartiri says. The concentrated electric field that emerges from the tip of the wire pushes the flame until it detaches from its fuel source. The effect, he says, "was very much unexpected."

Amplifiers that produce the high voltage (up to 50 kilovolts) and the kilohertz frequencies needed to douse the flames have become available only in the past three years, Cademartiri says. He explains that the electric field, which has a strength of a million volts per meter, exerts a force on charged particles in the flames. The positive and negative particles begin to accelerate in opposite directions. When the flow of the charges is high enough, the flame is pushed off the methane source. The technique could be used to develop a device for suppressing and controlling indoor fires, he says, but a lot would depend on the size of the flames, the fire conditions, and the fuel.

Matthew Goodman, a program manager at the U.S. Defense Advanced Research Projects Agency (DARPA), which is funding Harvard’s firefighting work, says that the agency wants to explore novel fire-suppressing approaches that are based on physical techniques, as opposed to today’s methods that attack the chemistry of the flame. The military’s main interest in the technique is for suppressing fires in enclosed settings, he says. "Fire in enclosed military environments, such as ships’ holds, aircraft cockpits, and ground vehicles, continues to be a major cause of material destruction and loss of war-fighter life," Goodman says.

Goodman speculates that the technology could be built into a vehicle or a ship hold’s fire-suppression system. It could also be made into a backpack device that firefighters could carry. They could use it to put out fires or create paths through flames to enter buildings or to help people escape.