Intentionally Set Fires
Frequently, Wildland firefighters will intentionally ignite small fires in the path of an oncoming wildfire in order to burn the nearby vegetation and deprive the larger fire of fuel before it arrives. Fire crews on the ground, armed with hand torches are typically tasked with performing such operations. More recently, however, firefighters have begun to take a loftier approach to this task (literally), choosing instead to set intentional fires from helicopters flying overhead. These aircraft will drop chemical-filled plastic spheres, colloquially known in the industry as “ping pong balls”, which ignite on impact with the ground and create a small line of controlled burns.
The Science Behind the Ping Pong Balls
In the firefighting industry, ignition devices dropped from an aircraft are known as “DAID“–Delayed Aerial Ignition Devices. Prior to dropping DAID, a helicopter is equipped with a dispenser which a trained specialist then loads with small plastic spheres containing potassium permanganate, an inorganic chemical oxidant. Once over the desired area, an arm on the dispenser injects each sphere with a precise amount of ethylene glycol (a solution similar to antifreeze) and lobs the sphere out of the aircraft.
Within several seconds, the chemicals in the sphere react with one another and generate enough heat to ignite. The sphere then hits the forest floor and bursts into flame, producing a small fire at the desired location (the plastic ball and its contents are completely consumed by this burning). When a series of ping pong balls are dropped concurrently, their resulting fires burn together and consume unburned fuels in their way, enabling crews to direct wildfires away from sensitive areas, decrease fire intensity, and reduce the potential for spot fires.
The Benefits of the Ping Pong Ball Method
Using helicopters and DAID allows fire fighters to set fires over large areas and in a short amount of time. Especially in locations with inaccessible terrain–an environment common with wildfires–putting fire crews on the ground can put the lives of the crew members at risk. Not only does it often take precious time for ground crews to access a given site in order to start controlled burns, but rugged terrain can also make it difficult for a crew to evacuate to safety during an emergency. Aerial drops provide a safe, efficient, and effective alternative.