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Video explainer of aerial ignition

“Plastic sphere dispenser” is one of the technical names for the machine used to execute strategic firing operations from helicopters. But everyone knows it as a ping pong ball machine. 
PSD ignition has been utilized in fighting the Yeti Fire as firefighters worked to build containment line and slowly bring the fire’s edge to control features that offer a high probability of success such as the Klamath River. Crews carefully strung fire along the ridges coming off of China Peak heading toward the river in order to prevent green pockets of unburned fuel at lower elevations from flaring up, spotting the ridge and causing control problems. 
A PSD machine is loaded into a helicopter and has a dedicated operator that rides in the backseat in addition to the firing boss and pilot up front. In this case, the operator was Joshua Collum, Senior Firefighter with the Happy Camp Helitack crew. As it was his first time working the capacity, his trainer and Happy Camp Helitack Captain, Ray Wilson, rode with.
The machine has a hopper that is loaded with the “ping pong balls” – plastic spheres that contain potassium permanganate – and the loading and firing device. This device injects the spheres with a small amount of ethyl glycol (antifreeze) that causes a chemical reaction which generates enough heat to ignite the ball once it’s on the ground. As the operator, Collum can control how many balls are dropped at a time (2 or 4 balls) as well as the frequency of the drops making this type of operation incredibly precise and efficient. 
“The firing boss decides when and how to fast to fire,” Collum said. “I verify the (ignition) pattern matches what he requests and monitor the chute, keep it flowing and make sure it’s operational.”
It’s that precise control that makes this technique so valuable in these applications.
“Using the helicopter offers a lot more control over the pace of ignition, how slow or fast you want to bring the fire along,” said Ira Graves, Air Operations Branch Director trainee for California Interagency Incident Management Team 10 and a former PSD machine operator. “Then, once you’ve done your ignition, you can back off and you have a great vantage point to assess your situation.” 
In addition to precision and efficiency, aerial ignition offers a reduced exposure to firefighters on the ground by preventing them from having to work in the steep, rugged terrain of the Klamath Mountains.  
“If you want your fire on the ridgetops, with a helicopter, you can line it in minutes,” Graves said. “With a crew It could take hours to get them into position, get it lit and then they’re hiking in very unfavorable terrain, probably in the dark with active fire. PSD use brings a safety factor into play.” 
While helicopter operations come with a degree of assumed risk as do all air operations, one way to further reduce the risk to crews that has come into play in recent years has been the use of Unmanned Aerial Systems. As the technology continues to emerge, UAS are being used more often on fires and becoming more valuable to incident managers.
UASs have been employed for various purposes on the Yeti Fire including using infrared imagery for reconnaissance, scouting possible line locations and aerial ignition as well. 
“It allows us to continue the precision ignition at night,” said Staci Dickson, lead Air Operations Branch Director for Team 10. “Aerial ignition is the mission with the most risk for our helicopters. We can’t do it at night with them, especially in this terrain. With the UAS, the humans are on the ground, only the machine is in the air.”