Shocking Wildfires Into Submission: A Proposal
Last year, California’s wildfire season culminated with both the largest fire on record (281,000 acres burned), and the most destructive fire on record (36,807 structures lost). Today, the Carr fire is the seventh-largest in California history, and it’s less than a quarter contained. A smaller yet similar fire is burning in Colorado. Like the truism that there will always be another war, there will always be another fire. However, while there are endless efforts to evolve fresh approaches to fighting wars, it doesn’t appear the same can be said for fighting wildfires. The military may be able to help — right now — in a way that has never done before.
The Traditional Approach
When fighting a smaller fire such as one engulfing a single building, it is most efficient to fight the fire from the ground at the source. But large forest fires generate massive heat, requiring more stand-off distance and rendering hoses and other equipment ineffective — in military parlance, an area denial problem. Even worse, when these fires get to the size and intensity of the Carr blaze, they create their own localized weather system that makes predicting the fire’s movement difficult. This is where firefighting from the air comes in.
CAL FIRE, California’s firefighting aviation department, operates a fleet of over 50 aircraft, including a modified DC-10 and the 747 supertanker used to drop chemical retardant. CAL FIRE is augmented by the California National Guard, which uses a fleet of helicopters and C-130s equipped with the Modular Airborne Fire Fighting System to employ water or chemicals. A spin on this, there are even innovative approaches that deliver chemicals via air-dropped parcels. But there are other ways to disrupt the trinity of oxygen, fuel, and heat.
A Turning Point
In 2008, a fire aboard the USS George Washington took 12 hours to put out and caused $70 million in damage. This inspired the Defense Advanced Research Agency (DARPA) to explore alternative firefighting methods. By 2012, they had developed a proof of concept that validated the theory that acoustic waves can be used to suppress and extinguish fires. In 2015, students from George Mason University developed a portable fire extinguisher that uses low frequency sound waves to put out fires. While it works, sound wave fire suppression works best on small-scale fires. But what about shock waves?
In 2014, the University of New South Wales’ School of Mechanical and Manufacturing Engineering tested the science behind the idea. As researcher Dr. Graham Doig noted,
The sudden change in pressure across the shockwave, and then the impulse of the airflow behind it pushed the flame straight off the fuel source. As soon as the flame doesn’t have access to fuel anymore, it stops burning.
Doig postulated that if the technique could be used to blow the flames out of the treetops of forest fires, it would slow the fire dramatically and make it easier to fight by conventional means and increase the time available to evacuate people.
The Air Force can put a bomb anywhere in the world within a three-foot circle, extremely close to friendly forces on the ground, all while avoiding collateral damage to buildings and infrastructure. The same personnel, equipment, and procedures could be easily adapted and integrated into firefighting — an air controller embedded with firefighters could use close air support procedures to direct air strikes.
A single B-1 bomber, carrying up to 84 500-pound air-bursted bombs, could tailor its effects to cover an area with shockwaves that mirror the footprint of firefighting tanker drop patterns. Or it could loiter for hours and integrate into multiple chemical drops. Obviously this would be more useful in areas further away from civilization, and could be used as a technique to shape or vector a fire to contain it. This was recently put into practice in Sweden, where a Gripen fighter jet from the Swedish Air Force dropped a single 500-pound bomb on a forest fire, momentarily depriving the blaze of oxygen and successfully extinguishing it within 100 yards of the detonation point. Despite this success, the delivery and warhead weren’t optimized for the task.
A detonating bomb produces blast, shock waves, fragmentation, and heat. The fragmentation of the bomb case causes considerable damage (the Swedish Air Force bombing was only feasible because the wildfire had spread onto a military bomb range). Additionally, since a large part of the explosive energy is expended to break open the case, it also inhibits the most desired attribute for fighting fires — the blast. In 2008, a similar problem was highlighted in Afghanistan, where a perfectly placed bomb could still yield undesirable damage due to the long distance the case fragments flew when it detonated. The answer was the 500-pound BLU-129/B low collateral damage warhead. This particular bomb has an explosive charge wrapped in a composite case that disintegrates upon detonation. Blast is the primary mechanism of the weapon, not fragmentation. The limited production run of 800 warheads ended in 2015, and are seldom used.
With an adequate case to reduce fragmentation, the blast could be further optimized with a different explosive filler. A thermobaric munition uses oxygen from the surrounding air to generate an explosion, resulting in a larger and longer-duration shock wave compared to a conventional explosion. While the thermobaric bomb has been criticized for its arguably inhumane methods, those same attributes make it well-suited to drop in the middle of a raging forest fire where the only thing it could potentially kill is the fire.
And this bomb needs to be air-bursted to optimize the shock wave. Fortunately, there is a variety of suitable radar proximity fuses already in use. This type of fuse was intended to maximize the blast radius for soft military targets by bursting the bomb in the air slightly above the ground (14 to 20 feet depending on the model). This means the bomb never impacts the ground, so it leaves no crater and doesn’t damage underground utilities.
Thus, the optimal munition to fight fires may be an air-bursted thermobaric munition with a composite case — which unfortunately doesn’t exist. Excluding exquisite weapons, the U.S. military currently only has two thermobaric warhead models, the BLU-118/B and BLU-121/B. Designed for penetrating reinforced targets, both bombs have cases too thick and an explosive charge too small to be useful.
Not many would claim that the Department of Defense acquisitions process is timely or responsive, but rapid munitions development to meet emerging needs is one of the few things it has shown to be good at. In 1991, the 5,000-pound laser guided bunker busting GBU-28 was prototyped, tested, deployed, and used in combat in Iraq in an astonishing two weeks. In 2001, a need for a thermobaric weapon to attack caves in Afghanistan led to the BLU-118/B in just 60 days. And in 2003, it took only 100 days to design and deploy a zero-explosion passive attack weapon to attack Iraqi electronics and fuel stores. How fast could the Defense Department move today if it had to develop a munition? This could be a useful exercise for both industry and the Pentagon.
A Scalable Solution?
Regardless if a new munition were developed for this mission, and the fact that using munitions to fight fires may be extremely effective in certain situations, the concept is simply not scalable or useful in most scenarios. A single B-1 bomber carrying 84 500-pound bombs could tailor its effects to cover an area with shockwaves, but the munitions cost alone would range from $250,000 (unguided) to $2 million (guided) per mission. Perhaps there is another option.
Knowing that both sound waves and shock waves can affect fire, what can produce these but is economically reusable and has none of the side effects of a traditional explosion? Simple: A sonic boom. Any aircraft capable of exceeding the speed of sound (Mach 1) creates a sonic boom along its flight path. While the public mostly associates the event with an audible boom, the pressure differential can easily blow out windows. It’s not a single event either. The sonic boom continues along the flight path of the aircraft, covering approximately one mile of ground per 1,000 feet of altitude.
Armed with this knowledge, the fleet of supersonic U.S. military aircraft provide a variety of altitudes, shapes and sizes that could be used to mission plan an effect over a region engulfed in flames. The permutations are nearly endless. For example, a string of B-1 bombers or fighters flying close and low could put down a large suppressive wave along the front of a fire. Or they could be configured in a wall, at various altitudes, or in a formation creating a wedge or angle effect to shape or vector a fire while awaiting reinforcements on the ground.
Correctly timed and integrated, airborne firefighting assets could immediately employ chemical retardant against the smaller fire, which presumably would be more effective than engaging the original larger flames. This could then permit firefighters on the ground to close with and engage the fire on a more manageable level. Integrating this into the current list of firefighting capabilities may produce synergistic effects that would help contain and quell the largest parts of the fire. If it were a military operation, this would be called force-packaging.
Ready, Aim, Fire
At best, maybe the collective output of any defense experimentation is that the fire is suppressed enough to dispel its local weather influence, reintroducing predictability to the firefighting effort. At worst, nothing meaningful happens on the ground and aircrews get some training.
What matters most is having the courage to try something new when an opportunity presents itself. This courage is echoed by countless Department of Defense leaders who have been calling for failing faster, more innovation, agile thinking, and disruptive ideas that present a multitude of options for decision-makers. The opportunity has presented itself: NASA has the knowledge on supersonics, the Air Force has the equipment, and nation has the wildfires.
For the Air Force, there is everything to gain and nothing to lose. For those affected by the fires, they have nothing to gain and everything to lose.
Mike Benitez is an F-15E Strike Eagle Weapons Systems Officer in the U.S. Air Force. The views expressed are those of the author and do not reflect the official policy or position of the Department of Defense or the U.S. government.
Image: Wikimedia Commons