This proposal would fill a ballistic projectile ie artillery or mortar shell with a liquefied inert gas, and fire it upwind of an isolated wildfire. The projectile would not detonate but would disperse LIG over the hot spot. This would cool the fire and displace air thereby removing two elements of the fire triangle, heat and O₂ (fig 1). Multiple shells would be required depending on the size of the fire.

A method of observing and evaluating results would also be required and could be accomplished with unmanned aerial vehicles (drones) with HD and IR cameras.

This system will not eliminate present fire fighting systems, but would supplement the current arsenal. It could also reduce the risk to front line personnel by keeping them at a safer distance.

The system would utilize inexpensive and available components. Consider liquid N₂ and a 155 mm artillery shell (empty). Assume this shell has a capacity of 10 kg of TNT, the volume can be calculated as 6 ℓ. When evaporated, 6 ℓ of liquid N₂ has the potential to displace 4,000 ℓ of air at 0% O₂. If we only need to reduce O₂ concentration in air from 21% to 15%, the level which no longer supports combustion, then the displaced volume increases to 67,000 ℓ. If we assume the latent heat of liquid N₂ is 48al/gm, then 6 ℓ of liquid N₂ has the potential to remove 240,000 cal of heat to it's evaporation point of -196 ºC. Depending on local humidity, the temperature drop could also cause condensation.

The only necessary modification to the shell involves the fuse. A new fuse could consist of a fill and discharge port with check valve, safety cap, and bursting cone. The fill/discharge port would be a simple tube with a fill adapter at external end and check valve at internal end. The shell and fill/discharge port would be stored and transported empty for safety. The projectile could be filled on site by a liquid N₂ tanker or portable liquid N₂ generator. A safety cap could be installed at external end of port if not fired immediately. Prior to deployment, a bursting cone would be installed to the external end of port. The bursting cone would have enough explosive charge to rupture check valve and cone allowing the discharge of liquid N₂ payload. The bursting cone would be triggered by time or proximity above wildfire. A secondary trigger would activate on impact with ground if primary trigger failed.

Novelty

I am not aware of any non high energy ballistic suppression system similar to this proposal in use.

Previously submitted in Canada to National Resources Canada, National Research Council and Department of National Defence in 2018, but it was declined.

Marketability

The primary market would be the preservation of life and property from wildfire.

There is commercial application in the growing private firefighting industry.

Acknowledgements

Wikipedia https://en.wikipedia.org/wiki/

ResearchGate https://www.researchgate.net/