A prototype of a firefighting robot that uses liquid nitrogen to quickly extinguish wildfires has been developed by a team at Northeastern University.
Designed with the dual purpose of keeping human firefighters out of extreme danger and extinguishing fires with a substance that doesn’t harm the environment, the tread-mounted robot will one day be capable of traversing rugged landscapes, moving into active fire zones and stopping wildfires before they spread, its developers suggest. 
Source: Matthew Modoono/Northeastern University
Currently, wildfire suppression relies on aerial water and chemical retardant drops, but water evaporates quickly while retardants threaten to contaminate watersheds and trigger harmful algal blooms.
The team determined that when applied to a fire, cryogenic nitrogen instantly expands into a gas, expanding roughly 1,000% in volume. By expanding this quickly, the fire is starved of oxygen while also plunging the ambient temperature of pine needles, scrub and dry brush down into the sub-zero zone. Importantly, no chemical footprint is left behind when the gas dissipates.
Although it isn’t quite ready to fight massive infernos, the firefighting robot can operate as a reconnaissance unit capable of precisely targeting localized hotspots.
In this capacity, the robot, which is autonomously or remotely operated, can navigate hazardous terrain and extinguish small wildfire hotspots before they spread.
For now, the robot is being tested in controlled forest fire conditions, but could one day be scaled up to full-size firetrucks equipped with cryogenic fire-suppression systems.
