A professor at Northeastern University has developed a unique firefighting robot that uses liquid nitrogen instead of chemical fire retardants to extinguish flames.
The technology could one day help firefighters tackle dangerous wildfires more safely while reducing harm to the environment.
The idea began almost by accident nearly 20 years ago. In 2008, Professor Yiannis Levendis was conducting an experiment to study old car and truck tires as a possible alternative fuel to coal. While burning small pieces of rubber in his laboratory, he decided on impulse to throw a spoonful of liquid nitrogen onto the fire.
The result surprised him.
The flames went out almost immediately.
Liquid nitrogen is extremely cold. When it comes into contact with fire, it rapidly changes from a liquid into a gas, expanding to nearly 1,000 times its original volume. This sudden expansion pushes oxygen away from the flames while also cooling the burning material, making it difficult for the fire to continue.
Levendis knew liquid nitrogen had already been used to help control fires in underground coal mines. He realized the same principle might work for wildfires, which have become more frequent and destructive in many parts of the world.
According to the U.S. National Interagency Fire Center, wildfires burned more than 5.13 million acres across the United States in 2025. That is an area larger than the state of Massachusetts.
One reason Levendis believes liquid nitrogen could be useful is that it leaves no chemical residue after it evaporates. Many wildfire retardants currently used contain chemicals such as phosphorus, which can wash into rivers and lakes after rain. High levels of phosphorus can trigger harmful algal blooms that reduce oxygen in the water and threaten fish and other aquatic life. Some fire retardants also contain chemicals that may damage soil.
The next challenge was finding an effective way to deliver liquid nitrogen to a fire.
Levendis considered several possibilities, including fire trucks equipped with special storage tanks or helicopters carrying cryogenic containers. While both ideas seemed possible, he eventually focused on a different solution: robots.
Working with Northeastern University students Hayden Hishmeh and Aobo Liu, Levendis built a small prototype robot that travels on rugged caterpillar tracks. About the size of a small trash can, the robot carries liquid nitrogen and sprays it through a hose to extinguish flames.
The robot can be operated remotely or eventually could become autonomous. This would allow it to reach dangerous wildfire hotspots that are too risky for firefighters. It could also attack small fires before they spread into large, fast-moving wildfires fueled by dry leaves, pine needles and brush.
The project received support from the Gordon and Betty Moore Foundation, which helped fund the equipment needed to build and test the prototype.
So far, the robot has been tested on small, controlled fires using forest materials commonly found in wildfire-prone areas of the western United States.
Although the technology is still under development, Levendis believes it has great potential.
In the future, he hopes the liquid nitrogen system could be scaled up for larger vehicles, including fire trucks, giving firefighters a new environmentally friendly tool to battle increasingly severe wildfires while reducing risks to both people and nature.
