Chen says his studies suggest that the number of passengers on board the plane doesn't significantly affect air flow. But the seating arrangement and ventilation system can change the way a toxin travels. Consequently, a new model would need to be created for each type of plane and all possible seating arrangements. Sensors for various biological and chemical agents would also need to be installed throughout the cabin. But Chen says that for any single contaminant, only one sensor is needed for every nine rows of seats.

Once a sensor identifies a contaminant, Chen's software finds the source using the air-flow model. Essentially, the system tracks the contaminant backward as it travels from sensor to source in a process known as inverse simulation. Chen says that in the event that a contagion or toxin is detected while the plane is in the air, the flight attendant could ask all passengers to put on a mask for their protection. Once the plane has landed, the passenger thought to be responsible for the release of the contaminant could be questioned by the appropriate authorities and the plane decontaminated.

Chen's inverse-simulation system could be ready for real planes in two years, he says. But first, he has to make it identify sources faster. "At present, the inverse modeling takes a few days for a twin-aisle cabin. Thus, the technology is only good for aftermath analyses," he says, adding that his system is currently limited by computer processing power and its own design.

Chen says that he's currently working on perfecting the algorithm. He also plans to switch from a central processing unit to a graphics processing unit, as the latter is far faster when handling this kind of simulation. Ultimately, Chen says, his system will be able to detect a contaminant in one minute, and he calls that estimate "rather conservative."

Still, to really safeguard public spaces like commercial airplanes, sensor technology will also have to improve. "Most chemical agents can be detected by sensors in real time, but not biological agents," Chen says. "However, the development on biological sensors has momentum. As soon as we have biological sensors that can give us real-time information, we can use it for our system and protect passengers and crew."