The potential for a person to be seriously injured by a drone strike appears to be dramatically less than the potential of being injured by firmer objects of the same mass, according to a study released April 28 by the Federal Aviation Administration’s unmanned aircraft systems (UAS) center of excellence. The FAA plans to incorporate the findings in a regulation governing flights of small drones over people, which is currently not allowed.
“UAS are more flexible; when they hit (a person) the foam and the plastic portions of the vehicle tend to strike and then the drone flexes,” said David Arterburn of the University of Alabama-Huntsville, the study’s principal investigator. “This is similar to a soccer ball hitting you in the head. When the soccer ball hits you in the head it bounces off and you don’t have all that energy transferred to your head. A lot of the energy that comes in the problem stays with the drone because of its flexibility, and that’s unique to this class of vehicles that are made from plastic and foam materials.”
Nevertheless, the study also indicated that drone camera payloads “are a huge problem; they need to be looked at more dramatically. They can be more hazardous then the drones that are carrying them,” Arterburn said. “If they separate they’re actually more significant because their velocities are higher and they’re stiffer.” Among other conclusions, the study found that blade guards are essential for rotary-wing drones to protect against lacerations. It also suggested that consumer electronics standards for lithium polymer batteries are not adequate for drones when considering the possibility of a fire, and that a “unique standard” may be needed.
The FAA and the Alliance for System Safety of UAS through Research Excellence (ASSURE), a Mississippi State University-led coalition that serves as the agency’s UAS center of excellence, presented the findings of the “UAS Ground Collision Severity Evaluation” study during a teleconference with reporters.
In April 2016, an FAA micro UAS aviation rulemaking committee recommended that operators be permitted to conduct limited flights of small drones over people if the drone presented a 30 percent or lower chance of serious injury as defined by the abbreviated injury scale (AIS), a scoring system developed by the Association for the Advancement of Automotive Medicine to quantify injury potential. The ASSURE researchers focused on the same probability of causing an AIS 3 injury—the level for serious—as the measure for its test results. Such injuries might include a concussion or small lacerations up to a skull fracture, Arterburn said.
Using an automotive crash-test dummy, the researchers compared the probability of sustaining AIS 3-level head and neck injuries from being struck by a DJI Phantom 3 quadcopter versus pieces of wood and steel, with each of the three objects weighing about 2.7 pounds and traveling at similar impact velocities. The probability of sustaining a neck injury from being struck by the drone was 11-to-13 percent when correlated with Federal Motor Vehicle Safety Standard 208, the standard the National Highway Traffic Safety Administration uses for automotive crash protection. Wood and steel each presented a greater than 60 percent probability of causing a neck injury. The probability of the drone causing a serious head injury was less than 1 percent, while wood and steel were each close to 100 percent.
“This is new research that’s based on test data,” Arterburn said. “The Federal Motor Vehicle Safety Standard 208 allows the correlation of what the dummy experiences in terms of force and neck movement to be correlated with that abbreviated injury scale.”
Earl Lawrence, director of the FAA’s UAS Integration Office, said the ASSURE study results will directly support the agency’s flights-over-people rulemaking effort. The FAA had expected to release a draft of that regulation by the end of 2016, but the rule is now being “reevaluated” to incorporate changes sought by other federal agencies—chief among them relating to security, according to Lawrence. He was not able to say when a draft rule will be made public.
Shenzhen, China-based DJI, the leading manufacturer of small recreational and commercial drones, welcomed the study findings. DJI has commissioned a study that concluded that drones weighing up to 2.2 kilograms (4.85 pounds) can be safely flown with low risk to people on the ground, far heavier than the FAA’s 250-gram threshold requiring drone operators to register with the agency.
“ASSURE’s report is the first thorough scientific study of the risk drones pose to people on the ground, and we are pleased that it validates our own findings that earlier measurement standards grossly overstate the risks of injury from a drone,” said Brendan Schulman, DJI vice president of policy and legal affairs. “ASSURE’s work provides a deeper scientific understanding of the kinetic and aerodynamic factors which make drones far safer than some had thought.”