the cause. The CAB launched an urgent research program in an attempt to identify conditions in which fuel vapors in the wings could have been ignited by lightning. Within a week of the crash, the FAA issued an order requiring the installation of static electricity dischargers on the approximately 100 Boeing jet airliners that had not already been so equipped. Aviation industry representatives were critical of the order, countering that there was no evidence that the dischargers would have any beneficial effect since they were not designed to handle the effects of lightning. They said that the order would create a false impression that the risk of lightning strikes had been resolved. The CAB conducted a public hearing in Philadelphia in February 1964 as part of its investigation. Experts had still not concluded that lightning had caused the accident, but they were investigating how lightning could have triggered the explosion. The FAA said that it would conduct research to determine the relative safety of the two types of jet fuel used in the United States, both of which were present in the fuel tanks of Flight 214. Criticism of the JP-4 jet fuel that was in the tanks centered around the fact that its vapors can be easily ignited at the low temperatures encountered in flight. JP-4 advocates countered that the fuel was as safe, or safer than, kerosene, the other fuel used in jets at the time. Pan Am conducted a flight test in a Boeing 707 to investigate whether fuel could leak from the tank-venting system during a test flight that attempted to simulate moderate to rough turbulence in flight. The test did not reveal any fuel discharge, but some evidence showed that fuel had entered the vent system, collected in the surge tanks, and returned to the tanks. Pan Am said that it would test a new system to inject inert gas into the air spaces above the fuel tanks in aircraft in an attempt to reduce the risk of hazardous fuel-air mixtures that could ignite. On March 3, 1965, the CAB released its final accident report. The investigators concluded that a lightning strike had ignited the fuel-air mixture in the number-one reserve fuel tank, which had caused an explosive disintegration of the left outer wing, leading to a loss of control. Despite one of the most intensive research efforts in its history, the agency could not