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The FAA also recognizes that the federal launch ranges may perform separate Ec analyses for three different
hazard categories, including debris, toxic releases and blast overpressure. When the FAA relies on a federal launch range’s Ec analysis to determine whether the FAA Ec requirement is met, the FAA is interested only in the debris
analysis performed by a range, and this provision makes that clear. For toxic releases and blast overpressure, the federal launch ranges implement specific safety requirements designed to keep toxic releases and the effects of blast from reaching the public. For example, if more than a given number of parts per million of a toxic release would reach people, a launch will be delayed until conditions improve. Likewise, if atmospheric effects threaten to carry overpressure impact to persons outside the federal launch site, a launch will be delayed. Because these measures achieve safety, the FAA will rely on them rather than implementing an Ec analysis requirement for toxic
releases and blast overpressure.
Space Access raised the question of whether an Ec of 30 x 10-6 meant that if an accident occurred and 100,000
people were exposed then 3 deaths would occur. Space Access at 8. The FAA wishes to take advantage of this opportunity to clarify the concepts involved. Ec is the expected average number of casualties per launch of a launch vehicle. The consequence measured is casualties, which includes serious injury as well as deaths, and the
measure is per event, namely, launch. Space Access based its question on the assumption that 30 x 10-6 is "3 per 100,000" persons. That Ec is a measure of casualties rather than deaths aside, expected casualty is measured for
each event, which, in this case is a single launch. Although Space Access is, of course, correct that an Ec of 30 x
10-6 is equivalent to 3 per 100,000, the 100,000 refers not to exposed persons, but to the number of launches that would have to be conducted before one would expect statistically that total number of casualties. One would have to launch 100,000 times to statistically reach 3 casualties.
Space Access sought clarification on the differences between individual and collective risk. In contrast to the more familiar measure of risk, namely, individual risk, which describes the probability of serious injury or death to a single person, the launch industry’s common measure of risk is collective risk. Collective risk constitutes the sum total launch related risk, that is, the probability of injury or death to that part of the public exposed to a launch. Collective risk is analogous to an estimate of the average number of people hit by lightning each year, while individual annual risk would be an individual's likelihood of being hit by lightning in any given year. Collective risk may be expressed in terms of individual risk if certain factors associated with any given launch are taken into account. Also, individual risk may be—and will be, in most instances— less than collective risk, depending on the size of the population exposed. For example, a collective risk of Ec of 30 x 10-6 for a defined population of one
hundred thousand people exposed to a particular launch results (assuming the risk is spread equally throughout the defined population) in a probability of injury or death to any one individual exposed of 3 x 10-10 (three per ten billion).
In its comments, Space Access argued for a stricter standard on the basis of what it understood to be other measures of risk. Space Access analyzed the FAA’s proposed measure in terms of two categories: background risk, which may be further categorized as a combination of voluntary and involuntary risk, and other launch risk thresholds. Contrary to the contentions of Space Access, the FAA finds that the comparison to voluntary risks is appropriate. Even, however, when compared to involuntary risk, if the risks of launch are expressed in terms of individual risk, launch risk usually compares favorably. In fact, it is possible to have an unacceptably high expected casualty value while still having an extremely low individual risk level.
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Commercial Space Transportation Licensing Regulations(31)
