This 1 in 3,200 is the chance that out of 6+ billion people, someone will get hit by debris, the odds that there will be at least one person. By comparison, the odds that at least one person on Earth will be struck by lightning are almost 100% - the chance that no one at all will get struck in the next year are 0%.
The math for this would be 1 - the chance of an individual getting hit (say, 1 - 0.00000000005 = .99999999995), taken to the power of the number of people on Earth (and remember that when fractions less than 1 are multiplied together, they move towards 0), then that value subtracted from 1.
Thanks, now I’m having nightmares of stat class, lol! Good info, thanks.