Too many negatives in this sentence. Trying to parse: "It may pose a real health risk; but, iirc, for each decade of air travel, the number of deaths by terrori

Too many negatives in this sentence. Trying to parse: "It may pose a real health risk; but, iirc, for each decade of air travel, the number of deaths by terrorists has been less than the combined impact of these new x-rays." Did I parse that right?