Number of men exposed and man-years at risk by category of exposure, duration of exposure, and years since first exposure.

* All men were exposed for ≥ 6 months.† Men who at first had low or moderate exposures and who were subsequently highly exposed contributed man-years at risk in the low or moderate categories initially and to the high category after their first exposure in that category. The numbers of men in each category, therefore, add up to more than 427 in all, as some men contributed to more than one category. Similarly, all men who contributed man-years at risk ≥ 10 y after first exposure and for durations of exposure of ≥ 2 y also contributed to man-years at risk ‡ High = men who may have been exposed to about 1–10 ppm hydrazine vapour in the ambient air; moderate = men unlikely to have been exposed to ≥ 1 ppm and probably Number of men exposed and man-years at risk by category of exposure, duration of exposure, and years since first exposure.