12 3.7 *e Safety of Operators Despite the nature of the work, no significant radioactive contamination of the personnel is reported to have occurred. People working in situations where airborne hazards could be anticipated wore face masks and good personal hygiene procedures were required. The operators wore dosimeters. Routine urine analyses and film-badge readings showed no significant exposure. It should be noted that of over 5,000 filters from air samplers, over 50 percent showed no contamination from transuranic elements, over 95 percent showed less than 1 percent of the maximum permissible concentration (MPC), and none showed more than 10 percent of the MPC (Defense Nuclear Agency 1980). Over 4,000 U.S. servicemen served on the atoll during the cleanup and 6 lost their lives (2 deaths resulted from industrial accidents, 2 from a recreational accident, and 2 from causes "unrelated to the environment"). . 3.8 Cactus Crater The Cactus Crater, which received all the contaminated debris and soil from the atoll, is situated on the reef side of the northern end of Runit Island (Figure 4). Most of the crater rim is on land, but before construction of the dome, about a quarter of the circumference was open to the ocean at high tide and another consisted of a narrow apit of coral. A surface shot in May 19583 produced the 350-fcot-wide and 30-foot-deep crater. About 200 feet to the northeast of Cactus Crater on the ocean side is a somewhat larger crater, LaCrosse, which was produced by a surface shot in May 1956. The rim of LaCrosse at high tide appears only as a few isolated rocks above the water. The original plan was to use LaCrosse Crater first and to.use Cactus only if there was more material than LaCrosse could hold. Por logistical reasons, however, the order.was reversed and Cactus alone proved to be sufficient size for the disposal operation. . The Cactus Crater was not formed in undisturbed rock. The Zebra Tower shot was detonated 217 feet southeast of Cactus in May 1948 and the Dog Tower shot, 291 feet southeast of Cactus in April 1951. These two shots caused fracturing of the rock around the site of Cactus (Defense Nuclear Agency 1981, p. 409). The Zebra Crater was filled in and oiled to prevent dust while the Deg Tower was being worked on, and the Dog Crater and contaminated areas were made “radiologically safe" by dumping the contaminated debris in the crater and then covering the contaminated area with clean sand. It is apparent, therefore, that there is a good deal of buried radioactive material near, but not inside, the Cactus Crater and that the surrounding rock is heavily fissured. . . When ,the Cactus device exploded, a large amount of rock. much of . it pulverized into small particles, was thrown upwards. Much of this material fell back into the crater so that the original hole was half filled with debris. The true crater is therefore twice as deep as it appears to be, and this was demonstrated several years ago when a hole was drilled through the debris to a depth beyond the bottom of the true Crater. A gamma counter was lowered down the hole and activity levels were recorded at different depths (Figure 5). At the bottom of the Cc ee i ruled = visible crater, the counting rate increased sharply from near zero to ‘about 4800 counts per second (cps). The counting rate then decreased