CHAPTER 17 It was found’°at shot Umbrella that 90% to 95% of air-sample activity collected in the test compartments was due to particles in the sudmicron eize range. The particles were readily airborne, and were capable of being respired. ration Wi : There was no detectable contamination of the interior of YAG 39, except for the slight contamination indicated in various seawater cooling systems and in the main trunk and pipe lines of the washdown system.31 3- British Experiments A mist was simulated at preliminary British trials, according to Ref. 92, and measurements were made of particulate deposited in the combustion-gas paths of the boilers. It was found that more than 95% of the particulate intake consisted of “large” size particles that were deposited in the plenum chamber and fans. About 15% to 20% of the total radioactivity that got past the fans deposited as small particles on the doiler brickwork, and about 20% of the small-particle intake deposited as soot in the boiler (10% in 4 the main tube banks and 10% in the economizer). 17,8.4 Summary Previous studies have indicated that the combustion-and ventilationair systems are the only means of contaminant ingress of significance aboard operable ships. For water-surface bursts, it 1s estimated that negligible amounts of contaminant would gain access to below-decks spaces via these systems. However, test data in verification of this estimate are meager, and no theoretical analyses of the situation have been performed. For underwater bursts, theoretical analyses indicated that in ships traversing the base surge from a Shot Baker type of burst, the doses due to contaminated aerosol reaching below-decks spaces via ventilation or combustion-air ducts would be small in comparison to the weather=- deck doses. However, it was pointed out that such doses could become significant to personnel who are well shielded from the weather- deck radiation. Also, the amount of deposition along the ducts, an unknown factor, would affect the total doses. Available test data from Shot Umbrella have, to an extent, verified the theoretical estimates. The weather deck transit dose on the DD-592 was slightly greater than 500 r in 30 min. In below-decks test compartmentss doses due to ingress of contaminated ventilation air were estimated®to be between 1.5 and 76 r. The minimum estimated ingress dose in each compartment is within + 50% of the theoretical estimate of 1.3% of the transit dose, althoughsome of the maximum estimated ingress doses are as mich as a factor of 7 larger than the theoretical estimate of Ref. 88. 17-10) The doses at Operation