CHAPTER 17 datas? 4 indicate that only about 80% of the total energy which is delivered by 10 ty, is effective in burning. Thus, the effective thermal-energy delivery time is taken as 10 t, and a plot showing the relationship between 10 t, expressed in seconds, and yield is given by Figure 17-3. Thermal-radiation data from shallow underwater bursts are nonexistent; thus, it is impossible to predict with any reliability the thermal radiation effects from euch bursts. The only evidence avail- able is the following quotatjon from Ref. 5 describing the Bikini Baker (Operation Crossroads) shot. . . "The thermal radiation was extremely intense during the first small fraction of a second; the practical effect of the thermal radiation was, of course, almost nil." At Operation Hardtack, no thermal effects were observed from shot Umbrella, which was slightly less than one-third the yield of shot Baker and was detonated at 5/3 the depth. Since no other data for shallow underwater bursts are available, it can only be estimated that thermal effects decrease, perhaps linearly, with depth of burst from the effects of surface bursts to noneffectiveness at burst depths scaled to that of Bikini Baker. 17.2.3 Criteria for Assessing Thermal Effects on Materials Criteria for assessing thermal damage are usually expressed in terms of the various radiant exposures and yields that produce the same de- gree of damage. These criteria have been determined from field-test and laboratory data. At field tests, damage was determined from targets located at known distances from surface zeros of known-yield detonations. References 6 to 15 are some of the American and British reports of both field tests and laboratory experiments to determine material-burn criteria. The most recent estimates of criteria for destruction of some of the combustibles that may be found topside on a surface ship are given in Table 17-1. ‘The tabulated values of cal/cm@ were determined by measuring the thickness of the specified materials, and using nomographs that correlate material, color, and weight, with the thermaldamage criteria. These estimated values, based on extrapolation from experiments with cellulose products and correlated with field-test and laboratory data, are criteria for the specified untreated materials at a relative humidity of 0%. For a relative humidity of 50%, values should be mitiplied by a correction factor of 1.2; for a relative humidity of 70%, by a correction factor of 1.27. While flameproofing helps prevent the spread of fire, recent experiments”**indicate that it reduces the ignition point of some materials, so that they will smolder, char, and be destroyed without flaming. The effect of flameproofing on = For ylelds and depths of burst see Table 17-2. **Dersonal communication from Stanley B. Martin, USNRDL. 17-9 et ne ee re te ene eeee — ~_ —_——~- = pee eeee me me wee