Operation Hardtack, Project 4.3, Effect of Light from Very-Low-Yield Nuclear Detonations on Vision (Dazzle) of Combat Personnel

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Detonations on Vision (Dazzle) of Combat Personnel Headquarters Field Command Defense Atomic Support Agency Sandia Base, Albuquerque, New Mexico This is an extract of WT-1664, which RESTRICTED DATA as of this date. Extract version prepared for: DEFENSE NUCLEAR AGENCY Approved for public release;

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REPORT DOCUMENTATION PAGE READ INSTRUCTIONS BEFORE COMPLETING FORM Operation HARDTACK - Project 4.3 Effect of Light From Very-Low-Yield Nuclear Detonations on Vision (Dazzle) of Combat Personnel Approved for public release; unlimited distribution. 17. OISTRIBUTION STATEMENT (01 Ih. .b.lr.ct m1.r.d In Block 20. I I dlll.r.nl I r o n R.porlJ IO. PROGRAM ELEMENT. PROJECT. TASU AREAL .URK UM IT YU Ye ERS This report has had the classified information removed and has been republished in unclassified form for public release. This work was performed by Kaman Tempo under contract'DNA001-79-C-0455 with the close cooperation o f the C1 as s if i cation Management Division of the Defense Nuclear Agency. -. Fort Monroe, Virginia Headquarters Field Comnand Sandia Base, Albuquerque, New Mexico 18. COWTCOLLIMG OFFICE NAME AM0 ADDRESS Defense Atomic Support Agency The general objective of this project was t o evaluate the dazzle effect on unprotected combat personnel a t a minimum safe distance from Shot Hamilton, UNCLASSIFIEDDD I 71 1473 EDITION OFI NOV 6 5 IS OBSOLETE

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This report has had classified material removed in order to make the information available on an unclassified, open publication basis, t o any interested parties.This effort to declassify this report has been accomplished specifically to. support the Department o f Defense Nuclear Test Personnel Review (NTPR) Program. The objective is to facilitate studies of the low levels of radiation received by some individuals during the atmospheric nuclear test program by making as much information as possible available to all interested parties. classified as Restricted Data o r Formerly Restricted Data under the provision of the Atomic Energy Actof 1954, (as amended) o r is National Security Information. This report has been reproduced directly from available copies of the original material. The locations from which material has been deleted is generally obvious by the spacings and " holes " in the text. Thus the context of the material deleted is identified to assist the reader in the determination o f whether the deleted information is germane tohis study. in preparing this report by deleting the classified material and ofthe Defense Nuclear Agency that the report accurately portrays the contents of the original and that the deleted material is of little or no significance to studies into the amounts o r types of radiation received by any individuals during the atmospheric nuclear test program. The material which has been deleted is all currently It is the belief of the individuals who have participated

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This report presents the final results of one of the projects participating i n the military-effect programs of Operation Hardtack. Overall information about this and the other military-effect projects can be obtained from WT-1660. the “Summary Report of the Commander, Task U n i t 3. ” This technical summary includes: 0) tables listing each detonation with its yield, type, environment, meteorological conditions, etc. ; (2) maps showing shot locations; (3)discussions of results by programs; (4) summaries of objectives, procedures, results, etc., for all projects; and (5) a

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The general objective of this project was to evdnate the dazzle effect on unprotected combat personnel at a minimum safe distance from Shot Hamilton, a fractionalkiloton nuclear detonation. The experimental procedure required personnel of three test groups (who were oriented at 90. 135 and 180 degrees sway from ground zero at a distance of 5,700 feet) to determine and record visual acuity immediately following the shot a d , in 'rapid sequence, determine a d record form and color perception of test objects at successively greater distances from the groups. The results showed no significant degradation of vision from dazzle under the conditions of this study. From review and analysis of previous studies of dazzle and dark adaptation it is concluded that loss of combat effectiveness as a consequence of dazzle will not constitute a major hazard for combat personnel.

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The primary purpose of this project was to obtain information on the dazzle effect that would be useful i n developing operational guidance for tactical commanders. A bonus objective was to provide the group of officers participating in -%- projgct the oppor--ty of witnessing the fifing of this prototype warhead The Project Officer aesir esf o &press appreciarion to Major General Leonard D, Heaton, The Surgeon General, formerly Commanding General, Walter Reed Army Medical Center, for making available the services of Colonel Austin Lowrey who acted in the capacity of ophthalmological consultant for the project.

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The project objective w a s to evaluate the dazzle effect on front-line combat troops, with specific objectives to determine the degree of dazzle to unprotected personnel at minimum safe distance from ground zero, and the duration of the dazzle effect before combat personnel could again become effective. 1.2.1 General. The dazzle effect, the after image, and the retinal burn constitute the major effects on the eye from the thermal and light portion of the energy spectrum of the nuclear detonation (see Table 1.1 for definitions). Dazzle is that condition in which the vision is confused by an excess of, or overpwererJ'by. light. It may%e caused by the irregular dispersion of light, particularly unpolarized light reflected from the ground or other surfaces or from clouds. The extent of dazzle is determined primarily by the intensity of the illumination impinging upon the eye and is not directly dependent upon orientation with respect to the light the image of the luminous source must fall upon some part of the retina in order for a scotoma to occur. After images occur following excessive 'retinal stimulation and are due to extreme bleaching of the retinal photochemical elements. Time, distance, color, and luminosity are factors in the production of after images. The after image primarily involves the central portion of the retina and may last from a few seconds to several hours following the viewing of a nuclear detonation. Retinal burns and s c a r formation are not part of the uncdmplicated case of after image formation. The term flash blindness has been employed to describe both phenomena, dazzle, apd after-image formation. Since flash blindness has the connotation of both permanence (which does not exist in either situation) and the formation of a disabling scotoma, the adoption of this term has led to a general misunderstanding of the nature and extent of the loss of effectiveness.which might follow exposure of the eyes to a nuclear hash. For the military, the connotation of blindness has been particularly unfortunate insofar as the factor of morale is concerned. The t e r m dazzle has received increasing acceptance as a synonym for both the true dazzle effect and after image formation. While this term may be subject to criticism for perpetuating the same type of ambiguity as w a s implied by the use of flash blindness, it has the advantage of more adequately describing the phenomenon with the greater probability of occurrence and lessening the anxiety occasioned by the use of the term The formation of the after image, on-the other hand, depends upon orientation since

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Retinal burns are caused by the focusing of visible and infrared radiation upon the retina at such levels of irradiance as to cause tissue destruction. Pupil diameter, distance, and atmospheric attenuation a r e factors influencing the size and severity of retinal burns. in scar formation and possible loss of, o r decrease in, visual acuity in that portion of the retina upon which the fireball was focused. ation depends upon the fact that while the radius of the image of the fireball upon the retina varies inversely with distance, the energy per unit a r e a distributed on the retina will be constant, except for attenuation by the atmosphere and the ocular media. While These burns can result in permanent damage to t h e eye terminating The occurrence of retinal burns at distances of many miles from the point of detonAfter image. A visual impression lasting after the image proper has ceased to Blink reflex. Reflex response of the eyelids to a sudden flash of light resulting in closure of the lids. On the average this.reflex requires 100 milliseconds to part exposed to view through the ophthalmoscope. Luminance. The characteristic properly of an object o r an area which makes it appear brighter or darker to the eye. Mesopic vision. Vision using bok rods and cones. Millilambert. Unit of luminance. One lambert equals l / x candle/cm*. N it Unit of luminance, equivalent to 1 candle/mt; o r 0.0929 candle/ft’. square millimeter of pupillary area froma surface having a brightness of 0.1 or greater than that of moonlight. Scotoma. A blind or partially blind area in the visual field which may be temporary less than that of moonlight this light intensity. The prtion of the interior of the eyeball around the posterior pole. The Unit of intensity of light at~theretina. The illumination received per Central vision which functions when light intensity is equal to Peripheral night vision which functions when light intensity is The central portion of the retina cannot function at Equal to 10/n x pupil area (mm’) x luminance (millilamberts). the inverse square law causes irradiance to drop sharply with distance the square of the radius of the image decreases proportionately with the square of the irradiance. An extensive study of retinal burns in Northern Europe resulting from viewing ‘solar eclipses with the eyes unshieJded showed that the extent of retinal detachment and the residual effects of scar formation have been over-emphasized. passage of a number of years there was a minimum amount of loss of vision and it w a s difficult to visualize the burn sites (Reference 1). which have occurred at past nuclear tests, all had minimal residual visual defects with one exception where the image of the fireball w a s centered directly over the Of the cases of retinal burns

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UnderSthe conditions of the test reported i n this paper, orientation of the groups of subjects was such as to preclude the formation of a retinal image. There was, therefore, nb possibility of either a temporary after image or a more permanent retinal THiis report deals solely with the dazzle effect except for such portions of the backgraund material which necessarily also include data on the after image and the retinal The majority of the ophthalmological studies conducted during past nuclear tests were designed to obtain specific information on the performance of filters, shutters, and goggles as well as to evaluate the effect of variofis types of lighting conditions on instrument reading and other specialized tasks of primary interest to aircrews. The data obtained by these studies does not lend itself to ready extrapolation to the specific conditions with which the ground forces are primarily concerned. the ability of the combat soldier to recover from dazzle and continue to operate effectively in a tactical role. The airman is placing increased reliance upon central vision in the performance of his operational task. As a consequence, the problem of dazzle, for him, can be defeated quite readily by the application of the principle of increased illumination of instruments o r other operating gear. The task of the infantryman, on the other hand, involves placing primary reliance upon the peripheral visual fields in the detection of form and movement in the dark o r near-dark when engaged in combat resolved by the general application of the principles learned at past tests. not be adversely affected by glare and that the duration of the dazzle effect at night when individuals are fully dark-adapted can be measured in minutes rather than in This is a difference not only in degree but also in kind which cannot be These studies did, however, indicate that-troops in a daytime environment would 1.2.2 Data from Nuclear Detonations. The Ophthalmological Survey Group which studied the Hiroshima and Nagasaki casualties investigated the impairment of visual acuity following those two detonations. than about 5 minutes was reported among the survivors. iduals within 2,000 yards of ground zero, no lesions were found in the fundus that were believed to be directly related to the flash of the nuclear detonation. In those cases in which impairment of vision was reported, the survey data does not permit of analysis on the basis of distance from or orientation toward the detonation point. At Operation Buster (Reference 2), a group of individuals positioned in an aircraft orbiting at 15.000 feet, 9 miles from ground zero, looked directly at the flash and then read test charts to check visual acuity. Unprotected test subjects suffered temporarily impaired vision ranging from less than 20/400 to essentially normal vision immediately after the flash; however, all recovered within 2 minutes. Other subjects in the aircraft facing 180 degrees away from the flash experienced no visual impairment. It was concluded th-at, generally, light-adapted subjects were not seriously handicapped by the nuclear flash at the distance at which they were exposed. located 10 miles from ground zero and oriented directly toward the burst observed the flash either through red filters o r , alternately, with the eyes unprotected. The red lens w a s selected in order to filter out the high short-wave content of the early part of the bomb spectrum and to permit reading of red-lighted instruments while using the filters. No case of flash blindness lasting for more In one group of 1.000 indivUnprotected subjects regained g o d mesopic vision in approximately

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132 seconds, while those wearing filters required 111 seconds to regain the same degree of vision. The ability to distinguish form at 0.001 ft-candle of illumination (approximately that of moonlight) was regained in 310 seconds for unprotected individuais and 245 seconds for t'nose wearing filters. When threshold illumination w a s reduced to 0.00001 ft-candle (clear starlit night) an average of 671 seconds was required for unprotected subjects to regain form vision. described a large white o r yellow-white absolute scotoma. shape and from 15 to 25 degrees i n size. in size to 4 to 6 degrees in area. The density of the scotoma became progressively less with decreasing size and at the end of 6 minutes most observers had difficulty in outlining the involved area. -Each of the two shots at which subjects were exposed were of approximately 14-kt yield. During Operation Upshot-Knothole (Reference 4), groups of subjects were exposed to a total of four shots ranging in yield from 1 6 to 51 kt at distances which varied from 7 to 14 miles. All subjects were dark-adapted and oqiented toward the fireball. Protection was afforded by combined infrared absorbing and red transmitting filters, .chosen to filter out a large portion of the.yisible and infrared spectrum while permitting reading of red-lighted instruments. of the total incident upon the eye by the use of the filters. sky, less than 0.001 candle/m*, perception …