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OPERATIONAL SIGNIFICANCE OF THE FLASH BLINDNESS PROBLEM Walton L. Jones Bureau of Medicine and Surgery Bureau of Naval Weapons A pilot who has dropped 17 atomic weapons during various tests describes his experiences in this manner: "At the moment of burst I typically am headed directly away from the burst point. When the burst occurs, the horizon disappears and everything seems to be covered by an overwhelming glow. I can distinguish no colors nor can I see any terrain features. It is as if I am ex- periencing the white-out suffered by aviators flying in Arctic zones." That pilot flies at altitude in a large stable aircraft which can be controlled by autopilot as required. His temporary loss of vision is not as serious as if these events were to occur while he was weaving his way around hilltops and through valleys, at as low an altitude as possible, while trying to maintain an accu- rate navigation course to a target he had never seen before. In- asmuch as many Navy missions are flown under just such cir- cumstances, the problem of flash blindness has come to be regarded as quite a serious one. This paper discusses in some detail the operational signifi- cance of the flash blindness problem, and then describes the major areas of effort being undertaken in attempting both to understand this phenomenon and to provide means for minimiz- ing its hazard. The specific devices which have been developed and which are being evaluated at this time, are discussed else- where in this Report. In considering the effects on vision of the light from a nuclear burst, there are, in fact, two major areas of concern: one deals with the permanent damage, or retinal burns, and the other with temporary impairment, or flash blindness. Fig. 1 presents formal 85

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EFFECTS OF VISIBLE AND THERMAL RADIATION FROM NUCLEAR BURSTS ON VISION PERMANENT RETINAL BURNS IRREVERSIBLE TISSUE DAMAGE IS CAUSED BY THE ABSORPTION OF EXCESSIVE THERMAL ENERGY IN THE RETINA AND UNDERLYING LAYERS PRINCIPALLY THE CHOROID FLASH BLINDNESS A TEMPORARY LOSS OF VISION PRODUCED BY OVERSTIMUL ATION WITH VISIBLE ENERGY THE PERIOD OF FLASH BLINDNESS IS THAT PERIOD DURING WHICH THE INDIVIDUAL CANNOT PERFORM HIS DUTIES BECAUSE OF LOSS OF VISION FIG. 1. definitions of these problem areas. Obviously, each area is of deep concern to the Navy. Since careful study of these areas has proved that any protection provided against flash blindness will also protect against retinal burns, attention has been focused on the flash blindness problem. Flash blindness is defined as that period during which the individual cannot perform his duties be- cause of loss of vision. From an operational point of view, the concern is actually with loss of performance capability rather than with loss of vision. Thus, if any features within the cockpit can be arranged to provide benefit, such as an automatic increase in cockpit lighting following exposure, the period of flash blind- ness can be decreased, even though the overstimulation of retinal chemicals has in no way been changed. Such a concept is impor- tant since it allows one to consider means of reducing flash blind- ness above and beyond the obvious one of providing direct pro- tection for the eye. As the problem of flash blindness is placed into operational perspective, one can see that in certain respects it poses a more difficult problem than those produced by the blast, shock, and thermal radiations from the weapon. Fig. 2 shows the area within which flash blindness might occur as related to the ther- mal envelope of the weapon. Note that when the burst point is in the central field of vision flash blindness may occur at a distance as far as several hundred miles from the point of detonation. If the burst occurs behind the pilot, however, relatively little flash blindness should occur unless there are clouds or other highly reflective surfaces within his direct field of view. The impor- tant point to note in this figure is that it is necessary to protect

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FLASH BLINDNESS HAZARD RELATED TO POSITION FROM BURST POINT FIG. 2. a pilot from flash blindness at much greater distances from the burst than is required for protection from thermal radiation effects on his skin. To achieve a genuine understanding of the operational impor- tance of flash blindness it is necessary to review certain per- formances which are required of Navy aviation personnel. Fig. 3 lists a few of these activities for which the maintenance of ef- fective vision is critical. The first of these, low-level daylight attack, provides an excellent example. Here the pilot is trying to fly the aircraft, maintain an absolutely minimum altitude, search for navigation checkpoints, and occasionally to monitor certain of his panel instruments. The demands placed on his vision are imposing. Research conducted by the Navy indicates that with present equipment for contour flying a pilot looks out- side approximately 90 per cent of the time in order to maintain geographic orientation. It is no wonder that pilots flying these missions estimate that if their vision were lost for as brief a period as 5 to 10 sec they would in all likelihood either crash or become hopelessly disoriented. Another item in the list of activities in this figure relates to night formation flights. There are certain Navy missions in which one aircraft, which has extensive navigation equipment, will lead other aircraft to target areas. Under these circum- stances, it is absolutely essential that the pilot of the aircraft 87

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PILOTS DAY OR NIGHT OPERATIONS • LOW LEVEL ATTACK • TERRAIN CLEARANCE • NAVIGATION CHECKS • INFLIGHT REFUELING • FORMATION FLIGHT • DECK OPERATIONS • TAXI • LAUNCH • LAND CARRIER PERSONNEL • NIGHT DECK OPERATIONS NAVAL AVIATION ACTIVITIES REQUIRING FULL USE OF VISION FIG. 3. being led fly a tight wing position on the lead aircraft. To do this he must be able to perceive the outline of the lead aircraft as well as its running lights. To try to follow by reference to the lights alone leads to autokinesis and subsequent severe seizures of vertigo. Thus, the pilot is in a situation in which he must not only be able to see outside the cockpit at all times, he must also main- tain a high level of dark adaptation throughout the flight. Obvi- ously, in this situation a period of flash blindness of even a few seconds would have devastating consequences. As a final item from Fig. 3, consider the night deck operations performed on a carrier. During night launch operations, for example, flight-deck personnel must maneuver jet starting equip- ment around the deck, guide aircraft to the launch position, and aid in preparing the aircraft for launching. While doing these tasks, they must avoid spinning props, jet intakes and exhausts, and moving tractors. The noise level is such that warning shouts are almost useless. And all this takes place on a deck that, on a moonless night, is illuminated only by red flood lights located seven stories up on the island of the carrier. Here, again, any light which produces flash blindness or even destroys dark adap- tation could be quite serious. Many persons have proclaimed that with airborne radar and 88

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radar-controlled intercept missions there is no need for con- cern with night vision. It is true that a pilot no longer tries to locate enemy fighters at night by purely visual means. But, as one can see from Fig. 3, there are many activities performed by Navy personnel, both at night and during the day, for which the maintenance of effective vision is of the utmost importance. Realizing the importance of maintaining the visual capability of Navy personnel under combat conditions, the Navy has had, for several years, an active program to investigate flash blind- ness and to develop protective devices and procedures. Fig. 4 shows the major areas of effort within this program. In an at- tempt to make the program as comprehensive as possible, efforts have ranged all the way from laboratory investigations of flash blindness, using high-intensity light sources, to the preparation of training and indoctrination materials for pilots. NAVY PROGRAM CONCERNING FLASH BLINDNESS PROTECTION AREAS OF EFFORT l LABORATORY INVESTIGATIONS OF VISUAL IMPAIRMENT FROM EXPOSURE TO HIGH INTENSITY LIGHT SOURCES 2 COLLECTION OF DATA FOR MODEL ALLOWING PREDICTION OF FLASH BLINDNESS HAZARD IN OPERATIONAL ENVIRONMENTS. 3 DEVELOPMENT AND EVALUATION OF FLASH BLINDNESS PROTECTION DEVICES. 4 PREPARATION OF TRAINING AND INDOCTRINATION MATERIALS FOR PHOTS FIG. 4. Early efforts were aimed primarily at providing protection from the thermal effects of the weapon rather than at protecting against flash blindness. At least in part, some protection from flash blindness has been provided by these efforts. For example, Fig. 5 shows a cockpit enclosure designed to be closed by the pilot, thereby protecting him from thermal effects. In later air- craft, this protective hood will close automatically when energy from the burst is detected. Thus, some measure of protection from flash blindness will be afforded, particularly from those weapons which produce extended fireballs. A number of studies have shown that the recovery of vision after exposure to a high-intensity flash is much more rapid if the visual task is brightly illuminated. It has been found, for 89

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READY POSITION f LIGHT BY VISUA- CONTACT CLOSED POSITION FLIGHT BY INSTRUMENTS OPERATION OF COCKPIT THERMAL ENCLOSUR- FIG. 5. example, that a period of flash blindness that would last from 20 to 30 sec under normal lighting can be reduced to approximately 2 sec simply by floodlighting the visual task with 50 foot-candles. Thus, an obvious means of reducing the period of flash blindness suffered by a pilot is to provide for an automatic increase in the intensity of cockpit lighting immediately following exposure to a burst. A system for automatically increasing the intensity has been developed. While thermal shields and automatic high-intensity cockpit lighting systems do offer some protection against the effects of flash blindness, the most obvious means of providing this protec- tion lies with the development of devices designed to limit the visible energy which reaches the eye. Fig. 6 lists areas which offer protection possibilities. As can be seen, these areas range from the use of a simple monocular eye patch to the highly so- phisticated television devices indicated under indirect vision techniques. AREAS OFFERING PROTECTION POSSIBILITIES AGAINST FLASH BLINDNESS 1. MONOCULAR EYE PATCH 2. PARTIALLY-OCCLUDING (FIXED FILTER) GOGGLES 3. FULLY-OCCLUDING (ACTIVE) GOGGLES 4. PHOTOTROPIC GOGGLES 5. PHOTOTROPIC CANOPY 6. INDIRECT VISION TECHNIQUES FIG. 6. 90

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As a means of providing a measure of protection while more efficient devices are developed, the Navy has considered the use of monocular eye patches. Figure 7 shows a pilot wearing an eye patch during a recent evaluation at the Navy Aviation Medical Acceleration Laboratory to determine the extent of visual im- pairment caused by light leaks around the patch. For a time there was concern that the afterimage produced in the exposed eye would cause a cortical blurring of the image received from the protected eye after the patch was removed. Recent limited testing, however, indicates that this blurring is not sufficient to cause alarm. Useful vision is regained in the protected eye almost immediately following the flash, while vision through the exposed eye may remain impaired for many seconds. The major problem with this protective device, however, is that since vision is so critical to most missions the maintenance of vision in one eye is generally regarded as only a poor interim solution to the pro- tection problem. Such patches, however, can be carried by pilots as a means of achieving some measure of protection during emer- gency conditions. For several years, the Navy has been investigating the pro- tection potential of fixed-density goggles. In 1958, general pur- pose light-restrictive filter goggles, known as LRFG-58, were issued. Fig. 8 shows these goggles being worn with the aviator's helmet and oxygen mask. Photometric transmission of these goggles was 1 per cent. It was hoped that they would allow a FIG. 7. 91

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FIG. 8. pilot to see well enough to fly during daylight by visual contact, and at night by instruments when the instruments were flood- lighted. In spite of the obvious protective benefit of 1 per cent trans- mission goggles, they are not being used by the Navy at this time. Primary reasons are excessive visual fatigue, limited peripheral vision, and an apparent insufficient transmission of light. Recently, however, the Navy and the Air Force have tested gold-covered visors with no peripheral vision limitations for use during daylight missions. The gold-covered visors also have a photometric transmission of 1 per cent. The improved field of vision and the apparent increased brightness in the yellow band seem to reduce problems of visual fatigue. Pilots who examined these materials initially indicated a 1 per cent coating was too dark to visualize other aircraft making the device unacceptable for daylight use. Accordingly, the Navy has changed to a 3 per cent coating which has met with much greater pilot acceptance and seems to involve only a nominal loss of protection. While fixed-filter goggles might provide adequate protection against retinal burns and flash blindness, they do impose a pen- alty of loss of vision because of the low transmittance of the filter. At dusk or at night this is unacceptable. Considerable effort has, therefore, gone into the development of "active" devices which are transparent normally, but which "close" when exposed to 92

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intense light. Another paper in this Report will be devoted spe- cifically to the characteristics of these active devices. As has been indicated, there are a number of avenues being pursued in the quest for effective protective devices. It is quite possible that more than one will be accepted as satisfactory for service use. Should this be the case, a specific protective device could be selected to match the particular hazards of a given mis- sion. However, such use of these protective devices cannot be- come a reality until more is known about the nature of the hazard. Thus, the Navy is developing a comprehensive model within which it should be possible to specify a typical or anticipated nuclear environment, and then to evaluate the extent of the flash blindness hazard for aviators flying missions within such an environment. Figure 9 shows the classes of variables which will be used in the development of the model, and, to some extent, the specific vari- ables falling within each class. One advantage underlying the development of the model is that missing parametric terms in the model can be identified which will thus tend to structure re- search efforts toward a meaningful goal. I.TMil IIIHI 1. IllilUi it tlsmn I. IIIMHI H tain nii li li|ll il mini 1. mull il liliutm i. Licitiii il dunlin iitusitf ni fintiii ). liitiici (in lint 4. litmiliiicil cnlituii t. littictiiitr it lirnii FIG. 9. VARIABLES IN ANALYTIC MODEL FOR PREDICTION OF FLASH BLINDNESS HAZARD One final developmental effort being undertaken by the Navy should be noted. Flash blindness protective devices, as they are delivered into the fleet, represent a class of equipment entirely new to pilots. These devices attempt to meet a requirement for which no previous equipment has been provided. Since they are so new and since many of them operate in a strange manner, their introduction into the fleet must be accompanied by a train- ing program designed to illustrate their method of operation and proper use. In addition, the flash blindness phenomenon itself 93

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should be so interpreted both psychologically and physiologically in a manner so that pilots understand and appreciate the inherent hazards. Considerable effort is being devoted at this time to the development of a comprehensive training program. Much of this program involves, as might be expected, training manuals and training films. However, at the heart of this program is what is termed a "flash blindness indoctrination and training device." It consists of a high-intensity flash source which simulates the light that would be encountered by a pilot should he be flying within haze conditions or over reflective terrain at the time of the flash. With this source it is possible to produce all of the features of flash blindness; that is, startle, intense afterimages, and visual incapacitation, without the risk of permanent damage to the visual system. By actually experiencing flash blindness, a pilot will better appreciate the need for protective devices and should be more highly motivated to use them correctly. Some of the reasons have been presented here as to why the Navy considers the problem of flash blindness to be quite serious from an operational point of view, and the extent of the programs being pursued to combat this hazard. In spite of the automatic characteristics of the modern weapon systems, the human eye continues to play a dominant role in many if not all military activities. With effective vision of such importance, it must be protected. 94

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THE NATURE OF RADIATION FROM NUCLEAR WEAPONS IN RELATION TO FLASH BLINDNESS1 J. H. Hill and Gloria T. Chisum Aviation Medical Acceleration Laboratory, USN Air Development Center The fireball of a nuclear weapon detonated in the atmosphere appears to radiate as a black body. The visible portion of the spectrum of this radiation produces a high-intensity flash that can cause flash blindness—the temporary reduction in visual sensitivity following exposure to a high-intensity flash. Although such a weapon flash can also cause retinal burns, this paper is limited to the nature of the radiation in relation to flash blindness. The minimum information about a light source necessary to determine whether or not it will produce flash blindness, and, if so, to design adequate flash blindness protective devices con- sists of the luminance, duration, and visual angle subtended by the source. Estimations of these dimensions of a light flash with a nuclear weapon fireball as a source can be deduced from infor- mation given in Glasstone, 1962. Although the weapon flash pa- rameters thus determined from scaling laws are, at best, esti- mates, it is hoped that the data presented will provide some guidelines for others interested in the problems of flash blind- ness research and development as they have for the scientists at Vision Research, Aviation Medical Acceleration Laboratory (AMAL). The thermal radiation from a nuclear weapon detonated at low altitude amounts to about 35 per cent of the yield of the weapon. The other 65 per cent is in nuclear radiation and mechanical energy as shown in Fig. 1. The ranges within which the latter 1. Opinions and conclusions in this report are those of the authors and do not necessarily reflect the views or the endorsement of the Department of the Navy. 95

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AIR FORCE EFFORTS IN THE FIELD OF FLASH BLINDNESS James F. Culver Ophthalmology Department USAF School of Aerospace Medicine, Brooks Air Force Base It is apparent that interruption of a pilot's vision at a critical time could prove disastrous. The problem, therefore, consists of repeatedly providing adequate vision for aircrew members up to the time of a nuclear flash, shielding their eyes from the flash, and then again providing adequate vision almost immediately. This is not a simple undertaking. The severity of the problem varies considerably, depending on the ambient illumination, i.e., during daylight the problem is minimal unless the observer happens to be looking directly at the detonation; however, night- time operation can offer an extreme hazard during certain flight operations. Flight testing has shown that pilots would prefer to have the protective device placed on the windshield or canopy rather than on the person to obviate interruption of instrument visibility during the closed state. The concept of a goggle-type protective device should not be completely discounted since there will be other operations associated with flying in which they could be most valuable. The problem of flash blindness and that of chorioretinal burns cannot be entirely divorced. Both can occur from a thermonuclear detonation. One happens to be of a temporary nature and the other is permanent. It is felt that a short summary and reference list of Air Force activities in these areas would be of interest to the members of the Armed Forces-NRC Committee on Vision. Ocular hazards were recognized from the beginning of the nuclear era, and protective goggles were provided for observers at the first nuclear device detonation at White Sands, New Mexico. Empirical data from subsequent weapons tests later indicated the extent of the problem of flash blindness and chorioretinal burns 134

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(Byrnes, 1953). Researchers at the U.S. Air Force (USAF) School of Aerospace Medicine continued to pursue field investigations of the ocular effects of nuclear flashes until the moratorium on on testing was declared in 1958. The occurrence of chorioretinal burns in rabbits was demonstrated at distances of over 300 nauti- cal miles from a thermonuclear detonation (Glasstone, 1962). During this period, prototype protective devices were also tested by the USAF Aerospace Medical Research Laboratory (Gulley, Metcalf, Wilson & Hirsch, 1960). During the more recent 1962 series of weapons tests, per- sonnel from the USAF School of Aerospace Medicine tested retinal-burn prediction models. This was the most comprehen- sive experiment of its type to date, and provided extensive, well- documented quantitative data which will also be of great value in flash blindness research. Parallel to the experiments carried out in the field of weap- ons tests, a laboratory program to establish the chorioretinal- burn threshold was continuing. Early projects were sponsored by the United States Air Force at the Medical College of Virginia and continued by the Defense Atomic Support Agency. The excel- lent work performed by Dr. Ham, Dr. Geeraets, and their group at the Medical College of Virginia is well known. Their early studies indicate that the macroscopic-burn threshold varied from 1 to 13 calories per square centimeter (cal/cm^), depending on the retinal image size, utilizing a constant input rate (Ham, Wiesinger, Schmidt, Williams, Ruffin, Shaffer, & Guerry, 1958). Subsequent work by this group indicated this threshold could be less than 1 cal/cm^ when the energy is delivered at a very high rate. Research on the effect of high-intensity flashes on the eye at the New York Eye and Ear Infirmary has also been supported by the United States Air Force. Their findings confirmed those of the investigators at the Medical College of Virginia in the areas where the two studies overlapped (Jacobsen, Cooper, & Najac, 1962; Jacobsen, Najac, & Cooper, 1963). Studies were also con- ducted at The Ohio State University where an attempt was made to determine the effectiveness of various spectral bands in the production of chorioretinal burns (Bredemeyer, Wiegmann, Bredemeyer, & Blackwell, 1963). It is apparent that there has been much effort expended in the past on the problem of chorioretinal burns; however, data obtained in these field tests and laboratory studies are of definite impor- tance in establishing eye-protection criteria. Recently, the em- 135

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phasis has again shifted primarily to the problem of flash blind- ness. Early field studies conducted in 1952 that were devoted to flash blindness have been supplemented by the initial experiments on the operational aspects of flash blindness conducted by the Air Force Aerospace Medical Research Laboratory (Metcalf & Ham, 1958). Personnel at the USAF School of Aerospace Medicine are presently conducting an in-house flash blindness program to define the operational aspects of this problem and outline a train- ing program. Currently, a research project directed toward a better understanding of the basic mechanism of flash blindness is being sponsored at The Ohio State University (Miller & Fry, 1963). Air Force efforts to provide urgently needed protection are outlined below. In 1955, the Air Force Systems Command initiated a project to conduct the development of eye protection from nuclear flashes. As a first step, feasibility studies of the electro-optical shutter (Kerr Cell) and the electromechanical goggle (Burger & Filer, 1964; Wayne-George Corp., 1959) were conducted. The Kerr Cell approach was found not be feasible for Air Force needs, and de- velopment of the electromechanical goggle was pursued. During this same period, investigation of phototropic, or self-attenuating, filters was also being made. These were parallel developments at the USAF School of Aerospace Medicine and the Aerospace Medical Research Laboratory. The phototropic approach has resulted in at least three eye-protection systems, including the indirectly activated phototropic goggles (Barstow & Lilliott, 1961), the one-way directly activated phototropic goggle (Krekeler, 1963), and the Dynacell directly activated device (Harries, 1963). Only the one-way directly activated goggle has been field tested and deemed to be unacceptable (Parkhurst, 1963). Recent studies have proved the electromechanical goggle to be unacceptable for pilot use. A further study of an electrochemical-type shutter found it also not feasible. This was an investigation of the electro- plating principle in a shutter system (Aitken, 1962). During this same period, the development of a fixed-filter eye- protection system has been under way. This has taken the form of protective visors and goggles. Studies indicate that a 1 per cent transmittance filter (gold-plated goggle) can provide ade- quate vision for flying during daylight. To coordinate research better and to prevent duplication of effort in this field, the Oculo-Thermal Section was established within the Ophthalmology Department at the USAF School of 136

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Aerospace Medicine in 1963. It is presently engaged in develop- ing design criteria for eye protection from nuclear flashes, and prototype eye-protective devices. As previously stated, the nuclear-flash eye hazard represents a continuum ranging from temporary flash blindness to permanent retinal-burn effects. Flash blindness is receiving the primary effort. In the study of chorioretinal burns, two criteria for dam- age have been used. One of these is a visually detectable thresh- old burn. This macroscopic lesion, although a gross approach to the problem, may very likely represent minimal significant retinal damage. More recently, with the development of a mathe- matical model for retinal burns, temperature rise in the retina has been utilized as the criterion of retinal damage. Some de- finitive work has been done by Ham, at the Medical College of Virginia, and by Jacobson et al. at the New York Eye and Ear Infirmary, on the temperature rise in the retina. However, this factor remains for the most part rather elusive and in need of considerable investigation. At the present time, an attempt is being made to define the critical temperature rise by comparing laboratory burns with burns received at nuclear weapons tests. It is hoped that this approach will throw some light on the nature of the critical temperature rise. The problem, insofar as the retinal-burn hazard is concerned, consists of developing reliable indicators for threshold retinal burns, then relating this signifi- cant lesion to nuclear weapon output for the various situations. In order to assess properly the flash blindness hazard, it is necessary to define the stimulus. As a result, an in-house proj- ect has been established to develop luminance values of the vari- ous detonation conditions. Weapons effects data from actual weapon tests are being utilized for this effort. A contract is presently being negotiated to develop a mathematical expression for flash blindness. This model will made use of the best avail- able data on recovery times and weapon illuminances, and if suc- cessful, will permit computer programming for development of flash blindness safe separation distance charts. Concurrent with the development of flash blindness separation distance charts will be the development of design criteria for eye-protective devices. In order to fulfill the second requirement of the section's mis- sion, a number of nuclear flash eye-protective devices are being developed. Even though design criteria for eye-protective devices offering a high degree of confidence are not available, estimates can be made of the required protection. This is especially true 137

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in the case of retinal burns. An improved filter visor transmitting 2 per cent in the range between 200 and 2,000 millimicrons has been developed. This visor should provide adequate retinal-burn and flash blindness protection during daylight hours. The 2 per cent transmittance allows normal visual response inside and out- side the cockpit in daylight. This item is to be brought into the inventory in early 1965. Other items under continuing development are: 1. Phototropic, or so-called self-attenuating, filters which darken on exposure to ultraviolet and shortwave-length visible radiation; 2. indirectly activated phototropic filters activated by flash- tubes; 3. dynacell phototropic filters which consist of highly sensi- tive phototropic fluids flowing through filter cells; and 4. electronic triggering systems for the indirectly activated filters. It is hoped that this short summary and reference list will be of value. Unfortunately, due to regulations, classified reports cannot be referenced; however, they are available to eligible investigators. REFERENCES Aitken, J. F. Electrochemical light modulator. Wright-Patterson AFB: MRL tech. doc. Rep., 1962, No. 62-29. (Final Report, Philco Research Corp. Contract AF 33(616)-7828). Barstow, F. E.,& Lilliott, C. Development of flash blindness protective goggles. Bedford Mass.: EG&G Inc. Rep. 1961, No. B-2288. Bredemeyer, H. G., Wiegmann, O. A., Bredemeyer, A., Blackwell, H. R. Radiation thresholds for chorioretinal burns. Wright-Patterson AFB: AMRL tech. doc. Rep., 1963, No. 63-71. (DDC AD 416652). Burger, W. R., & Filer, H. C. Electromechanical goggle. Wright-Patter- son AFB: ASD tech. Rep. 1963, No. 63-451. (Final Report, The National Cash Register Co. Contract AF 33(600)-43570). Byrnes, V. A. Flash blindness. Report of Project 4.5, Operation SNAPPER. Brooks AFB (Tex.): Weapons Test Rep., 1953, No. WT-530. Glasstone, S. (Ed.). The effects of nuclear weapons. (Rev. ed.). Wash- ington: US Atomic Energy Comm., 1962. Gulley, W. E., Metcalf, R. D., Wilson, M. R., & Hirsch, J. A. Evaluation of eye protection afforded by electromechanical shutter. Brooks AFB: Weapons Test Rep., 1960, No. WT-1429. (Report of Project 4.2., Operation PLUMBOB). Ham, W. T., Jr., Wiesinger, H., Schmidt, F. H., William, R. C., Ruffin, R. S., Shaffer, M. C., & Guerry, D., III. Flash burns in the rabbit retina. Amer. J. Ophthal., 1958, 46, 700-723. 138

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Harries, R. W. The dynacell and focal plane concepts of phototropic ophthalmic nuclear flash protective device. Wright-Patterson AFB: ASD tech. Rep. 1963, No. 63-658. (DDC AD 424140L). Jacobson, J. H., Cooper, Blossom, & Najac, H. W. Effects of thermal energy on retinal function, Part I. Wright-Patterson AFB: AMRL tech. doc. Rep., 1962, No. 62-96. (DDC AD 290808). Jacobson, J. H., Najac, H. W., & Cooper, Blossom. Effects of thermal energy on retinal function, Part II. Wright-Patterson AFB: Final Rep., 1963. (Contract AF 33(616)-7685)(DDC-AD 434726). Krekeler, J. H. Development of an irreversible photo-thermosensitive ophthalmic nuclear flash protective device. Wright-Patterson AFB: ASD tech. Rep., 1963, No. 63-658. (DDC AD 424140L). Metcalf, R. D., & Horn, R. E. Visual recovery times from high intensity flashes of light. Wright-Patterson AFB: WADC tech. Rep., 1958, No. 58-232. (DDC-AD 205543). Miller, N. D., & Fry, G. A. Visual recovery from brief exposure to very high luminance levels. Ohio State University: Interim Report, 1963. (Contract AF 33(657)-9229), (DDC-AD 434729). Parkhurst, D. J. Operational test and evaluation of phototropic goggles. ENTAFB (Col.): ADC Rep., 1963, ADC/73AD/63-26, (DDC AD 428073). Wayne-George Corp. High-speed electromechanical goggle. Wright- Patterson AFB: WADC tech. Rep., 1959, No. 59-114. (DDC-AD-215828). 139

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A FLASH BLINDNESS INDOCTRINATION AND TRAINING DEVICE James F. Parker, Jr. BioTechnology, Inc. Relative to the flash blindness problem area, a flash blindness indoctrination and training device has been developed for the Office of Naval Research and the Bureau of Naval Weapons by BioTechnology, Inc. The purpose of this device is to demonstrate to pilots who might operate in nuclear combat zones what would happen to their vision, and consequently, to their mission capa- bility if they unexpectedly encounter the light from a nuclear burst. It is anticipated that this device will serve two training functions. 1. Indoctrination training. The device can be used to demon- strate dramatically the effect of "startle" and temporary loss of vision on the performance of typical flight activities. 2. Proficiency training. The device can be used to demonstrate the protection afforded by various protective systems and pro- cedures, and will allow practice in the use of these systems and procedures. The basic elements of the flash blindness device are: 1. Flasher unit. The light source is a xenon gas discharge electronic flash-tube of the quartz helix type. This unit delivers approximately 400,000 lumen-seconds (sec) of visible energy in 2 milliseconds, which simulates the initial pulse of the weapon. Simultaneously with the initial flash, three 300-watt bulbs are illuminated and gradually extinguished over a 4-sec period. This simulates the dying out of the weapon fireball. 2. Focusing hemisphere. Light from the flash source is bounced off a silvered hemisphere of 4-ft radius and is directed toward the position of the pilot, who is seated at the front of the device. 140

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3. Diffuser screen. The screen diffuses the light with approxi- mately a 30 per cent loss in intensity so that it is more repre- sentative of that which might be experienced in a nuclear environ- ment. This screen allows also for the projection of a color film which presents a view of typical terrain as seen by a pilot flying a low level, high speed mission. 4. Pilot's instrument panel. This panel provides tasks for the pilot which are representative of those performed by aviators. It can be used to demonstrate the performance decrement which occurs following exposure. 5. Operator's panel. The instructor uses this panel in con- trolling the over-all operation of the device and in monitoring pilot performance. Fig. 1 shows the major components of the device, the photo- graph being taken at the moment of flash. The operator control panel, pilot's panel, and diffuser screen are shown in this figure. FIG. 1. Major components of flash-blindness device. 141

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Fig. 2 shows the reaction of a subject as he receives the initial pulse of light. One of the most important uses of this device is to illustrate the dramatic decrease in visual recovery time which occurs when the illumination of the visual task is increased. A number of subjects have been tested in this device, under somewhat un- controlled conditions, and their recovery times noted. Table 1 presents the range of recovery times for the two conditions of illumination of the visual task. The visual task in this instance consisted simply of reading three digits, which were white against a black background, as soon as possible following the flash. FIG. 2. Subject photographed at moment of flash. TABLE 1. Range of Visual Recovery Times for Two Conditions of Illumination of the Visual Task Illumination Range of recovery times 0.5 foot-candles 20-90 sec 30 foot-candles 4-7 sec 142

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VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT James W. Miller, Chairman

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