Attachment 7 Aircraft Decontamination Study, prepared by 1st Lt. William J. Jameson Aircraft Decontamination Study Prepared by 1st Lt. William J. Jameson 1. During the period 24 June 57 through 31 July 57 an aircraft contamination study was performed with a T-33A aircraft, #53-5 105, belonging to the 4526th Test Squadron (S). During this period the aircraft was flown through the clouds on five (5) PLUMBBOB events on the wing of the first F084C sampler as it made its cloud penetrations. The events were Priscilla (24 June), Hood (6. July), Diablo (15 July), Kepler (24 July), and Owens (25 July). 2. The procedures used in this study are outlined in the attached "Contamination Buildup Study", Appendix 1. 3. The operational requirement that only one (1) 7-33 aircraft be used in this study, participating in a limited number of penetrations, placed certain limitations on the data accumulated. Despite these limitations, however, several renewal conclusions can be derived from the study. a. Contamination Buildup: Due to the limited participation in the PLUMBBOB series, but more particularly die to the vagaries of the shot schedule, the noticeable contamina- tion buildup was comparatively slight. After Owens, however, some buildup was apparent since Keppler had been fired the previous day. For example, the average contamination dose rate at ILLEGIBLE plus 48 hours was approximately twice that which would be calculated on the basis of a standard fission product decay 1 applied only to the measured Owens contamination of the T-33 (i.e. 27 r actual reading versus 23 r calculated). (See Appendix 2). at ILLEGIBLE hours the average dose rate was approximately three (3) times the dose rate predicted for Owens contamination alone. Prior to approximately ILLEGIBLE hours the average dose rate (average of all readings on the aircraft) apparently followed a straight I=Iot-1.6t.2 decay curve.1 (ILLEGIBLE decay scheme for fission product gamma radiation is in agreement with previous observations of ILLEGIBLE which is generally considered standard.2 The decay scheme generally associated with fission products is I=Iot-1.2 for gamma plus beta radiation. Since ILLEGIBLE intensities at early times after landing were more often than not off scale of the highest range beta sensitive ILLEGIBLE available,3 the gamma decay data was used in this study.) At early times after ILLEGIBLE dose rates on the contaminated buildup from previous shots. Consequently, the dose rate contribution from buildup contamination was negligible until decay during the first few hours after ILLEGIBLE had brought the Owens dose rate down to the same order of magnitude as the buildup contamination rates. The total decay scheme observed after the Owens event followed fairly closely 1 I-radiation intensity at time ILLEGIBLE in hours after burst. Io = Intensity at t-lbr after burst 2 Proj. 2.66, Early Cloud Penetrations: ILLEGIBLE; Preliminary Report, Operation ILLEGIBLE: HQ PC/AFSWP; p. 31. 3 "ILLEGIBLE" ion chamber 2 the predicted ILLEGIBLE scheme formed by superimposing or adding the rather unusual observed gamma decay scheme from Keppler to a t-1.6 decay for Owens. Since the test I-33 was not flown for six (6) days after Owens and there were no severe rain storms to wash away contamination, it would appear that the buildup should be quite close to that predicted by adding decay schemes of succeeding events. This buildup is more graphically represented by Appendix 2. The Owens gamma decay in extrapolated to indicate the decay scheme Owens would possibly have followed if there had been no contamination on the aircraft from previous events. It is interesting to note that this extrapolated decay is almost identical to the t-1.6 decay observed on Priscilla and that there was no buildup contamination on the aircraft prior to Priscilla. b. Personnel dosage and Contamination: (1) Pilot Exposure: The pilot mission exposures for the five (5) penetrations were very close to the pilot exposure of the companion F-84. The average exposure for the T- 33 was 717 ILLEGIBLE for the T-34 companion the average was 713 mr. The average exposure increment, T-33 over F-84, was less than 15; the extreme difference was 16%. The dissimilarities in the two aircraft could account for the differences. (2) Personnel contamination: Localized clothing and skin contamination was apparent on both ground crew and aircrew members engaged in routine maintenance or pre-flight activities with the T-33. Approximately 34% of the contaminated clothing turned in by all ground activity personnel (F-84 and B- 57 maintenance, sampler recovery, decon, etc.,) was from the T-33 ground crew. ILLEGIBLE 3 maintenance at ILLEGIBLE), was from the T-33 ground crew. ILLEGIBLE the period ever which these records were maintained (Diablo thru Owens) only 7 F-84 or B-57 ground crew members were required to turn in contaminated (over 7mr/hr) clothings. During the same period the T-33 crew members were required to turn in clothing 22 times. There was three T-33 penetrations and approximately 18 F-84 and B-57 penetrations on these three shots. it would appear, then, that during this project the frequency of individual ground crew clothing contamination for the contaminated T-33 was approximately ILLEGIBLE by ground crews working on ILLEGIBLE T-34's and B-57's. This tends to lend confirmation to the estimate that more than 95% of the removable contamination is removed from aircraft surfaces by decon. It also points up the logistical problem of sampling clothing chances to maintenance personnel working on aircraft which have not been decontaminated. It should be noted that no major engine maintenance was performed at ISAFB during the period embraced by this study. It should also be noted that the recorded contamination levels on personnel were never in excess of 50 mr/hr and seldom exceeded 20 mr/hr. (3) Ground Crew Radiation Exposure: The average ground crew exposure on the T-33 appears to be ILLEGIBLE higher than that of the F-ILLEGIBLE ground crews. During the study the average exposure per T-33 ground crew member ILLEGIBLE. The average exposure to the ground crew members of the F-84 companion aircraft (Tiger 1) which flow in formation with the T-33 ILLEGIBLE. The average exposure for all F-84 participation during the same period was 102 ILLEGIBLE. 4 The average overall ILLEGIBLE exposure for all events through ILLEGIBLE August was 110 mr/man/mission. Thus, the T-33 crew members received approximately ILLEGIBLE the exposure as the crew members working on the deconned F-84's. (The average figure for the B-57 ground crews was approximately 200/mr/man/mission.) c. "Lead Vests": Incidental to the rest of the study was an attempt to evaluate the overall effectiveness of the lead vests. On each flight both ILLEGIBLE were fitted with lead vests which had been instrumented with film badges from and back. On Priscilla these vests had badges on each side. To improve the statistics involved, on the remaining shots 25 badges were used. The average overall exposure decrease attributed to the lead vest based on the results of the five (5) shots was 6.0%. The ILLEGIBLE decrease based on Priscilla alone was between ILLEGIBLE. On the Priscilla event, however, the front of both the pilot's and the observer's vests became contaminated in excess of 20 mr/hr and it is probably that at least an hour elapsed before the badges were removed from the contaminated tape fastening the badges to the vests. This could account for at least a portion of the difference in apparent vest effectiveness between Priscilla results and the average. If Priscilla results were discounted as erroneous, the average for the subsequent shots would indicate a 4.ILLEGIBLE apparent decrease in dosage. (See Appendix 3). d. Fork Lift vs. Ladders: It was the experience of both pilot and observer that there was no problem in descending from the T-33 aircraft by means of the standard ladder if normal precautions were observed. 5 No contamination of flying clothes was observed that could be attributed to brushing against the contaminated aircraft while ILLEGIBLE out by means of the ladder. 4. The scope of this study was certainly limited if one desires definite conclusions on the aircraft contamination problem. The results, however, permitted the few generalized statements made above and a more limited number of generalized conclusions. a. It appears the aircraft decontamination results in an appreciable savings in personnel exposure and contamination for routine ILLEGIBLE maintenance. It is doubtful that B-57 maintenance personnel working on non-decontaminated aircraft could complete a 15 event operation without exceeding the normal operational limits of 3.0 r per quarter and 5.0 r par year. The issue of contaminated clothing exchange would certainly be multiplied. It is doubtful, however, that this would present a serious problem except for aircrew personnel equipment. Hereover, such test limits are very conservative ILLEGIBLE applied to a tactical situation. There is no indication from this study with Air Force tactical criteria for exposure an decontamination limits. b. I appears that the lead vests affect a dosage reduction of approximately 6% which is somewhat less than previously supposed. c. It appears that the standard aircraft ladder provides a satisfactory method of exit from the sampler aircraft. 6