Armored Medical Research Laboratory Fort Knox, Kentucky PROJECT NO. 4 - DUST EXPOSURE IN ARMORED VEHICLES Final Report On Sub-Project No. 4-1 - Determination of Dust-Loads and Characteristics of Dusts Encountered in Operation of Armored Vehicles Project No. 4-1 10 September 1945 ARMORED MEDICAL RESEARCH LABORATORY Fort Knox, Kentucky Project No. 4”1 File 724-31 10 September -94$ 1* IR0J3CT NO, 4* Dust Exposure in Armored Vehicles. Final report on Sub-ireject 4-1, Determination of Dust-Loads and Characteristics of Dusts Encountered in Operation of Armored Vehicles. a. Authority - Letter Commanding General, Headquarters Armored Force, Port Knox, Kentucky, File 400.112/6 GNOHD, dated September 24, 1942. b, lurpose - To determine the characteristics and concentration of dust encountered by armored personnel, with particular reference to the silico- sis problem. 2, DISCUSSIOK: Dust concentrations representing a wide variety of opera- ting conditions and the free silica content of the respirable portions of dusts from operating areas have been determined. These findings are considered in relation to the possible silicosis hazard among armored personnel. Details are given in Appendix A, 3. CONCLUSIONS: a* Owing to the low free silica content of the respirable dust, the flocculent nature of dust clouds and the limited duration of exposure, silicosis is unlikely in armored personnel as a result of their military operations, b. Dust generated by armored vehicles under extreme conditions of operation causes temporary discomfort and interferes with effective operations. 4. Ri&OlMSNDATIOKS: a. Every effort should be made to reduce the amount of dust generated by armored vehicles and development of a practical air cleaner for use with positive-pressure ventilation of the tank crew compartment should continue, b. Dust protective goggles and expendable respirators should be pro- vided for armored personnel when needed, NOTE: The recommendations as set forth in this project have been concurred in by Hq. Armored Center and the iresident, AGF Board No, 2, Submitted by t Theodore F. Hatch, Lt. Col*, SnC Robert H, Walpole, Captain, FA APPROVED /■:< ■«- - - :t..-• WILLARD MACHLS Colonel, liedical Corps Commanding 1 Incl. Appendix w/table APPENDIX The dust concentrations to /vhich armored personnel are exposed vary widely— from imperceptible levels to dense clouds which may reduce visibility to almost zero. Cloud concentration varies with type and dryness of the ground and with intensity of operation. The dust conditions at times constitute a great nuisance, cause temporary discomfort and interfere with operations; for these reasons every effort should be made to reduce the amount of dust generated by armored vehicles, irogress has been made in this connection through improvement in design and exhaust terminals and application of dust skirts and work is in progress by Ordnance on the development of practical air cleaners for crew-compartment venti- lation systems of the positive-pressure type. The purpose of the present report is to review the dust problem from the standpoint of the possible health hazard, with particular reference to silicosos as the dust disease of primary interest. Silicosis is caused by the specific action of crystalline silicon dioxide (SiC2) which has accumulated in the deep air spaces of the lungs as a result of prolonged exposure to dusty air containing fine particles of this material. The particles of Si02 in the air must be small enough to penetrate to the terminal air sacs of alveoli (less than 2 microns of 2/25000th inch in diameter, practi- cally) and the rate of accumulation of Si02 in the lungs must exceed a certain minimum level in order to produce the disease. The period of exposure required to develop silicosis varies from months to years, depending upon the percentage of free silica, the fineness of the dust and the concentration to which the individual is exposed. Silicosis is an industrial disease, occurring chiefly among hard rock miners and stone cutters working in flint, granite and other rocks rich in quartz. Operations such as sand blasting, crushing, packaging and handling finely pulverized materials of high quartz content are also hazardous. Taking the granite cutting industry as a typical example, the conditions which lead to silicosis are; free-silica in the stone, cutting processes which produced much extremely fine dust, dust concentrations generally above $0 million particles per cubic foot and, in many instances, well above 100 million, exposure of 10-20 years. A dust concentration of 10 million particles per cubic foot has been established as the maximum safe level for continuous exposure in this indus- try. Not all industries in which quartz-containing dusts are produced have had serious silicosis problems. Foundry dust, for example, contains twice as much free silica as does granite dust but silicosis is relatively rare among foundry men. Silicosis has not been reported among farmers, tractor operators or earth excavators nor does it apparently occur among desert dwellers despite the high quartz content of most soils. One explanation for the apparent freedom from silicosis in these cases is that the free silica content of the dust is not uniformly distributed with respect to particle size, being concentrated in the larger particles. Thus, a total sample of foundry dust, for example, may contain free silica whereas the portion of the sample smaller than 2 microns in diam- eter will contain as little as 5%, Since only the small particles penetrate to the alveoli it is evident that the hazard is not measured by the composition of the total sample. Another determining characteristic is the degree of dispersion, or its opposite, the degree of flocculation of the dust. Naturally occurring dusts (finely pulverized earth, natural sands, etc.) are not easily dispersed as sep- arated particles. In the absence of fairly powerful disrupting forces, the finest particles remain attached to the larger ones in the dust cloud and the size of the flocculated material limits the depth of penetration into the lungs. Granite cutting processes evidently generate separate fine particles. Kany foundry operations, on the other hand, merely throw material into the air without breaking up the flocculated masses. Similarly, earth excavation and the like do not really disperse separate particles. Hie absence of specific lung damage in the cases cited is of significance in connection with the dust problem in armored vehicles since the nature of the dust and method of dispersion are probably similar. Further information on the nature and magnitude of dust exposures in armored vehicles is given below. 1, Dust Concentrations - Owing to the wide variety of conditions of operation of armored vehicles, a representative measure of dust concentration to which personnel are exposed can be given only in terras of the range of concentrations encountered—*from low to high activity. Data covering such a representative cross- section of activities are presented in Table 1, Most of the samples were collected by the Desert Warfare Board in the California Desert Training Center area and sent to the Laboratory for analysis.* The findings, as presented in Table 1, are separated into groups according to activity. Concentrations range from a minimum of 9*0 million to an extreme of 1500.0 million particles per cubic foot. During halts, in base camps and the like, representing relatively inactive periods, the dust concentration is generally below 50 million particles per cubic foot. At the other extreme, when tanks are travelling over dry, pulverized soil in close formation, the concentrations will be found in the hundreds of million. Clearly, the average daily exposure will vary widely, depending upon the pattern of activity. For days of generally low activity, it will be below 100 million; on days involving considerable convoy driving, the average will be greater than 100 million particles per cubic foot with short periods of extreme exposure during the day. 2. Particle Size - The particle size of the airborne dust raised by armored vehicles may be expected to vary with the fineness of the soil and the degree of attrition* The fineness of soils in the California desert area was found in a series of 38 samples to differ widely, as seen in the following tabulation: Percent of Samples Average Number of Particles Less Than 2 ju Per Gram of Soil 15.8 3.3 x 107 26.3 7.6 x 107 42.2 7.7 x 10s 15.8 1.2 x 1010 * The Desert Warfare Board letter report. Study of Silicosis Hazard in the Desert, 15 February 1944. For the same degree of ground disturbance, one would expect greater atmospheric dust concentrations with the finer materials. Roughly, this proved to be the case with the samples listed in Table 1, but a clear relation was lost owing to the widely different degrees of activity. Samples of airborne dust collected over well-worn driving ranges at Fort Knox had a median particle size of approximately 1,0 p, with 90% of the particles less than 3.0 ju. Air floated material from Arizona desert was somewhat smaller, median 0.7$ }x and below 2.$ ji, By weight, however, 90% or more of the material was larger than 3*0 in both cases. No information was obtained on the degree of flocculation in the dust clouds. As compared with industrial dusts, however, the settling rate of the dust was high, indicative of a relatively high degree of flocculation. 3* Free Silica Content* - The free silica content of the total sample of air- borne dust collected in the California desert was found to be 36$. A sample of air-floated dust from the Arizona desert contained 18$ free silica and a soil sample (screened through 323 mesh) from the California area had only 12$ of quartz. In the case of the Arizona sample, containing 18$ in the total sample, a fraction having an average particle size of 11.0 ji contained 25$ free silica whereas a finer fraction (average 3*5 /0 showed 12$, or less than half as much. The average free silica content of the fraction of 30 soil samples from the California desert was found to be 4*0$, ranging from 0.5 to 7*2$. The bulk of the remaining material was muscovite (mica) with smaller portions of acid soluble substances—calc it e and halite. By chemical analysis, the «< 2 ja fractions were found to contain an average of 45*9$ total silica (free and combined) whereas the total soil samples contained 62$, Since the silica content of moscovite is approximately 45$, it is evident that there could be very little free silica in the fine fraction. 4. Discussion - That armored personnel are, at times, exposed to extremely high dust concentrations is evident from Table 1. It is also evident, however, that the average daily concentration will vary widely, depending upon activity. Analysis of the <2 micron fractions of soil samples and of airborne samples indicate that the free silica content of the inspired dust is considerably below the level generally associated with development of silicosis. The flocculation of naturally-occurring pulverized material further limits the hazardous nature of the dust, finally, the intermittent exposure of armored personnel to extreme dust concentrations, and the limited duration of exposure as compared with the years of daily contact with dust which proceeds the development of silicosis in the mining and stone cutting industries markedly reduces the potential hazard. Despite the intermittent high dust concentrations, the finding of low content in the inspired dust, the flocculent nature of natural dusts and the limited exposure of armored personnel coupled with the favorable past experience of workers in somewhat similar dust conditions, generally precludes the likelihood of silicosis among armored personnel. This does not lessen the dust problem from the stand- point of temporary discomfort, or interference with operations, iifforts to reduce the dust produced by armored vehicles should continue and personal protection in the form of goggles and throw-away type respirators should be provided for use where needed. * All results were obtained by X-ray analysis. 3 TABLE 1 SUMMARY OF DUST CONCENTRATIONS TO WHICH ARMORED PERSONNEL ARE EXPOSED OPERATIONS Dust Concentrations Millions per Cubic Feet 1, Minimum Activity Airborn dust from Infantry camp; some from a road grader 9.0 Motor pool of a Medical Battalion; slow traffic 12,0 Bivouac area, Sunday afternoon, fresh breeze 15.4 Div, Surg. Tent, Hdqrs., Camp area 21.0 Air Base; planes taking off clean runway 21.7 Motor pool; ambulance driving in loose sand 22.5 Infantry training on Regt, parade ground 25.0 Ordnance unloading depot. Only three vehicles moving 27.7 Army truck road. Dust raised by staff car 27.7 Regimental area of Camp; normal traffic 29.0 Gas dump; no vehicular movement. Light to no breeze 29.2 Repeated passage of t-ton truck on tank trail 29.2 Railhead with light traffic; no convoy movements 3l.o Railhead with little traffic 32.0 Hdqrs. Camp; light traffic, fresh breeze 32.2 Ordnance unloading depot; heavy wind storm; no traffic 34.5 2, Moderate Activity Infantry column; 4 companies ahead of sampler 41.0 In convoy behind half-track 41.2 Asst, driver1s seat; light tank midway of column of tanks (Co] 42.7 Evacuation Hospital Area; sandy surface, fresh breeze 44.2 Corner Tank Battalion Motor Pool; 16 tanks and 1 truck moved 48.7 Entrance to railhead; almost continuous truck traffic 51.0 Troops drilling—no traffic 51.7 3. High Activity Maneuver road; dust raised by staff car 75.0 Convoy of cargo trucks spaced 100 yards 79.0 From £-ton truck and wind-blown dust 104.0 Deliberate dust disturbance by £-ton truck 113.0 Convoy of trucks and towed 75 mm guns 131.0 Repeated passage of i-ton through pulverized silt bed 160.0 Alongside moving tank column 187.0 Inside tank following another 150 yards 219.0 Convoy of trucks passing by 250.0 Following i-ton truck 472.0 Thirty feet behind half-track; loose sand 750.0 (Contfd next page) TABLE 1 (Cont'd) OPERATIONS Dust Concentrations Millions per Cubic Feet 4. Extreme Activity (conditions deliberately fixed for maximum dustiness) Medium tank operating alone on dry driving range, 10 mph 145.0 Medium tank operating alone on dry driving range, 10 mph 350.0 One tank trailing another, dry driving range, 10 mph 610.0 One tank trailing another, dry driving range, 10 mph 700.0 End of column of 5 light tanks, 10-15 mph 250.0 Five tanks in wedge, sampled in 6th center tank 450.0 Midway of column of 6 light tanks, driving into wind 1250.0 Midway of column of 6 light tanks, driving into wind 1500.0 5. Summary Average Range Minimum activity 25.0 9.0 to 35.0 Moderate activity 46.0 41.0 to 52.0 High activity 231.0 75.0 to 750.0 Extreme activity 620.0 145.0 to 1500.0