Document rxj0mkaOqxYYk60dqvGqzdDNq

PLAINTIFF'S EXHIBIT ASA-666 i It iPt 7:;v;v 'a-.*' ,w -::1 - : * Ti3 5.; 'n- , - r Reprinted from Tub JnciuAfr or Isourrnut, ITtcibn akd Tottcotouv Vol, 2$, Kn. 1, January, t!M8 A HEALTH SURVEY OF PIPE COVERING OPERATIONS IN CONSTRUCTING NAVAL VESSELS* Walter E. Fleischer,1 Frederick J. Vii.es, Ji.\,; Robert L. Gadf.3 and Philip Drinker4 yt N INDUSTRIAL heallh inspection of an important U. S. Navy Contract Yard indicated that dustiness from miscellaneous pipe covering operations was considerable and that a few of the employees had what ap(>earcd to he asbestosis. This is a well-known industrial disease caused by only one thing--prolonged breathing of asbestos dust. The clinical manifestations are shortness of breath and an unusual chest picture by X-ray. fn industry' the disease is often dis abling, but it is much less frequent than silicosis, with which it very properly is classed. It was not felt that experience in a single yard was enough to justify any general statements on working conditions in other yards, and certainly was no cause for alarm, but the results warranted check-tips elsewhere. Accordingly, arrangements were made to examine by chest X-ray the pipe covcrers in two Government Navy Yartls, A and B, and in two Navy Contract Yards, C and D. Examinations were made of the working conditions including dust counts of the air breathed with microscopic and chemical analysis of the dust itself. We would point out that this procedure is customary in making such surveys of occupational diseases--medical examination of the workers and a study of the nature and concentration of the contaminants in the air breathed. Pipe Covering Material An important ingredient of pipe covering material used on U. S. Navy vessels is amositc. This mineral is a magnesium iron silicate of variable composition. The name is the generic one for an asbestos type of fibrous mineral mined in South Africa. The chief reasons for the wide use of amositc Received for publication September 21, 1945. Pabfabed by permissionof the U. 5. Navy. The opin>- f""* ad aMertiani contained herein are the private ones writers, and are not to be construed as official or the views of the Navy Department or the 5?*ci3rJl Asst. Chief Health Consultant "IXIsbL H(S) USNR, Health Consultant, life*. B(S) USNR, Health Consultant. Health Consultant, U. S. Maritime Commis- felt ami pipe covering in naval work arc its low thermal conductivity, light weight, strength, and refractoriness. When the felt anti pipe covering were first developed, we were still building vessels under the Washington Treaty of Limitations in Tonnage, and every pound saved meant that much more armor, guns or ammunition for a given displacement, to say nothing of more economic operation for the weight involved in insulation. Amositc pipe covering weighs about 14 pounds per cubic foot, with a temperature limit of 750F. as compared to magnesia with a weight of 16 pounds per cubic foot, anti a temperature limit of 500 F. High temperature amositc pipe covering weighs about 18 pounds per cubic foot as compared to 26 pounds per cubic loot for other high temper ature insulations. Because of the lower con ductivity and the higher temperature limit of. the amositc tyj>c, less of it need be used in a com bination covering than other types of insulations. The development of amositc felt started in 19.14 when a need existed to secure a thermal insulation lighter in weight and thermally more efficient than the materials (blocks and cement or asbestos blankets) which were then being used on destroyer turbines. The Navy approved the type developed by a manufacturer in September, 1934. Originally amosite was used only for turbine insulation, but it proved so satisfactory that its field of application enlarged to include insulation of valves, fittings, flanges, etc. From the initial destroyer, it has been used on almost all the destroyers built since that time and on all other combat vessels built since before the War. Pipe covering was a later development in late 1935 and early 1936. Due to the manufacturing problems involved, it took a longer time to evolve into a satisfactory shape, and its first use on naval vessels was in 1937. Since that time its use has spread markedly and it was used on the great majority of naval combat vessels built during World War II. Water-repellent amosite felt was developed during the early part of 1942, as a replacement ior hair felt in the insulation of cold water lines to prevent sweating. Hair felt had the disad- ASARCO ELP 0002810 10 JOURNAL OF INDUSTRIAL HYGIENE AND TOXICOLOGY [tot. ZB, no. il Jan. t Vintage of being combustible and as it was orranic, when it became wet it moulded or rotted and could harbor vermin. At this time fires on board certain naval vessels convinced the Navy of the desirability of eliminating any combustible material from on board ship. Eventually waterrepellent amosite was made in strips of 50 foot lengths and of suitable width to .enclose the circumference of the pipe and enclosed in an extremely light-weight muslin to facilitate hand ling and reduce the dust, which the water-re pellent agent accentuated. I. Description or Operation's and Working Environment Asbestosis results from breathing asbestos fibers of relatively long length, such as 15 to 75 microns. It is not caused by breathing chopped up asbestos fibers of one or two microns (1). Therefore we are concerned with the presence in air of asbestos fibers which can be seen as such under low power of the ordinary microscope. The clinical picture of asbestosis can easily be complicated by the presence of diatomaccous earth, a form of amorphous silica, which can cause silicosis and is probably a more serious health risk than asbestosis. Another dust which may be present is magnesia, MgO, which is in very common use as a heat insulator and is harmless. Therefore our analyses were done to indicate how much" fibrous type of asbestos dust was present in the air breathed, how much silica was present (especially as diatomaccous earth), and how much of the harmless ingredients like iron oxide and carbonates. Pipe covering may be divided into seven different operations as follows: 1. Laying cut and cullin[ 2. Band saw cutting S. Sewing and freparation of boots and jackets f. Cement mixing 5. Molding 6. Grinding 7. Installation on board ship1 1. Laying out and cutting Rolls of the insulating felt arc unwrapped and unrolled on a large layout table or on the floor of the shop. This material, with the exception of the type known as water repellent amosite, is then well wetted with a fine water spray. It is marked into measured sections and cut witht ^ a rotary electric hand saw. The cut sections are i the rolled up and cither used immediately or stacked ! wi! in the storeroom. I a* Usually one to three workers are employed at I of this operation. During the handling, unwrapping j tl and unrolling of the asbestos, considerable dust : * arises, but appears to settle readily. A very fine j < water spray should be used for wetting down the i ' material as a high velocity spray stirs up dust. ; Once it is wetted the handling and cutting of the j material causes little visible dust. AU of the j four yards surveyed wet down the insulating : material described above. I One Navy Yard has an clabotatc exhaust system for the layout table. The entire top of this table is covered with small perforations through which the air is exhausted. This table is sufficiently large that no more than two-thirds of the top is ever covered with material and room air is thereby exhausted through the other third. While no velocity or capacity measurements were made on this system, data presented later in the report ! indicate that this control measure had a marked effect in reducing the dust count. 2. Bond sow cutting A standard band saw such as is found in wood working shops is used to cut insulation blocks and boards into desired shapes. Tliis operation produces large amounts of air-borne dust, most of which settles slowly. Normally there Ls only one worker on this operation at any one time. Inasmuch as this is a very dusty operation, the band saw should be enclosed in a room by itself and should be equipped with adequate local exhaust ventilation both above and below the saw tabic. Because of the mechanical difficulties in locating this exhaust properly, some of the dust will escape into the air and the operator should therefore wear an approved dust respirator. 3. Sawing and preparation of boots and jackets In this operation jacket covers for valves and pipe joints arc fabricated. The work consists of cutting asI>cstos cloth with shears, padding the jackets with insulating material, and sewing with wire or asbestos cord. These operat: .ns give rise to only slight amounts of visible dust, and exhaust ventilation and respiratory protection arc neither required nor used. There is usually a large number of workers doing this operation in one large room. 4. Cement mixing ASARCO ELP 0002811 Jan. 1946} PIPE COVERING OPERATIONS 11 For protection and to give a neat appearance the insulation on board ship is usually covered with cement containing a high percentage of asbestos fibers. In mixing, the proper amount of water is added to the dry asbestos cement and thoroughly agitated with a hoc. Occasionally small amounts of asbestos cement are mixed in a pail with a trowel. Considerable dust is raised when the asbestos cement is dumped into the mixing trough and during the early stages of mixing. Ordinarily this process is done in a separate room and only one operator is exposed. Tlie dustiness of this operation warrants the use of exhaust ventilation or respiratory protection or both, although neither is generally used. Petrographic analyses of asbestos cement in dicate that the amount of diatomaccous earth may be as high as 87 per cent by count. 5. Molding Molding is the process of building up the insula tion to fit odd shapes of boilcrwork and piping. A form is made to the exact shape of the part to be insulated. Block insulation is laid on, adjoining sections glued together, exposed surfaces sealed with asbestos cement and the whole mold covered with asbestos doth. When dry, the molded insulation can be lifted oil the form and is ready to be installed on board ship. This operation is usually done in the shop next to the sewing operation. Very little dust is produced from this operation and no special ventilation or respiratory protection is required. 6. Grinding Several shipyards reclaim their scrap pieces of prefabricated sections of insulation by grinding up this material and using it in the asbestos cement, all of which contributes considerable dustiness. Normally this job is done at infre quent intervals and only one or two men are exposed, but the operation should be isolated, general room exhaust supplied and an approved respirator worn by the operator. 7. Installation of pipe covering on hoard ship There are a number of operations involved in pipe covering on board ship. Insulation felt is wrapped and pounded tightly around Urge pipes and joints and fastened firmly in pUce with wire or asbestos cord. Pipes and boilers are covered with prefabricated sections, which necessitates some hand sewing to fit the sections. Ready mixed cement is applied to fill in spaces and give a smoother finish. Some insuUtion is wrapped with glass doth or asbestos doth for greater strength. The only operations that produce much dust arc the wrapping and pounding of amosite and the sewing of sections. Nearly all of the compartments on board ship arc involved in this work, although most of it is concentrated in the machinery spaces. Usually the greater number of pipe covcrcrs work on board ship and rcUtively few men in the shop. The spadng of workers ranges from one or two men doing a small job in a living space to as many as twenty or thirty men working on ten or more jobs in the engine room. Temporary exhaust ventilation is seldom used on board ship for pipe covering and very few of the workers wear respir ators. Because of the varied nature of pipe covering operations in ship compartments, general exhaust ventiUtion is to be preferred. If the compartment is large, such as the main engine room, five air changes per hour arc needed. In small com partments, such as living spaces, ten to fifteen air changes per hour are required. II. Composition op Materials Used According to Navy Specification the rovings of asbestos insulating felt (amosite) shall contain not less than 95 per cent asbestos fiber of the following composition: Silica (SiOj) percent minimum.............................. 47.5 Iron oxide (FejOJ per cent maximum.................... 45.0 Magnesium oxide (MgO) per cent minimum......... 0.0 Typical analysis of the two types of asbestos fibers in general use are tabulated bdow: CkrytttiU Ametiu Silica (SiOi)......................... 39.05%.............. 50.24% Magnesia (MgO).................. 40.07%............ 3.90% Alumina (AltOO.................. 3.67%.......................... ........ Ferric oxide (FejOj)--Xntor............. 7.80% Ferrous oxide (FeO)............ / /o.............. 32.00% Sodium oxide (NaiO)............................ :......... 2.12% Combined water (NiO)....... 14.48%............. 3.00% Therefore amosite alone will not comply with Navy Specifications because of the low magnesia content and must be mixed with chrysotilc asbestos to equal or exceed the 6.0 per cent mini mum value for magnesia. On the other hand, chrysotilc cannot be used alone because of its silica content which is below the minimum 47.5 per cent specified by the Navy. The two types ASARCO ELP 0002812 12 JOURNAL OF INDUSTRIAL HYGIENE AND TOXICOLOGY [vol. 28, no. of asbestos fibers must be mixed together in the proper proportions to satisfy the values set for magnesia and silica. The amounts of these materials used to form this mixture therefore would be 6-43 per cent chrysotilc asbestos and 94-57 per cent amositc asbestos. These two fibers differ mainly in their physical characteristics. Chrysotilc is capable of being readily separated into very fine fibers with a soft silky feel, whereas amosite is harsher and requires more manipulation to fiberize it. One authority has stated that the chrysotilc has the finest in dividual fibers, and amositc the coarsest. Bc- and sewing were done with a small amount space for storage. Cross draft ventilation w provided by open windows on both sides of t room. Work on board ship was not supplied wi exhaust ventilation. No asbestos workers were found wearing ri pirators. U. S. Wavy Yard B. There were SO men working in the shop and men on board ship. The shop was divided ir four main rooms: Layout, Sewing, Cement, a Storage and Band saw combined. With 1 TABLE I Summary or Materials Used at Each Yard per Month j NAVY YARD A NAVY YARD % CONTRACT TARO C Amositc- 58,200 sq. ft. 50,000 sq. ft. 40.000 sq. ft. Amositc (water-repellent) -- 15,000 sq. ft. -- Prefabricated sections (molded and block) 600 sq. ft. 1.200 sq. ft. " 1.730 sq. ft. 39,900 linear ft. 115,000 linear ft. 18,800 linear ft. Asbestos cloth Metallic twine ' Asbestos yarn 76.500 sq. ft. 106,600 sq. ft. ' 150 lb. 34,700 sq.ft. -- Asbestos paper - 5.500 sq. ft. 4,000 sq. It. Asbestos board 2.TOO linear ft. 6.000 sq. ft. 150 sq. ft. Asbestos cement 34.400 lb. 15,0001b. 57.500 lb. CONTRACT YARD S 6,325 sq. ft 3,300 sq.ft. { 15,700 12;. .-1 40,000 sq.ft. -- 5,500 sq. ft. -- 38,5001b. cause of this difference we may suspect a decided decrease in the number of respirable fibers (below 200 microns in length and 5 microns in diameter) whenever amositc is used in preference to chrysotilc asbestos.III. III. Pipe Covering Facilities at Individual SlttPYARDS U. S. Navy Yard A. There were 84 men working in the shop and 467 men on board ship. The shop was divided into two rooms, one of which was primarily for storage and occasional grinding and band saw cutting operations. The only mechanical exhaust ventilation in the shop was provided for the grind ing, mixing and band saw cutting operations and was inadequate. In the other room layout, cutting exception of the Cement Room, the doors betv these were normally left open. The work in the Sewing Room consisted me of fabricating and sewing valve boots and jack All the cement used on board ship was mixe the Cement Room. There was no exhaust tilation for either the Sewing or Cement Rc The band saw was equipped with a flexible exh tube above the table and an exhaust around blade below the saw table. The layout t was equipped with exhaust ventilation as dcser above. There was no exhaust ventilation supj on board ship for pipe covering and no woi were found wearing respirators. Contract Yard C. There were 51 men working in the sh^ c on board ship. Layout, cutting ana"ce: ASARCO ELP 0002813 /** tm PIPE COVERING OPERATIONS 13 gfoini were done at one end of the shop. Dust bestos content, ranging from 85 per cent magnesia respiftots were occasionally worn during these (10-15% asbestos) to amosite (95% asbestos). procedures. the other end of the shop the When asbestos cements contain large amounts fabrication of boots, jackets and molds were of diatomaceous earth there is a resultant silicosis carried out. A small amount of such fabrication hazard as indicated above. uti done on board ship. In general we feel that dust counts below 5 Material was cut with a band saw in a separate million particles per cubic foot by Konimeter room and the operator wore an approved dust indicate good dust control. respirator. The dust from this saw was exhausted Our figures in Tabte 2 were determined by the through a slot under the table which caught only Konimeter and not with the Impingcr instrument. a part of the dust given off above the table. We used the Konimeter because it is light, easily There was no exhaust ventilation in the shop, portable and takes records which can be kept other than for the band saw, and none for the indefinitely. As is indicated in Table 3, the pipe covering operations on board ship. All floors, dustiest operations arc band saw cutting, cement walls and rafters of the shop were cleaned at mixing, and installation on board ship. frequent intervals with an industrial vacuum cleaner. Most pipe covering on board ship was V. Medical Findings applied in the evening during the second shift.IV. The incidence of asbestosis among pipe coverers Contract YardD. as determined by chest X-ray is given in Table There were 8 men in the shop and tfiO men 4. The relation between years of exposure and working- on board ship. Pipe covering operations per cent asbestosis is included in Table 5. were done in two shops. In the main one, boots Due to frequent turnover of shipyard workers and jackets for pipe valves and connections were and the length of time required to X-ray a large fabricated and surplus material stored. In the number of workers, the number X-rayed may not smaller shop the operations consisted of layout equal the number of pipe coverers. At Contract and cutting of amositc, water repellent amosite Yard C X-rays were examined of men who had left and fire felt. There was no exhaust ventilation the yard while at Navy Yard B a few pipe coverers in either shop nor for the pipe covering operation were not X-rayed. At Navy Yard A the 48 on board ship. All the asbestos cement was mixed X-raycd out of 551 were all older men working in a compartment on board ship. The only worker in the shop. who wore an approved dust respirator was the Some of these pipe coverers had had pre-shipyard man who cut the two types of amosite. There experience in the asbestos industry, but the tables was no band saw cutting of asbestos in this card. arc based solely on shipyard exposure. At IV. Analyses or Settled Dust and Dust Counts Contract Yard C, for example, the Asbestos Shop estimated that about one-third of their pipe coverers had worked with asbestos before coming There are no established figures for permissible to the yard. or safe dustiness in pipe covering operations. The one case of advanced asbestosis at Contract Dreessen et ah (2) in their study of asbestosis in Yard C had worked in the asbestos industry for the asbestos textile industry suggested 5 million 23 years before coming to work in the yard. At particles of total dust by impingcr as a threshold Contract Yard D the two cases of moderate for that industry. We should like to point out asbestosis had worked, 22 years and 30 years at that the asbestos textile and asbestos pipe cover pipe covering in their yard. ` ing industries differ widely in their dust exposures. All of the X-tay films used in the above data In textile plants workers usually continue at were first read by roentgenologists of the Medical Sc jobs with fairly constant dust exjxrsurcs Department of the yard and then by one of the rome years, whereas the pipe coverer may authors (W. E. F.). Dr. W. C. Dreessen, U. S. . between shop and ship and from small to P. H. S., was kind enough to examine the three ship compartments with a wide variation positive plates and he agreed on the diagnosis. &Bt exposure. Since only three workers out of the 1074 X-rayed to the textile worker, the pipe had asbestosis, and each of the three had been materials differ markedly in their as a pipe covcrer for more than 20 years, it would ASARCO ELP 0002814 TABLE 2 Analyses or Settled Dcst and Air Samples Jin. 1 OrtBATXOK oi !! I * h. n SS SC mMto x Sto sXa M= a mottpoot fZ < ac tao e 1/7 Is" Crt *C% I ** i'l c* iS 4 C II s PS \B i L2 11 If* 0 Iz^ OUST covsrs .MPPCF)- Total dust i1 1 ASBESTOS DOST i TZk ertrr ASBESTOS Ranee of Aver. ! Ranee of Aver (nose) counts aje t counts age ___ Layout and cutting Navy Yard A....................... Navy Yard B...................... Contract Yard C................. Contract Yard D................. 95 98 95 95 16 6 12 6 10 8 12 tr 30 5 to tr 26 6 8 tr 24I 26 10 2 3.5- 8.7 6.1 0.21-0.50 0.35 5.7- 6.0 40l 18 12 7 1.6- 6.5 4.2 0.01-0.54 0.23 0.6- 7.9 26] 14 15 4 17.1- 25.2 20.5 1.13-4.30 2.18 6.6-19.5 29| 21 10 5 6.5- 16.5 10.9 0.09-1.16 0.63 1.4- 8.7 Bai Sev CeGr Ce Cutting with baud saw Navy Yard A...................... Navy Yard B....................... Contract Yard C................. 98 98 Molding operations Contract Yard C................. 98 Contract Yard D................. 95 97 9 63 8 tr 2 tr 1 1 2 11.0- 19.2 1S.1 0.10-0.14 0.12 0.7- 0.9 4S| 16 12 2 32.4- 46.6 39.5 2.8- 3.2 3.0 6.6- 8.7 10! 4 12 3 18.2-100+ 73+ .9-12.8 6.19 4.3-12.8 I 8 66 3 tr 7 6 10 4 9 7 tr 4S 10 12 1 Sewing & prep, of boots & jackets Navy Yard A....................... Navy Yard B (Sewing as bestos doth) (Stuffing with amosite)... Contract Yard C................. Contract Yard D................. 98 98 95 98 12 tr 9 tr 8 8 11 tr 26 6 11 3 6 6 8 tr 2 3.3- 6.1 4.6 .01- .06 0.03 0.3 -1.0 42 21 16 3 3.3- 6.0 6.8 0.0- 9.4 0.1 0. -6.4 38 20 IS 1 2.1- 2.1 0. 0.3 0. 28 12 14 2 10.6- 12.3 11.4 .45- .79 .62 3.7 -7.4 38 28 14 5 3.9- 10.9 6.0 0. - .05 .03 0. -0.5 Storeroom Contract Yard D......... . 95 IS 8 7 tr 26 32 12 Cement mixing Navy Yard A...................... Navy Yard B..................... Contract Yard C................. Contract Yard D (on board ship)................................. 16 5.4- 30+ 31 + 0. -0.52 0.2 0. - 0.7 2 67. -100+ 84+ 1.6 -1.7 1.7 t.4-- 2.5 2 33.8- 48.7 41.3 1.6 -4.7 3.1 4.7-10.0 5 19.6- 40.0 32 0. - .02 .01 0. - .001 Grinding scrap materials Navy Yard A............. 88 8 20 16 i 10 33 12 15 9.4-100+ 50+ 0. -1.6 .47 0. -2.6 General room Navy Yard A....................... Navy Yard B....................... Contract Yard C................. Contract Yard D................. 49 0.2- 24.6 10.0 0; -1.4 0.08 .02-0.3 2 1.6- .3.3 2.4 0. - .01 .01 0. -0.6 4 0.0- 21.6 14.2 0.34-1.7 .8 3.8 -7.9 5 3.9- 10.9 6.0 0. - .05 .02 0. -0.5 Aboard ship Navy Yard A....................... Navy Yard B....................... Contract Yard C................. Contract Yard D................. ! 30 65. -250. 142 !o. -0.17 0.02 0. -0.05 15 84.4-192.0 128 ll.36-5.21 2.8 1.1 -3.7 15 25.3- 89.0 49.2 0.23-2.38 1.10 0.5 -6.8 15 8.0- 22.1 11.00. -0.21 0.03 0. -1.0 * .Yale: MPPCF -- Million particles of dust per cubic foot of air. 14 j | ! f I ll ASARCO ELP 0002815 J Jan. lfJ6\ PIPE COVERING OPERATIONS IS TABLE 3 Comparison or Dustiness or Various Operations in Each Shipyard OfXIATtOH XAVY YARD A NAVY YARD B CONTRACT YARD C C0XT1ACT YARD O ToUl duit Asbestos dust ToLi! dust Asbestos dust Tout dust Asbestos dust Toul duilj Layout and cutting.................... Band saw cutting........................ Sewing and fabrication............... Cement mixing........................... Grinding...................................... General room............................. UPPCf* 6.1 1S.1 4.8 31.0 50.0 10.0 0.35 0.12 0.03 0.2 0.47 0.03 UPPCP 4.2 39.5 4.8 84.0 0.23 3.0 O.t 1.7 2.4 0.01 UPPCF 20.5 73.0 11.4 41.3 2.18 6.19 0.62 3.1 14.2 0.8 strecp 10.9 0.63 6.0 32.0 0.03 0.01 6.0 0.02 Shop average........................... 30.0 Ship average............................ 142.0 0.25 0.02 26.9 123.0 1.0 2.8 Note: MPPCF - Million particles of dust per cubic foot of air. 32.0 49.2 2.6 1.1 7.6 11.0 0.23 0.03 TABLE 4 Incidence op Asbestosis Among PirE Coverers SCITYAU) KOKBXt or rtrs covxb- XU XUUBtl SAXt-tO XOMBXE or CA>C* or Assrrrnsts MTTi1n>i- Mod Ad erate vanced Navy Yard A.......... 551 48 0 0 0 Navy Yard B.......... 7S0 662 0 0 0 Contract Yard C.... 174 196 0 0 t Contract Yard D... 168 168 0 2 0 Totals................... 1683 1074 0 2 i 1 TABLE 5 Rixationship Between Length or Exposure ant Incidence or Asncsrusis txais :x nn covnixs IXDUSTkV 0-2 2-5 5-10 ptluos 1 Exposed........... 26 13 8 3 [Navy Yard A Affected........... 0 0 0 0 Percentage... 0% C% 07, 0% Exposed.......... 225 435 67 22 Btsvy Yard B Affected........... 0 0 0 0 Percentage___ 0% 07c o%! o% t Exposed___ Snnlract Yard C Affected___ Percentage.. 0 105 45 17 0 001 0% 07o 0% 67, Exposed... 26 118 5 9 Watract Yard D Affected___ 0 0 0 2 percentage. 0% 07, 0% IOC" appear that asbestos pipe covering of naval vesselsl 'I is a relatively safe occupation. However, it must\ be remembered that these men rotated among the | various operations of pipe covering and were not j continually exposed to high concentrations of asbestos dust as found in band saw cutting and cement mixing. The suggestions made relative to exhaust ventilation and respirator}'-protection are therefore of value in maintaining this low incidence of asbestosis. Discussion The extremely low incidence of asbestosis found, 0.29 per cent, or 3 cases out of 1074 pipe coverers, stands in marked contrast to the high dust concentration found in several of the pipe covering operations. As shown in Table 3, the total dust concentration for band saw cutting ranged from 13.1 to 73.0 million particles per cubic feet, for cement mixing from 31.0 to 84.0, and for installation on board ship, from 11.0 to 142.0. The solution of this apparent discrepancy lies in a characteristic peculiar to the pipe covering trade, that is lack of a necessity for specialization. In general, pipe coverers are capable of doing all of the operations described above, and the worker may be changed from one operation to another or to different jobs in the same type of operation without loss of efficiency and according to the demands of ship construction. It is therefore apparent that a pipe covercr's environment may change every few days or few weeks at the most with a constant fluctuation in the dust concentra tion which he breathes. Therefore, the figures given in Table 3 for shop average and ship average cannot give a composite picture of the asbestos ASARCO ELP 0002816 16 JOURNAL OF INDUSTRIAL HYGIENE AND TOXICOLOGY [tel. 23, no. I dust that a worker may breathe over a period of years. It is further apparent that to obtain such a picture, daily dust counts at each specific job in each ship compartment and in the shop together with the time spent on each job would have to be compiled separately for each worker. In this respect, asbestos pipe covering differs markedly from the asbestos textile industry where dust concentrations for an operation do not fluctuate widely and where a worker will usually remain at a specific job for some years. A further factor in maintaining a low incidence of asbestosis is that in band saw cutting, grinding, and cement mixing only one or two men arc in volved and the work is usually done at infrequent intervals such as several times a week. Finally, pipe covercrs also apply glass wool', rock wool, magnesia, and other types of nonasbestos insulation, all of which decreases the amount of exposure to asbestos dust. It seems likely to us that if the pipe covercrs studied had worked steadily at any of the above operations where the amount of asbestos dust in the air was consistently high, the incidence of asbestosis among these workers would have been considerably greater. In view of the varied character of the environmental dust exposure in the pipe covering industry on naval vessels, it is manifestly impossible to set a threshold. VI. Conclusions i 1. The character of asbestos pipe covering i industry on board naval vessels is such that i conclusions drawn from other asbestos industries 1 such as textiles, cannot be applied. 2. The operations of band saw cutting, grinding, cement mixing, and installation on board ship should be equipped- with exhaust ventilation to keep the total dust concentration low. 3. The incidence of asbestosis among pipe covercrs in the shipyards studied was low, 0 29 per cent or 3 cases out of 1074. In view of the nature of shipyard pipe covering work, this low incidence is not surprising. j 4. Since each of the 3 cases of asbestosis had ' worked at asbestos pipe covering in shipyards for more than 20 years, it may be concluded that such pipe covering is not a dangerous occupation. REFERENCES (1) Lanza, A. J.: Silicosis and asbestosis. Oxford University Press, New York, New York, 1938. (2) Dxeessen, W. C. et ah: A study of asbestosis in the asbestos textile industry. Bull. No. 241, Public Health Service, U. S. Treasury Department, 1938. (3) Fahey, J. C: Ships and aircraft of the United States Fleet. 2nd War Edition, 1944. Published by Ships and Aircraft, 1263 Broadway, New York, New York. ASARCO ELP 0002817