Document mqkMb9OY88VmJqebY20Qj8kxZ

THE JOURNAL OF STDUSTRIAI JL AND KJ ^v"*' 'l *-ii * VOLUME 28 JANUARY, J5^6--NOVEMBER, j94b r **g^~Sl3gSSr V * , * 1I l I % % ' PUBUSHED BY THE WILLIAMS & WILKINS COMPANY Baltimore, Md. MH19 . ..____Q *qa " :isr-si*^3tC^':52*>^?cvif>.`55>;S3 ... ^y^Z->^g~iSafe=aJ .-..' iiZS& r<rr;z&a?.ss* : -: *4 ^| '^SSfilil \s'"'v >,, UCC 017585 ...... "" OEPOsnITION * /^PEYXUHIlBf IT AW f/fgA miss /.vgggg; ''Sal >-' VlfeV.* A HEALTH SURVEY OF PIPE COVERING OPERATIONS IN CONSTRUCTING NAVAL VESSELS'* . . .ter E. Fleischer* Frederick J. Viles, Jr.,5 Robert L. Gads* and Philip Drinker4 N INDUSTRIAL health inspection of an important U. S. Navy Contract Yard indicated that dustiness from miscellaneous covering operations was considerable and that r of the employees had what appeared to be itosis. This is a well-known industrial disease id by only one thing--prolonged breathing of >tos dust. The rfmtral manifestations are mess of breath and an unusual chest picture I-ray. In industry the disease is often disg, but it is much less frequent than silicosis, which it ve^ properly is classed, was not felt that experience in a single yard enough to justify any general statements on ing conditions in other yards, and certainly no cause for alarm, but the results warranted r-ups elsewhere. Accordingly, arrangements made to examine by chest X-ray the pipe reis in two Government- Navy Yards, A and nd in two Navy Contract Yards, C and D. ninarions were made of the working conditions ding dust counts of the air breathed with jseopic and chemical analysis of the dust 5 would point out that this procedure is unary in making such surveys of occupational ses--medical examination of the workers a study of the nature and concentration of aontammants in the air breathed. ; Pipe Covering Material . . i important ingredient of pipe covering rial used on U. S. Navy vessels is amosite. mineral is a magnesium iron silicate of ble composition. The name is tbe generic or an asbestos type of fibrous mineral mined uth Africa. -* e chief reasons for the wide use of amosite eeeived for publication September 21, 1945. shed by permission cf the U. S. Navy. The opin- nd assertions contained herein are the private ones writers, and are not to be construed as official or dag the views of the Navy Department or the ; service at large. ' >mdr. MC, US.VR, Asst- Chief Health Consultant tut- H(S) USNR, Health Consultant. euL H(S) USXR, Health Consultant. . oie: Health Consultant, U. S. Maritime Commis- felt and pipe covering in naval wort are its low thermal conductivity, light weight, strength, and refractoriness. ` When the felt and 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 die weight involved in insulation. Amosite pipe covering weighs about 14 pounds per cubic foot, with a temperature limit of 750*F. as compared to magnesia with a weight of 16 pounds per cubic foot, and a temperature limit of 500 F. High' temperature amosite pipe covering weighs about 18 pounds per cubic foot as compared to 26 pounds per cubic foot for other high temper ature insulations. Because of the lower con ductivity and the higher temperature limit of the amosite type, less of it need be used in a com bination covering than other types of insulations. The development of amosite felt started in 1934 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 indude insulation of valves, fittings, flanges, etc. From- the initial destroyer, it has been used on almost all the destroyers built since that rime 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 WTorld War IL .. Water-repellent amosite felt was developed during tbe early part of 1942, as a replacement for hair felt in the insulation of cold water lines, to prevent sweating. Hair felt had the disad- UCC 017586 " 32 ' 10 JOURNAL Of INDUSTRIAL HYGIENE AND TOXITOLOCY [W. It. m. 1 Jon. Ji- vantage of being combustible and as it was organic, when it became wet it moulded or rotted and could harbor vermin. At this lime fires on boaid certain naval vessels convinced the Navy of the desirability of eliminating any combustible material from on board ship. Eventually water* repellent 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. L Description or Operations and Worzznc 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 diatomaceous 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 diatomaceous 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 out end cutting 2. Bond saw cutting 3. Sewing end preparation of boots and jackets 4. Cement mixing 5. lidding 6. Grinding ' 7. Installation on board ship 1. Laying out and cutting Rolls of the insulating felt are 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 with a rotary' electric hand saw. The cut sections are rolled up and either used immediately or stacked in the storeroom. For the ir with ashes; Usually one to three workers are employed at of wa* this operation. During the handling, unwrapping lharV- and unrolling of the asbestos, considerable dust small arises, but appears to settle readily. A very fine a pail water spray should be used for wetting down the when material as a high velocity spray stirs up dust. mirin; Once it is wetted the handling and cutting of the mixin material causes little visible dust. AH of the separ. four yards surveyed wet down the insulating The c material described above. * of ex One NavyYard has an elaborate exhaust system or be for the layout table. The entire top of this table Pet is covered with small perforations through which dicatt the air is exhausted. This table is sufficiently may ' large that no more than two-thirds of the top is 5. ever covered with material and room air is thereby Me exhausted through the other third. While no tion 1 velocity or capacity measurements were made form on this system, data presented later in the report insul: indicate that this control measure had a marked sectic effect in reducing the dust count. with 2. Band saw cutting with A standard band saw such as is found in wood- .* insul working shops is used to cut insulation blocks and to b: boards into .desired shapes. This operation USU2. produces large amounts of air-borne dust, most - . oper. of which settles slowly. Normally there is only .. oper one worker on this operation at any one time. prot< Inasmuch, as this is a very dusty operation, . 6. the band saw should be enclosed in a room by . Sc itself and should be equipped with adequate local prefi exhaust ventilation both above and below the up : saw table. Because of the mechanical cemt in locating this exhaust properly, some of the dust will escape into the air and the operator should dust quer therefore wear an approved dust respirator. . 3. Sewing and preparation of bods end jackets In this operation jacket covers for valves and pipe joints are fabricated. The work consists of cutting asbestos doth with shears, padding the expc gene resp * 7. `T jackets with insulating material, and sewing with wire or asbestos cord. These operations give rise to only slight amounts of visible dust, and exhaust ventilation and respiratory protection are neither required nor used. There is usually Vx* wra %.and i* or : 1 a large number of workers doing this operation in one large room. ; son ' #mix 4. Cement mixing . `a s A 2142 1 s-iSSSfsj ' ?' 'iTT.rr-. *- *-1-'*-:'* * Vi:-*' ' 1- ' -A'-:.* - * ^,-'. *** UCC . 017587 - * *' . -. :f\Z nrK COVERING OPERATIONS 11 protection and to give a neat appearance ulalion on board ship is usually covered cment containing & high percentage of 5 fibers. In mixing, llie proper amount r is added to the dry asbestos cement and. ;hly agitated with a hoe. Occasionally amounts of asbestos cement are mixed in .vith a treweL Considerable dust is raised Lhe asbestos cement is dumped into the trough and during the early stages of . Ordinarily this process is done in a e room and only one operator is exposed, istiness of this operation warrants the use aun ventilation or respiratory protection :, although neither is generally used. >graphic analyses of asbestos cement in- that the amount of diatomaccous earth : as high as 87 per cent by count hiding ling is the process of building up the insula- fit odd shapes of boDerwork and piping. A made to the exact shape of the part to be id. Block insulation is laid on, adjoining > glued together, exposed surfaces sealed bestos cement and the whole mold covered sbestos doth. When dry', the molded on can be lifted on the form' and is ready nstalled on board shy. This operation is done in the shop next to the * sewing tax. Very little dust is produced from this on and no special ventilation or respiratory ion is required. inding . al shipyards reclaim then scrap pieces of icated sections of insulation by grinding ; material and using it in the asbestos all of which contributes considerable ss. Normally this job is done at infre- intervals and only one or two men are l, but the operation should be isolated, room exhaust supplied and an approved or worn by the operator. slcliclitm of pipe covering on board ship : are a number of operations involved in vering on board ship. Insulation felt is i and pounded tightly around large pipes ats and fastened firmly in place with wire stos cord. Pipes and boilers are covered rcfabricatcd sections, which necessitates and sewing to fit the sections. Ready icment is applied to fill in spaces and give thcr finish. Some insulation is wrapped with glass doth or asbestos doth for greater strength. The only operations that produce much dust arc the wrapping and pounding of amositc and the sewing of sections. Nearly all of the compartments on board ship are involved in this work, although most of it is concentrated in the machinery spaces. Usually the greater number of pipe coverers work on board ship and relatively few men in the shop. The spacing 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 ventilation is to be preferred. If the compartment is large, sudx as the main engine room, five air changes per hour are needed. In small com partments, such as living spaces, ten to fifteen air changes per hour are required.' ' IL Composition op Materials Used According to Navy Specification the rovings of asbestos insulating fdt (amosite) shall contain not less than 95 per cent asbestos fiber of the following composition: . Silica (SiOa) per cent minimum................ ........... 47.5 Iron oride (Fe:Oj) per cent maximum...................45.0 Magnesium oxide (MgO) per cent minimum......... 6.0 Typical analysis of the two types of asbestos fibers in general use are tabulated below:. CkryttliU AmiiU Silica (SiOi)......................... 39.05%........... 50.24% Magnesia (MgO)................. 40.07%............ 3.96% Alumina (AJsOa)................. 3.67%..................... Ferric oxide (FegOi)........... \ - ............ 7.80% . Ferrous oxide (FeO).......... / * ........... 32.00% Sodium oxide (Na-O)....... ....................... 2.12% Combined water (N-O).........14.48%............ 3.00% Therefore amosite alone w21 not comply with * Navy Specifications because of the low magnesia content and must be mixed with chrysotSe asbestos to equal or exceed the 6.0 per cent mini mum value for magnesia. On the other hand, duysotilc 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 ' A2 - .UCC 017588 ri '' T I !j i-5 irl (A i* * fif':t. vi *< l1 }? !. 3 12 JOURNAL OF INDUSTRIAL HYGIENE AND TOXICOLOGY fee/. 2&, no. J of asbestos fibers must be mixed together in the and sewing were done with a small amount of proper proportions to satisfy the values set for space for storage. Cross draft ventilation was magnesia, and silica. The amounts of these provided by open windows on both sides of the materials used to form this mixture ihcrcforc- room. - would be 6-43 per cent chrysotile asbestos and Work on board ship was not supplied with 94-57 per cent amosile asbestos. exhaust ventilation. These two fibers differ mainly in their physical No asbestos workers were found wearing res characteristics. Chrysotile is capable of being pirators. readily separated into very fine fibers with a soft U. S. Kevy Yard B. silky feel, whereas amosite is harsher and requires There were 50 men working in the shop and 700 more manipulation to fiberize it. One authority men on board ship. The shop was divided into has stated that the chrysotile has the finest in four main rooms: Layout, Sewing, Cement, and dividual fibers, and amosite the coarsest. Be- Storage and Band saw combined. With the TABLE 1 Summary or Materials Used at Each Yard tzx Mokes XAVTYAaSA VAvrnut COKTXAC? Y*a e Amosite 58,200 sq. ft. 50,000 sq. ft 40,000 sq. fL Amosite (water-repellent) -- 15,000 sq. ft. -- Prefabricated sections (molded and block) 600 sq. ft. 1,200 sq. fL ' 1,750 sq.fL 39,900 linear ft. 115,000 linear it. 18,800 linear fL Asbestos doth ' 76,500 sq. fL 106,600 sq. ft. 34,700 sq. fL Metallic twine Asbestos yarn . 1501b. * Asbestos paper .-- . 5,500 sq. fL 4,000 sq. fL Asbestos board 2,700 linear ft. 6,000 sq. fL 150 sq.fL Asbestos cement 34,400 lb. 15,0001b. 57,5001b. coKntAcr Y*a 6,325 sq. fL 3,300 sq. fL 15,700 linear fL 40,000 sq.fL 5,500 sq.fL -- 38,500 lb. cause of this difference we may suspect a decided exception of the Cement Room, the doors between decrease in the number of respirable fibers (below these were normally left open. 200 microns in length and 5 microns in diameter) The work in the Sewing Room consisted mostly whenever amosite is used in preference to chrysotile of fabricating and sewing valve boots and jackets. asbestos. * . ( All the cement used on board ship was mixed in the Cement Room. There was no exhaust ven- III. Pipe Covering Facilities at Individual tOation for either'the Sewing or Cement Room. Shipyards ' . The band saw was equipped with a flexible exhaust U.S. Nary Yard A. tube above the table and an exhaust around the There were S4 men working in the shop and blade below the saw table. The layout table 467 men on board ship. The shop was divided was equipped with exhaust ventilation as described into two rooms, one of which was primarily for above. There was no exhaust ventilation supplied storage and occasional grinding and band saw on board ship for pipe covering and no workers cutting operations. The only mechanical exhaust were found wearing respirators. ' ventilation in the shop was provided for the grind Contract Yard C. ing, miring and band saw cutting operations and There were 51 men working in the shop and 123 was inadequate. * In the other room layout, cutting on board ship. Layout, cutting and cement A21 42 3W Jen. IS^ miring respirai procedu fabrica: carried was dor Mate room a respirai through a part c There other l pipe co\ walls a frequer. cleaner, applied Cmir There working were dc and jac fabrics', smaller and cu and fire in eitbt on boar in a cor who vc man w: was no IV. An Ther or safe Dreessc the asl partide for tha that tk ing ind In ter specific for son rotate 1 large s: in dust In c coverer UCC 017589 rirr. covering ormumoNS 13 j" vvre done at one end of the shop. Dust riiors were occasionally worn during these rdures. At the other end of the shop the Lotion of bools, jackets and molds were -d out. A small amount of such fabrication done on "board ship. . . iterial was cut with a band saw in a separate and the operator wore an approved dust rator. The dust from this saw was exhausted :gh a slot under the table which caught only t of the dust given off above, the table, ere was no exhaust ventilation in the shop, than for the band saw, and none for the :overiag operations on board ship. All floors, and rafters of the shop were cleaned at snt intervals with an industrial vacuum tr. Most pipe covering on board ship was :d in the evening during the second shift. ttract Yard D. . ere-were 8 men in .the shop and 160 men sg on board ship. * Pipe covering operations done in two shops. In the main one, boots sekets for pipe valves and connections were ated and surplus material stored. In the ir shop the operations .consisted of layout fitting of amosite, water repellent amosite ire felt. There was no exhaust ventilation ler shop nor for the pipe covering operation ird ship. All the asbestos cement was mixed unpartment on board ship. The only worker vore an approved dust respirator was the vho cut the two types of amosite. There 0 band saw cutting of asbestos in this yard. xalyses of Settled Dust and Dust Counts * re are no established figures for permissible e dustiness in pipe covering operations, icxf et ah (2) in their study of asbestosis in bestos textile industry suggested 5 million es of total dust by iropinger as a threshold at industry. We should like to point out he asbestos textile and asbestos pipe cover1 ustries differ widely in their dust exposures. ctUe plants workers usually continue at : jobs with fairly constant dust exposures me years, whereas the pipe coverer may between shop and ship and from small to ship compartments with a unde variation t exposure. rontrast to the textile worker, the pipe :'s materials differ markedly in their as bestos content, ranging from 85 per cent magnesia (10-15/o asbestos) to amosite (95% asbestos). When asbestos cements contain large amounts of diatomaccous earth there is a resultant silicosis hazard as indicated above. In .general we feci that-dust counts below 5 million particles per cubic foot by Konimeter indicate good dust control. Our figures in Table 2 were determined by the Konimeter and not with the impingcr instrument. We used the Konimeter because it is light, easily portable and takes records which can beJtept indefinitely. As is indicated in Table 3, the dustiest operations are band saw cutting, cement mixing, and installation on board ship. . * V. Medical Findings The incidence of asbestosis among pipe coverers as determined by chest X-ray is given in Table 4. The relation between years of exposure and per cent asbestosis is included in Table 5. Due to frequent turnover of shipyard workers and the length of time required to X-ray a large number of workers, the number X-rayed may not equal the number of pipe coverera. At Contract Yard C X-rays were examined of men who bad left the yard while at Navy Yard B a few pipe coverexs were not X-rayed. At Navy Yard A the' 48 X-rayed out of 551 were all older men working in the shop. ' * Some of these pipe coverers had had pre-shipyard experience in the asbestos industry, but the tables are based solely on shipyard exposure. At Contract Yard C, for example, the Asbestos Shop estimated that about one-third of their pipe coverers had worked with asbestos before coming to the yard. . The one case of advanced asbestosis at Contract Yard C had worked, in the asbestos industry for 23 years before coming to work in the yard. At Contract Yard D the two cases of moderate asbestosis had worked 22 years and 30 years at pipe covering in their yard. . All of the X-ray films used in the above data were first read by roentgenologists of the Medical Department of the yard and then by one of the authors (W. E. F.). Dr. W. C. Dreessen, U. S. P. H. S., was kind enough to examine the three positive plates and be agreed on the diagnosis. Since only three workers out of the 1074 X-rayed had asbestosis, and each of the three had been a pipe coverer for more than 20 jtats, it would 55*?- A2 1 UCC 017590 ;i i: ` ti \ i : V ----- onunw Layout and cutting Navy Yard A.......... Navy Yard B.......... Contract Yard C.... Contract Yard D... TABLE 2 Analyscs o>* Sr.TnxD Dost ax Air Sawizs u its rev? LESS IRAK to KICtONS BY COUNT nurr count* CMJ'J'CF)* Vv* ev*> mwsi cXar. uw *we IS ss* aO. '*H Slf-l r O * O Z" Total dust ts;e of Avtrcount* a ASBESTOS BUR JUnsr c.f Aver couat* *te mcccr ASBESTOS (raase) 95 16 9S 10 95 30 95 26 6 tr tr tr 3.5- E.7 6.10.21-0.50 0.35 5.7- 6.0 1.6- 6.5 4.2 0.01-0.54 0.23 0.6- 7.9 17.1- 25.2 20.5 1.15-4.302.18 6.6-19.5 6.5- 16.5 10.9 0.09-1.16*0.63 1.4- 8.7 Cutting with band saw Navy Yard A........... Navy Yard B..'....... Contract Yard C.... 98 98 11.0- 19.2 15.1 0.10-0.14 0.12 0.7- 0.9 [32.4- 46.6i39.5 2.8- 3.2 .0 6.5- 8.7 18.2-100+ 73+ .9-12.8 6.19 4.3-12.8 Molding operation* Contract Yard C. Contract Yard D. 9S 95 Sewing & prep, of boots & jackets Navy Yard A..................... Navy Yard B (Sewing as bestos cloth) 9S (Stuffing with amcsite)... 9S Contract Yard C... ......... 95 Contract Yard D................ 98 3.5- 6.1 4.6 .01- .06 0.03 0.3 -1.0 3.3- 6.0 6.8 0.0- 9.4 0.1 0. -6.4 2.1 2.1 0. .3 0. .10.6- 12.3 11.4 .45- .79 .62 3.7 -7.4 3.9- 10.9 6 00 ' - .05 .03 0. -0.5 Storeroom Contract Yard D... 95 15 26 32 12 Cement mixing Navy Yard A................... . Navy Yard B..................... Contract Yard C................ Contract Yard D (on board ship)............................. 5.4- 30+ 31+ 0. -0.52 0.2 0. - 0.7 67. -100+ 84+ 1.6 -1.7 1.7 1.4- 2.5 33.8- 4S.7 41.3 1.6 -4.7 13.1 4.7-10.0 19.6- 40.0 32 10. - .02 :oi 0. - .001 Grinding scrap materials Navy Yard A....... . 88 20 16 10 33 12 15 9.4-100+ 50+ 0. -1.6 .47 0. -2.6 General room Navy Yard A.............. . Navy \ ard B. Contract Yard C.......... Contract Yard D.......... 0.2- 24.6 10.0 0; -1. o.cs .02-0.3 1.6- 3.3 2.4 0. - .01 .01 0. -0.6 0.0- 21.6 14.2 0.34-1.7 .8 3.8 -7.9 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. 65. -250. 142 10. -0.17 0.02 0. -0.05 S4.4-192.0 12S 1.36-5.21 2.8 1.1 -3.7 25.5- 9.0 49.20.23-2.38 1.10 0.5 -6.8 8.0- 22.1 11.ojo. -0. 21j0.03 0. -1.0 Note: MPPCF Million particles of dust per cubic foot of air. 14 A 2 1 42 b Jen. I94Q oruu Layout and cutt' Band saw cuttin Sewing and fabr. Cement mixing.. Grinding.......... General room... Shop average. Ship average. Note: MPP IKC3DEXCZ OT sarrsAaD Navy Yard A. Navy Yard B. Contract Yard Contract Yard Totals........ Helatioxser* Navy Yard A Navy Yard B Contract Ya: Contract Ya; UCC 017591 >-J PIPE COVERING OPERATIONS 15 TABLE 3 Couj'af.json or Dustiness of Various Off.ratioxs in Each Shipyard munes NAVY YAKD A NAVY YAKS COKTUCT YAKB C COKTtACT YAkO B Tout dust Asbestos dust Toul dust Asbestos * dust Toul dust Asbestos dust - Toul dust Asbestos dust t and cutting................... aw cutting...................... ; and fabrication.............. it miring.......................... B*......................... ......... upper 6.1 15.1 4.8 31.0 50.0 10.0 0.35 0.12 0.03 0.2 0.47 0.08 UPPCF 4.2 0.23 39.5 3.0 4.8 0.1 84.0 1.7 -- 2.4 0.01 UPPCF 20.5 2.18 73.0 6.19 11.4 0.62 41.3 3.1 -- 14.2 0.8 UPPCF 10.9 0.63 -- 6.0 0.03 32.0 0.01 6.0 0.02 o average.......................... 30.0 0.25 26.9 1.0 142.0 0.02 128.0 2.8 32.0 49.2 2.6 1.1 7.6 0.23 11.0 0.03 'eta MPPCF * Million particles of dust per cubic foot of air. TABLE 4 oence op Asbestosts Among Pits Coverers stowen errrve ccvxs- w x- XAVZXt XVMBXK or exist or AS1U70KS Mini* Mod* Ad saal ente vanced Yard A. *.... 551 48 0 0 0 Yard B.......... 750 662 0 0 0 act Yard C.... 174 196 0 0 1 act Yard D... 168 168 0 2 0 appear that asbestos pipe covering of naval vessels is a relatively safe occupation. However, it must be remembered that these men rotated among the various operations of pipe covering and were not 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 respiratory protection are therefore of value in maintaining this .low incidence of asbestosis. 1633jjs* oooeooao* 1074 0 2 1 * Discussion The extremely low incidence of asbestosis found, 0.29 per cent, or 3 cases out of 1074 pipe TABLE 5 tionship Between Length or Exposure and Incidence or Asbestosis MRTYASS TEAM IS rot COVTMHO ' EKBUSTKY 0-2 2-S 5-10 10 plus Exposed.......... 26 13 8 3 Yard A * Affected.......... 0 0 0 0 Percentage.... 0% 0% 0% 0% 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. ' Tne 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 [Exposed.......... 225 435 67 22 * Yard B j Affected.......... 0 0 0 0. [Percentage.... 0% 0% 0% 0% ' Exposed.... met Yard C * Affected.... Percentage.. 0 105 45 17 0 001 0% 0% 0% 6% the operations described above, and tbe 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 coverer's environment may change every few days or few weeks at the most with a constant fluctuation in the dust concentra [Exposed... met Yard D j Affected.... [Percentage. 26 . 118 . .5 9*c- 0 .V i \ 03, -07c 0,7c 22% tion which he breathes. Therefore, the figures given iy Table 3 for shop average and ship average cannct:give a composite picture of the asbestos 11 * .tAV.-.v ' tr- UCC 017592 SB? 16 JOURNAL OF INDUSTRIE HYGIENE AND TOXICOLOGY froL ZS, no. J dust that a worker may breathe over a period ol years. It is further apparent that to obtain r.uch 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 yean. 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 are in volved and the work is usually done at infrequent intervals such as several times a week.. Finally, pipe coverers also apply glass wool, rock wool, magnesia, and other types of non asbestos insulation, all of which decreases the amount of exposure to asbestos dust. It seems likely to us that if the pipe coverers Studied had worked stcadQy 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 vcssels.it is manifestly impossible to set a threshold. VI. Conclusion's 1. The character of asbestos pipe covering industry on board naval vessels is such that conclusions drawn from other asbestos industries 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 coverers 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. 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) Laxza, A. J.: Silicosis and asbestosis. Oxford University Press, New York, New York, 193S. (2) Paresse.v, W. C et al.: A study of asbestosis in the asbestos textile industry. BulL No. 241, Public Health Service, U. S. Treasury Department, 1938. (3) Fakev, J. C: Ships and aircraft of the United States Fleet. 2nd War Edition, 1944. Pub- . Kshed by Ships and Aircraft, 1265 Broadway, New York, New York. '. . EXPOSURE Station oj indviris: ELDING W construe often pre plates upon c prevalent on dec surfaces are aff measures indude application of hea fame, to a distorts or accompanied b Shrinking is of i ments or confined the operation xr measures are in u recently provided shrinker develop: . of nitrogen poison 10 days later fro: Three other wo exposure experien symptoms, but : following day. The purpose of the exposures v small, unvent2at( ' . * . The torch ore the convention: . In most instanc . annular ring a which supplies of water arounc lation of the tor * steel plate can b As with oxyace size of the torch of metal eacoir ducted on thin s range common! czparity of the A 2 1 42 7 Received lor 1 Industrial K '. 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