Document mp0718eaQx5aQLQeOgjKDoxyg

FILE NAME: National Safety Council (NSC) DATE: 1953 May DOC#: NSC026 DOCUMENT DESCRIPTION: NSC - National Safety News - Practical Aspects of Dust Suppression G rin ding b o o th s equipped wiih iocai d o w n d raft exhaust. Face pro te c tio n is also p ro v id e d . PART II Practical Aspects o f Dust Suppression By W. B. LAWRIE M. Sc., F.R.M.S., A.I.M. OCAL exhaust ventilation sys- matter to capture the dust cloud. Here again there is an urgent 1 systems normally consist of a Far too little is known about the need for better cooperation be $ hood, duct and a dust collector. mode of --dust formation, and tween process men, machine de Theoretical c o n s id e ra tio n s are propagation from its p o in t of- signers and ventilating engineers. usually concerned with hood de- origin. The aerodynamics at this E very dust-producing process sir gs, duct designs, and fan char end of the local exhaust system should be carefully studied with a "-ittw acteristics. But the major problem have unfortunately received note- view to devising working methods is to get the dust into the duct. ing like the attention given to the which allow total enclosure. This Dnce the dusty air is safely somewhat easier problems of dust should be done before open hoods thi ough the hood and into the conveying and theoretical fan de are considered. In many cases duct it can easily be conveyed to sign. total enclosure has not yet been a c.ust collector. It is quite another The first necessity in any local achieved, but the point at which Lais article, Part II of one which appeared originally in the Brili.sk Joirnal of Industrial Safety, is pre sented in condensed form through cot rtesy of the Royal Society for the exhaust ventilation system is to capture and contain the dust. It is probably true that this has been achieved only where it has proved the dust is generated should still be enclosed so far as this is prac ticable, and the partial enclosure should be designed so that the Pn mention of Accidents, London. Part possible to enclose completely the wolume of air inside it is as small I, thich appeared in the February is sue, dealt with the more general aspet s of dust suppression. Illustrations a re f r om industrial plants in the U. S. A. point of origin of the dust. It is certainly true to say that total enclosure represents the most effi cient and the cheapest method. as possible. This implies a close fitting hood with a small opening. Where it can be arranged such a design has advantages over the big 28 Natlan-al Safefy N e w s, M ay, 1953 e , ,\ ` -W 4!>' A 1 ^ J * I- J *1 Is> * } ^ I ( . iL - i rL v. (1p(.|] fume cu board type of enrio~i:re which has a large area .u'rnss which air has to be cxiracted. Tbesf large open faces nfecl large vo umes of extraction ;1jr and give a correspondingly iarae, heat loss Even the high air volumes used provide only low velocities over the face of the .iwming, and may not give efficient ,,)111ro1 of the dust. More though.'; should be devoted (o the use of high velocity air curtains which, operate on small air volumes. These would result in much smal er heat losses, and there is reason to believe that they provide more efficient dust con trol. High n.ocity air curtains mav be obtained from suction fans, or they may be provided by jets. The jet may, of course, dis sipate dust, i: a dusty object is lowered into i b u t it can be em ployed in conjunction with an exhaust hood, when the positive, high-velocity, .ow-volume air cur tain it gives i ; used to direct the dust into the ixhaust hood. A careful study of the process generating the dust may suggest adaptations which will facilitate application of local exhaust ven tilation. A good example appears in the modern mechanized foundry wffiere moulds are placed on a conveyor belt. Molten metal is poured into each mould from a ladle which is supported on a block and tackle running on an overhead rail, The systeiii can be*'operated intwo ways. Ei i.aer the moulds can move past the ladle which remains stationary, or the ladle can be moved along the conveyor belt from mould to mould. Fumes are evolved as the .metal is poured into the mould and local exhaust ven tilation is app.ied to control them. If the ladle remains stationary, and the moulds are brought to it, the area of the pouring operation is limited to ' his one position, so local exhaust ventilation need only be applied to a small area. If the ladle is moved along the conveyor, fumes are generated along its full length so that the local exhaust ventilation must be applied over a much bigger area. When large num bers of ma chines or processes operating in a single room have to be fitted with local exhaust ventilation, it is al most certain that there will be a high rate of air extraction from the room. This involves a corre spondingly high heat loss. Efforts are being made to sup ply cold air to the local exhaust ventilation system. If this could be done, unheated air from out side would feed the local exhaust units and be extracted and re turned to outside atm o sp h ere without being heated, and without affecting the heat balance in tire room. Much more thought needs to be given to this idea, which would offer great savings in fuel costs. Local exhaust v e n tila tio n is sometimes applied to enclosures of the fume cupboard type in small rooms. The reason for the smallroom is that the dusty process- is thereby separated from other work. In these cases great care must be taken with the supply of air from outside. If the fan on the fume cupboard is large, the rate of air extraction through the hoocl may be so high that a negative pressure is set up in a small room. In consequence, the opening of a door may allow such a rush of air into the room that the direction of air flow across the hood face is reversed, and the dust blown all over the room by the erratic eddy currents which result. This effect is not so appar ent in large rooms. Recent Developments Much exploratory and develop ment work has been undertaken recently in one industry and the results have heen published. In 1948 a rapid dust estimation technique was devised to permit rough comparisons between condi tions in different foundries and to facilitate collection of dust sam ples. This method shows the resid ual dust concentration in the air and permits an estimate of the efficiency of various dust-suppres sion measures. In half a dozen buildings se lected at random, it was noticed that the dust concentration in the roof exceeded that at the breathing level, which suggests that general ventilation might be defective. It was also noticed that swing-- To page 142 In is man is ti ing m ag n esium ings in a b s o th e q u ip p e d exhaust ventilatio n . cast with P O IS O N IVY OINTMENT proved in the field with eight years' case history poisonous a ' must" m plant hazard. Give your field workers this proved protection against poison ivy, oak, and sumac. Use as a preventive or cure. Packaged by MSco under the Unit System to fit all standard unit type first aid kits. Accepted today by numerous field operative industries as all first aid kits to combat the /K Write for complete details. Medical Supply Company " I t pa ya to b u y --fr o m M ed ica l Supply** R O C K F O R D , IL L IN O IS * IN C A N A D A , IT ' S S A F E T Y SU P P LY CO. 'j n a k e q l o y e s l ^ BEFORE x LEATHER RUBiiER OR COTTON THIS IS WHAT "WASH-RITE" DOES... T h ro w all you d irty , w o rn le a th e r, ru b b e r or cotton g lo ves in oursteel drum , S Y p to us, W e co rrectly d e a n , ste rilize , C O M P LE TE LY REPAIR, sort, 'e sh o p e, p a ir and ship them b a ck to yo u a s se rv iceable as ne-v. D epending upon the g loves and their u sag e, g lo ves are b eing re -cla im ed b y us 3 to 5 tim es. W e s p e cia lize o n ly in laborc lo ry controlled re -cla im in g of ru b b er, le a th e r and cotton gloves, aprons an d clothing. Write for literature. JO V e a rs o f P ro v e n S e rv ic e Y O U R GOO 3S FULLY INSURED . . .WORK GUARANTEED AFTER CORNELL AVENUE INDIANAPOLIS 2, INDIANA size public buildings. Steel cables stretched be1 steel towers or poles are frequ ly used to protect high vol electrical equipment, in fac[. most all very high voltage tr mission lines have one or ,,, grounded conductors located aboyf^ the phase wires (which are ,-j, erally carried on suspension ,, sulators) to protect the Sy< ,, against a stroke. The same sy: pJ, is sometimes used for oil tank other structures. Wire fences, particularly mhqfljYt mounted on wood posts, may , I ry a lightning stroke a long ()${?' tance and frequently kill Clllr|,,i, grazing along such a fence lin^&'V; Wire' fencing should be grouril at intervals of about 150 feelS prevent the transmission oilit hazard to persons or animal a distance from the point finally struck. With present engineering krto; edge, almost any structure cap made reasonably safe from li|, ning damage. Steel-frame bull ings are inherently protected';; the foundations are reasoruihl^|j,^t| ; deep, but occasionally damag--i.i '-j! done to brick, stone, or terra bJMs? ta copings when lightning ma its way through such material? the steel frame beneath it. .`/I I can be taken care of by aj strip or small angle of metal plnr along the outer edge of the, sonry and connected at inlet to the building steel. The basic principles of ning protection should 'be stood by every safety eng since it is both an occupatjH and an off-the-job hazard. J Diist Stlppression -- From page 29 . -:^ j. ; frame grinders without local haust ventilation gave dust .' vSn-pte-l centrations sim ilar to tho: swing frames fitted with ret -j. hoods and extraction fans. suggested that remote hoods inadequate. '"'i' T&!" An average of samples tak 1tfjjL:'1 pedestal grinders was then assc ; because these machines are "'I---J'j.jl mally fitted with local exhaust 1 tilation through the wheel gu ' | The average dust concentra,|l,4^;|;,;i:p obtained was compared with partiema quantitat {rations mined v fihowever, the mov larly whi tion was This c develop m the dust i graphed new tech empirical in an a: natural fi of origin, object v.-a serve the tern. First re abrasive local exb 'laboratordust cloui laic in a the wheel the fine chisel mis operator, along the Observ; floor-stanc cal exhai Was notict the wheel that the d the front < traded b\ In one streams w grinder fit h'lation. 0 caused by ttof,or>a[ Sai IfT " k . , Jjy portable .Tinders, pneui P' ,-niseis and sw ing frame mr:jl|!tl,iiTS- alt who h were operat,, plmtil: exhaust. It was antic.i- ' (U,ui ;|-al there wot. id be a cor.sid.yp difference between these c, avorages, but this did not ; to be the cate. This result 'll.I.).. h1oV due to the fact that the |u,tJet systems are drawing aver, ,|ustv air front all over the ,,'nrkro'im, or it mat indicate that j.ical exhaust ventilation was ... good as expected. \\ liile this explorrtory work was proceeding, the engtneers engaged lM new" designs foi dust control inuuratus asked to; a method by ,,hicii the dust movements in the .,jr could be seen. They did not particularly want the, method, to be quantitative, because dust concen trations could already he deter mined when necessity. They did, however, want to set the locus of tint moving dust cl suds, particuhirlv when local exhaust ventila tion was applied. This demand wa; met by the development of means by which the dust could be seen and photoxrnpiiecl with a cine camera. The new technique has seen used for uirical development work, and . an attempt to determine the natural flow of dust from its point nf origin, in certain nstances. The object was to use tie dust to ob serve the aerodynamics of the sys tem. First results have shown that an abrasive wheel running without . local exhaust ventilation and in laboratory conditions, may give a dust cloud which appears to circu late in a vortex above and behind tie wheel itself. It was seen that tie fine dust from a pneumatic onisel might flow up he arm of the operator, and was not projected along the path of the metal chips. Observations were also made on floor-stand grinders atired with local exhau st ventilation, when it Wa3 noticed that the fan effect of the wheel itself might be so great toat the- dust was projected from he front of the guard, and not ex acted by the fan. In one instance, two dust hreams were seen ctr a pedestal '""nder fitted with extraction ven-ion. One stream was obviously caUsed by the fan effect of the No,Eancf/ Sofefy News, Mzy, 1953 M tjs y / r ... F f THE No, 504-S Sizes-- 5-13 Wear a Reece "Strong Toe." Comfortable leather uppers. 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Because of tli, strrjnjf upward convection currents over # furnace it has been normal in t(l(s past to fit a hood and fan over top to collect the rising fur These hoods are often a nuisam especially if cranes are necessa The high-frequency furnace is sm all diametej, a n d so it w i found possible ^to avoid the hoodk"' by applying a very high velocib"" '' air curtain immediately over thfffeli furnace. d lfe l|f In this instance the curtain is not a jet, as used on the dressing- bench, but is provided by suction fans. The exhaust appliances are below floor level and offer no re striction to the process work. T hs~" amount of air handled has -beeiiH reduced so that the heat loss fromr the building is smaller and tW: fumes have been controlled. Conveyor belts dealing wit fuming moulds are often pas: through an ex h au sted tunnel) which may be of co n siderably length. Large volumes of air ma) be needed to exhaust these tunnelvsdj so efforts have been made in Sw( den to supply some of this ^ ^ direct from outside in order tO-W reduce heat loss in the ro o n V y These efforts have been so success:^ ful that in certain instances morc^ji than half the ventilating air 13_ J never heated. Conclusion It is impossible, in a generalj;,,, survey, to discuss in detail any'pt single feature of the diverse ai>A j complicated devices used to suppress dust. If dust suppression B rightly approached, it is not ea3)V j to discuss more than one indusirym'j although it is obvious that if du3W | were completely controlled in 0I'ei(!ji4 r nursi- it vr-' r.Tnc!'r kia(j "iriks ^ ox !T^nt r Twen> '1niV (i r`<Tf v ^riris National Safety News, M ay, industry; a proper understanding ,f the scheme woulc offer many .^pstions to other iindustries, ilUhD f or these reasons orne features dust suppression have been ob,ved with a view I0 suggesting practical aspects ess mtial to ul;jniate success. Examination of n any p lan ts , J t 5s to the conclus on that the ^ct necessity is a mo -e liberal ap<)ro1ch to the whole matter. It is ...seiitial that all avail ibie methods ,,nnulci be examined, and that the twuii scheme should represent an intesration of every available re- -nurce. [n particular, a r ractical out- l,,,,k demands that 1ical exhaust ventilation should no! be regarded as the only way of <.ust suppresdon. It will doubtles 1 have to be applied in many case i, and it will continue to serve over a wide field, Nevertheless, greater fficiency will lie obtained, as it is ;irogressively embodied in plans wl ch incorporate other ideas. - So far as local exh aust ventila lion is concerned, th rne is still a peat need for careful study of the aerodynamic conditio is at the en'ace to hoods, and ti is manner in ,h the mechanics of dust genoration influences thes : conditions, Instances of recent pi actical work have been given to ;1lustrate the value of empirical ilevelopment, because it appears, ;hat calculadons of air flow may not necessa. fity indicate the effici ;ncy of dust control. Industrial Healtl. ' --!'rom, page 60 1lo not fade in the winter, and ,reas of dilated capillaries in the ; lHn surface. The thing which is : nI most clinical imf ortance, of i " orse. is the tar wart since this '* Very closely related to the tar' ; --vacer. Of these 241 men, 66 had tad one or more tar warts. The rarHest wart developed after 11 Months of exposure and the long*** exposure before the developilcni of a tar wart was 41 years, ''enty-six of the men had had r ) one wart and the others had u varying numner: up to 63 on one individ tal with 26 s exposure. eventy per cent of the tar TM _ _ __ by the CURRAN CORPORATION A high performance volatile, liquid-phase, non-toxic, non-flammable solvent, a specific replacement for carbon tetrachloride. A self-emulsifying di-phase safety solvent for cleaning and scouring; non-burnable, non-toxic . . . does not tend to de-fat the skin. A high-performance safety degreaser of the aromatic type -- excellent for metal dry cleaning. 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