Document EvZgzk85N7Jdv91BXxZXgbGqx

21 Are We Controlling Dust? HE way damage claims are piling By STUART W. GURNEY* and Tup these days makes it dear that dust counting investigators are not the only ones who can think in terms DAVID S. BEYER** of millions. Hence the employer has two incentives for reducing injurious dusts-- the protection of his employees and the protection of his pocket book. It is possible in many cases to improve conditions by diluting the dust content Many simple principles in volved in dust control are not of the air through general ventilation. Our subject, however, is limited to the removal of dust by exhaust systems, generally understood or ap plied. Meanwhile, claims for which, after ail, is the more positive real and imaginary injuries are method. There are a few simple prin ciples which our day - to - day contacts accumulating with 10,000 industrial concerns convince us are not generally understood and certainly have not been applied in the majority of installations that have been made in the past. We shall try to define and then illustrate some of these prin ciples. State Codes (ion of water does not. by any means, eliminate the dust hazard. Konimeter samples taken in the vicinity of wet grinders will often prove this to any one's satisfaction. Illinois goes beyond the mere speci fication for dust removal and ask? for A number of states have had refer ences to dust elimination in their labor laws tor a good many years. It is safe to say, however, that for various reasons, a static suction equivalent to five inches of water; New York is satisfied with two inches. Wisconsin, in their recently adopted General Orders, specifies at such as lack of funds, inadequate tech nical staff or indefinite knowledge of desired standards, no state has as yet what place static suction shall be meas ured and requires not less than two inches of water for gase---but for dusts, thoroughly enforced these, laws. fumes and vapors it is to be measured Four out of five leading industrial by the expression 2 plus sp. gr. over 4. states whose codes we investigated (in It may be remarked here that, with cluding Massachusetts, Connecticut. everything else equal, a high static suc New York, Illinois and Wisconsin) rule substantially that workers on machines or in processes (hat create dust, fumes, etc., shall be protected by exhaust sys tion will give a higher velocity at the point, of origin of the dust, fume or gas than a low one; but this alone i- not a measure of the effectiveness of any tems. After this good start some quali fying phrases like "as well as possible," ``in amounts which may be harmful." ere., are added, which leave many exhaust system. Wisconsin orders call for definite air velocities of 60 feet per minute for gases - and for dusts, fumes and vapors ! 7u chances for differences of opinion be tween the state inspector and the em ployer. All five states agree that grinding, buffing and polishing wheels should be exhausted, although two of the states exempt from these provisions wheels on which water is used. 'I'his s-mis ill- advised. since a study of wet and dry grinding in Connecticut by Winslow and Oreenhurg 'I', Public Health Reprint No. oloi has shown that the applica- I t i'H t-:nit im-er imj f * C n - rif-i<-icnr .-tM* ''hi.-f Knuinwr, Ichwt.v Mutual [ n, ii r:r nc>" ' ' (iti pH n v, | *it. ?A.\i A Kb 1935 Fia. 1. How an itu-mise in air-flow reduces the 'Oncentmtinn of dust. times the specific gravity and not to he less than SCO feet per minute except under certain conditions. This is getting closer to a real measure for exhaust ventilation, for, after all. it is by the velocity we are able to impart to the particles of dust or fumes at their point of origin, by current of air, that we can move them from where they are and put them where we want them. Wisconsin alone, of all these states, has adopted a different principle--that of specifying a limit to the number of dust particles of respirable size per cubic foot of air. After all, this is what we are primarily interested in, to keep the dust contamination down lo a point where it will not be harmful. Specifications for certain pipe sizes and air velocities may or may not do the work, depending on the shape of the hood, distance from dust source, and other variables. One is reminded of the situation several hundred years ago where argument ran high about the effect of gravitation on falling bodies. Galileo settled the controversy by drop ping weights from the leaning rower of Pisa. What we need in the use of ex haust equipment is a few more Galileos who will Ire satisfied only with actual working tests I National Standards These variations and conflicting pro visions in the state code? merely reflect (he general lack of authoritative .v ,ndards. It is fortunate that detinue -:eus are now being taken by the American Standards Association to develop the proper basis for such codes. There are two committees working cm this proolem: the Ventilation ('"de Committee, sponsored by the \meriran Nioiety of Heating & Ventilating Engineers, arid the Exhaust Code Committee, sponsored by the International Association of in dustrial Accident Boards and < Yunmissions. At a recent meeting of the latter com mittee it was recommended that a na tional advisory committee of clinical, pathological and other experts fie ap pointed who could determine "threshold values." that is. the dividing line between permissive and harmful amounts of dust and toxic fumes in the air. While con siderable work has already been done. Distance from flood-1mists Fig. 2. Velocity of air-iiow Uei-reitsf-r rapidly with distance front the inlet. much additional research will Lie re quired before these standards, which are the very foundation upon which the others relating to exhaust systems neces sarily rest, have been fully determined. The committee also arranged to ap point sub -< ommittees to take up the following specific subjects: 1, Abrasive cleaning 2, Chromium plating ?. Granite cutting 4, Rock drillings 5, Spray coating In addition, a Sub - Committee on Fundamental Principles of Design and Operation and Maintenance of Exhaust Systems will be appointed. The work of these committees will take time, but we now have some assurance that a sys tematic study and evaluation of the ` arious elements entering into the whole problem will fac made. Practical Considerations air flow was incieased to a little over 2S0 cubic feet per minute the dust concen tration had dropped to 4O,00U.000--.i marked improvement. As the air-flow was further increased, the drop in dust concentration was relatively slower, ami it took a volume of about 480 cubic feet per minute to bring the dust concentra tion down to ten or fifteen million partides per cubic foot, which was con sidered reasonably safe for this type of dust. It is accordingly possible sometimes to fake an installation that is not satis factory and, if the remainder nf the system is well designed, by merely speed ing up the blower or adding a larger one. to bring about the desired results. Arrangement of Hood Inlets: Another very important consideration is to get the inlets of the exhaust system as dose <ts possible to the source of the dust. The drop in efficiency as we get further away from the inlet is really surprising to one who has not studied the principles involved. Jf we have the open end of an exhaust pipe or air dust in operation, the air tends to flow in from all sides, even from behind the opening. It is somewhat as though the exhaust inlet were in the center of a sphere and the air was drawn from every part of the sphere into the pipe. As we move away from the end of the pipe the velocity drops very rapidly, so that the velocity at five inches from the hood may be less than It) per cent of that right at the hood inlet. This-is a most important .considera tion to keep in mind, It is not uncom mon to see an exhaust inlet a few inches in diameter with which the person mak ing the installation hoped to draw dust from a distance of several feet, and the air-flow even a font or two away from the entrance to tie inlet may be negli gible. Another important consideration in the design of the inlet is the addition of a flange, the effect of which is to cut down the air that would flow in from behind the opening, thus drawing it near ly all from the front. The effect of this is to increase the efficiency of the system substantially and extend the scope of the exhaust without appreciably increas ing the power consumption. Other Considerations: Aside from these two features there are various other points of lesser im portance that should also be given con sideration before a good exhaust instal lation can be hoped for. For example, air cannot he "pulled" from a distance by merely directing an exhaust pipe towards the point in ques tion, but it can be "pushed" or blown, directionally, for a considerable distance. This principle may be used advantage ously in directing the dust towards the opening of the exhaust inlet and thus getting the desired results with a lower exhaust velocity and power consumption than would be required if such suction alone were depended upon. This prini iple has been applied effectively in drilling material containing asbestos, where the exhaust inlet is placed at one ride of the drill and a small air jet at the opposite side of the drill, blowing across the table turns the particles that would flv out from this side mid directs The two most important considera tions in an effective exhaust system are: 1. Velocity of air tiow, and 2. Arrangement of the inlets ftrom the standpoint of neumey m the dust source, shape, etc.) Air Velocity: Many an installation that is otherwise all right fails to remove the dust success fully merely because there is not enough air being drawn through the system. Fig. 1 illustrates some tests, that we made under actual working conditions by Theodore F. Hatch, Department of Industrial Hvgiene. Harvard -School of Public Health. These tests were run on a machine used in dressing stone and you will notice that with an air flow through the hood of 240 cuhir feet per minute there were over J00.00O.U00 dust par ticles in the surrounding air. When the Fie. i. PUriiijt rtirtubi in front of the "dolly wudit-r" reduced tilt- ojieuiiic into half and ultima doubled the velocity of air flow at the bottom of the .ipenini:. NATIONAL SAFETY NEWS 23 them back into the exhaust system. It is also being applied to foundry shake out work. fit her . onsitierations in designing ex haust systems, such as the elimination of unnecessary bends or curves, the pro vision of dean-out doors, the construc tion of the joints, etc., are well covered in the current handbooks and State In dustrial * odes, such as those of New York (see Bulletin No. 12 of the State Department of labor. X. Y.l or Wis consin isee (teueral Orders on Dusts. Fumes. Vapors and Oases. Industrial Commission of Wisconsin) and will not he gone into further here. Where there is a general ventilating installation and tine or more exhaust systems, care must be taken to see that they do nut. "buck'' or offset each other. ()ne of onr engineers recently demon strated this point in a factory by means of an anemometer, which showed a good draft right at a dust-producing machine, but as it was withdrawn from the ma chine the anemometer slowed down, coming to a standstill at just about the position of the operator, and then re versing beyond him. showing the air beyond this point flowing toward the general ventilating system, in this case there was a dead space right around the operator from which neither system was effectively removing the dust. After an exhaust system has been in stalled it should be (i-sied by faking actual dust counts to see that the dust is really being cut down to the desired point, and such counts or perhaps check Rouimeter samples should be taken at intervals, after the installation has been made, to see (hat it is still functioning properly. 'The fact that the dust particles that cause the trouble are so small that they are invisible under ordinary conditions (less than 10 microns or 1 2500 of an inch in diameter) often makes it hard to t onvince the practical plant manager that there X ,mv dust present: if also makes it. impossible to tell, without the use of -pedal instruments, whether the completed exhaust system is actually re moving the dust. Qualitative Dust Analysis The present consensus of opinion on the development of dust diseases is that besides cjuantity <if dust (usually ex pressed in millions of particles of respir able size per cubic foot of air the i/xulitv of the dust also must be known, particularly the percentage of free silica tSiO ) in the particles under 10 microns Pitt. r. View of primary rook rrtishcr II. enclosed exhaust bucket conveyor !. primary hopper K, and exhaust ducts leading to filter unit /. This rock crushing plant contains many excellent examples of exhaust ventilation for particularly difficult situa tions. It has resulted in a reduction of dustiness to less than 5.1100.000 particles per cubic feet tested by standard mutineer. 1". .S. Department of Public Health technique, i Photo by Division of Industrial HVssiene. State of Masmrhusctts,t in size. A chemical analysis of dust will not give this result and so measure ac curately the relative hazards of dusts. In our opinion, the most practical method for analyzing and evaluating these tine dust particles is by means of a complete petrographic analysis. 1'his consists of the microscopic examination of individual dust particles under polar ized light, which permits the identifica tion of each particle by determining its optical properties. rntil recently, petrographers have generally considered that mineral par ticles must be over 10 microns before they could be identified with any degree of accuracy. As health hazards are ifferred only by the sizes under ID microns and the inineraiogical composi tion of the larger sizes is not necessarily the same as those under 10 microns, it became desirable to further refine the technique of petrographic analysis, it has been found that, working with mag nifications of about 1800 diameters and a light source of high intensify, mineral particles as small as one miernn ran be accurately identified. Before an exhaust system ran be defi nitely approved as giving satisfactory health conditions, some such determina tion of dust composition must be made, in addition to the count of dust particles. big. 2> illustrates an interesting case in connection with a "Dolly Washer" used in textile plants for spotting fabrics, -tc. While this system deals with fumes, the principles are identical with those involving dust. '('his equipment, uses trichlor-ethylene and in spite of the exhaust system which you will see over the washer, the fumes were escaping into the room as indicated by qualitative tests with a Turner Halide detector i which depends on the color of a dame to indicate roughly the intensity of the concentration). Readings t Katat were taken at Ax locations in the opening, as indicated below the drawing: a curtain was added which reduced this opening by about one-half and further readings showed the air velocity at the bottom of the opening had been approximately doubled. Tests of the air indicated freedom from contamination. Maintenance ft might seem like an insult to one's intelligence to say that after an exhaust system has once been installed if should be maintained in good operating rendi tion. However, the numerous cases one encounters in the plants where this .>i>vtotts necessity is not tarried out, indit ate that it is really one ot the major considerations. Vases are not unknown where the blower has in some manner hemme re versed so that the air is being ejected and diffusing the dust rather than draw ing it in: other instances where the effi ciency of the system has been lowered or its value nullified by clogging up. disconnection or wearing out of the piping, etc., are all ton common. One concern of which the writers have (Please turn fa pa%p -ri i JAM.WRY. 1935 M*NDjy] Are We Controlling Dust? I Continued from page 23 J RAIL CLAMPS PROVIDE SAFE CONDITIONS Eliminates the dangerous practice of placing blocks of wood under the car wheel for bracing. Recommended as the surest and safest possible stop for use on run ways in repairing a crane, on load ing platforms, temporary sidings, car stops, on air ferries, under tipples, and for cars on grades. Rigidly constructed of open hearth annealed cast steel, tool steel key. Made to fit any rail from 40 to 110 pounds. Easily and quickly removed Guaranteed against breakage Used and recommended by lead ing steel companies, manufacturing plants, mines, grain elevators, ce ment plants and quarries. Sivle A--Sij.Wf Each Our Engineering Department will design clamps to meet special track conditions. Let us have your oper ating problem and we will make recommendations. INDUSTRIAL PRODUCTS COMPANY Accident. Prevention Equipment 800 W. Somerset St. Philadelphia, Pa. knowledge, has a "IT" tube permanently installed in one of its main exhaust systems so that the foreman or safety man can tell at a glance whether there are any changes that would indicate a break-down in the system. All such in stallations should have regular inspec tions by some competent person as a routine part of their upkeep. Checking Exhaust Systems There are several instruments that may be used in checking tip the results of exhaust systems as follows: For Air Velocities: Anemometer - (useful, but results must be used with judgment much below S00 feet per minute!. Kata thermometer -- (depends on cooling effect of air current; requires rather careful manipulation -- good for low velocities less than 500 feet per minute). For high velocities in ducts pitot tube (for velocities over 1000 feet per minutes special vane anemometers'). For Air Volumes: Orifice meter, or venturi meter. Where none of these instruments is available a rough check can ire taken by the use of smoke, or flags or streamers, held near an exhaust opening to make certain that there is a good draft intake: however, this does not tell definitely whether all of the dust nr vapors un being drawn in. The Smith - (Jreenburg impinger ;sused by the United States Department of Public Health is the generally accept ed .standard for dust counts in this country. For the purpose of an approxi mate dust check, however, probably the best and simplest instrument that has yet been evolved for field use without special laboratory training is the Konimeter in which the dust-laden air is impinged at high velocity against a dry or coated glass slide. While this instru ment was originated abroad anti at the present, time must Ire imported, steps are under way to snake available a simplifier! type of Konimeter along the lines described in a paper by Hatch and Thompson in the Journal at Industrial Hvstirne for March, l`H4. fit is be lieved that such an instrument could be marie up for around $100, or about half of what (he .corresponding imported instrument would cost.) Line important advantage of this instrument is that it gives the sample on a standard glass microscopic slide which is excellently adapted for direct petrographic analysis to which reference is made later. While the Konimeter does not give a precise tlust count that can be com pared exactly with the !,'. S. Public Health htandard. it does give an ex cellent check on relative conditions and tan be used in picking out the worst conditions, registering improvements, etc. St enables the skeptical manager to actually see the "invisible" dust, hence has a great educative and sales value to the safety engineer, if used with judgment. Perhaps you have inferred from this discussion that it is a real engineering job to lay out a proper exhaust system, and not one that can be taken care of satisfactorily by merely calling in the "tin-knocker" and telling him to go to it, as is so often done. Even the so-called "ventilating engi neer'' is frequently 'stumped" when it comes to problems of removing dust of the type we are considering. He has been used to ventilating schonlhouses and other buildings, or removing visible dust, particles, and usually thinks in terms of so many air changes per minute. He often ioses sight of the fact that he may be changing the air in one part of the room ten times and in another parr may be changing it only slowlv, or it may be completely stagnant. In a i ase which recently came to mir attention, n well-known firm of consult ing engineers insisted that the general exhaust system which they had put in a plant was the best possible method for minimizing the exposure, and must, be producing satisfactory results because it was arranged to move TT/'d" cubic t,,e' of air per minute. Even when it wa> pointed out that there had been eight claims for disability resulting from fume inhalation during the year, it was hard to convince them that further steps were necessary. Respiratory Equipment The Amplest form of respiratory equipment is the filter respirator, im provements have been made in recent years along the line of providing more efficient filters and larger filter areas that reduce the breathing effort. Mjch res- N.VimNAL SAFETY NEWS pirators have a dennite value for tem porary use such as sweeping up, clean ing nut bins, shoveling materials, etc., but they require careful fitting and con stant supervision to et* that they are being properly used. It is our opinion, after watching the sincere efforts in a number of plants to enforce the use of these respirators, that it is rather impracticable to require them to he used on a full-time operation, (>ne notices the men, under these t onditions, surreptitiously pushing the respirator aside and gasping in free air like a fish out of water. Certainly, if they are to he used any considerable length of time, frequent rest periods should be allowed where the men can get out into the free air fora few minutes refreshment. There are the large air-fed helmets, with which mnsi of us are familiar, used for sand blasting. etc., which have been carried to a high state of perfection for the pur poses to which they are adapted. We believe, however, that much more use could be made advantageously of the type of apparatus that lies midway between the filter respirator and the airfed helmet, namely, the light, air-fed respirator which i.overs the nose and mouth but leaves the rest of the face exposed. With a light hose attachment this device offers considerable freedom of movement, and if air outlets were supplied so the host- could be quickly transferred from one outlet to another, it would seem to be practicable to use. them over a considerable area. They afford the advantages of a pure air supply without excessive weight and wirhout the restriction to breathing that is imposed by the filter respirator. PUT non-slip footing right on your workmen s shoes. Then they are protected from accidents due ro tvherever their work may take them in your plant. In Gro-Curd and Raw Cord Soles and Heels, auto tire cords are embedded upright in live, durable rubber. Cord ends, kept bare by wear, provide positive gripping friction between sole and flooring. Hundreds of Safety Directors have found that to keep workmen on their feet is to reduce the toll of serious, costly accidents. Workmen like Gro-Cords and Raw Cords because they deliver long wearing service--are more comfortable. Write now for sample soles to test on your own shoes. A complete line of safety rubber footwear, Gro-Cord equipped, is also available. GRO-CORDS and RAW CORDS are widely used in Dairies, Iran and Steel Faundries. Railroad Shops, Auto Factories, Gas and Electric Plants, tee and Fuel Stations, Stone Quarries. Mines, General Warehouses. The Lima Cord Sole <& Heel Co., Bep. t-F, Lima, . Conclusions \ J A I'Hif'i-:-ttrnr.l ,tni cv bauu -v -rtriJ Cht- oust .if iiw /unit ,*iui ft-movt-s ! A hi fh<* mn-vf c-fftT'tw- it :r ifis. -S .. m.fvtt mi? fhr <iust pH'h- Ifi'ji- ft ts ftiniv- positive and c-ffmivc tucc im/urnil r'ofii.jrinii ShtUUm- dtrrc t,-*wr-r i dm t uiMnl1 this- s, 1 rht* I r.nisf.int .ttffkh. >fi Mr.., v ' -qitoitf' fhu use tit r<-snir.ifors\ A vsfuust \\ stem requires ,i fhmmiyl) ltn*w11'dpt* r-nui^eeimg principle*. M-iiiv mdus^i'-d tn*t.i|Lit1*in4 m the past havtixvn nut.thlv \v'-1k m tilts taspect, T C'.tierui f<-s>N *,vnji dust roiintimr * .sam pling f-qtj jpuirnf ,.1-y i.tte' -a IV jft*T fill* in- ; ualfjfinn Jus !x-t*n utanpls-jv,^ r> whether ut mif it hiKu;-. thou: ; t- A-witA re.iuc 'm-i m dflSl OUKemutlOH, i. I'rovtvniT! must hr nude >' .tt-mit:c nuunh'iumr and upktvp. prrtcrahlv v, jfh rherk' trsfs oi qu'l i'intr!i:r<fmil\ .it U'UUlat ntutvaU, I sfrer > ui-M.:*'! >*'\ 'usraM.ttin'i h.i^, . hrt-u ! NON-SLIP A ` : \ ; a. u :Tiiuimf `iv- E^umred t pritornufue >'f an exhaust sfrni -aandanh j vs| .'t p-iuns / dust>n.Sv aiv ncu>*arv. ' ,I\mt\ry. ib.r, SOLIS Jl ND HEELS Close Hopper-Bottom Car Doors with EASE and SAFETY Prevent smashed fingers, strained backs, ruptures and other serious injuries, by using the Prescott Safety Tool--Saves time--Is inexpensive. ffrilt tor price* ttnd details The Trumbull Mfg. Co. Warren, Ohio