Document 6Bm9vO5XanE9qxj7Dq1wQ7XoR

.-STATE LEGAL' PLAINTIFF'S EXHIBIT GAR-89 i. MARCH 1956 Vol. 73, No. 3 See alxa irtdej- on pnr/r 31G 20th Annual Safety Equipment Issue Two Sections: Section 1 . ' - ' Section 2: Service Guide 2.1 ' PLANT DESIGN - AND CONSTRUCTION Plan Plants for People. Light for Safer Work. Know Your Kloots. .Stairs. Ramps, Fixed. I^*d<Jers.:----- HOUSEKEEPING AND MAINTENANCE * ' Housekeeping and'Sanitation. Rodent'anti Insect Control.. . . .' . What Color'Dries. Portable -Ladders.- Scaffolds, Work Fumittiiv...... '13. 17INDUSTRIAL' HEALTH ENGINEERING . ... ... \ . ' Vo-ntrlaiiotf. Washrooms and Lockers. Skfn Infections. Heat and Humidity. Controlling Air-Borne Bacteria, Drinking Water.' F<kx1 Service ........................................................................................................... tw 4. NOISE CONTROL Measurement of Noises Enginccring-Gontrdl. Fiir-Defender*. ` Medical Control. Hearing Aids......................................................................... S*.' 5. PERSONAL PROTECTION-PART 1 Eye Conservation. Respiratory Protection. Prolection for the Head...Ill 6. PERSONAL PROTECTION-PART 2 Foot Protection. Leg Protection. Safety Clothing. What to Wear, Plastics for Every Purpose. Safety Belts and Harnesses.............. 151 7. . MATERIALS HANDLING- - --- ......... ............. .... ' " '' Fundamentals. Trucks and Tractors. Wire Rope. Chains and Chain Slings, Fiber Rope;.Hoists and Portable Cranes. Conveyors----- 207 8. MACHINE OPERATION AND GUARDING Guarding the Machine. Electrical Equipment, Hand and Power Tools. .231 9. PLANT PROTECTION Fire-Fighting Techniques. Handling Flammable Liquids. First-Aid Extinguishers. Automatic Protection. Spontaneous Ignition. Plant Organization .......................................................................................... 10. MEDICAL AND HEALTH SERVICE Medical and Health Service. Care of the Injured. Resuscitation Methods and Equipment............................................................................... 11. SAFETY PROMOTION AND TRAINING Training and Maintaining Interest. Signs for Instruction. Direction and Warning. How to Plan Effective Meetings..................................... No*ac Edlion.il Director. Cnmi- :it Publications Caxmak FiKit. Editor Wuxiam R. Vat. Associate Editor Raith Moses. Art Director II. W. Cmampux. Advertising Manager Rcxttrr O. Jokdi. Assistant Advertlsinc Manager Olive* Mickila, Advertlsinc Production Manager * Natioxal S aftty Nzw* is published monthly by National Safety Council. Copyright 1 DSC bv National Safety Coun cil. Printed in Xl-S.A. Entered as sec ond clas* matter June 21. 1921. at the Post Office at Chicago. Illinois, under the aci of March 3. 1873. Subscription rale: to members. $5.50 per year, single copies 55 cents: to non-members. $7.50 l>er year, single copies. 75 cents. Quan tity prices for yearly subscriptions and single Issue on reque>t. Member Audi! Bureau ot Circulation; Indexed in In dustrial Arts Index. 4/l.niW) rnpie.i nf this ir.xur xrrrr priiife.-/. Editorial ........................................................................................................................ Fatalities Up in 1955 ................................................................................................ Accident Investigations--D. Paul Cochran ....................................................... Ionizing Radiations--F. A. Van Atta ................................................................... What's So Special About Women? ....................................................................... The Boy and the Peddler (Diary of a Safety Engineer)--Bill Andrews . Wire from Washington............................................................................... .............. Coming Events ............................................................................................................. The Worker's Armor--Carter Kendall ................................................................ The Safety Library .................................................................................................... Is the Purchasing Agent on Your Team? ........................................................... Recognition of a New Industrial Disease--N. Gitlmor Loup. Af.D. end Fred Porter, M.D........................... ............................................................. Falls Have Many Causes ......................................................................................... Void; of the Reader ............................................. .................................................... Personals ...................................................................................................... . .. President's Medal Awards ............................................................. . Safety Films ....................................................................................... . Safety Posters........ ............................................... ................................... I -WWWllXW *`-v:' :- ;v`'%&ikv$U& 428; CHECKING PERFORMANCE, OE LOCAL EXHAUST SYSTEMS Published by the National Safety Council - -- 425 'North-Michigan Ave.f-Chicago 1 T;*-fII.~`'T- 1.. Changes' in manufacturing procedures;!!! the iast-`few.'years . have resulted in the.use of more toxic materials and in the gener ation of more finely divided par ticles and greater quantities of . smoke "and fume. " At' the . same ' ' lime, there has been a greater effort to maintain a safe, com fortable atmosphere for the em ployee. 2. It has been estimated that about 80 per cent of the contami nants are controlled by ventila tion, and" today mafiy operations ' have ventilation included in the original installation. Although a ventilation system is considered necessary for safety and comfort on new installations, i sponsibility for its satisfactory perform ance is seldom assigned to any one individual. Therefore, it frequent ly is not tested when put into op eration and is allowed to become inoperative from lack of mainte nance. ' 3. Excellent handbooks have been written on installation of local exhaust systems, but too little has been ;given on how to maintain them in top operating condition. There are two reasons for this lack of information. 4. First, a local exhaust system usually is not a piece of produc tion equipment. Its maintenance may be slighted in favor of ma chines essential to the manufac turing process. Second, a local exhaust system has a dual aspect. 5. Strictly, it is an engineering or mechanical device, consisting of sheet metal, fans, motors, ar resters, etc., whose performance is specified in terms of rate of air flow, static pressure, rpm. etc. TMr Dal* 5ht w ana of I *' publi-.had by . tKa National Safaty ' Council, reflecting eiparionco from many source!. No! avery acceptable wfaty procedure in tba field it ne- __ ettarily included.. TKit. Data.. Sheet thoulJ not be confuted with Ameri can Standard Safety codet. federal lawj, inturaneb reevirementt, itate Uwt. rulet and regulation), cr munic ipal ordinance!. This aspect Ls the responsibility of the engineer. 6. Yet the basic purpose of a local exhaust system is mainte nance of health or comfort, and sometimes fire prevention. Its effectiveness is measured by how well it removes dust, fume, vapor, or gas that would otherwise make working conditions unsafe or un healthful. This aspect is the con cern of the industrial hygienist, who has been mainly responsible for developing exhaust and dilu tion ventilation for the control of atmospheric contaminants. 7. In the absence of an indus trial hygiene engineer, the safety engineer is usually responsible for the exhaust system. Whenever necessary, he should consult the industrial hygiene personnel of the state health or labor depart ment, of his company's insurance carrier, or of the home office if he is in s plant of a large cor poration. 8. Management should try to develop in the plant engineer greater interest in the principles of local exhaust ventilation. Be cause these systems have been installed for health reasons, the plant engineer may' not feel re- sponSibre f 6 r -.the i ^satisfactory;: performance. .The safety engineer, on the other hand, who docs have an interest in the safety of work places, is generally unfamiliar "with the principles of such sys tems. . 9. Therefore, in a' plant which does not have an industrial hy giene engineer, neither the plant engineer nor the safety engineer pays much attention.to ventila tion systems designed for the con-, troi of air contaminants. In such a plant, the safety engineer shpuld be concerned with the satisfac tory performance of ventilation systems. With the guidance, of outside industrial hygiene engi neers, he can become sufficiently familiar with ventilation equip ment and terminology to check, to some' extent, the performance of local exhaust systems. 10. The purpose of this data sheet is to suggest methods by which a local exhaust system can be checked when first put into operation, to determine if it ful fills the specifications, and by which it can be rechecked at in tervals, to determine when, where, and what kind of mainte nance is needed for maximum efficiency. 11. The performance of the system should be the responsibil ity of the plant engineering and maintenance departments. If, as in many cases, this responsibility is not now assigned and the equip ment is not maintained, then it may be well for the safety engi neer to try to interest manage ment in assigning the responsibil ity to the proper people. Hatioocl Safety Ncwi, Morfh, 19S& 11 Definition of Terms. % 12. A local exhaust system is one, that removes an air-borne, contaminant, such as dust, fume, vapor, gas, odor, or hot air, as near its source as possible. A gen eral exhaust system, or general ventilation, by contrast, removes air from the room after the- con:, taminrmt has spread.-The general exhaust method merely, dilutes the room air by bringing in clean outside air, while the local ex haust traps the material at its source before it is dispersed throughout the room. 13. A hood, is a specially de signed fitting at the entrance of the duct to cause the flow of air to form a pattern that will best control the contaminant It is a partial enclosure around the source where the contaminant is produced, connected with an ex haust duct, usually round sheetmetal pipe, to an exhaust fan. 34. A booth is a hood, usually rectangular or box-shaped, that encloses the operation on the two sides, the top and bottom, and the back, with only the front or face open. 15. A collector (arrester) is a device for removing the air-borne material from the air stream. It may be a cyclone or centrifugal collector for large-size particulate material like rough-grinding dust, or a cloth Alter for finer dust, or a water-wash, fog or spray device, electrostatic precipitator, dynamic precipitator, or other type. ity of air in these ducts (hence, air flow in cfm) for d:fTercnt in dustrial processes and industries. These arc minimum "standards lbarraysL-he.mot*..-Good engineer-. - ing practice often calls for even larger air flows than those indi cated in the codes. The engineer should have a copy of slate regu lations. . Plans for new exhaust systems often have to be approved by the state before installation, and" he should find out if this is the case.in^his sta,t6.:"--_ 21. The engineer should secure a blueprint showing piping layout, i( possible,.together with data giv- - ing the cfm the designer intended to exhaust, from .each .hpodv Tor new systerbs,'blueprints will'be available. For old systems, the plant maintenance or engineering 1G. Every cxha.ust fan oper ates by inducing a suction or neg ative pressure in the duct leading from the hood. This means that the air in the duct is below at mospheric, pressure so that room air rushes into the duct This negative pressure is an indication of the air flow, commonly ex pressed in cubic feet of air per minute (cfm}, that enters .the duct. The negative pressure may be directly related to air flow or, in the case of a plugged duct, in versely related. 17. The negative pressure is easily measured by gauges of var ious types, the basic one being a U-tube or manometer (a piece of glass tubing shaped like a U. the legs being about 8 inches long) half filled with water. A rubber tube from one leg is held at the point where negative pressure is to be measured, and the other leg is left open to the atmosphere (Figure 1). 18. The unit of pressure, which may be positive ("blowing out") department may not have a drawing.\ It- is-.still passible* however^ that he can get the layout and . data by writing to-the.sheet metal company from "which his plant bought the equipment. 22. From this material he can determine whether an old system is the same today ns it was when - it was-installedy or whether it- has suffered the fate of all-loo-manv exhaust systems-^has had extra branches added or changes made that may now render parts of it less effective. 23. Rare is the exhaust system that does not require understand ing and cooperation on the part of the man who works at the proc ess. Sometimes ho has to modify his work habits to permit certain hoods to be used. The engineer should always find out:just how the designer of the system in tended it to be used. The engi neer can often help by seeing that the men know the why of their exhaust systems and know how to use them. or negative ("sucking in") is Air Samples inches of water, abbreviated w.g. (water gauge). It is the elevation 24. If the equipment handles silica dust; asbestos fibers, or of one water column above the other toxic materials, such as top of the other. chromic acid mist, lead fumes or General dust, or solvent vapors, the sys tem may be exhausting the "cor 19. A good local exhaust sys rect" volumes of air (according tem is a well-engineered project, to the blueprint), the fan and col based on precise design data--not lector may be in A-l condition-- merely a collection of piping. yet a health hazard rnav still exist. 20. Many states have codes The final and all-iinportnnt meas that specify duct sizes and veloc ure of whether an exhaust system is cgntroTIing-^ hazard- is'whcther.- - laincd -involv'c vdelsured sarid ex* the air in the working-region is ` acting methods for which experi clean enough to breathe without ence and judgment are necessary. injury. This question can be an- In the.plant .where an industrial swercd only by taking air sam- hygienist is employed, the prob _ pies and apalvzijig tbern .tp/find... atem,;f<Uht-^V-ithin is_j.ujis^iction,.. out if the contaminant is below the maximum allowable limit.* These tests are needed because a person cannot look at a dust cloud ' 26. In the absence of a staff industrial hygienist, the safety engineer may obtain the services of the stale bureau of industrial . or smell toxic vapor and tell hygiene (in cither the health or if the condition is unsafe. . labor department),'the services of 25. Collection of -air samples, the insurance carrier or of private both in general working areas and consultants. Such services may . in-ventilation ducts, is .a principal__ .. also be found in institutes of. in activity of the industrial hygien dustrial health or divisions of in ist. It is. therefore, imperative dustrial hygiene in some of the .. that the safety engineer have such medical schools or in schools, of . personnel secure this information. public-.health... .. Not only, .does. the . collection, -of .... ->;.-.27v Once . it-., .has. been-..deter--, samples require exlensrve experi- ... mined through air samples'that once, but also the interpretation an exhaust system is keeping an of the results and. equally impor exposure within safe limits, the tant, the analytical procedures negative pressure or "suction" in <rom- which-.the results sro ob- eacK- branch duct; the'pressure'- Most 'state labor or health departments have now incorporated maximum allowable limits in their co<lcs: these limits should be observed. Engineers in states which do not have such limits are referred to "Table of Chemical Hazards," Section 41. Accident Preven tion Manvel jor lnduxlrial. Operations, 3rd- edition *.1955), published' by the National Safety Council. drop across the collector (if one is. used), and the negative pres sure at the fan inlet may be meas ured. At any future date, if re checks show that these pressure reading.: are the same and if no .changes have been made in the /process, the hoods, " or 'raw" ma-' terials handled, it can be assumed EXHAUST SYSTEM NO.. Vnatl*.................................... M Q *Oft <> ------------------* *'< 1310 10 T 0* CLOTH | CHECKED BY................. Material `Mlat Mbam'.ad. CZ\ N, 1----------- T--* `4*5 c,,< LrJ-3- ,r4- (7) KU. !!. 10 4o c*w AT " 1*. i c*o **. & a* 4* - - z^ . 4 ! Cfv J .-./J' C'" -o>3 c. -- O-- Tut (ilnt Condition nf hood ind braneb (Battered? Removed? Plotted? Heealrl) A B C 0 E T C H J Calleiter fiiulinn (tl-(H) ilnia Uit .. Hour* of COMMENTS at men. and YOUR tommnntl (me back. It necmary|: HAd Svetlan water) Orlilnally Chocked 2.0 2.1 2J 2.0 i.i 2.1 2.2 i.O 1.0 J.O Interval belvn. cat. htklft . . .............hr*. Flqure 2. Safety di'ectO'"t -nipec*-on report. fhat-thc:hazard/is still undcr.'cbiir' Y trol." (Cross drafts, as from a man- cooler, will change the control.) 23. Arranging for air samples and suction tests is the responsi- hilily o(. ^jbp . safety ^ enjginejer rather than the maintenance en gineer. (It is also frequently con sidered a responsibility of the designer.) ' 29. When the air contaminant is not toxic but. causes merely a comfort problem-, .little is gained by air sampling. - .. Chedltfng tbe^yilefrii A ,30. For -two reasons, it is well to .make a complete check of the exhaust .-system:. First, it can be. .determined .whetbex.it.ls meeting... 'specifications for -air volumes, re- . sistance of ducts,. horsepower, etc. Second, this information will be available for reference when the system is* recheckedvat later dates. 31.- Some of the measures'which will provide the safety engineer, in the absence of an industrial hygienist, with a program for checking the performance of a local exhaust system are .dis cussed below. - ........... - 32. Layout. The safety engineer should get or make a simple line drawing showing the layout of each main duct and branch, to gether with the location of the arrester, fan, and motor. He should measure the duct diame ters and note them.on the draw ing. He should also secure the open face dimensions of hoods and record them. He should note on the sketch the type and size of fan, motor, drive, and arrester. This drawing need not be elab orate, or even to scale, and can be taken from the drawing of the system mentioned earlier. 33. Test holes should be drilled in each branch. The easiest and cheapest method is to make a 1/16-inch hole, leaving no burrs on the inside of the duct. (See Figure 1.) It is not necessary to cover or plug such a test hole when it is not in use. Sometimes a one-inch length of small cop per tubing or even a small brass petcock is fastened permanently over the hole, but these refine ments are not necessary. Each hole should be circled with a ring of white or yellow paint, and its Norional Safely N-*w. Moit.S, 1956 13 `7 . . .... ..... . .... number or loiter painted on the on blast gates. object and listen to hvJtr the pipe duct --the test points for.- the whole system being numbered -.37. .Each method has advan tages. If blast gales arc used, "ring." showing there is no appro-., eijble jvttlcment of material in it. The frequency of periodiy .checks serially..-Qn the sketch,.-each test- they- shcfold dje- bolted' 'Or -welded *' wilT vary wTtli the typo of service hole, with its number, should be marked, 34. Balancing the system. Be after the system is balanced, to prevent tampering. Blast gates should not be used on a long, I>crformcd by the system. Some systems will need checkups week ly; others, monthly. fore routine inspections arc be complicated system. 40. Interpreting suction pres gun, and even before air samples 3S. A record form (Figure 2) . sure readings. Jf the suction pres arc taken on a newly installed can be mimeographed for each sure at a test hole differs.by more . system; the.system must be "bal- exhaust system, with a suction than 10 per cent from the original anccd," that is; the proper amount pressure reading printed for each readings (printed on the report of air must, be .flowing. through ,, , test hole. These readings arc made form fv*The rrt'sdn Cart g^TiorSlh? each hood. Also, in the case of dust exhaust systems, the air velocity in branches and main ducts must be high- enough to ' immediately, after the system has been balanced, arid dust'counts (or other air-samples) hove been made :lo show that-the air-.con- l>e flgured*out without difficulty. Figure 3 shows how to interpret. ` thc.U-tubc values. . " ..... 41. Estimating control velocities prevent,^ettling.oi m_atcria]y,which -. t landnant.is under..control. -:.. <>t'.rvcldcil?.. cofit(rats! 'Qhe of. the - leads Id plugging. ' V . "'39.' Periodic checks. Each time' most important factors is that the 35. In the original design, one the safely engineer makes an in control velocity at the source of of two means of balancing a sys spection. he fill:: out a report form. the contaminant or the face of the tem is used. The more common is1 (o' provide blast * gates (dampH He compares the suction pressure .booth j(where tbe source inside. readings^ he finds' on rCcheck' Willv the booth) can lie quickly meas ers) in each branch which can the original readings printed on ured by a sensitive direct reading be opened or partially closed so the report. He makes the follow instrument such as the vclomctor that each hood, regardless of ing observations and records the or thermo-anemometer. Where whether it is near the fan or at a results: the source may cover a consider distance, handles its proper amount of air. a. Look at all hoods- See if they are battered, partially removed, miss able area, the maximum and mini mum should be indicated. 36. The other method is to size ing. or mangled in any way. 42. Source, location,, direction. . the diameter-of the; branches so that more or less air is introduced lo serve the same, purpose as blast gates. This must be done before ' b.- Sec' if the'-mahufatturihg process and machines have l>ecn altered in any way. Make certain that strong' cross drafts are not- pre venting the air contaminant from and velocity of make-up air. In addition to the amount and tem perature of the make-up air, its source and method of distribution the system is installed, since once entering the hoo<Ls. may be almost as important to the duct work is in, the duct diameters are fixed. Figure 2. adapted from Brandt, Industrial c. Whatever the provision for make up air. make sure that replace ment air has ample opportunity to enter the room. successful control of the hazard as the design of the exhaust sys tem itself. Since air blowing out Health Engineering, shows a bal d. Tap the duct at various points of a duct carries 30 times as far anced system that does not relv with a screwdriver or other metal as the same volume of air mov ing toward a similar exhaust duct u a-i ********* *`*~ T-i j Li';! (Figure 4), it is very important that the make-up air be diffused in such a way that no disturbing cross currents interfere with proper functioning of the exhaust hood. Frequently, such s. disturb kr iVr!:! 1 1 1 : ' ance can be anticipated if the essential facts arc noted, and iim ' i; M | i smoke tests may confirm its pres ence. 43. Maintenance orders. When Hi*CU4 [TIT] 1 i11ii i l"'- i'! the system needs mechanical re pairs, such as replacement of worn ducts or hoods, filter clean out, duct cleanout, fan belt ad justment, etc., the safety engineer should see that work orders are (A) Du rr*ilr p*rtiHr pluqq*<i. <*utlq crtC r*lilfn<. Ndi cleaning. () lncrl*d failltnnea Of plugging in haadar pip* or in branch. (C) OaCraaiad fan capacity, open cUanoul door, or diijolntad pif-a. (0) Firtl branch pip partially pluqqcd torcawhr* balwcan hradar and tail hola n.ar hood. (E) Firt branch pip* partially plugged torrahrc bal-aan tad hola and hood laca. (FI Incraatad raviitanca dut to pluqqinq in h*adr pipe at "X." processed to the maintenance de partment according to the plant's customary procedure. 44. Record filing. The safety engineer should keep a file of his Figura 3. How IJ-tube r^cdinoi can be JUrd to ihow where plugging hat occurred. (Courtesy "Tennetten induttrial Hygiene Hews.' I9S0.J inspection reports and reports of air samples. MyOnn-r fo/c-v N-V.V Al--. !></ . ir~ rw tfn if^ iriB T iirrT 'T 45. Periodic air samples. If toxic material is handled by the system, in addition to the initial air-.<a'hi>plc.'5,>* tho`"1htfus1fi5t lit* "' gicnist or safely engineer should arrange for periodic samples of the air-borne contaminant in the . workroom. . a FAN 1----------- 81.OV/urn . ....J.i.iru* o fact -.a?..... i "mux jct o'Cminc. Inspection by . Maintenance Engineer . 46. The maintenance engineer should check, and .lubricate- the .. fan. motor, and drive on schedule.' just as he would .any other piece, of machinery. If .the exhaust-sys- tent has any .special interlocking ... -gates, .jnplojvdriven dampexs,- sttjb- .-. 'cnoids, or ' .he.-liftei-^tKcse' parts'-- should cotnc under this inspection and should be observed through a cycle to assure that they arc operating: i ? m'- .* 47. He should check the inside of the collector with a-flashlight each week, using an access door in the casing. The clean-air side of the collector should be exam ined to see that there are no ac cumulations of dust, which would mean that the collector was not functioning properly. He' should look in the hoppers-, to see that-: they are not overfilled and should check bag collectors for tom or leaky bags. 48. Wet collectors should be checked for plugged .>ray noz zles, plugged drain pi) js, sludge accumulation, and pipcr water level. 49. Fan speed should be checked monthly with a tachometer. Fan blades and scroll should be exam ined for wear and dirt accumula tion. For this check, a hinged inspection door in the' side of the fan casing or in the outlet duct near the fan discharge is neces sary. Design for Maintenance 50. Good first design will hold down maintenance problems later. 51. Hoods and ducts. The hood should be placed as close to the source cf contamination as pos sible. The source should be en closed if possible, with enough openings left for air to enter. Can opy hoods should be used spar ingly. Too often the operator puts his head between the hood and the: contaminant so that he may get an even greater exposure than he would if there were no \; / EXHAUSTING `arnoifudaV'- * . fact vc lociT Y CM a - i*t> r now (!; . - \..- Fiqairo 4.' Effect of air blowing OUT of A pipr i fclt.meny fe< way. but An <r| hujt pipe Ko no effect beyond few inchei from pip* end. Thus it cannot "pick up" me tor ial unleit pipe end hood ere close to the dust source. (Courtesy "Industrie! Ventilation--A Manual of Recommended Practice.") . . hood. II particles are thrown off by the machine (c.g. a grinder); ' the hood and the exhaust duct should be placed so that material will be thrown into them. Acces sible cleanout doors should be provided in ducts, collector, and fan housing.- - ' ' 52. Sheet metal thick enough to ..minimi?. erosion should be used-. For corrosive materials, ducts' should be lined with resistive coat ings or made from suitable corro- sion-resistanl material. If con densation may be a problem, the need for thermal insulation, "drip" elements, water traps, etc. should be considered. The possi bility cf a fire hazard, depending upon the material to be handled.* should also be considered. ` 53. Construction details are of utmost importance: gradual ta pers. baffled hoods, wide-sweep elbows. 30 degree angle of entry to main. etc. Design of a "bai- "Standards for the Installation of Bloxcer and E.rhaust Systems for Dust. Slock, and Vapor Removal or Convey ing. Pamphlet No. 91. National Fire Protection Association and National Bureau of Fire Underwriters. American Standards Association, Z33.1-1950. Although the basic purpose of ven tilating systems is to serve health and comfort, the use of these standards will result in a system which is also of value fic-m the fire prevention stand point sinre it will not transmit smoke anti flame through fire walls anti throughout the premises. The stand ards also provide valuable reference with regard to the other components of the system and related fire extincuishinc apparatus. aneed" system, instead of relying on blast gates, should bej consid ered. Total pressure loss should be calculated carefully, not guessed at. Natural drafts and cross currents of room air that may keep the contamina its from entering the hood should be noted. 'the hood -should be ar ranged so- that it will interfere as little as possible with th< worker _ and still be effective. 54. Collectors. The collector should be selected for he sub stance to be handled, considering such factors as particle size, dust loading, wettability,corrosion,etc. Thought should be given to com munity air pollution that may re sult if there is no collector or if too much contaminant is exhaust ed to the outside. 55. If. a bag-type filtor is se lected: a. Consider size, storage 1 opper ca pacity, free-flowing hoppers. b. Provide a permanent outside lad der and catwalk for e.sy access; with nonflammable dusts, light the inside of the filler housing for case of inspection. c. Provide a motor-driv :n shaker rather than a manually-operated one wherever possible. d. Provide lime-delay relays and interlocks so that when the fan wheel comes to rest, af er the fan motor has l>cen turned off. the shaker motor starts operating and continues for two or tircc min utes. after which it stohs and the fan can then be restarted. 56. Fan and motor. jThe fan should bo put on the jelean-air Jniinnc' t4ar<h. 1956 is side of the collector. When flam and other parts of the system will mable solid materials or vapors interfere as little, as possible.with arc passed through the system, his work. the -provisions -of NFPA and - '63.-For testing exhaust systems NBFU Bulletins No. 01* should visually, smoke tubes are com be followed. r mercially available (or may be 57. Fan guards and a test hole made by dipping cotton into ti for a tachometer to take speed tanium tetrachloride) . The smoke readings of the fan should be pro given off reveals the path of the vided. Service and inspection air currents as they enter a hood. doors should be placed in the side Smoke tubes are a boon to the of the fan housing, or in ducts at safety engineer. Using them, he the inlet,.'and outlet- of'-the fan/. can show the operator how a Hood Resistance of the fan discharge works and thus often, convince stack . should. .be kept low. A him how- important baffles .are, weather rap should be omitted how `necessary -it is .to - have the wherever possible.-. ' hood.close to the.dust source, and- Voirits bii .fting ' soorx, . ......<v ,. .. 64.' Two common- fallacies need 58. Here are some over-all con clearing up. First, because peo siderations that should be kept in ple can feel air blowing out of an raind in the testing of local ex air line some feet away from the haust fcystetrts.-: ': end-of. -the pipe',' they thfnk dusty. 59. ' One of the initial steps that air can be "sucked into" an ex may :be taken is to ensure that haust hood from several feet outside vendors or contractors away. It cannot. ' Air can be provide a meaningful guarantee "sucked" only 1/30 the distance it of performance for their equip can be blown (Figure 4). In ex ment or system. Then the vender hausting, the air velocity at a dis is made responsible for equip tance of one diameter from the ment or;'systems' "which do not. *' pipe end is about 10 per cent of perform properly; the velocity in the pipe; in blow ' 60. Many- a good exhaust sys- ' ing, this 10 . per ; cent figure is tem has been overloaded and reached 30 diameters from the made ineffective .by the addition pipe. of hoods in later years. Before 65. Suppose, for example, that hoods are added, it should be a pipe 6 inches in diameter has ascertained that the present air traveling through it at a ve equipment can handle the addi locity of 4,000 feet per minute. tional air flow which will be Six inches from the "sucking" needed without robbing the ex end, the air velocity will be 400 isting hoods. feet per minute (hardly detect 61. Make-up air is sometimes a able by feel); at the blowing end, bigger problem than the exhaust the 400 fpm velocity is reached system itself. Provision should some 15 feet from the end of the be made for the air to get into pipe. the room to replace the air ex 66. A second fallacy is that hausted. In winter the make-up downdraft ventilation or hoods at air may have to be tempered. A floor level are required because room should never be closed up organic solvent vapors, like ben tight and "air bound." zene (benzol), trichloroethylene, 62. The man on the job must carbon tetrachloride, and the like, know the reason for the exhaust are heavier than air. Heavy gases system and must understand how introduced into air tend to fall to use it. Better yet, the safety before they become mixed with engineer should consult with him the air. Thus, a vapor train of before the installation is made, to pure gasoline can form and travel make sure that hoods, enclosures, along the floor many feet. 67. However, as vapors are giv Bulletin No. 91. Blower and Exhaust en off from industrial processes, Systems, National Fire Protection As sociation, 60 Btitterymarch St, Boston 10. Bulletin No. 91, Exhaust Systems for Dust, Slock, end Vapor Rtrmoval, National Board of Fire Underwriters.. 80 John St., New York. the atmosphere contains not pure vapor, but a mixture of vapor and air. Even air saturated with the vapor remains saturated for a very short time; it soon becomes diluted with more air because of random convection and wind cur rent in the room. 68. A concentration of 1,000 parts per million of benzene, which is 25 times the maximum allowable health limit, is only 1.0017 times as heavy as air (al though pure benzene vapor is three times as'heavy as air). That is,' the ratio of weight of air- to ' weight of the benzene-air mixture is only .100. to 100,17.--There could ; _ never be any .sinking or stratify ing of even this dense. (1,000 parts per million) benzene concentra- . > tion. Consequently,-a side or- back hood would bej.ust.as effective-ax. a' downdraft:hood. / - . REFERENCES Perhaps the best .technical reference not' only-'for design of' exKaVIst systems? * ' but also for checking of them, is: In dustrial Ventilatioji--A Manual of Rec ommended Practice, published by the American Conference of Governmental Industrial Hygienists (3rd ed., 1954), available from the Committee on In dustrial Ventilation, P. O. Box 453. Lansing. Mich. . The following give information on .. design of exhaust systems for various processes, as well as information on the toxicity of industrial materials: . . Accident Prevention Manual for In dustrial Operations, Nationsi Safety Council, 3rd Edition. (1955). Industrial Health Engineering, Allen D. Brandt. John Wiley & Sons, Inc. Heating, Ventilating, Air Condition ing Guide. The American Society of Heating and Air Conditioning Engi neers (published annually). Plant Process Ventilation, W. C. L. . Hcmcon, Industrial Press, 1955 edition. Industrial Dust. Drinker and Hatch. 2nd edition (1954). Excellent references for fire preven tion considerations are listed below: Flammable Liquids and Cases, Vol. I; Combustible Solids, Dusts, Chemi cals and Explosives. Vol. II. National Fire Codes, 1955. National Fire Pro tection Association. ACKNOWLEDGMENT The original draft of this data sheet was prepared by Willis G. Hazard, Owens-Illinois, a*: a project of the Health Maintenance Committee of the Automotive and Machine Shop Section. National Safety Council. A second draft was prepared by Frank A. Patty, Gen eral Motors Corporation, with approval of Mr. Hazard. This publication has been reviewed by members of the Na tional Safety Council and representa tives of chapters of the American So ciety of Safety Engineers. It has been approved for publication by the Publi cations Committee of the Council's In dustrial Conference. 16 S'otionol Sat':ly Nwi, Mar<hj 1956