Document mB5vzdapnq5YQaQKN0GZ4DJkd

Pollution and Controls in Industry K. E. ROBINSON, Ventilation Engineer, Division of Industrial Health, State Department of Health, Lansing, Michigan You have heard lectures and discussions that the concentrations of the atmospheric mostly on the general principles and contaminants are toxic rather than a seri theories involved in the control of air conous nuisance, we have found that most in taminants. In my discussion, I am going to dustries will consider a practical approach stress the other side--the practical applica in eliminating the air pollution problem tion of these principles and theories. A gov arising from their plant. One of the most ernment agency such as ours is in an ex successful methods we have of working out tremely favorable position to make this a satisfactory solution is to get both the typo of presentation because we are direct citizens and the management of the indus ly involved with the pollution problem from try together. In this manner, management the time the initial complaint is received realizes the extent of the nuisance, and the to the time when a study is conducted to people of the community realize the prac evaluate the collection equipment installed. tical difficulties facing the management in Whether the contaminant be fly ash, eliminating it. alpha-napthoquinone, or odors from a near Investigations by the Michigan Depart by rendering plant or millpond, we are even ment of Health have turned up a wide va tually called in to investigate. These inves riety of contaminants (Fig. 1), and some tigations can be initiated by the irate house are very difficult to control. In some in- wife who is disturbed by sulphide odors, or the plant manager who maintains that dust from a nearby abrasive reclaiming plant is ATMOSPHERIC CONTAMINANT Asphalt, mo/ten NUMBER OF PLANTS INVOLVED* ruining the bearings in Jnis expensive ma chinery. Baking omi (point) odors Bromine Buffing dost Actual legal authority on these problems rests squarely with local governmental CMdumaxtdo Cataum tydroxide Cement dust units. In the Michigan Department of Cottondust DDT dust Health, we can act in an advisory capacity Ffyosh only. Many of the air pollution cases we are asked to investigate come from local foundry dust Fluorides Grove!dust governments who do not have the techni cians and the equipment to work on the cases or because the local officials are re luctant to act, fearing that the company will suspend operation in their town. They Hydrogen Sulfide Iron dust kon oxide Leod oxide and tomes Mdpondodors MonocNorberuene Nophthotenes Qxxfe of Mtrogen would rather have the state take the brunt of this burden. In all cases, we make every Pant mst Phosphate fertilizer dusts Phthatic ontydnde effort to be of assistance to the local autho rities, to the people of the community, and ftohng pbnt odors Rendering plant odors Rockwool dust to the industry involved. The year-to-year increase in the number Rubber (bumf) odor Rubbish burning SAca dust of requests received for service on air pol lution problems, from six in 1940 to nearly Smoke Sotoents Sulphur dtoxide a hundred in 1949, indicates the prominence of air pollution in our everyday life. Many of the plants at fault are probably not of sufficient size to afford to spend a great Sutphunc ocxl VNenc (tso) odd Welding tothes Wood dust Zinc oxide Miscellaneous deal of money on contaminant control. De spite the fact that we are not backed by a Some plants mspons&e for seven! contaminants specific statute and are rarely able to show Pig. I. VOL. 11, No. 1 INDUSTRIAL HYGIENE QUARTERLY Page 65 stances, a satisfactory method of collection is still to be found, and we welcome any suggestions you may have. There is, of course, no perfect method of collection for any contaminant. When faced with the problem of collect tion, there are four things to be considered: first, the selection of the method or collector which is suitable for the job; second, the initial cost of the equipment and installa tion--and whether this cost is justifiable considering the extent of the nuisance; third, the maintenance on the equipment (a big item with many collectors), and whether it is within an acceptable range or requires frequent expensive replacements and high maintenance costs; and fourth, whether dis posal of the collected material is difficult or costly. The following case histories demon strate that these considerations are ex tremely important factors in every air pol lution problem. i ^Case No. I A IR pollution problems involving odors are often extremely difficult to cope with. One of the biggest problems is the elimina tion of odors. Our sense of smell is often an excellent method of chemical analysis; its delicacy is often greater than any chem ical analysis we can run in the laboratory. There are many materials which we can smell long before the concentrations are high enough to enable us to run a chemical determination. Since odors may be due to these minute concentrations of gases and particulate matter, they are extremely hard and often almost impossible to eliminate from the air. . Inasmuch as rendering operations are practically a necessity in all good-sized communities, this case will serve to sum marize some of the difficulties we have had with them in several of the cities of the state. The complaints concerned obnoxious stenches which permeated the residential areas near the rendering plant. Upon inves tigation it was observed that the operating techniques in most of the departments were unsatisfactory, and that a good deal of the odor could be eliminated by improved sani tation and work methods. Several recom mendations concerning housekeeping and sanitation procedures were made, including the following: 1. That the sanitation and housekeeping be well planned to include all operations, and that one or two individuals be delegat ed the responsibility of carrying out the program. 2. That an ample supply of steam and hot water be provided for cleaning and rinsing purposes. 3. That the building receive a thorough initial cleaning, and that certain structural changes be made, such as re-surfacing floors with an impervious material. 4. That a central wash station be pro vided for all containers and a storage space provided for all clean containers. 5. That materials coming into the plant which were not to be used immediately be stored in properly enclosed containers. 6. That a driveway be constructed of im pervious material which could be flushed off. In addition, local exhaust ventilation for certain operations was recommended. Shortly after our study of the operations, a group of citizens and the city filed a suit asking that an injunction be issued to re strain the company from polluting the at mosphere with offensive odors. In court, the company stated that in an effort to abate the stenches and smells emanating from the plant, they were acting upon our recom mendations. In addition to our recommen dations, they had installed two modern cookers; a modernized, used cooker; a new septic tank; a condenser water tank; an ad ditional sewer, and an ozone generator. They had enclosed the elevator shaft with steel, entirely segregating it; purchased an additional boiler, and agreed to construct a new driveway. The driveway was to be of concrete or other comparable material, and was to be made non-absorbent. The court found that the nuisance did exist and had existed for a long time, and stated that the plaintiffs were entitled to the relief sought by them. The company was ordered to wholly abate the nuisance within 30 days; with additional time, if necessary, to com plete the installation of the new boiler. The complaints of the residents, the legal action taken and the efforts made by the company to eliminate the odors have helped a great deal to minimize the amount of atmospheric pollution taking place. Since the completion of the previously mentioned work, there have been no fur ther complaints to the court. It is our opin ion that the ozone generators mask the Fi*r * odors for the plant employees but do not affect the odors emanating from the plant. It is obvious that effective sanitation and housekeeping programs have to be main tained if the odors from rendering plants are to be minimized. Case No. 2 ~\JOW let us consider a plant producing ^ phthalic anhydride. I have selected this plant because it is a good illustration of practically all the four considerations in selecting a collector which I have outlined. The plant is large and centrally located in a residential district. The neighborhood is contaminated by a strong pungent odor as well as small quantities of particulate matter. The problem of collecting the an noying stack effluents which are given off by 14 stacks is difficult, and is further ham pered by the pyroligenous acids which are produced and can result in explosions and fires. Correspondence with manufacturers of phthalic anhydride and with industrial hygiene units in this country indicates that the same difficulties of collection exist everywhere. In an attempt to solve these problems, a committee was formed of members of the chemical engineering department of a near by university, outside engineering consult ants, representatives of the company, and several of our engineers. The first attempt to control the contaminant was with the use of steam jets in the tall stacks with the thought that the addition of steam might result in satisfactory collection. It was found that the steam did not help and, in fact, increased the nuisance to the neigh borhood. Following this, a standard com mercial wet collector was tried and also found unsatisfactory. While this was being done, the proper ties of the material were studied and it was found that the contaminant had a tend ency to seed and adhere to the ductwork or any other material it contacted. An experi mental, box-like duct (Fig. 2) was built. The thought was that a large portion of the material going through the tortuous passage would seed sufficiently and adhere to the baffles, theye amount of objectionabl Although large amouj were collected, the odo: lessened appreciably. P at collection, an attem] dense the vapors on a less steel wall. Howeve the material would no surface, nor was enou to solve the problem. A good many things box, such as using ori velocity in order to imp a plate. As shown by 1 method removed much as previously brought < the odor. Following months oi lectors, a special higl was installed and appe ally well. However, r quired and it was fount ing from the firlt sec had a pH of slightly o of neutralizing this t was prohibitive. By this time, sufRc carried on in experim lead us to believe that caused by a by-produi Fig. Vol. 11, No. 1 INDUSTRIAL HYGIENE QUARTERLY Page 67 to the baffles, thereby minimizing the amount of objectionable material given off. Although large amounts of the material were collected, the odor did not seem to be lessened appreciably. Following this failure at collection, an attempt was made to con dense the vapors on a water-cooled, stain less steel wall. However, it was found that the material would not adhere to the wet surface, nor was enough vapor condensed to solve the problem. A good many things were tried with this box, such as using orifices to increase the velocity in order to impinge the material on a plate. As shown by Figs. 3, 4 and 5, this method removed much of the material but, as previously brought out, did not decrease the odor. Following months of work on these col lectors, a special high pressure fog unit was installed and appeared to work unusu ally well. However, much water was re quired and it was found that the water com ing from the firlt section of the collector had a pH of slightly over two and the cost of neutralizing this to allow for disposal was prohibitive. By this time, sufficient work had been carried on in experimental laboratories to lead us to believe that the strong odor was caused by a by-product, alpha-naphthoqui- none, and that concentrations as low as 1 ppm would be objectionable. Some time after this fog unit was dis mantled, the company was approached by two men who had developed a catalyst for burning organic matter from stack effluents. They had had very good success with this catalyst in eliminating odors from wire bak ing ovens and, judging from previous in stallations, the system would be reasonably inexpensive to install. Fig. 6 shows the type of system that had been used on the gases from the baking oven. The company de cided to try an experimental unit, and a system which might possibly work was de signed. Experiments in the laboratory with the catalyst showed that a high temperature would be required. Subsequent work with the unit proved that 400C was the mini mum temperature at which the catalyst would operate. Previous trials had proved that the ducts would clog unless arrange ments were made to keep them open, and so a counter-flow system was designed to keep the ducts warm with the thought that the heat from the catalyst would hold the ma terial in the vapor state. An experimental unit was installed, using a gas flame to increase the air temperature sufficiently for operation of the catalyst. It was found that a good deal of work was Fig. 6. Fig. 7. Page 68 INDUSTRIAL HYGIENE QUARTERLY March, 1950 necessary to achieve an even temperature lector used when the plant was operated for and even distribution of air through these the government and also that the power catalysts. When this was accomplished and house was operated more efficiently and all of the leaks were finally stopped (this gave off no fly ash. was very difficult because of the high ex In making our investigation, we found perimental temperatures), the system oper several reasons for the complaints. One was ated quite satisfactorily. that the plant had been built along the At the present time, work is going for water's edge to take advantage of dock fa ward on the design of a unit which can be cilities and, unfortunately, the major part installed to control the contaminant from of the city was on a bluff overlooking the each of the 14 stacks. Fig. 7 gives an idea plant. Most of the houses of the community of the size and complexity of the piece of are actually higher than the top of the apparatus to eliminate odors from this plant stack of the plant. Like many war plants, in comparison to the very simple catalytic this one was designed for a specific oper arrangement used in another plant with a ation which utilized the flue gases for a car different material. bonization process. The flue gases required Regarding this air pollution problem, I scrubbing which, while consuming a great should like to emphasize the desire on the deal of power, was justified by the fact part of the offending company to find a solu that the gases would be re-used. In peace tion of the problem which will be economi time operations, the carbonization process cal and satisfactory to the residents of the could not be used and the company could community. Practically all reasonable ap not economically justify the use of such a proaches were tried. One method appeared scrubber. Contrary to the belief of. some to be satisfactory, but this produced a citizens, the power plant is being operated water pollution problem almost as great as more efficiently now than ever before. .Fly the air pollution problem. ash collectors are in use, but, like all collec I should also like to bring out here that tors, they are not 100% effective, and some one of our greatest difficulties results from escaping fly ash settles on the residences the fact that it is almost ^impossible to use nearby. a system developed for one operation on At the present time, an addition to the another operation in a different plant with stack is being planned and will undoubted out many major and often expensive ly be built when weather permits. It will changes. be interesting to see whether the addition of this extra height will eliminate the com Case No. 3 plaints, or will simply deposit the fly ash common atmospheric contaminant is fly on residences a little farther out. It appears ash. Practically every city and village to us that proper installation of electro is confronted with this problem. I have se static precipitation might be more justifi lected one fly ash problem from our files be able than a gamble on high stacks for dilu cause it brings out a point that may be of tion purposes. interest. \ The plant is situated in a community of Case No. 4 9000 people and employs about 120 workers. 'THE collection of air contaminants in the When the plant was built for war purposes manufacture of calcium carbide is al the citizens were elated because it gave a most as important a problem as the manu big industrial boost to the community. Now facture of carbide itself. In our investiga there are some citizens who wonder whether tions into the manufacture of carbide by their elation was not somewhat prematurei one large concern, we found that this was Throughout the war, the plant worked on a universal problem among the carbide a round-the-clock basis with no complaints manufacturers. While much work has been from the people of the community, but after done and many engineering organizations it was taken over by a private company, the have attempted to solve this problem, we local city officials began receiving com believe that contaminant control will not be plaints. The principal complaint was due to satisfactory with present collecting devices fly ash. The people of the community were unless manufacturing procedures are im of the opinion that there had been a col proved. Vol. 11, No. 1 INDUSTRIAL HYGIENE QUARTERLY Page 69 Calcium carbide is manufactured in the electric furnace by fusing a mixture of lime and coke. The yield from this reaction varies a great deal depending upon the quality of the coal and lime used. The gases and much of the particulate residue from the reac tion are removed from the electric furnace by exhaust fans. The particulate matter taken off from this reaction can run over 100 tons per day. Now if the efficiency of a collector installed to remove this particu late matter from the air runs as high as 96%--and this figure would be high for any collector--it would leave four tons of this material to be thrown into the open air and over the community. If you disperse this four tons of residue into the atmosphere, you can understand that it would do a fair ly good job in covering the community in 24 hours. This is the actual problem in con-' trolling air pollution created by a carbide plant. While this air pollution is not a health hazard but a nuisance, it reaches extremely annoying proportions. It is par ticularly damaging to the painted surfaces of houses and, in some instances, it ruins the finish on automobiles, furniture, etc. ^ In our work with this particular plant, we collected air samples throughout the plant and in the surrounding neighborhood. The results of the study are shown in Fig. 8. The management, in attempting to alle viate this air pollution, had installed Cott rell precipitators in the stack. The reasons, for selecting electrostatic precipitation as a means of collection were: first, experience has shown that electrostatic precipitation, in most cases, works satisfactorily on par ticulate matter, and, second, the company owned a share of the water rights and pro duced its own power in that community. On our investigation, we found that there were several limiting factors in attaining complete success in the collection of the ma terial. We discovered that the dust-laden flue gases were cooled and moistened by a bank of water sprays before entering the precipi tator units. The efficiency of the precipita tor varied considerably, owing to the fluc tuation in temperature and humidity of the flue gases. Another factor controlling the success of these precipitators was the com pany's limited water rights. While what power they produced was cheap, production required the greater portion and the re- PATA SMUT L--Ilf 8mb1h letetleq Pact Ceoat root vt. e*(os)2wt. *c*Co Hllltes ?utleln Ite/lOH3 >tc/10M3 la ~ For Cuble Feet of Air' ef *lr ef Air Street So. 1 Street So. 2 0.326 0.415 5.5 9.74 13.% 7.4 l.U 15. 1. Soltl*d lbiet Slant Voter ea lenities (carbon) Total tile* Co.-* Ca(CB)* Fe 7*3 Pmt ImIwii Pint froa Exh.uet Stack below 0.0* 24.1* 1.7* 67.1* 7.2* Wat or I*ee oh Xeiltton (carbon) Total elllea Ca'*eCa(0B)2 ft i ToS X.ji M.3* 1,9* Cf.6* 7.1< I 1 s lewtln Cottroll Sot So. 1 SwkiIo So. 1 2 5 4 5 6 7 Tot.l Yolght Pry Xit Oralne nor Cable Feet at oi Arerse* 0.093 0.102 0.OJ5 0.107 0.029 0.161 0.122 0.0956 Fated volo" 150,000 CM 0.0M6 x 190.000 x 60 x 14 2,950 peunfta dtut nor day froe, lat fc. 1 7,000 Sotoi He dat* far Sat So. 2 but raaulta aheold ba wi*nb!a to Cottroll Sat So. 1 Fig. 8. Carbide Chemical Manufacture mainder was insufficient for constant suc cessful precipitator operation. We recommended that the company in stall automatic current and voltage controls; that local exhaust ventilation at the fur naces be improved, and that other collectors be installed between each furnace and the precipitator. But every recommendation re quiring an increase in the amount of power used, whether for wet collection or addition al electrical precipitation, brought the re ply that the power consumption could not be increased at the time and that all available power was necessary to produce an amount of carbide to justify the existence of the jjlant. In addition to the various aspects of the problem just mentioned, the fact that the company is the largest single plant in the area, employing about 500 people makes its existence necessary if economic stability is to be maintained in the city. While it might be possible for the residents to take legal action against the company, in view of the important place the industry occupies in the community it is doubtful if such action is wise. The situation I have just outlined is not unusual. Every collector installation has its limiting factors, and you can determine from the account I have given that these can be extremely perplexing. Page 70 INDUSTRIAL HYGIENE QUARTERLY March, 1950 Fig. 9. Case No. 5 pROM inquiries we have received from all over the country, the control of air con taminants from chemical fertilizer plants is of interest to many engineers and com munities. For that reason, I have selected a chemical fertilizer plant in which I be lieve we have been quite successful. The usual air contaminant from the phosphate fertilizer plant is due to the dust and vapors given off during the mixing of sulfuric acid with calcium phosphate, resulting in exces sive pollution of the atmosphere with phos phate, fluoride and sulphate dust and silicic acid. -: The equipment used by the company for controlling the materials given off during the mixing consisted of a wooden paddle type blower which sucked the gases and solid materials from the mixing process up a tall wooden scrubbing tower. Several hap hazardly-placed water sprays were used in an attempt to effect water scrubbing and collections of the materials given off. As a result of our investigation, the com pany, in attempting to determine what equipment would be suitable for complete collection of the contaminants, had high- pressure fog spray equipment installed and requested that we conduct test runs for de termining its effectiveness. The installation was very effective and the results of our tests are shown in Figs. 9 and 10. Visual observance of the stack during operation of the process with the high-pressure fog spray collection equipment both on and off indicated satisfactory collection as shown. After a period of use during which the fog spray equipment was satisfactory, the Fig. 10. company gradually cut down on the water pressure used and finally reached the point where it was considered wise to discontinue the use of a high-pressure pump and install in its place an ordinary pump-capable of delivering pressure up to 120 pounds per square inch. No further complaints about the mixing process have been received. How ever, we recently received complaints con cerning a dusty material which was con taminating the neighborhood, and upon in vestigation we found that a great deal of dust was being liberated by the natural draft ventilators during the mixing of a high nitrate composition fertilizer. It was suggested to the company that bag type collectors be used for collecting this dust. No follow-up investigation has been made, and no additional information is available. It appeared from our work on this plant that the fog spray method of collection is very well adapted for fertilizer plants of this type, providing, of course, the effluent can be satisfactorily disposed of. Another fertilizer plant which has been constructed since, with fog filters installed, has proved satisfactory. Case No. 6 'J'he next case is that of a manufacturer of asphaltic base sound-deadening coat ings. The contaminant involved is once again odors. The plant is located in a city of approximately 2400, and employs about 85 people. Neighborhood residents com plained of the foul-smelling stack effluent given off during the processing of flux oils. The process, known in the trade as "blow ing asphalt," consists of blowing air VOL. 11, NO. 1 INDUSTRIAL HYGIENE QUARTERLY Page 71 through molten asphaltic flux oil which is maintained at a temperature of about 500F. During the process, certain volatile com pounds are formed and the lighter por tions of the flux oil itself may be distilled off, owing to the elevated temperature. Requests for information concerning con trol of the "blowing" process were answered by two large oil companies who supply the company in question with their flux oils. One suggested the use of an electrostatic precipitator or "routing the vapors through a furnace where all hydrocarbon particles are burned, giving off a normal stack gas." The other suggested condensing the vapors into a liquid or washing them with water "by which means the greater part of the more volatile portions are knocked down in the form of a liquid." A third inquiry to the author of an article on petroleum base protective coatings brought the reply that he knew of no completely successful method of controlling the stack effluent but thought that it could be successfully collected if passed through "at least two stages of water spray." - The company did not believe that it could consider the costly electrostatic precipitator installation and, because of the highly in flammable nature of the process, ruled out furnace burning of the stack gases. At our suggestion it was decided to try a high- pressure water spray process, and a near by manufacturer provided the company with a pilot model so that test runs could be made. Although it could easily be seen from the draining water effluent that much oily type material was being collected, the fog spray process did not completely eliminate the foul-smelling white smoky material which went through the collector and out of the stacks. Fig. 11 is a data sheet cover ing our fog spray test findings. Although additional test runs with a larger capacity water spray unit might have proved more effective, no further work has been carried out. The problem of collecting the contami nant remains unsolved, but the company plans to continue the search for a suitable collection apparatus and has informed the city council that it will shut down the blow ing operations whenever the prevailing winds result in contamination of the neigh borhood. ytXJOM. *. h| tprj CttlNiln / 2fn*Mt fni flu Ml Hnli| hww 1, <*lt . Mm. i to n, mi *ir rim MiM. 1 12 Mlilo m, *lrflew 1hi h. 1 JO twttlM m rt tow air flm 70 eutw ' fellaeWr ltrflv tea MHiW* n mi Htw lalt OMlat lalrt 1*. It*. * Tuk ?*ap. 71v Mtt M. iMh) { Oal./NU. 155- (*f> (*> 1 **0 5 a.* *50 *30 m 2 *50 520 10.0 *58 90 2*5 5 *50 J a.* --' - **5 AlVflM' OatlM (() 02 212 212 1, MInUm tfflelaaelM la fc, 1 12 21 u' 31 l>lt 11*11? Mil Ml*IKbtly iichti? Ml* lljhtl? xMuflc*tir el* 1 l**tl7 Ml* OMlet _ martial Mini Mini iicbtir Ml* 11*2*17 Ml* (UnIa1*Mfir` ea. ft.) 0.*9 1.86 1.18 0.9* 0.** 1.89 OMlat (Oral fir *. ft.) -- 0.17 0.17 0.15 o.s 0.2* Fig. 11. Asphaltic Base Coatings JfflotMoy f . CellMt lea (*) 91 86 8* 55 87 Case No. 7 WTE WERE requested by a city health de partment to investigate numerous com plaints concerning hydrogen sulphide odors. Stack samples collected during the mixing of sulphur with hot purified lard oil indi cated high concentrations of hydrogen sul phide. The gases emanating from the mixing process were passed through beds of lime stone and water in an attempt to collect the hydrogen sulphide. Our study indicated that the collection procedure was ineffective. Knowing of no process which would success fully eliminate the hydrogen sulphide, the company had installed a high-pressure fog spray collection unit so that test runs could be made. The results of our study on this unit are shown in Fig. 12. Ordinary water was used as the spray medium, and the col lection of the hydrogen sulphide was un successful. In an effort to decrease the amount of hy drogen sulphide given off, the company de creased the reaction temperature and in creased the reaction time. No follow-up study has been conducted since this modi fication of the manufacturing process, but we plan to evaluate the new procedure as soon as possible. At the time of the test runs using the fog spray collector, it was suggested that an al kali solution in place of plain water also be Page 72 INDUSTRIAL HYGIENE QUARTERLY March, 1950 aeuasg A. Ton spray Installation for eolleetln* nixing tank effluent gases 1. B28 concentration! (Inlet and Outlet) Staple ge B*S Concentrations (nillterme nar cubic fact) Inlet Outlet Collection Ifficl.Aoy if) l 166 140 24.8 2 *90 415 U.3 3 800 775 3.1 2* Air qoTenent data tact 4lBeter (inchee) tael area (square feet) Air velocity (feet Teralmite) Ai r veliaf (euble feet per nlnnte) Inlet 6 0.199 2865 562 Ontlet 7 0.267 2110 #3 \ tatet Collecting asdlwt water Fig. 12. Oil and Grease Company used for testing purposes, but such a run was not made. Case No. 8 ^OMPLAINTS were received from citizens living near a chemical company engaged in the manufacture of pharmaceuticals. During part of the processing, atmospheric pollution with bromine took place and caused disturbance throughout the neigh borhood. The complaint was investigated and it was learned that the pollution dis turbance resulted during the warm weather months only. In order to eliminate the annoyance, the company agreed to compound the materials involving the use of bromine during the winter months. No further com plaints have been received. Case No. 9 ^OMPLAINTS were received from the people ' residing near a small chemical plant en gaged in the manufacture of iso-valeric acid. It was learned that the company was considering a new location but its capital was limited. Unable to relocate because of lack of funds, the company was forced to abandon the contract for the manufacture of iso-valeric acid. Conclusion VV/E believe these case histories may serve to bring out the importance of the four considerations previously men tioned; namely, the selection of a suitable method or collector, cost of the equipment and installation, maintenance of the equip ment, and disposal of the collected material. They also show that there is no cut-anddried method of controlling the contam inants involved in the term air pollution. At the present time it is our belief that, in many cases similar to the phthalic plant mentioned, even the plant operators do not know what their problem is. We hear a good deal about smoke and fly ash elimina tion, possibly because we know more about how to eliminate them than most of the other contaminants found. Obviously, the lack of knowledge is the biggest handicap in the control of odors.