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of 12 asbestos fibers, five microns or longer, per cubic centimeter, and this was later modified in 1970 by reducing the time-weighted average to five fibers per cubic centimeter with a maximum or peak of 10 fibers per cubic centimeter at any one time.
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Partnership for Prevention-
The Insulation Industry Hygiene Research Program
Irving J. Selikoff, M.D. *
PARTNERSHIP FOR PREVENTION -- THE INSULATION INDUSTRY HYGIENE RESEARCH PROGRAM
Dr. Irving J. Selikoff, Director, Environ mental Sciences Laboratory, Mount Sinai School of Medicine, New York City, and Director of the Insulation Industry Hygiene Research Program, describes this unique cooperative effort by an international labor union, Johns-Manville, science and government to conduct a preventive hygiene research program for insulation workers. Dr. Selikoff explains why the program was needed, how it was formed, and some of its accomplishments.
A08043
Reprinted from INDUSTRIAL MEDICINE AND SURGERY
Vol. 38, No. 3---------- Miami, Fla. 33156 Printed in US.A.
t OCCUPATIONAL MEDICINE
162
Partnership for Prevention-
The Insulation Industry Hygiene Research Program
Irving J. Selikoff, M.D. *
The nation's first cooperative effort by an international labor union, industry,
medical science and government to conduct a preventive hygiene research program for insulation workers has been in productive operation for a year and a half. In the development of specific techniques and equipment to control and prevent exposure to dusts, as well as in the experience of cooperative support, the program will have application far beyond the insulation industry.
It is an achievement of modern medical methods and
applied industrial hygiene practices that it has been
possible in the course of a relatively few years, to detect
the long-term effects on workers of an important
occupational health hazard, to identify major sources of this hazard, and to take positive steps toward its
reduction and, we hope, eventual elimination.
That this required the combined efforts of clinical and
epidemiological medicine, the cooperation of an international union and its 18,000 members, and the
direct involvement of a major industrial concern and its
facilities for applied research should not be surprising.
The Insulation Industry Hygiene Research Program has
three major goals: the prevention of dust formation; the
control and limitation of dusts that are unavoidable, and preventing inhalation of dust by those exposed to it. The avenues of approach toward these goals involve both
human elements -- changing work practices of the insulating workmen -- and technological elements -- changing methods of manufacturing and application of
insulating materials. The program has been functioning for somewhat over
a year, and it appears that the threshold of control has been crossed. For example, we have developed a new type of respirator intended specifically for use where
'Program Director, and Director, Environmental Sciences Labo ratory, Mount Sinai School of Medicine of the City University of New York.
fThe Advisory Council membership is: Irving J. Selikoff, M.D., Director, Environmental Sciences Laboratory, Mount Sinai School of Medicine (UHRP Director and Chairman); E. Cuylcr Hammond, Sc.D., Vice President. American Cancer Society, New York, N. Y.; Albert Hutchinson, General President, International Association of Heat and Frost Insulators and Asbestos Workers, Washington, D.C: J.B. Jobe, Vice President, Johns-Manville Corporation, New York, N.Y.; Fred L. Pundtack. Vice President, Research and Development, JohnsManville Corporalion. New York, N.Y., and George W. Wright, M.D., Director of Medical Research, St. Luke's Hospital, Cleveland, Ohio.
fibrous dust generation cannot be avoided. New types of containers for mixing asbestos cements are being used; insulating materials are being coated with a spray that keeps particles from shaking loose during transportation and handling. Prefabricated fittings have been developed that will preclude working with loose materials in tight places. New control methods are being tried for application of sprayed insulation materials on major construction projects. Better methods for collecting and disposing of dust-generating wastes are being tested. Prototype ventilating systems for power saws used in cutting insulating products are proving remarkably effective in preventing production of respirable dusts.
JOINT PROGRAM BEGUN IN 1968 This joint enterprise enlisted the support of the Johns-Manville Corporation, a major producer of insulating materials; the International Association of Heat and Frost Insulators and Asbestos Workers; the Environmental Sciences Laboratory at Mount Sinai School of Medicine; and the Bureau of Occupational Safety and Health of the U.S. Public Health Service. Subsequently, the Sprayed Mineral Fiber Manufacturers Association, Inc. added their participation. The cooperation of insulating contractors throughout the country and regional groups of contractors who are directly involved in all aspects of applying insulating materials, was freely given and appreciated. For coordination of the program and to assure continuing input of new concepts and new techniques, we established an Advisory Council with representatives of medicine, labor and industry -- the elements directly concerned with the application of preventive measures and with their widespread adoption throughout the insulating and related industries.t While today we can check off the progress already made toward solving some of the occupational health
INDUSTRIAL MEDICINE, VOL. 39, NO. 4, APRIL 1970
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AO8O44
163
programs and can look ahead with confidence that further strides will be made, it is instructive to review the events leading to the identification of the hazard and to consider why recognition and corrective action was taken only recently. The lessons learned may be applied to other industrial situations.
It is too easy to indulge in what might be called the demonological theory of industrial hygiene history. One version would place the responsibility for early identification of risk and its correction upon industry and then indict it for trading human health for profits. Similarly, the other side of this counterfeit coin puts the blame on organized labor for having been more interested in premium pay for hazardous work than in eliminating known hazards. Both conclusions are too convenient and are essentially erroneous. It is much neaav the truth to say that both industry and labor shared in. ignorance and neglect of the problem. Science and medicine are also at fault here for inadequate attention to environmental and occupational health.
In retrospect, however, it is possible to see why recognition was so long in coming. We now know that it may take 20 to 30 or more years from onset of exposure before the effects of this particular hazard begin to manifest themselves in the morbidity and mortality of the workers.
In the asbestos mining and manufacturing industry, the risk of heavy exposure to the occupational dusts had been recognized for some years. And this primary industry has understood the need to install ventilation systems and other dust control devices to reduce the hazard. Experience had indicated that reduction of dust
IRVING J. SELIKOFF
levels and exposures could result in greatly improved health experience among asbestos factory workers.
But the extrapolation of that experience to another classification of workers -- specifically those who fabricate and install insulating materials -- was a more sophisticated task for clinical medicine and epidemiology.
An immediate problem is that the insulating v.orkers are not a centralized homogeneous group that can be studied at once, but are composed of units of small numbers that do not immediately exhibit conspicous definable trends or patterns of health. For example, the 18.000 unionized insulation workers in this country are dispersed among some 850 employers - an average of 17 workers per employer, with only one-sixth having more than 20 employees regularly. The unions are organized by locals and only two of these locals have as many as 700 members each. Further difficulties were imposed by the fact that 30 or 40 years after an insulation worker had been first exposed, he frequently was retired and no longer easily traceable.
With the full cooperation of the New York area locals of the. Heat and Frost Insulators and Asbestos Workers Union, my associates and I set up in 1962 a program to compile the work history and health records of the 632 men who were members of the union on January 1, 1943. Each of these men was traced through 1962. Among these men with exposure of at least 20 years to asbestos and other insulating dusts, there were 255 deaths, 52 more than the expected number based on comparable U.S. mortality figures. Analysis of causes of death revealed 12 due to asbestosis, 42 deaths attributed
FIGURE 1. Members of the Advisory Council of the Insulation Industry Hygiene Research Program joined a team of industrial hygienists on a construction site field trip to observe environmental conditions of insulation workers. From right. Dr. Irving J. Sclikoff, Program Director, Dr. E. Cuylcr Hammond, Vice President, American Cancer Society, Dr. Fred L. Pundsack, Vice President, Research and Development, Johns-Manvillc Corporation.
22 INDUSTRIAL MEDICINE, VOL. 39, NO. 4, APRIL 1970
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to lung cancer, and four from mesothelioma, a malignant tumor rarely reported among the general population.1
STUDY SHOWS HIGH RISK OF DISEASE Here we had, then, the first solid evidence that these insulation workers were experiencing exposures to dust inhalation in the basic asbestos industry. Our continuing study of the work and health records of this group of union members confirms the higher risk of respiratory disease and cancer for the insulating workers than exists among the general population. There were 632 members of the New York area locals of the asbestos insulating workers' union on Dec. 31, 1942. By Dec. 31, 1968, 300 were dead from various causes, including 30 from asbestosis, 72 from lung cancer, and 22 from mesothelioma.2 Apart from the occupational hazard, a most significant relationship between lung cancer and the combination of cigarette smoking and insulating work has been revealed. This particular phase of the study started in January 1963 when 370 men of the original 632 were still alive. By November 1, '69, 36 cases of lung cancer had developed. The group of 283 cigarette smokers contributed all but one of the lung cancer cases. This finding suggests that among these workers who smoke cigarettes, the risk of dying of bronchogenic carcinoma is 92 times that of men who neither smoke cigarettes nor work in the insulating industry.3 Here obviously is a preventive problem involving the personal habits rather than the work habits of a large group of workmen. Confronted with the evidence of job exposure to asbestos and other dust hazards, the first urgent task was to seek to identify the sources of exposure. It is known that a large proportion -- something over 50% -- of the asbestos used in this country for the past 40 years has gone into the construction industry in one form or another. It is fortunate that the greatest part of this has been in products in which the asbestos is "locked in" that is, it is bound with cement or plastics or other binder so that there is no release, certainly no sianificant
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FIGURE 2. Insulating workers, members of the Asbestos Workers Union, test prototype dust masks for efficiency and comfort on Illinois job site. Each of Uiese masks incorporates slight design differences.
FIGURE 3. A proposed method to eliminate a major source of dust at construction sites has been the development of a plastic mixing bag for asbestos cement. Bags are partly filled with dry cement at the factory. Water is added on the job through a valve at the top of the bag which accomodates the nozzle of a hose, and the result is mixed up in the bag.
release, of asbestos fiber in either working areas or general air. Such products as floor tiles, roofing felts, asbestos cement products, siding material, and the like contain the locked-in fibers.
Attention therefore was turned to those insulating products which were capable of generating dusts on the job -- through handling, sawing, fabricating, applying, mixing, as with loose asbestos cement, spraying, and waste disposal.
Examination of these activities, where there was obviously generation of dusts, quickly taught us that we were to be concerned with what happens at three levels of exposure: first, the insulating worker who is most directly and intimately subject to dust exposure; secondly, other construction workers who may be working in the vicinity of dust generation or who may be called upon from time to time to come into intimate contact with insulating materials: and third, the nearby ambient air which, under many circumstances, will certainly receive the drift of dusts and fibers from insulating activities.
Our primary concern, of course, is with the insulation worker, not only because we have established the risk fpr him but because if his exposure is brought under control, then the other problems will be resolved automatically. There is some evidence of increased respiratory disease risk for other construction workers, although we do not know its extent or whether this is because of direct contact with the material or indirect
INDUSTRIAL MEDICINE, VOL. 39, NO. 4, APRIL 1970
23
A8046
165 IRVING J. SELIKOFF
FIGURE 4. Spraying of girders and spandrels with mineral fibers for fire-proofing can be conducted with reduced release of mineral dust into the air through containing the operation behind tarpaulin covers, as shown here on the new World Trade Center building in New York Gty.
exposure in the vicinity of insulating work. And while
there is at present no evidence of community risk from asbestos fibers in the ambient air, it is only prudent, especially with our concern for reducing general air pollution, that job-generated dusts and Fibers be prevented from drifting into the community air.
Much of the technology for dust prevention and control was developed and used in many mines and plants; the technique for adapting these to the particular jobs and job-sites of insulation workers continues to present challenges. We are currently required to work toward these related goals simultaneously - the prevention of dust inhalation by workers who are now exposed, the limitation of dusts that are presently unavoidable, and ultimately, the prevention of dust formation.
SAFE PRACTICES BEING DEVELOPED Immediate protection against dust inhalation was among the more urgent problems. Although various respirators and dust masks had long been provided for those working in heavy concentrations of asbestos and other dusts, we found in actual practice only 4% of
FIGURE 5. An inside view of the spraying of ceiling joists with mineral fiber at the World Trade Center Building. The spray area is sealed from other work areas at the elevator shafts as well as at the windows. The operator wears a respirator.
union members surveyed said they always used a mask on a dusty job and almost 30% said they never used such protection. We immediately turned our efforts toward developing a new type of respirator -- one that would not only be effective against the fibers and dusts generated in insulating work but, more importantly, one that would meet the workers' requirements of comfort, convenience, and good vision.
We have not yet achieved our goal, but we are perfecting a new type disposable mask that is specifically designed to meet the requirements of those who will wear it. The first field use tests in the spring of 1969 revealed some shortcomings that sent us back to the design laboratory. We are confident that the result will be a respirator that will be more acceptable to insulating workers and that may be adapted for many other occupations where breathing masks are required -- but too seldom worn. As our colleague. Dr. Cuyler Hammond, has said, it is far better to have a mask that is 100% used, even if not fully effective, than one that is fully effective but never used! We are developing a mask that will be both effective and worn.
What we aim to achieve is a working environment in
FIGURE 6. A newiy-dcveloped portable suction attachment for portable power saws on construction sites is nearly 100% effective in collecting dust In the picture on the left a section of asbestos pipe covering is being cut with the use of the suction attachment. The picture on the right shows the dust which would be released into the air if the attachment was not used.
24
INDUSTRIAL MEDICINE, VOL. 39, N^jlgAPRIL 1970
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which dusts are so fully controlled that respirators may never be necessary. One stumbling block has been that in
installing insulation it is necessary to mix some asbestos cement on the job site. This is spread and applied to seal joints and to fill in comers where pre-fabricated material is not practical. Previous and present practices call for mixing this combination of asbestos and cement or other binding materials in open troughs or mixing bins. Almost every step in this process generates some dusts -- from the emptying of bags to the mixing of the material with water. At present, we are testing two different methods of packing an asbestos-cement mixture so that the water can be poured into the container and wetted down into the so-called "mud" without generating dust. We know that this will work, and it is merely a matter of determining practical sizes of containers, the best material for the bags, and the most convenient means of applying the water and mixing within the bags.
Many insulation fittings are manufactured at a plant, packed and shipped in containers that are opened at the job site. It was found that these fittings were shedding during the handling, so that the containers themselves were emitting dusts and the fittings continued to shed during handling. Industry research laboratories developed a method of spraying these fittings with a wax-like substance before packaging. This dust-suppressing spray method, developed at the Johns-Manville Research and Engineering Center, prevents the dust from shaking loose and has, therefore, provided another means by which we prevent the generation of dust -- our ultimate objective.
Although shaping and fabricating of insulating materials is sometimes done in shops that are fitted with special dust-collecting devices, there continues to be much individual sawing on the job site -- either with hand or power saws, which have not had dust collectors. We posed this problem to makers of portable power saws. Now there are pilot models of power saws with suction attachments that are nearly 100% efficient in dust prevention.
Even as these positive and constructive steps are being developed, we discover that new and difficult questions
arise. Monitoring for dust counts still needs refinement
- and we do not actually know what the minimum necessary level is. Therefore, we seek to achieve as near zero generation as possible. Attention has been turned to the collection, transportation and disposal of construction wastes -- which in New York City alone amounts to some 2,000 tons a day. The manufacturers and applicators of sprayed insulating materials are developing new methods and work practices to contain the dusts involved in this operation. Shipyards pose special problems that our technical people are studying.
And there is still the practical problem of making sure that the new methods and techniques are adopted by employers and workers and applied to their daily procedures. Fortunately, we are getting excellent response from contractors and contracting groups, and the participation of union members is assured. Each union member contributed S10 to help support the program (it is thus his program!). A quarterly report of progress is published, and is sent to each union member, to contractors, other union groups, industrial hygienists, educators, physicians and other scientists, and government officials involved in occupational health activities.
This partnership for research into prevention of the occupational health hazards of the insulating industry -- forged by labor, industry, science and government -- has proved useful. It is possible that it will provide a key to similar partnerships in other industries where occupational health problems exist.
REFERENCES
1 Selikoff IJ, Giurg J, Hammond EC: Asbestos exposure and neoplasia. JAMA 188:22-26, 1964
2 Selikoff IJ, Hammond EC, Chure J: Mortality experiences of asbestos insulation workers. Proc Jnt'l Conf Pneumoconiosis, Johannesburg, 1969. In press
3 Selikoff IJ, Hammond EC, Churg J: Asbestos exposure, smoking and neoplasia. JAAM 204(2): 106-112, 1968
Reprint requests: Industrial Medicine and Surgery, P.O. Box S46, Miami, Fla. 33156
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INDUSTRIAL MEDICINE, VOL. 39, NO. 4, APRIL 1970
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asbestos dust control; 4. To correct misleading and uninformed reportage on
asbestos-health problems; 5. To publicize the unique benefits and importance of
asbestos in protecting human life and property.
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a! ASBESTOS i
1 February 1974
The Editor "Time" Time and Life Building Rockefeller Center New York, N. Y. 10020
Dear Sir:
The article, "Death from Dust", January 28, describing conditions at an asbestos insulation plant in Tyler, Texas, should not be viewed as reflective of the situation existing in the vast majority of asbestos manufacturing plants in the United States.
For many years, the industry has recognized the potential serious health hazards of excessive asbestos inhalation and has installed sophisticated control equipment and instituted improved work practices to reduce dust concen trations to acceptable levels so as to provide a safe and healthy working environment for industry employees. In addition, the asbestos industry throughout the vrorld is conducting, sponsoring, or cooperating in extensive medical and technical research to learn even more about the health hazards of asbestos and the.means for their control.
'R. H. MMi ereness Executive Director
RHM/cg
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^;uqs3l03 neaun question parplexes expans
When asked to comment on research directions before an international con ference on the biological effects of in gested asbestos in Durham, N.C.. last month. Dr. Paul F. Holt of Reading
University, England, summed up the feeling of the whole conference in his response. The main question to be in vestigated, he said, is: Does asbestos matter, or doesn't it?
Coming after more than 40 years of published research on the biological ef fects of asbestos--research that has been greatly intensified over the past 10 years in the U.S. and abroad--this seems a very preliminary question to still be under investigation. Neverthe less, although asbestos is known to cause severe lung damage and to raise the likelihood of certain cancers devel oping following heavy exposures, the effect of smaller doses on the general population isn't at all clear.
It seems very farfetched that asbes tos could be dangerous, Dr. Holt says, but if it is, then everyone is in very se rious trouble. And indeed they would be. It seems likely that asbestos occurs naturally in much of the drinking water in the U.S. Environmental expo sure to it is increased by filtration of certain beverages and pharmaceuticals through asbestos filters. Used exten sively in construction for its fireproof ing qualities, asbestos contaminates the air in most office buildings and stores. An examination of lung .sections of people living and working in New York City has shown some fibers in the lungs of every person examined. Simi lar results probably could be found in any other urban area in the nation.
Clearly, there is a need to determine whether this constant and widespread exposure is hazardous. To help evalu ate the danger associated with asbestos exposure as it is now understood and to examine new directions in research to enable a more complete understanding of the effects of asbestos ingestion and exposure, the National Institute of En vironmental Health Sciences and the Environmental Protection Agency sponsored last month's conference. At tended by some 130 scientists and pub lic health officials from 12 countries, the conference emphasized the limited amount of information available on the effects of low-level, prolonged expo sure. The scientists also pointed out how difficult it is to obtain accurate information on these effects.
There are three serious difficulties in determining the effects of asbestos on human health, the conference speakers agreed:
The term asbestos itself is mis leading, for it encompasses a whole group of minerals that are distinct from, each other in chemical composi tion, particle size, and probably biolog ical tffeet.
Many of tliewe p:utides are so
small that detection is extremely diffi cult and time consuming, placing re straints on the scope of research that can be reasonably undertaken.
Perhaps the most serious diffi culty in asbestos research, however, is the very long period between initial ex posure and evidence of. biological ef fects. In the case of mesothelioma, an asbestos-induced cancer of the linings of the abdomen and chest, this time period is usually 25 to 35 years.
Asbestos is any of several silicate minerals existing in fibrous form. The Federal Register lists six main types of asbestos mineral, each with its own chemical composition. To add further confusion, each of these chemical forms exists in both a fibrous or "asbestiform" variety and in a nonfibrous type that is sometimes considered an asbestos mineral and sometimes not.
Chrysotile asbestos is the most dis tinct asbestos form and the one most widely used in industry. A magnesium silicate hydroxide, chrysotile exists in nature as a bundle of very small fibrils, each less than 5 microns in length and about 0.2 micron in diameter. These fi brils are hollow, and their large surface area and relatively high surface charge allow for great adsorption of trace metal ions to these particles.
The other asbestos minerals, collec tively referred to as the amphibole minerals, have a significantly larger fiber diameter and are solid fibers. They have sodium, calcium, and iron occurring in their lattice structures, in addition to magnesium and randomly substituted trace metal ions. Although not used as extensively for industrial purposes, the amphibole minerals com monly are found as contaminants of talc, chrysotile, and other widely used minerals.
Chrysotile fibrils are too small to be detected by conventional optical mi croscopy. To identify these particles positively, Dr. Arthur M. Langer of Alt. Sinai School of Medicine in New York City explains, a combination of transmission electron microscopy, se lected area diffraction, and microchemical analysis is needed. Others be lieve that scanning electron micro scopes could be useful in detecting chrysotile in combination with some type of chemical identification, but all agree that the main drawback to any detection technique that requires elec tron microscopy is the time involved for each analysis--about one man-day per sample. Any investigation of the occurrence of asbestos in the general population or in the environment must consequently be very limited in scope.
Amphibole asbestos fibers are larger. But they also require sublight micro scopes for careful examination and cannot be positively identified without additional mictocheinical or selective area diffraction analysis.
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The research workers at the confer ence expressed great hope that ad vances in automated analysis would make more extensive sampling possible by cutting down on the time required for analyzing each sample. Dr. Eugene P. White of Pennsylvania State Uni versity, for example, described a com puterized system for examining small particles using a scanning electron mi croscope that is currently used in his laboratory for analysis of coal mine dust.
The most serious deterrent to under standing the biological effect of ingest ed and inhaled asbestos, however, is the long incubation period of certain asbestos-induced effects. Asbestos workers in the shipbuilding industry in the U.K. in the 1930's began to develop statistically high incidences of the pre viously rare cancer form mesothelioma in the late 1950's, more than 20 years after their asbestos exposure. Since that time, many other cases of the dis ease have been reported in patients who worked with asbestos 25 to 35 years earlier.
Dr. Irving J. Selikoff, director of the Environmental Health Sciences Center at Mt. Sinai School of Medicine, pre sented data to the conference from sev eral mortality studies of occupationally exposed asbestos workers in New York and New -Jersey. His studies show in creases in interthoracic cancer and mesothelioma more than 20 years after heavy asbestos exposure.
In addition, he found that although lung cancer deaths did not appear to be more frequent among nonsmoking asbestos workers than among the gen era! nonsmoking population, they were very much mure frequent among smok ing asbestos workers than among other smokers. In one stud', uf 17.800 asbes tos insolation workers, of whom 0590
A0795 1
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Asbestos cement worker wears mask to screen out chrysolite libers
were smoker?, there were five to six times the predicted number of deaths from lung cancer among the smokers. A smaller study of insulation workers in New York showed 10 times the ex pected number of deaths caused by lur.g cancer among the workers who smoked cigarettes.
The question of most concern to public health officials, and the area of most intensive research at present, is the effect of asbestos exposure at inter mediate levels and the effect of lowlevel exposure to asbestos in combina tion with low levels of other carcino gens that are often present in the environment.
Research on these questions takes two directions. The most reliable infor mation on the health hazard of asbes tos to man will come from one of the research directions, studies of the ef fect of the mineral on man himself. Thus, the studies that Dr. Selikoff and his associates have begun on asbestos workers in New York and New Jersey are being continued and expanded. Dr. Selikoff points out that there are some cases of mesothelioma in New Jersey that cannot be traced to any asbestos exposure. These are being further in vestigated to see if a cause for them can be found. Multiple effect correla tions. such as that between cigarette smoking and asbestos fiber inhalation, are being looked for also.
Dr. Ian Webster of the National Re
search Institute for Occupational Dis eases in Johannesburg, Republic of South Africa, told the conference of a massive effort by the South African government to establish the danger of asbestos exposure. South Africa mines both amphibole and chrysotile types of asbestos. The government hopes to conduct mortality studies on all of the workers in these mines since 1953.
Most of the workers come from no madic groups living in the desert re gions of South Africa. They work in the mines for brief periods then return to their homes, making them very diffi cult to keep track of. Nevertheless, the government hopes to be able to follow a substantial number of these workers and determine, at the very least, which asbestos forms are the most dangerous ones.
The other direction of current asbes tos research uses laboratory animals to study details of the effect of the fibers on tissues. The drawbacks of making inferences from animal models were re peatedly pointed out by speakers at the conference. Especially in cancer re search, different animal species often respond substantially differently to the same agent. Consequently, many dif ferent animal models must be used and compared if animal response is to be reliably extrapolated to humans.
Animal studies scent to show that al though inhaled asbestos can be found in the diaphragm, liver, and the epi
dermal layer close to the gastrointesti nal tract, ingested asbestos is \try poorly absorbed, if at all. through the lining of the stomach and colon. Dr. John M. G. Davis of the Institute of Occupational Medicine, Edinburgh. Scotland, could detect no asbestos passing through the stomach or intesti nal walls of rabbits fed asbestos fibers in his laboratory. However, Dr. ..t. D. Pontefract of the Canadian Food Re search Laboratories injected an asbes tos sample directly into the stomachs of laboratory animals and was able to detect about 0.1% of his sample in the epiderm. In studies with baboons. Dr. Webster found that very little ingested asbestos penetrates the walls of the stomach and colon and that almost all that does is of the smaller chrysotile type. Studies with inhaled asbestos also show that the fiber that is ab sorbed is predominantly the chrysotile type.
Conclusive evidence on the effect of environmental levels of asbestos on man, or even reliable estimates of what that level is, will not be available for some time. In the meantime, current asbestos exposure may be causing can cers that will not be detectable until the next century. Thus, representatives of regulatory agencies present at the conference agree with asbestos research workers that asbestos presents too much of a threat to human health to be used indiscriminately until conclu sive evidence is available. There is not yet complete agreement, however, on what sort of regulation should be im plemented.
Dr. William Eisenberg of the Food and Drug Administration explains that it is not possible for FDA.to run elec tron microscopy analyses of all the po tential sources of asbestos contamina tion under its jurisdiction. At present, analysis by polarized light microscopy is used to determine purity of foods and drugs, even though this method probably misses many of the smaller and more easily absorbed asbestos fi bers that may be present in these ma terials. FDA's main concern, according to Dr. Eisenberg, is with parenteral drugs rather than with substances that enter the body through the gastrointes tinal tract, since relatively small amounts of ingested asb.estos appear to penetrate the body. Last September FDA began taking steps to eliminate the use of asbestos filters in the pro duction of parenteral drugs.
EPA's Gordon Everett calls for stan dardization of reporting data so that the necessarily limited amount of data collected in each study can be usefully compared with results from other stud ies. He points out that information on the biological effects of asbestos is very limited and that the effects of many asbestos substitutes have not been in vestigated at all. Before asbestos use is banned, it should be certain that a safer alternative is available, he cau
tions.
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UNION CARBIDE
(Tifidriaasbestos______________________________
UNION CARBIDE CORPORATION METALS DIVISION P.O.BOX 579 NIAGARA FALLS, N.Y. 14302 TEL: 716-278-3376
GRINDING CALIDRIA ASBESTOS PELLETS
The following discussion is intended to assist in equipment selection and Pi anning for use of CALIDRIA Asbestos products in pellet form, to take advantage of their higher bulk density, dust-free nature, and free-flowing properties.
The pellets are cylindrical, about 3/8 in. diameter and up to 3/4 in. long. Bulk density is about 44 lb. per cubic foot. No additives or binders are used; they are held together by natural forces. For some applications, a cracked pellet form is available, in which the pellets have been crushed to minus 3 mesh. Either form has a negligible amount of minus 325 mesh dust, which is the important fraction in airborne contamination.
For size analysis of the ground products, we recommend wet screening by either the Bauer-McNett method or by hand-jigging. Some operator training is necessary in the latter method to obtain reproducible results, particularly in tile finer mesh sizes.
Storing and feeding pellets is simplified by their free-flowing, ncn-abrasive nature. Cone-bottom bins or hoppers with a 90 included angle are self-emptying. Almost any feeding and conveying equipment will work with asbestos pellets. For accurate feeding, a screw feeder or weigh-belt feeder is preferred, rather than vibrating feeders. The pellets can be air conveyed, but due to their granular nature, high air to solids ratios are required and some dust will be generated. Pellets are available in bulk hopper cars holding up to 90 tons, and in 50 lb. or 100 lb. multiwall paper bags. Arrangements can be made for other containers to suit customer requirements.
Dry grinding may be done in a variety of equipment: disc mills, grate hammer mills, air-swept mills, etc. Disc mills are suited to coarser grinds and have the advantage of requiring a minimum of air cleaning equipment. Grate hammer ills, such as the Jeffrey and the Mikro-P, are versatile in application and pro duce a minimum of "tramp" oversize, but dust collection is necessary and screen maintenance can be a problem, particularly if an extremely fine grind is desired. Air-swept mills, such as the Raymond Vertical and the Bauer Hurricane, are well suited to medium and fine grinding in production operations. Table I summarizes some of the factors involved in selecting dry grinding equipment.
A079 i2
-3 A particularly effective wet grinder for pumpable slurries consists of a high-speed (16,000 FPM tip speed) vertical hammer mill, such as a Reitz, with the grinding chanter enclosed by grooved hard alloy liner plates. Asbestos and process liquid are introduced at the bottom and overflow the top of the grinding chamber. Screen main tenance problems are eliminated, and the grind can be controlled by varying feed consistency, hammer spacing, and residence time.
R.E.Byrne/bsn 2/9/71
4
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Asbestos beefs up plastics and adhesives to extend their use
Highway markers are bonded with inexpensive, asbestos-modified adhesives. Two components are mixed and dispensed from cart before applying reflectant.
The first single-crystal whiskers to be used by man were asbestos. Since the whiskers' high strength was first measured in a laboratory, scientists have been trying to find ways to harness the potential of asbestos in structural materials.
The tensile strength of single crystals of asbestos has been meas ured at more than 800,000 psi-- as strong as the strongest glass filaments. But so far, strengths achieved in composites do not go beyond those achieved with glassmat reinforcements.
The thorn to date. One of the chief drawbacks of asbestos has
been the inability of researchers to incorporate homogeneously more than 10% to 20% asbestos with structural resins. With only 4% or 5%, resin mixtures become unman ageably viscous.
But this very deficiency is'being turned to advantage by Union Car bide chemists, who have developed a number of thixotropic uses for their new resin-grade of chrysotile asbestos. The Union Carbide mate rial, because of its high purity and fine particle size, is easier to in corporate in resinous compounds. Union Carbide's filler is cheaper than other thixotropic agents.
Opening new fields. Union Car bide mines an area in California. Asbestos was discovered there just a few years ago, and it is believed to be the largest source of highpurity asbestos ore in the world. The extra-high purity of this grade has opened up a whole new range of uses for asbestos.
An important difference in the California grade of asbestos is its random orientation, which permits the wet-processing system. Wet processing breaks up individual fibers into easy-to-handle dust-free pellets. The separation of fibers yields a more efficient reinforcing effect in resin-based products.
Another application for asbestos is as a reinforcement for thermo plastics. Adding 20% asbestos to Nylon 6 doubles both the flexural and tensile strength of the unrein forced material. The increase matches the strength improvement obtained with chopped-glass fibers.
Saving money. Most other appli cations for the new grade of as
bestos have been in viscosity-con trol uses such as with epoxy and polyester compounds. Of course, some reinforcing effect also results.
For example, traffic-marker ad hesives based on epoxy resins have been made 600 to 700/lb. cheaper by using the asbestos thickener.
About 30 gm of adhesive are used by the State of California's Highway Dept, in putting down round-button pavement markers. About 3 million of these markers will be applied by the end of this year: The use of asbestos has added up to some important savings for the California tax payer. (2.127)
from PRODUCT ENGINEERING/October 21, 1968 Copyright 1968 McGraw-Hill, Inc.
Use by permission of Product Engineering
A07936