Document D0awBaDypQ82bOr1yOZ9BRRn

FILE NAME: National Safety Council (NSC) DATE: 1938 Apr DOC#: NSC010 DOCUMENT DESCRIPTION: NSC - National Safety News - "Mixed" Dusts and "Protector" Dusts //M ix ed ,/ Dusts and //Protector// Dusts By L E R O Y U. G A R D N E R , M. D. Director, The Saranac Laboratories, Saranac Lake, N. V. 'Experiments show that certain dusts inhibit the action of silica dusts. More research is needed, however, to obtain conclusive data IN' 1933 we undertook a field study for one of the gypsum companies and were impressed by the fact that men who had been exposed for many years to atmospheres contain ing gypsum dust showed no evidence of silicosis. Experiments were then inaugurated in which animals were compelled to inhale high concentra tions of quartz mixed with gypsum dust. Both guinea pigs and white rats failed to develop the silicotic re actions which would have been ex pected from the amount of silica in- , troduced, into the atmosphere. Subsequently field studies in the iron ore, cement and other industries furnished evidence that other nonsilicious materials might prevent or at least retard the inhalation of silica dust. Animal experiments with mix tures of hematite and quartz dust have shown very definite evidence of protective action against silica. Calcium flouride apparently falls'in the same category. Granite, a natural mixture of quartz' and various sili cates, is known to cause silicosis in human beings but its action is so slow that fifteen or twenty years of expo sure is necessary before disease devel ops. Inhalation experiments with this dust have invariably failed to produce silicosis in animals. Recent injection experiments have demonstrated that tissue reaction to quartz in this combination is long de layed. ' The same quantity of quartz that would provoke specific tissue^, changes in two months, if it were in jected in pure state, is held in check for two years when it is administered with the silicates of granite. A. p ap er re a d a t a sp ecial m eeting- of Air H ygiene F oundation, Inc., P itts burgh* Pa., N ovem ber 30. 1937. - Such observations in animals are not new, for experiments have fre quently failed to reproduce disease with mixtures of silica and other sub stances which are well known causes of silicosis in human beings. Either the experimentor claimed to have caused the "early stages" of the dis ease, although his illustrations indi cated that such was not the case, or h e condemned t h e experimental method. In many cases he concluded that associated irritations of the lungs due to infection, mine gases, etc., were essential. It seems much more probable that the failures were due to the presence of protectors which delayed the rate of reaction to silica. Modifying Factors Quite recently the Banting Insti tute has published a report of experi ments in which it was shown, that me tallic aluminum had prevented the de velopment of silicosis in rabbits. The observations covered a period of six months during which time controls subjected to pure quartz dust devel oped early silicotic nodules. Animals breathing a mixture of quartz con taining one per cent aluminum formed no nodules. These observations would seem to furnish another example of the same general principle. This protector is apparently active in very small quan tities. Whether it will continue to prevent silicotic fibrosis from devel oping over a period of several years remains to be demonstrated. The evidence now available makes it seem improbable that a silica hazard is defined solely by the number and size of the silica particles in an indus trial atmosphere. The other compon ents of a dust modify its action. Some, may inhibit, others retard and per haps some will be found to prevent its injurious effects. Because these possibilities are recognized it becomes difficut to set up definite standards of permissible dustiness in industrial atmospheres. A concentration of quartz particles which may be ex tremely dangerous when associated with "contaminating" particles of one type may be quite harmless when mixed with some other material. Not enough is known about the action of protector substances to war rant the recommendation that they be employed to prevent silicosis in indus try. Our aim should be to reduce existing dust concentrations rather them to increase them by adding more dust. Even though it may be shown that the health hazard is slight or non-existent, excessive dust concen trations are at best a nuisance; they often interfere with effective produc tion and in extreme cases they add an accident hazard. I would very strong ly oppose the recommendation that protector ducts be used to attempt to prevent silicosis at the present time. Fragmentary Knowledge But I do believe that we should at tempt to discover more about their action. At present our knowledge is fragmentary. We know that many apparently unlike substances may act as inhibitors. Some are more potent than others. Some seem to exert their effects within the body, preventing the' silica from acting on the tissues. Some, like gypsum, seem to combine with the silica in the atmosphere, forming clumps which are too heavy to remain suspended in air and too large to pass the barriers of the nose and upper res piratory tract. We should know more about the underlying principles which govern the behavior of different mixtures. We should investigate the action of various substances commonly associ ated with quartz in industrial atmos pheres. If they have protective ac tion, we should discover in what pro portions they are effective. We should know whether their effects is perma nent or temporary. We should discover how and why such substances influence the reaction to silica by the body. With such information at hand it may be possible to apply the knowl- ( Please turn to page 74 ) National Safety News, A pril, 1938 25