Document 3QqnkM2JOvzenZ0bmpkBww550

Industrial Hygiene Importance ol Dust By N. V. Hendricks Chief Engineer Industrial Hygiene Service. Georgia Department of Public Health Nearly all types of modem industry are concerned with dust and its control. Courtas? M. 8. A. Co. FIG. I. THE MIDGET IMPINGER USED FOR COLLECTING ATMOS tiate between the PHERIC DUST SAMPLES. origin of these materials, a defi nition of them is in order. THE annual cost to industry DUSTS are formed by the re from uncontrolled dust duction of earthy materials and amounts to a staggering figure. Ianre usually produced by such ope many cases the problem of dust is rations as crushing, grinding, dismissed by management as only buffing, etc. The particle size of a nuisance. In other plants, the dusts may vary considerably, recovery of certain dusts is eco ranging from sub-microscopic to nomically sound, especially where visible. the particulate matter may con FUMES are formed by conden tain precious metals or may carry sation and sublimation. Chemi valuable processing stock. Aside cally, they are metallic and are from any nuisance or economic usually the oxides of such metals loss resulting from the escape of as zinc, and lead. The particle dust there are certain dust ex size is usually below one micron. posures which may result in acute ; Smoke comes from the burning health hazards. This is especial- | of organic material and its par ly true of dusts containing a hign ticle size is usually less than one- Percentage of free silica, asbestos, half micron. or other toxic materials. Where Mists and Fogs result from the health considerations are involv condensation of water vapor on ed in such exposures, legal aspects suitable nuclei, and the particle Present themselves. In most states size will vary with given con where occupational diseases are ditions. compensable, specific coverage is given to those disabilities result General Properties ing from the inhalation of silica dust. As a substance is reduced in particle size, there are certain Definitions general properties of the material which are changed. On breaking Aiany times true dusts are con up a solid into finely divided par fused with fumes, smokes, mists, ticles, the surface area is greatly ad fogs. In order to differen enlarged and therefore the space occupied is greatly increased. As an example, a piece of quartz one centimeter on each side when crushed to where the particles of one micron in size will present a system containing 10" number of particles. The total surface area will be 6 square meters. If these dust particles are dispersed onto the atmosphere in such manner that the concentration will be 100 million particles per cubic foot, the space occupied by this dis persed system will be 10 thousand cubic feet. The chemical activity of a solid is considerably increased by a reduction in particle size. Thus the rate of oxidation is increased as is evidenced by occasional dis astrous dust explosions. The phe nomena of adsorption becomes more important as gases are more easily adsorbed on the surface of the smaller particle. From the standpoint of health hazards resulting from dust ex posures, the physiological proper ties of dust vary somewhat with the particle size. It is an accepted fact that with exposures to silica dust, the smaller the particle size, the greater the "hazard. Physiological Response Drinker has summarized the re actions resulting from the inhala- SOUTHERN POWER & INDUSTRY fo'r NOVEMBER, 1944 A 41 tion of dust by classifying the re sponse into four groups. These are: (a) Pneumoconiosis--The dusts producing this type reaction are harmful only when inhaled. The principal materials producing this type reaction are free silica and asbestos dust. On inhalation, these two materials produce specific lung pathology and from the standpoint of disability, present the most important of the dust ex posures. (b) Toxic Reaction--(As poison ing by lead, cadmium or radium) These materials produce harmful effects when taken into the body both by inhalation and ingestion. With reference to lead and its compounds which may be present in the atmosphere as particulate matter, it has been fairly well established that entrance into the body Dy inhalation is more im portant mode of entry than the same material taken by mouth. This is primarily due to the fact that when such materials are tak en into the body by inhalation, the major portion is taken into the blood stream, whereas, a consider able part of that taken by mouth is removed by certain organs of the body. (c) Metal Fume Fever*--These conditions result from the inhala tion of finely divided fume par ticles. The importance of metal fume fever has been brought to the attention of industry by the great amount of welding which has been an important industrial tool for the past few years. Where burning or welding is done on sur faces which have been galvanized, the problem of metal fumes be comes immediately important. FIS. 2. THE ELECTROSTATIC PRECIPITATOR AS USED FOR COLLECTINO ATMOS PHERIC SAMPLES OF OUST AND FUMES. INSERT SHOWS RATE OF SETTLINS OF OUST. inis is aiso a promem m where the pouring done. (d) Allorgy--This type is in general produced by and certain organic dusts, 1-'3r Common Industrial Dusts Carbonates are usually combin ed with either calcium or mag nesium. They normally occur in nature as calcite and magnasite or as dolomite, which contains both magnesium and calcium as the carbonate. Limestone and marble contain considerable amounts of these carbonates, as do the materials from which ce ment is made. Due to the solubility in body fluids, these materials are remov ed when taken into the body by inhalation. The presence of car bon dioxide in such fluids is an important factor influencing their solubility. The same thing applies to the presence of carbon dioxide in water which comes into contact with these materials. In the pres ence of carbon dioxide the car bonate is converted to the more soluble bicarbonate, thus adding to the ease with which it is remov ed by solution. Experimental and practical ob servations on carbonate dust in dicate that these materials are not harmful when taken into the body by inhalation. This is probably due to the fact that they are easi ly removed due to their solubility. Sulfates are common industrial materials and this general class may be illustrated by gypsum, which is calcium sulfate. This is a common material and is widely used in many industrial opera tions. It is generally considered that this type material is non-tox ic and does not present any par ticular problem from a health standpoint. Oxides vary considerably . in their physiological reaction. In general the nature of the reaction will be dependent on the type metal from which the oxide is de rived. Where such metals are specifically toxic, as would be the case with arsenic or lead, a spe cific toxic reaction could be ex pected from the inhalation of the oxide. However, other oxides ap pear to be relatively harmless, particularly where the metal is of a non-specific type. This is true of iron oxide. The mining of iron results in the exposure of a great number of men to the oxides of 62 SOUTHERN POWER & INDUSTRY for NOVEMBER, I94i