Document 0ne3OLKBGOzVx085Moka9p9O

Fundamentals of Industrial Hygiene Fundamentals of Industrial Hygiene i' * UCC 022488 ATIQNAL ENVIRONMENT lware that flammable liquids are irticular care. Posters and signs effectively. No Smokinc signs ings and areas where smoking is nmable liquids. CHAPTER Pneumoconiosis-Producing Dusts by Fred Cook, M.S. Pneumoconiosis is a tongue-twisting term of Greek derivation, meaning "lung" and "dust." As such, it may be applied to everyone because all the air we breathe contains some dust, and some dust is retained in every person's lungs. More specifically, pneumoconiosis is taken to mean a fibrous hardening of the lungs caused by the irritation created from the inhalation of dust. All dust, smoke, fumes, vapors, and gases cause some irritation; and some fibrosis is present in every lung. With this in mind then, the lungs of older people might reasonably be expected to exhibit a greater degree of fibrosis due to these causes than the lungs of youngsters. This is frequently the case. It follows that increased exposure to dust of any kind will increase the amount of pneumoconiosis in any individual's lungs; and it is also true that at some point, pneumoconiosis reduces the lungs' efficiency. One of the first symptoms of its presence is shortness of breath. Unfortunately shortness of breath is also a symptom of aging (which may be accentuated by many causes), and a simple diagnosis of pneu moconiosis does not in itself mean that shortness of breath or any other symptoms must be ascribed to this cause. One of the pneumoconioses that involves additional specific lung changes and is often associated with disability is silicosis. Silicosis may also be present to a degree without producing symptoms or inconvenience. This disease is caused by the inhalation of finely divided free silica dust. 95 UCC 022489 3-PNEUMOCONIOSIS-PRODUCING DUSTS Free silica is the term commonly applied to crystallized silicon dioxide (Si02), which most commonly occurs as sand, but is also widely distrib uted in hard rocks and minerals. The percentage of crystalline SiOa in a mineral dust mixture is the usual basis for evaluating the hazards asso ciated with the breathing of the mixture. See Table 3-A. TABLE 3-A CRYSTALLINE SIO, IN VARIOUS MATERIALS Material Normal Range Crystalline SiOt~% Foundry molding sand Pottery ware body Brick and tile compositions Buffing wheel dressings Road rock Limestone (agricultural) Feldspar Clay Mica Talc Slate and shale 50-90 15-25 10-35 0-60 0-80 0-3 12-25 0-40 0-10 0-5 5-15 Another kind of pneumoconiosis, involving specific lung changes, is called asbestosis caused by the inhalation of asbestos dust. There are several other lung diseases caused by specific mineral dusts, but they occur rarely because exposure to the offending dust is uncom mon. Long exposure to very high concentrations of mineral dusts that do not produce specific lung changes can still be expected to result in some degree of pneumoconiosis even though symptoms may not be noticed. Those responsible for the protection of the health and safety of work men employed in the dusty trades must first find a means of evaluating the dust exposures, and must then apply the best available control measures to keep exposures within acceptable recommended safe limits. The solution of each of these parts of the problem frequently requires the assistance of specialists. To evaluate the exposures, it is first necessary to determine the compo sition of the dust that remains suspended in the air workmen breathe. Operations that involve crushing, grinding, or polishing of minerals or 96 UCC 022490 died to crystallized silicon dioxide as sand, but is also widely distribpercentage of crystalline Si02 in a s for evaluating the hazards assoe. See Table 3-A. 3-A ABIOUS MATERIALS iNormal Range Crystalline SiO,-- 1} tions > ) 50-90 15-25 10-35 0-60 o-ao 0-3 12-25 0-40 0-10 0-5 5-15 ivolving specific lung changes, is m of asbestos dust, ; caused by specific mineral dusts, S to the offending dust is uncomlcentrations of mineral dusts that can still be expected to result in though symptoms may not be of the health and safety of workft first find a means of evaluating ipply the best available control eptable recommended safe limits, the problem frequently requires ecessary to determine the compo;d in the air workmen breathe, nding, or polishing of minerals or mineral mixtures frequently do not produce air-borne dusts of the same composition as that of the material being fabricated. We are usually primarily concerned with the percentage of crystalline Si02 that is suspended with other dusts in the air. In many mineral' mixtures, the crystalline Si02 is harder than the balance of the mixture, and most crushing and grinding operations produce air-borne dust with a lower percentage of crystalline Si02 than is found in the original mineral mixture. Occasionally, when the grind ing operation involves a great deal of impact force, the situation is reversed. In pulverized materials, the crystalline Si02 is frequently found in larger particle size than the softer components; and when this is the case, the handling of pulverized materials may also produce a higher percent age of the softer components in the air-borne dust which is produced by handling methods, These factors make it necessary to actually obtain a sample of air borne dust, and to analyze this sample if the composition is to be used in evaluating the hazard associated with breathing the dust. The extremely small size of the dust--zero to 5 microns--makes chemi cal methods of analysis, which depend upon the differential solubility of the various components, too unreliable to be used alone. Petrographic analysis (using a polarized microscope) and X-ray diffraction analyses techniques are usually preferred. These require equipment and proce dures not commonly found in chemical laboratories. Table 3-A indicates the normal range of crystalline Si02 found by analysis of many minerals and industrial compositions. Measurement The measurement of air-bome dust concentrations involves a technique which admittedly does not collect all of the dust in the air. In this country, evaluation of the harmful effects of dust has been made on the basis of those dust particles collected by impingement; and when relating harmful dust concentration to values so obtained, this technique must be used. The safety professional commonly measures the size of air-borne dust particles in units known as microns (Figure 3-1). (A micron is one thousandth of a millimeter or approximately one twenty-five thousandth of an inch.) The standard technique used to evaluate dust concentra tions does not collect or count dust particles much smaller than one micron, and it can readily be shown from settling formulas that dust 97 UCC 022491 3-PNEUMOCONIOSIS-PRODUCING DUSTS exposure. So that an exposure can be properly evaluated, the percent age of uncombined silica must be determined by petrographic analysis using a polarizing microscope or, preferably, by X-ray diffraction ana lyses and special analytical chemical procedures. With the exception of asbestos and some talcs, the silicate dusts do not ordinarily cause a serious disabling lung condition such as is produced by free silica. Much higher levels of silicate dusts can be tolerated. In many industries, men have worked with silicate dusts that con tained no free silica without development of disability or of nodulation in the lungs. The X ray may show shadows indicating dust deposits in the lungs, but the pneumoconiosis is essentially harmless. Disabling pneumoconioses from exposure to abnormally high concen trations of mica, tremolite talc, and kaolin dusts have been described in the literature. The clinical signs are not the same for these silicate dusts as for free silica. The body does not have adequate defense against indiscriminate amounts of dust of any kind. Therefore, although specific symptoms have not been described for many mineral dusts, the general experience would indicate that dust levels should be kept below the threshold limit values shown in Table 3--C. Asbestosis Asbestos is a general term applied to several minerals having a fibious character. These asbestos minerals are hydrated s-ilicates of magnesium with variable amounts of iron, calcium, sodium, potassium, and alumi num present as impurities. Asbestos when inhaled produces fibrous tissue in the lungs of both men and animals. It has been shown that fibers of asbestos must be present for the production of asbestosis. Other silicate minerals of the same chemical composition but nonfibrous in form produce no reaction or a relatively mild reaction, but not the severe reaction of fibrous asbestos dust. These facts lead to the conclusion that asbestosis is mainly the result of physical irritation of the lung tissue and not of a chemical action, which is thought to be one of the causes of silicosis. It is suspected that lung cancer may be induced by asbestos. Anthracosilicosis Anthmcosilicosis, a complex form of pneumoconiosis, is a chronic disease caused by breathing air containing dust that has free silica as one (Text continues on page 116.) 112 E li5 rc o O4* P CM 55 eS OtU cHcoo 3 Q <cc zw 22 m< -j cc I<5- CZ!--O3 O D. LU o _LUI Utoi 'S js s & 5:2 e -a -~S-3 cs-us i- UJ w LU > CC O u. o UJ .E S5*i >o COC .E. o' o> a3) cr 01 c 1- 1 20 ei -o --E foc --co .--5gs --c s- o C2TJ c gec i oo x: --: O jfl qj 03 05 Is H to <u Q> > O to ~ CO xC;D Ofc* o < T3 .52 E < jz2ntj c>, oouo '3a o o UCC 022492 9 _oj a E tn + O to OJ C>> a. O Oeg UCC 022493 UCC 022494 RING, AND PROTECTION `.t'l * * ` capillary _ i * V ;ph of a portion of the shows the anatomy of where gases pass to Anat. Record, 17:241. learly quiescent (because the rosols will be deposited, Thef| lese aerosols act almost n, unlike the mucous lining b tfie airways, but which serves the same cleansing function. This fluid Hows upward in the sacs, toward the bronchioles, apparently by capillary action, and will carry with it deposited particles or dissolved particles and gases. Aerosols that are not removed from the alveoli in this manner may fall prey to the mobile phagocyte cells, which are the type of white blood cells capable of ingesting particles. These cells, once laden with foreign matter, may: (a) migrate to the small bronchioles, where the mucous lining carries them out of the system; (b) pass through the alveolar membrane into the lymph vessels associated with the blood capillaries, or (c) be destroyed (if the contaminant is cytotoxic) and break up, re leasing the particles into the alveolar sac. If the aerosol is not removed by these means, it may form a deposit in the sac. Such deposits may or may not acutely effect lung health. All of the defense mechanisms discussed are subject to some deteriora tion and slowing down with age or ill health. So an older worker's lungs will not cleanse themselves as quickly or efficiently as those of a younger person. Also, some contaminants may impede the defense mechanisms themselves, increasing the rate of retention of the contaminant in the lungs. Hazards Now, let's look at some of the unhealthy conditions to which the lung is subject, associated terminology, and some typical hazardous substances. The membrane lining in the nasal passages can be affected by a number of causes. The resultant condition is called rhinitis. Inflamma tion in the larynx is called laryngitis, that of the bronchial tubes, bron chitis. Constriction of the tube muscles, in response to irritation, allergy, or other stimulus is called asthma. In the lung sacs, a number of conditions can develop: Pneumonitis--produced by an outpouring of fluid in the lungs in response to irritation. This fluid production is analagous to the protec tive mechanism of a blister in response to a burn. Pneumonia is the same condition, but involving greater quantities of fluid. Emphysema--in which the walls of the individual grapes (alveoli) rapture or dilate. The wall of the resulting larger sac has lost its naturally elastic recoil, and so does not exaust air as efficiently, and does not offer the large area for gas transfer afforded by the several smaller sacs. This condition is on a tremendous increase today, 605 UCC 022495 17--LUNGS: ANATOMY, HAZARDS, MONITORING, AND PROTECTION Pleurisy is caused when the outer lung lining (the visceral pleura) andi the chest cavity's inner lining (the parietal pleura) lose their lubricating properties. The resultant friction causes irritation and pain. Lung cancer. No doubt exists that certain aerosols predispose the lungs.1 to cancer. This disease, like emphysema, is on the increase. ' Pneumoconiosis (dusty lung). This is a catchall word for various pulmonary manifestations of dust inhalation, whether the dust is harmful or not. Two common forms of pneumoconiosis are silicosis and ashestosis. The typical pathological condition in harmful pneumoconiosis is the existence of fibrotic (stringy) tissue in the alveolar sacs, at the "Y* branches in the small bronchi leading to the alveolar sacs, or at lymph: nodes in the lungs. This fibrotic tissue, caused by some dust particles,, reduces the efficiency of the lungs by making them less resilient, and by" reducing the effective working surface for gaseous exchange. A simple benign pneumoconiosis with little disturbance of pulmonary function1 can also predispose to such diseases as pneumonia and tuberculosis. -: Contaminant effects Inhaled contaminants that adversely affect the lungs fall into three = general categories: Aerosols, which, when deposited in the lungs, may produce either' tissue damage, tissue reaction, disease, or physical plugging. .. Toxic gases that produce adverse reaction in the tissue of the lungs , themselves. ` Toxic aerosols or gases that do not affect the lung tissue, but are passed : from the lung into the blood stream, where they are carried to other . body organs, or have adverse effects on the oxygen-carrying capacity of the bloodstream itself. (See Chapter 11, "Toxicology.") - An example of the first tvpe is asbestos fiber, which causes fibrotic growth in the alveolar tissue, plugging the ducts or limiting the effective, area of the alveolar lining. Other harmful aerosols are certain fungi found in sugar cane residues, producing bagassosis. Hydrogen fluoride is a gas that directly affects lung tissue. It is a ' primary irritant of mucous membranes, causing chemical burns. ' Inhalation of this gas will cause pulmonary edema, and direct interfer ence with the gas transfer function of the alveoli lining. UCC 022496 MONITORING, AND PROTECTION ir lung lining (the visceral pleura) and; : parietal pleura) lose their lubricating causes irritation and pain. J lat certain aerosols predispose the lungs * ysema, is on the increase. This is a catchall word for various nhalation, whether the dust is harmfulneumoconiosis are silicosis and ashes-mdition in harmful pneumoconiosis is /I tissue in the alveolar sacs, at the "Y"2| ling to the alveolar sacs, or at lymph tissue, caused by some dust particles,, by making them less resilient, and by/ face for gaseous exchange. A simple disturbance of pulmonary function ( as pneumonia and tuberculosis. rsely affect the lungs fall into three =' 1 in the lungs, may produce either se, or physical plugging. ' reaction in the tissue of the lungs affect the lung tissue, but are passed m, where they are carried to other > on the oxygen-carrying capacity of ir 11, "Toxicology.") (sbestos fiber, which causes fibrotic ^v.- ag the ducts or limiting the effective harmful aerosols are certain fungi -a ing bagassosis. 1 iirectly. affects lung tissue. It is a ibranes, causing chemical burns, monary edema, and direct interfer- the alveoli lining. Typical of the lung's role in passing toxic gases into the blood stream, without itself being harmed, is the case of carbon monoxide. The CO passes through the alveolar walls into the blood, where it ties up red corpuscles so they can't accept oxygen, thus causing oxygen starvation. Cyanide gas has another effect--it prevents the utilization of molecular oxygen by cells. Sometimes several types of lung hazards occur simultaneously. In mining operations, for instance, explosives release oxides of nitrogen. These impair the bronchial clearance mechanism, so that coal dust associated with the explosions is not efficiently cleansed from the lungs. Aerosol deposition In the case of gases, the concentration that reaches the alveolar sacs will be nearly the same as the concentration in the air breathed. With aerosols, this is not the case. Large particles, more than 10 microns, will be deposited long before they reach the sacs, through gravity and impaction. Only the smaller particles will reach the alveoli. In the sacs, Brownian movement of the particles results in deposition by diffusion. Since the very small aerosol particles are the only ones that are likely to reach the alveoli in great quantities, and since the alveoli are the most important area in the lungs, it is clear that the minute aerosols are potentially more harmful than larger aerosols. (This fact points up the fallacy of using a coarse filter mask for dangerous aerosols: it will pass the very particles that are most hazardous.) Monitoring respiratory hazards There are a number of reasons for carrying out sampling procedures: In emergency situations, for instance where someone has already fainted. The handicap here is that the event is passed, and sampling will only give an estimate of what contamination levels prevailed. Areas where emergencies are ready to happen. An example is tank entry. It is assumed a hazard exists, and monitoring is carried out to verify the assumption and to define the hazard accurately. Sampling for chronic exposures. Sampling to investigate complaints. Monitoring for compliance with regulations. 607 UCC 022497 3NIT0RING, AND PROTECTION Fig, l7-4.~Examples of,4 emergency and nonemcrgency respirators. The air,-' line respirator (top) has aux iliary air supply to allow es-',Lcape in case the line should rifi break. The cartridge respi- ;&a r&tor (below) is not for vse^im~in atmospheres immediately , hazardous to life, blit rather^ as a defense against pro-'ij'longed exposures to low gasliig and vapor concentrations and t| harmful aerosols. egative pressure in the facepiece fitted masks, inward contaminant , tis, pressure-demand breathing has he facepiece exhalation valve and a slight, positive pressure in the liable with ratings up to two hours 7j||| on to be available. The closed-cirive training than the open-circuit 1) personnel spend 30 hours train- V ing with such apparatus before they are qualified. Usually, the only limitation of self-contained breathing apparatus is the possibility of poisoning by skin absorption. The gas mask operates with a negative pressure upon inhalation, and therefore the mask should be carefully fitted and the wearer should be alert for symptoms of leakage. Both multipurpose (formerly designated "universal") and special-purpose canisters are available. The USBM recommends that where possible canisters designed to re move specific gases or vapors be used. Because gas masks cannot be used in oxygen-deficient atmospheres or in high concentrations of gases and vapors, they are being replaced in many cases by self-contained breathing apparatus and the third type described next. The hose mask with blower. The latter type incorporates a hand-oper ated or motor-driven blower, and the wearer may use up to 300 feet of large-diameter, wire-wrapped, oilproof hose. If the blower fails, the wearer can breathe through the large hose alone with no more resistance than is encountered in a gas mask. It is important that a safety profes sional be standing by the blower to make sure that only respirable air is supplied at the intake. Air line respirator with auxiliary self-contained cylinder. Air line res pirators alone are not regarded as safe for use in immediately dangerous atmospheres. Should the air supply fail for any reason, the wearer cannot get air through the valves and small-diameter hose. But with the auxiliary air cylinder, the wearer can breathe supplemental air while making his exit from the hazardous atmosphere. Nonemergency respirators Respiratory protective devices intended only for use in nonemergency situations should ideally be used only as temporary measures while engineering controls for contaminants are being installed. They are, however, widely used in industry as a primary line of defense against inhalation hazards (Figure IT--4). A supplied-air respirator, the air line respirator with continuous flow, is particularly suitable, when equipped with helmets or hoods, for lead grinding or abrasive blasting. Dispersoid respirators can be divided into three classes; those for use UCC 022498 17--LUNGS: ANATOMY, HAZARDS, MONITORING, AND PROTECTION as protection against (a) pneumoconiosis-producing dusts and mistSI? (such as silica and asbestos); (b) toxic dusts, metallic fumes, and mistsj not significantly more toxic than lead (zinc dust, lead fume, and chromic! acid mist are examples); and (c) radionuclides and highly toxic dusts'T fumes, and mists--significantly more toxic than lead (such as all radio * nuclides and beryllium). , This third classification is subdivided into three groups, with a differ/**/ ent type of dispersoid respirator for each: half-mask respirators are^^t* suggested for use in contaminant concentrations up to 10 times the-/- " threshold limit value, full facepieces up to 100 times the TLV, and/ positive-pressure dispersoid respirators up to 1000 times the TLV. `1 Nuisance dusts and mists are included with silica and asbestos in the first class (a), above. U.S, Bureau of Mines approved respirators should,'." be used even for nuisance materials such as coal, sawdust, and flour// since no one can foretell the possible effects of breathing such materials) ' and the legal complications that may arise from unapproved nuisance- dust respirators may be more costly and troublesome than the use of the _ approved respirator. ' 1 Chemical-cartridge respirators are designed for use in low concentra-/- tions of gases or vapors and are also frequently equipped with filters for / 41 protection against dusts and mists, during paint spraying. Employee training ' As is true with all protective equipment, respiratory protective devices will be effective only when acceptable to the worker. The best way to achieve acceptance is to explain exactly why the respirator needs to be worn, and what might happen if the respirator were not worn. Where nonemergency respirators are used, the wearer should be al- : lowed to try on several styles from various manufacturers to choose the : one best suited to him. In addition to convincing a worker of the need for wearing a respirator,: r and providing him with a comfortable model, he must be trained to wear ;v it correctly. Such training may vary from showing the user how to check the facepiece fit of a small dust respirator, to training sessions of several , hours for the more complicated self-contained apparatus. During initial training, special emphasis should be placed upon face piece fit. Several simple tests will disclose improper fit. The exhalation valve can be closed and the wearer exhales (a slight positive pressure should build up in the facepiece without leakage of air at the seal). Or 616 " UCC 022499 MONITORING, AND PROTECTION noconio.sis-produciag dusts and mists : ' toxic dusts, metallic fumes, and mists ; "ad (zinc dust, lead fume, and chromic } radionuclides and highly toxic dusts, ore toxic than lead (such as all radio- vided into three groups, with a differ-. for each; half-mask respirators are t concentrations up to 10 times the ;ccs up to 100 times the TLV, and tors up to 1000 times the TLV. rluded with silica and asbestos in tire of Mines approved respirators should ds such as coal, sawdust, and flour, le effects of breathing such materials, ; iay arise from unapproved nuisance-? and troublesome than the use of the e designed for use in low concentra' frequently equipped with filters for during paint spraying. ^yy r ,r^-* .; >ment, respiratory protective devices ile to the worker. The best way to ctly why the respirator needs to be espirator were not worn. are used, the wearer should be alarious manufacturers to choose the of the need for wearing a respirator, model, he must be trained to wear rom showing the user how to check ator, to training sessions of several ntained apparatus, hasis should be placed upon faceclose improper fit. The exhalation ;xhales (a slight positive pressure, >ut leakage of air at the seal). Or ^ '.?;( T. : 1^ the filter or cartridge inlets or the breathing tubes are closed off and the wearer inhales (the facepiece should collapse and remain collapsed for a few seconds). These initial procedures can be carried a step further by allowing the wearer to check the fit he has obtained in an odorous but harmless atmosphere, such as that created by isoamyl acetate. Maintenance The U.S. Bureau of Mines recommended procedures for cleaning and disinfecting respirators include new disinfectants replacing such materi als as formalin and alcohol. After disassembling the respirator, clean and disinfect facepiece and breathing tube in warm (120 F) cleaner-dis infectant solution. This may be prepared from quaternary-ammonium, detergent, and alkaline-salt compounds that are available from respirator manufacturers and other sources. Rinse thoroughly in warm water since the wearer may be allergic to quaternary-ammonium compounds. Or clean facepiece and breathing tube in a warm (120 F) liquid detergent solution, rinse in warm water, then immerse for 2 minutes in one of the following: (a) hypochlorite solution (50 ppm chlorine) prepared by diluting concentrated hypochlorite solution (5 per cent chlorine) with water; (b) aqueous iodine solution (50 ppm iodine) prepared by dis solving soluble iodine compound in water. 'Note: 50 ppm is equivalent to 0.005 per cent. Chlorine and iodine solutions stronger than 50 ppm maij damage rubber parts. Air dry in a clean place. Clean and inspect other respirator parts according to manufacturer's instructions. Reassemble respirator and store in a clean, dry place. 617 UCC 022500 CES th, haii- and nails where arsenic mav.'l nd detected about two weeks after"; >re beginning of exposure and where.3 't- persists for months and sometimes! in years after the exposure is terminate an Inhaled arsenic is excreted to a: id siderable extent through the kidnei id and can be detected in the urinljj ir. within a few hours of the start of.1 i- exposure and for a long time after.ljj te The compound BAL (2,3-dime r. capto-1-propanol) was developed"^ h an antidote for arsenical gas poisos it ing. It is effective in prevention's a poisoning from otherwise harmful doses of the arsenic compound^ general, and in the treatment of < - ing eases of poisoning, although ica 3 have been reported in which BAL twij ; not effective. . Arsine (arsenic hydride). Sev&i and acute industrial poisonings "will arsenic are likely to be the result inhalation of arsine, often produc accidentally when hydrogen is ge ated in the presence of a mated which contains arsenic. The gas been reported in the acid cleaning1^ filter plates, in the handling of dross from a light metals plant, in 1 cleaning of tank cars which have he sulfuric and hydrochloric acids, in I cleaning of pipes with an acid taminated with arsenic, in the preciplj tation of cadmium with metallic 5an< and in other operations. Arsine gas causes a characterisfc syndrome of massive hemolysis:Iei3 ing to renal failure, ft is associate with nausea, vomiting, diarrh change in skin color, disturbance^] vascular tone, electrocardiograph*! ibnormalitv, and liver disfunction. If the patient survives long enough, manifestations of chronic arsenic poi soning may appear. After exposure, i latent period of 1 to 36 hours may ,'iisue. Inhalation of 250 ppm is instantly lethal. Exposures of 25-50 ppm for half an hour are lethal and 10 ppm are lethal after longer expo sure, The mean lethal dose (LDs.) is unknown in man, but in small mammals is about 0.5 mg/kg. Arsine gas can be fixed by tissues other than blood. It binds to the kidneys and liver and inhibits respiration of slices of these tissues in vitro. In low conlentration exposures, clearance of arsine from plasma, where it dissolves into the erythrocyte, is rapid and ef ficient. When high concentrations of arsine gas are suddenly dissolved in plasma, in large acute exposures, the amount of circulating arsine may exceed the binding capacity of the erythrocytes, and the gas may dam age vital organs directly. This would explain death due to arsine poisoning before hemolysis occurs. The possibility of arsine formation should alxvays be considered when there is freshly formed hydrogen around ores of the heavy metals, since arsenic is widely distributed in small amounts and only a trace of it is re quired to produce enough arsine to be troublesome. Asbestos is a hydrated magnesium silicate found in the minerals chryso lite, amosite, crocidolite, and tremolite. Practically all the commercial asbestos used in this country is chryso lite, It is used almost exclusively for heat insulation or for textiles which must resist high temperature, such as heat-resistant clothing and brake lin ings. Inhalation of excessive quantities of asbestos fiber can produce a fibrosis in the lungs similar to that found in silicosis but somewhat milder and usually not so rapidly progressive. Like silicosis, the condition develops and advances slowly and is equally resistant to treatment. There is also good evidence that inhaled asbestos causes lung cancer. Asphalt. Although asphalt itself is considered to be substantially non toxic, it may cause inflammation or dermatitis on contact in some individ uals. Careful supervision of worker's persona] cleanliness is essentia] in the prevention of dermatitis or other ill effects. Skin contact with the asphalt should be avoided--individuals work ing with asphalt should wear suitable protective equipment, including gog gles to protect the eyes. The effect of exposure to vapors from liquid or cutback asphalt depends on the par ticular solvent added to the asphalt. Steps should be taken to hold the solvent vapor concentration in the breathing zone below its threshold limit value. Where operations re quire heating or grinding asphalt in side a building, suitable ventilation should be provided, B Barium, in the form of its soluble salts, is toxic on both ingestion and inhalation and highly caustic when applied to the skin. The carbonate 751 UCC 022501 the various processes in mining and preparing anthracite (hard) coal and, to a lesser degree, bituminous coal. Anthracosis. A disease of the lungs caused by prolonged inhalation' of dust that contains particles of car bon and coal. :. Anthrax. A highly virulent bac terial infection picked up from in fected animals and animal products. A n tibio tic, A substance produced by a microorganism usually a mold or fungus, which in dilute solutions kills other organisms, or retards or completely represses their growth, ' normally without harm to higher or ders of life. - Antibody. Any of the body globu lins that combine specifically with1 antipens and neutralize toxins, ag glutinate bacteria or cells, and pro- cipitate soluble antigens. It is found naturally in the body or produced by the body in response to the intro- iuction into its tissues of a foreign iubstance. . <>' Antigen. A substance that, when ntroduced into the body, stimulates he production of an antibody. : Antimony. Gray metal often asociated with lead and arsenic. Hazirdous from inhalation and ingestion. Soluble salts may cause dermatitis. Antioxidant. A compound which etards deterioration by oxidation. : mtioxidants for human food and aninal feeds, sometimes referred to as reshness preservers, retard rancidity f fats and lessen loss of fat-soluble itamins (A, D, E, K). Antioxidants , Iso are added to rubber, motor luricants and other materials to inhibit eterioration. Anti-particle. A particle which iteracts with its counterpart of the ' same mass but opposite electric charge and magnetic properties (e.g., proton and anti-proton or neutron and anti-neutron), with complete an nihilation of both and production of an equivalent amount of radiation energy. The positron and its anti particle, the electron, annihilate each other upon interaction and produce gamma rays. Antiseptic. A substance that pre vents or inhibits the growth of micro organisms; a substance used to kill microorganisms on animate surfaces, such as skin. Aplastic anemia. A condition in which the bone marrow fails to pro duce an adequate number of red blood corpuscles. Approved. Tested and listed as satisfactory by an authority having jurisdiction, such as U.S. Department of the Interior, Bureau of Mines, or U.S. Department of Agriculture. Arc welding. One form of electri cal welding using either uncoated or coated rods. Aromatic, Applied to a group of hydrocarbons and their derivatives characterized by presence of the benzene nucleus (molecular ring structure). See also aliphatic. Arsenic, Silvery brittle crystalline metal. Hazardous from inhalation and ingestion. Usually encountered as arsenic trioxide. Artificial abrasive. Materials, such as carborundum or emery, sub stituted For natural abrasive such as sandstone. Artificial radioactivity. That pro duced by bombardment of a target element with nuclear particles. lodine-131 is an artificially produced radioactive substance. Asbestos. A hydrated magnesium silicate in fibrous form. The fibers are believed to be the more hazard ous component of asbestos dust. Asbestosis. A disease of the lungs caused by the inhalation of fine air borne fibers of asbestos. Asepsis. Glean and free of mtcroorganisms. Aspect ratio. In air distribution outlets, the ratio of the width of the core of a grille, face, or register to its length. Asphyxia. Suffocation from lack of oxygen. Chemical asphyxia is produced by a substance, such as carbon monoxide, that combines with hemoglobin to reduce the blood's ca pacity to transport oxygen. Simple asphyxia is the result of exposure to a substance, such as carbon dioxide, that displaces oxygen. Asthma. Constriction of the bron chia! tube muscles, in response to irritation, allergy, or other stimulus. Atmospheric pressure. The pres sure exerted by the weight of the atmosphere--about 14.7 pounds per square inch, which is equivalent to the pressure exerted by a column of mercury (Hg) 760 mm high. See absolute pressure and gage pressure. Atom. All materials are made of atoms. The elements, such as iron, lead and sulfur, differ from each other because they contain different atoms. The word "atom" comes from the Greek word meaning indi visible. Now we know it can be split and consists of an inner core (nwcleus) surrounded by electrons which rotate around the nucleus like the planets around the sun. As a chemi cal unit, it remains unchanged during any chemical reaction, yet may un- UCC 022502