Document XRyZbxGv1RzQVE1Vm6pYOZMb4

t lections from the inhalation of bac teria and fungi exists in several in dustries. Pulmonary anthrax from the inhalation of dust containing an thrax spores has occurred among em ployees engaged in the handling of woo! and the crushing of bones from infected animals. 105. Fungi (molds) growing on grain has been found in the sputum of workmen shoveling the grain and are believed to be the cause of out breaks of respiratory disorders. Fungi found in.sugar cane residues '(bagasse) are believed to be part of the cause of hasuysous. Fungal spores formed under the bark of sonic trees have been blamed for respiratory dillicuhics among em ployees who debark dry logs. 106.. Although the incidence of iKcuputionjIly related bacterial and fungal infections is found to be relatively low, the respiratory effects can he. troublesome and. in the case of pulmonary anthrax, even fatal.' The basic methods of control are the' same as those`for the pneumoconio sis producing dusts, hut sterilization and disinfection must he raided. Radioactive Dusts *. 107. A radioactive contaminant may offer a chemical toxicity hazard in addition to an ionizing radiation exposure, and it may be present as a g.is. dust. fume, or mist. ION.. Radioactive contaminants taken into the body may be deposited in xarious organs where they consti tute sources of interna) radiation. Ihe chemical characteristics of ihc_ radioactive-contaminant or isotope determine the organ in which it will he deposited. The excretion rate is also dependent upon the chemical nature of the isotope, because the radioactive isotopes of an element follow the same metabolic process as do the stable isotopes of that ele ment. 109. If a radioisotope has been deposited in the body, the internal exposure is regarded as continuous until the isotope is lost by radiologi cal or biological decay. In some eases, exposures may last a lifetime. Tor u JctailcJ dbcussion of radio* .iviis > and an oMcn-ive bibliography, w the chapter entitled "loni/mp Kadia* lion" in the .ti <./i tu f'r> vi iiiii>it Mtiitiml r luJii\rriol fJ.'VMfi.nn, puhti'hcd by the National Safely Council. 110. Since'radioisotopes are se lectively taken up in individual or gans. they may cause only localized irradiation; The radiosensitivity of the organ dictates the extent of the hazard of a particular radioactive substance. Solubility and particle size determine how much of the ac tive material will gain access to and remain in the blood stream and var ious organs. ' 111. If radioactive air-borne con tamination is known to be present, control measures arc mandatory. If the presence of contamination is un known but suspected, sampling must be done to determine whether or not air-borne concentrations of the ra dioisotope arc below the threshold limit value. 112. Good -personal hygiene and good operating techniques arc much more important in the handling of radioactive materials than in the han dling of most other materials used in industry. 113. Engineering controls for radioactive dusts are similar to those for other Justs and.depend primarily, upon capture at the point of genera tion. The difference lies in (he fact that controls.for radioactive dusts must be extremely efficient. Thresh old limit values for radioactive par ticulate matter are very low. and in some cases 100 per cent efficiency in ' capture and * retention is required. Permissible Dustiness 114. Threshold limit values of mineral dusts and toxic dusts--that is. time-weighted average concentra tions considered permissible for ex posures of eight hours per day, five days per week--have been pub lished by the American Conference of Governmental Industrial Hygien ists. These values have been obtained from the experience of many groups in industry and from laboratory studies on animals. They are re viewed annually and changed as nec essary on the basis of experience. 115. These values are set only as guides for the best practice and are not to be considered absolute values. There is reasonable assur ance that occupational'disease will not occur if exposures are kept be low these levels. On the other hand, occupational disease is likely to de velop in some people if the recom mended levels are exceeded consis tently. 116. The currently recommended threshold limits of particular dusts can be found in the most recently published ACGIH list,or the ACGIH can be consulted, directly. Information on threshold'limits also can be obtained from (he National Safety Council, state occupational health ageheies, the American Indus-' ' trial Hygiene Association, and com pensation insurance carriers. II?. No one' knows the exact concAtralion at which men will start to develop silicosis, asbcsiosis. or lead poisoning. With some toxic. dusts, however, experience hai been wide enough to establish the present threshold limits as fairly reliable. 118. For example, if the level of lead in a workroom is kept below 0.2 mg/cu m. experience has shown that Cases of'lcid intoxication will not occur. Experience also has shown ihgt many men can tolerate lead levels well above 0.2 mg/ ` cu m without signs of trouble. M}nerol dusts 119. In the United States, the threshold Hmits for mineral dusts are expressed in millions of par ticles per cubic foot of air fmppcf). The concentration of a mineral dust is determined by counting dust par- tides that are less tytan 10 miefons in size in an aliquot sample after sampling a known volume of air in a known volume of liquid. In some European countries, mineral dusts are weighed, and permissible levels are expressed as milligrams of dusl per cubic meter of air (mg/ cu m). in England and some other areas, the number of particles per cubic centimeter is the current basis of measurement. 120. In comparing United States and foreign dust counts, it is helpful to keep in mind`that 100 particles 1 per cubic centimeter ts equivalent to approximately 3 million particles per cubic foot. 121. It is difficult to compare dust counts with results obtained on the basis of weight. However, with either type of measurement, a thresh old limit can be set as an objcc- . tivc. Experience has shown that maintaining dust levels below the recommended threshold limits has resulted in a great decrease in the incidence of occupational diseases. 122. Threshold, limits are based on the percentage of free silica where this .substance is the impor- 100 National Softly Ntwi, Zona 1963 . }ii i I . -tant constituent of the dust. If sili cosis is to be prevented, these limits must not be exceeded. Concentra tions of dusts containing less than 5 per cent free silica should not exceed 50 million particles per cubic foot (mppcf). Concentrations of dusts containing from 5 per cent to SO 'per cent free silica should not exceed 20 mppcf. Dusts containing more than 50 per cent Tree silica should be kept at concentrations below 5 mppcf. 123. As" more experience accu mulates, original threshold limits sometimes can be modified. In some cases, it has been necessary to lower the limits, for the objective is to ^ protect the more susceptible, indi viduals.. In a few cases, experience has shown that the limits were too stringent* and it has been possible to raise the limits to allow for more reasonable controls. Toxic dusts 124. In alt countries, threshold limits for toxic dusts arc expressed in milligrams per cubic meter of ' air. With toxic dusts, the average levels must be kept below the sug gested threshold limits. In'fact, it is advisable to keep the levels of toxic dusts as .lew os practical in the specific circumstances. Little in the way of experience or data will be developed if the levels arc kept unusually tow, but few if any cases . of occupational disease will occur from these dusts. . Nuisance dusts .1 125. Even though a dust may be considered generally innocuous and not be recognized as (he direct cause of a serious pathological condition, its level should be kept as low as is practical. Dust levels well below the suggested' threshold limits arc desirable. 126. A concentration of 50 ' mppcf ts suggested as the threshold limit for a number of nuisance dusts. With good engineering prac tice, there is .no need for this level to be exceeded. Any reduction be low this level will increase the com fort of employees and improve plant housekeeping. Methods of'Control 127. Various methods of con trolling dusts, mists, and fumes arc available.- Basic engineering dictates - where possible an operation should Ftgvta 3. loch of lfia grinding vhtah it partially anctatad by an txhawtt hood. (Ntctant local rfcawif It od>ir*od by drawing tKa dvtf into lha fcoodi, throvgb brandi dwell, and iota a antral duct irhid* loedi to tfca collection palm. (Cowrtcty Atrcocon Poundrynon'i Sadaty) be made dusttess through control at the source. This method is always the most effective.' for it either com pletely prevents the contaminant from entering the workroom atmos phere or limits to safe levels the amounts that' do escape. In addi tion. this method, is generally the least expensive. 128. When control at the source is not possible, other methods may have to be considered. Any one or a combination of the fallowing types of dust control may bo needed to limit the exposure. I a. The dusty operation may be en closed. with or without a local exhaust system. An inclosed op eration generating large quantities of dust usually needs to be ex hausted. or the dust will leak into the surrounding atmosphere. Ex amples arc sandblast cahincts or sandblast rooms and the dry boxes - used to handle radioactive materials. b. The dusty work may be performed In a separate building or may be isolated by partitions to reduce the number of employee exposed to the dust. The employees who are still being exposed should be pro tected by respiratory. protective equipment. c. A less hazardous material may be substituted. For instance, steel shot may be used instead of silica sand in abrasive cleaning. d. Keeping the'materials moist may be a practical means of control. Examples are the careful and prop er wetting down of aisles in a foundry and the use of water in . drilling. e. Local exhaust systems- may be in stalled with virtually full or partial enclosure. Examples arc an ex haust hood on a grinding wheel (Figure 3) and an exhaust hood at a bagging or filling operation. f. General room ventilation can be used to dilute the dust by adding large quantities of air and thus preventing build-up of dust con centrations. Examples of this meth od arc roof fans and roof moni tor windows. But it generally is inefficient and expensive to attempt to control contaminants by dilu tion. g. The dusty work may be performed at. night or on week-ends to reduce the number of employees exposed. Cleaning dust accumulations from overhead beams, for instance, is . preferably done during a weekend: The employees who arc exposed should wear appropriate type of respiratory protective equipment. h. The number of working hours at the particular exposure can be re duced. However, other methods-of control arc preferable. i. Use of respiratory protective equip ment approved for the exposure by the U.S. Bureau of Mines can give excellent protection against all types of dust, but in most cases should be considered as a tem porary control measure. In a sandblast room, however, air-sup- plied helmets usually arc required continuously during operations. Respiratory protective equipment, Notienol Safety Newt, June 1943 101 I | . i '.I i 3