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Respirators and Dust Controls THE ACHIEVEMENTS IN DUST-CONTROL AND DUSTPROOF MEASURES TAKEN SINCE THE FOUNDING OF THE PEOPLE'S REPUBLIC OF CHINA QIUHUA QIN Eng. B. Department of Economy, Technology and Labour Protection ofthe All-China Federation ofTrade Unions Mr. Chairman and fellow delegates. At the invitation of the International Labour Office, the Chinese trade union has been offered the opportunity to be able to attend the Vllth International Pneumoconioses Con ference. Therefore, I would like first of all to thank die ILO for its kind invitation. It is my wish, Mr. Chairman, to ad dress the Conference on our efforts to control dust in China for the purpose ofpromoting mutual understanding, exchang ing information and experience in the course of this Conference. THE ACHIEVEMENTS MADE IN CHINA IN THE DUST-CONTROL WORK With regard to dust harm affecting our country, we insist on priorities given to die preventive measures against dust harm and apply the principle of three-stage prevention namely, at the first stage, to eliminate dust harm and control (hist sources; at the second stage, to provide check-up regularly to ensure die early diagnosis ofdiseases; at the third stage, to make sure that diseases are controlled and treated at a possible early stage. The stress is placed upon the first stage prevention when applying the above-mentioned principle. To apply this principle, the state, with the active participa tion ofour trade unions, has formulated in die last thirty-odd years a series of laws, decrees, instruments and standards. In 1956, "The Safety and Health Regulations at Workplaces'' was promulgated and applied following which, "The Resolu tion on the Prevention of Silicon Dust Hazards at Workplaces" was published. Then "101-56 Standard"-- health design standards on dust concentration--was set by die state, based upon which the maximum allowable concentra tion (MAC) of the dust is set to 2mg/m3 if free silicon diox ide content is greater than ten percent in die dust and MAC is set to 10mg/m3 if less than ten percent. In 1958, the rele vant departments issued * `The Provisional Regulations on die Technological Measures Against Silicon Dust Hazards at Workplaces," illustrating demands on the practice to control dust. In 1962, the state formally promulgated "The Health Design Standards on the Industrial Enterprises, " prescribing in detail the provisions on ventilation and dust sources con trol at the workshops. In 1979, that Standard was revised. In 1963, "The Managerial Measures against Silicon Dust Hazard" was put into practice on a trial basis in our country, thus making our work on dust-control even more systematic. Therefore, these laws, decrees and standards have constituted a very important guarantee for the prevention and treatment of pneumoconiosis. Particularly, in recent years, the State Council, taking into account new problems arising from the economic reform ofour country, has made "the Decision on Strengthening the Work of Preventing Dust and Toxicant and Pneumoconiosis," thus pushing die dust-control work further. Positive steps have been taken in China actively by various industries, enterprises and relevant departments in accordance with the state's laws, decrees and regulations. Three nation wide working conferences on dust-control were held in 1957, 1962 and 1985 respectively, summarizing and spreading after wards the experience on dust-control throughout the country. In the field ofdust-control, we focus our attention on our own efforts by taking such comprehensive measures against dust as: to transform old enterprises; to improve technology and regenerate equipment. Ofmany years in China, we have found out a number of ways of our own to prevent and treat pneumoconiosis, i.e. mechanical ventilation; wet-operation; dust-sealing; personal protection; maintenance and manage ment of dustproof installations; technological innovation and improvement of technology; regular check-up for die workers exposed to dust; propaganda and education on dust-control. This comprehensive measure against dust has been proved by the fact to be a successful experience suitable to China's situa tion. And we have already achieved tangible results. Accord ing to the statistics collected from 16 key refractory factories, the average working age to acquire silicosis in the 1950s was 7.55 years; in the 1960s 14.52 years; in die 1970s 20.73 years; at the early stage of the 1980s it was 25.89 years. There has been a big reduction in the dust concentration in factories. Various steps have been taken to control dust in all industries in accordance with their own industrial features and ex perience. Take coal mining for example. A whole series of effective measures against dust has already been taken as follows: 1. Wet-drilling; 2. Coal seam infusion to increase moisture content; 3. Making use of "water stemming" i.e. to suppress dust by incompressibility and vaporization of water at exposure; 4. Spraying to minimize dust in the course oftransportation and blast loading; 5. Mechanical ventilation, dust suppression by water mist and purification of airflow; 6. Replacing dry-mix shotcreting with wet-mix shotcreting; 7. Cleaning the fallen dust in the tunnels, on the rock sidewalls, support and road so as to prevent dust from floating again. Sucun Coalmine of die Xinwen Coal Mining Management Bureau in Shandong province, well-known for its dust-control 1025 Respirators and Dust Controls work throughout our country, has taken nothing but the abovementioned measures. By so doing, up to now, none of die miners employed in 1959 has suffered from pneumoconiosis. In our country, great importance has been attached to train ing and scientific research in this respect. So far there are more than twenty universities and colleges where departments or specialities of safety and health have been set up; there are thirty-one research institutions with more than four thousand research fellows all over China. THE PRESENT COUNTER-MEASURES AGAINST DUST IN CHINA AND THE ROLE OF THE TRADE UNIONS Being a developing country, in the last thirty-odd years since die founding ofdie People's Republic of China, tremendous work has been done in the field ofprevention and treatment ofpneumoconiosis and fairly great progress made. However, as is known, the occurrence of pneumoconiosis is closely related to the development of die industrial modernization. China is now undergoing the primary stage ofsocialism under which, except some modern industries, a large number ofour industries still remain quite backward, falling behind those modem levels for several decades or even a hundred years. In recent years, there has been a big boom ofrural enterprises. The mode ofproduction in most ofthose rural enterprises is fairly backward. Apart from that, our management and technical levels on dust-control for the time being remain quite backward on die one hand, and on the other, the level of science, technology and culture ofour workers as a whole is not high enough. This is the situation in our country under which dust harm still remains very serious and pneumoconiosis can not be controlled yet. Therefore, we are still faced with a very arduous task. I think that almost all the developed countries in the process of their industrialization have gone through this dust-harm stricken period, longer or shorter, respectively. And this seems to be one of the com mon features of all die countries to prevent and treat pneumoconiosis. The crux of die problem lies in how we should, proceeding from our own situation, draw lessons from other countries so as to shorten this dust-harm stricken period. First, the government has promulgated ` `The Regulations on the Prevention and Treatment of Pneumoconiosis" and inspects the application ofthe Regulations in enterprises of different economic forms; Second, it is stipulated by our government that for die newly-built, extended, rebuilt, on-going projects or those projects introduced from abroad, the dustproofinstallations must be designed, constructed and operated simultaneously with the principal part ofthose projects mentioned above. The state departments responsible for labour, health and environment protection as well as the trade unions have die rights to examine, check and approve the projects. Without die signatures of the above-mentioned organizations, the projects can never be put into operation, thus to ensure that new dust sources will never be produced again; Third, a great importance is attached to the research on the dust-free or dust-reducing techniques as well as new anti dust technique. In the course ofour Seven-Five-Yearplan, die state has allocated special funds to place the item ofoc cupational dust-harm control, prevention and treatment 1026 techniques into the state target projects of science and technology, thus making efforts to resolve completely die problem of dust hazards; Fourth, it is necessary to enforce macro-control by the state over the work ofpreventing dust, the management ofenter prises and guidance to the industries and to carry out train ing on dust-control techniques for the leaders at different levels and workers as a whole for die purpose of enhanc ing their awareness of preventing dust and the abilities to protect oneself. As far as our work on occupational safety and health is con cerned, the system ofcombining state inspection, management by enterprises and industries and trade union supervision is practised. Therefore, die trade unions have important roles to play in die dust-control mainly as follows: 1. To participate, representing the interests oftheir members and workers, in die studies and formulation of laws and decrees related to diem. 2. To take part in the procedure of design, construction and operation of the anti-dust installations related simultaneously with the principal part ofdie projects and to supervise the management of enterprises to bring the dust under die control in a well-planned way and to draw and use funds for dust-control purposes in accordance with die regulations. 3. To organize and mobilize workers and trade union members to carry out activities of technical cooperation so as to pool the wisdom and efforts ofeveryone involved to control dust. 4. To exercise mass supervision to raise criticism and con structive suggestions over those enterprises with dust hazards problems. A deadline is imposed by trade unions to the settlement ofthe dust problem and workers and staff members will be organized and supported by the trade unions if necessary to refuse to work under serious dustharm stricken conditions of their workplaces. 5. To carry out an extensive education and propaganda ac tivities among die workers and trade union members. 6. To strengthen cooperations and exchanges with the ILO/CIS and all the countries the world over, learning from their advanced experience. At present, die All-China Federation ofTrade Unions is mak ing positive efforts to prevent pneumoconiosis. Last year, a general survey was carried out in die dust-stricken enterprises from all 29 provinces, municipalities autonomous regions ex cept Taiwan province of our country. In addition, a major analysis was made to die 125 workplaces where dust hazards remained serious still. As a result, the foundation has been laid to better represent and safeguard die interests and rights of die workers and staff members. Mr. Chairman and fellow delegates, I sincerely wish that through this Conference we will be able to strengthen the exchanges and cooperations between China and all die countries die world over, and at same time to ob tain useful experience and measures of other countries so as to speed up the work to prevent and treat pneumoconiosis in my country. Thank you Mr. Chairman. Respirators and Dust Controls RISK ASSESSMENT OF PULMONARY EXPOSURE TO RESPIRABLE DUST WHILE WEARING DUST RESPIRATOR UNDER SIMULATED WORK CONDITIONS BEHZAD S. SAMIMI, MSPH, Ph.D., CIH Division of Occupational and Environmental Health Graduate School of Public Health San Diego State University San Diego, CA 92182-0405, USA INTRODUCTION One ofthe most serious problems influencing the effectiveness of respiratory protection in die workplace is the degree of fitness between worker's face and respirator mask. This prob lem has been the focus of several investigators, particularly during die past decade. 1'2'5~7-9-13 In spite of significant ad vancement in development of numerous types of respirator masks, difficulties are still encountered with respect to the ability ofworker to obtain an efficient face seal with the mask of a "tight-fitting respirator." Despite the requirements for thorough qualitative and/or quantitative fit testing of tightfitting respirators on workers in order to select the best fitted respirator mask, under actual working conditions the degree ofassurance as to (1) how long a respirator mask will remain fit, (2) what factors affect the face-seal efficiency die most, and (3) what would be the potential exposure risk involved, are still uncertain. In addition to facial hair and morphology, which have been studied by several investigators in the past, factors such as repeated and prolongedhead and body motion, rate of respiratory ventilation, respirator strap tension, temperature and humidity, etc. may affect the respirator fit resulting in increased exposure risk to air contaminants. hi our laboratory, we have developed a unique automated mo tion and breathing system that utilizes NIOSH-adopted dum my heads. These dummy heads have been used by NIOSH and other investigators for respirator bench test. The purpose ofthis attempt was to develop a respirator testing system that simulates the actual working conditions. The prime objectives were: (1) to test the integrity of respirator masks, (2) to study the effects of dynamic factors that affect the respirator mask face seal such as head and body motion as well as breathing rate and frequency. Other factors that may also affect respirator seal, such as strap tension, temperature and humidity, can also be studied with this system. INSTRUMENTS AND METHODS System Components The experimental system consists ofa dummy, referred to as "Dusty", equipped with automated motion and breathing system. Dusty is installed inside a 1000-liter inhalation chamber and is connected to the motion and breathing systems outside the chamber by means ofcables and tubings. The ma jor components of the system are described below: The chamber. The chamber is equipped with gas and vapor generation systems and a Wright (hist feeder. Other commonly used aerosol systems such as DOP, mineral oil or salt aerosol can also be used to generate the desired concentration of aerosol. The aerosol concentration within the chamber is monitored by means ofa light-scattering particulate counter. In case ofuse ofgas or vapor for experiment, the concentra tion can be continuously monitored by means of an infrared gas spectrophotometer and strip chart recorder. The chamber is also equipped with a dynamic airflow system and necessary gauges for temperature, pressure and airflow control. An elec trostatic precipitator followed by an absolute filter, con tinuously cleans die chamber air from air contaminants before discharging it to the environment. (Figure 1) Human-form dummy (Dusty). Dusty comes in three different sizes: small, medium and large for use with various size respirator masks. Dusty's face is made out of soft and flexi ble plastic and approximates normal shape of human face. Similar dummies, as stated earlier, have been used by NIOSH Respiratory Research Section in Morgantown, WV, for primarily Bench Test.2 (Figure 2) Motor drive/indexers. The 3180-PI Motor Drive/Indexers us ed in this system are line-operated, energy efficient motor drive modules. An integral power supply provides the necessary DC voltages required to operate the indexer and drive. The indexer/drive modules are capable ofdriving step ping motors allowing a wide range of functions. The index ers are also used for memory storage up to 400 lines ofpro gram in non-volatile memory.3 There are three drive indexers in this system: A, B and C. Each drive/indexer controls one motion ofdie dummy in two opposite directions. Drive/indexer A also controls the breathing system. Stepping motors. There are three stepping motors in die system: 1, 2 and 3. These motors are controlled by motor/drive indexers. A, B and C, respectively. Each motor runs in two opposite directions: positive and negative. For 1027 Respirators and Dust Controls Figure 1. Inhalation chamber and automated motion and breathing simulators. example, in vertical motion of Dusty, positive motion is "moving up" and negative motion is "moving down." hi horizontal rotation (turning head) moving head to the left is positive and to die right is negative. In vertical translation (nodding head), forward head motion is positive and backward movement is negative.3 Indexerprogrammer. The SSP-500 indexer programmer is a dedicated programmer which is designed to be used with a variety of diive/indexers including the 3180-PI used in this system. All functions, parameters, data, and commands for the microseries indexers can be easily entered, edited, upload 1028 ed and downloaded using this device. All information is clear ly displayed on die two-line by 40-character liquid crystal display (LCD) panel. Seven function keys, Bi-Directional Cursor Locators, Numerical Keypad, Entry, and Mode keys provide easy and convenient data entry. All programming functions are menu-driven, and are presented in a clear, easy to follow sequence. The SSP-500 is designed to be eitherhand held or affixed on an exterior surface.4 Breather. The Breather is a box containing a vacuum/com pressor pump and two three-way selenoid valves which alter nate the flow ofair from and to the vacuum/compressorpump. Respirators and Dust Controls I Figure 2. Human-form dummy (Dusty) used in the system. The opening and closing ofthese valves are controlled by the Drive/Indexer "A". The frequency of opening and closing ofvalves (same as respiration frequency) can be changed by programming the Drive/Indexer through the Indexer Pro grammer. A breath warmer/humidifier is also used on the ex halation line. For inhalation, die computer opens up the two valves in direction from die Dusty's mouth toward die vacuum pump; as a result, Dusty inhales the contaminated air from die chamber through die respirator being worn. At the end of inhalation cycle, the computer reverses die direction of airflow by switching die two selenoid valves in the opposite direction. i.e., from the pump toward Dusty; as a result, room air is pushed through the warmer/humidifier and then into the Dus ty's respirator cavity and out into the chamber through the respirator's exhalation valve. Volume and rate of breathing is adjustable through the indexer programmer. Therefore, in creased rate of breathing can be set corresponding to the assumed rate of a worker's metabolic rate. Portacount. Portacount is a highly versatile particle-counting instrument. It can accurately measure respirator fit factors, filter penetrations, and particle concentrations. Based on the 1029 Respirators and Dust Controls technology ofcontinuous flow condensation nucleus counters, the portacount counts individual airborne particles from varie ty of sources. The instrument has two modes: Count Mode and Fit-test Mode. In die Count Mode, the portacount measures die concentration ofairborne particles, whereas in the Fit-test Mode, the instrument measures die concentrations ofparticles inside and outside a respirator and calculates the respirator penetration or protection factor.8 METHODS The system can be used to conduct variety ofexperiments on respirators. For example, to assess the risk ofdust exposure associated with a specific respirator fit under a certain head and body motion and/or breathing rate, die following pro cedure may be followed: 1. The "test respirator" is fit-tested on Dusty's face by means of die Portacount, until satisfactory fit is achieved. 2. The Chamber is set on desired flowrate and dust (or other aerosols) generation rates so that the desired concentra tion is achieved within a reasonable time, i.e., approx imately 5 minutes. 3. Dusty's motion and breathing systems (as programmed) are activated to run for a pre-determined length of time. 4. Dust concentrations outside and inside respirator is record ed continuously throughout the experiment. The extent of dust penetration into the respirator either through die face seal or any other route is detected at any time during die experiment and recorded on die strip chart. Any fluctua tions in dust penetration for example, can also be matched with the Dusty's motion and breathing pattern. Such ex periment is expected to provide answers to questions such as: (1) how long the respirator mask remains fit before a dust leak occurs? (2) which movement disturbs the respirator face seal, and to what extent? (3) what would be the effect of inhalation (negative pressure inside respirator mask), exhalation and/or breathing rate on dust penetration through die respirator? and (4) what would be die estimated risk of dust exposure involved under a set of conditions. Operating the Robotic Dusty Programming and operating the motion/breathing system, as stated earlier, is done through die Indexer/Programmer (Figure 3). The following is an example ofthe many programs used in this system. In this example. Dusty will carry out a consecutive combination ofbead and body motions: i.e., turn ing head, pumping tire, jogging in place, bending, turning bead while bending, and turning while nodding. These mo tions will be accompanied by breathing at a rate of 15 respira tions per minute and approximately 750 mL of air per respiration. When using this program, the first mode appearing on the display of die Indexer/Programmer is die "OPERATING MODE" (Figure 3). The function by beneath each lower case word will act on that word. For example, f7 key activates die indexers. Pressing this key will bring the display in Figure 4 which is "SELECT FUNCTION". Pressing f7 key (mo tion) again will move die system to the "MOTION" options 1030 SSP500 OPERATING MODE buzzer ndxr f4 f6f vJ a *2 Jw ** 1w jh 7* 12 45 T8 3 6 9 */ 0 mooe HSELECT MENU Figure 3. (Figure 5). Here, die operator has several options; however, in this example, pressing f3 key (exec) would be die right choice. The next display (Figure 6) is "EXEC MOTION". Here again, several options are available; however, since die operator is asking Dusty to carry out all the motions, f4 key (all) should be pressed which will activate all indexers. This will take the operator to the last step ofthis program: "AUTO EXEC MOTION" (Figure 7). Out ofseveral options available in this mode, pressing fl key, CYCST (Cycle start) will start the system. Dusty will start die head and body motions, as stated earlier, in a consecutive fashion while breathing. In dexer/Programmer display during the operation would be "AUTO EXECUTING" (Figure 8). The system will continue to operate until die end ofpre-set time on die program unless die operator wishes to stop the system at any time by press ing fl key (stop). Pressing f4 (hold) may also be used should the system have to be stopped momentarily. The robotic Dusty can also be run manually for each single motion by pressing fl (man) in the "MOTION" mode (Figure 5). The next screen will show "ATT'N INDXR (01-99)" (Figure 9). The cursor on this screen will be flashing asking for die Drive/Indexer number of choice. Using die numeric key pad, one of die three indexers is activated by typing a zero and then the Indexer number: 01,02 or 03. Once an Indexer is chosen, die "DATA ENTRY" key on the edit SELECT FUNCTION clear save stat 4 1 f2 f & motion 1 121 3 4 5I 6 7 8 LiJ hd 0 1 mode ' KSELECT MENU 7 Respirators and Dust Controls Figure 4. Indexer/Programmer is pressed to activate die next screen of choice: "MANUAL MOTION" (Figure 10). The number in the upper left, here shown as "OX", will be the number of the indexer chosen. Several options are available on this screen. The one primarily used in manual control ofthe system is f2 (Jog). Pressing 2 will activate a continuous motion of the Dusty depending on the Indexer number chosen. The screen appearing during this operation will be "JOG MOTION". In addition, the system can be programmed and executed to carry out varieties ofdesired motions or combination ofmo tions (up to 999 choices). To execute the desired motion, f5 key (N) should be pressed during die AUTO EXEC MOTION (Figure 7). Using the numerical keypad, the desired motion number is then entered and followed by pressing "DATA EN TRY" key. The system is now ready to execute die desired motion indefinitely by pressing fl key (Cycst). Ifthe system is stopped at any time during the operation. Dusty must be4 `returned" to its ` `electrical home' ' before a new cy cle can be started. This is done by pressing f6 key (reh) in "MANUAL MOTION" mode (Figure 10). REFERENCES 1. Breysse, N. et al.: Critical Review of International Standards for Respiratory Protective Equipment n. Gas and Vapor Removal Efficiency and Fit Testing. Am. Ind. Hyg. Assoc. J. 44:762-767 (1983). 2. dflRoza,R.A.etal.:ReproduribilityofRespiratorFiiasMeasuredby Quantitative Fit Tests. Am. Ind. Hyg. Assoc. J. 44:788-794 (1983). 3. Instructions for SLO-SYN Micro Series Motion Controls Indexer/Pro grammer, Type SSP-500. Superior Electric, Bristol, CT 06010-7488 (1988). 4. Instructions for SLO-SNY Micro Series Motion Controls. Packaged Preset Indexers, Types 3180-PI. Superior Electric, Bristol, CT 06010-7488 (1988). 5. McGee, M.K., Oestenstand, R.K.: The Effect ofthe Growth ofFacial Hair on Protection Factors for One Model ofClosed Circuit, PressureDemand, Self-Contained Breathing Apparatus. Am. Ind. Hyg. Assoc. J. 44:480-484 (1983). 6. Matvwial Imritufj* for Occupational Safety and Health: Evaluation ofthe NIOSH Certification Program. NIOSH Publication No. 80-113 (1979). 7. National Institute for Occupational Safety and Health: Human Variability and Respirator Sizing. NIOSH Publication No. 76-146 (1976). 8. PORTACOUNT, Operation and Service Manual. TSI Incorporated. St. Paul, MN 55164 (1987). 9. Ryan, C. etal: Critical Review ofInternational Standards for Respiratory Protective Equipment. 1. Respiratory Protective Equipment for Par ticulate Laden Atmospheres. Am. buL Hyg. Assoc. J. 44:756-761 (1983). 10. Sketred, O.T., Loschiavo, J.G.: Effects ofFacial Hair on Face Seal of Negative-Pressure Respirators. Am. bid. Hyg. Assoc. J. 45:63-66 (1984). 11. Smith, TJ. etal: Inhalation Exposure of Cadmium Workers. Effects of Respirator Usage. Am. bid. Hyg. Assoc. J. 45:63-66 (1984). 12. White, N. etal: Critical Review ofInternational Standards for Respiratory Protective Equipment, m. Practical Performance Tests. Am. Ind. Hyg. Assoc. J. 44:768-773 (1983). 13. Wilke, K. et al: New Methods for Quantitative Respirator Fit Testing with Aerosols. Am. buL Hyg. Assoc. J. 42:121-125 (1981). 1031 Respirators and Dust Controls EXEC MOTION auto sngl cont all ' 4i 1j fJ w^ f4 4i w^ f6 etc / ^7i 0 1 23 4 5 "6 789 +/ 0 f \ {MODE \ DATA SELECT ENTRYJ ^MENU ) 00 AUTO EXEC MOTION cycst pos N etc (f 1 f2 f3 f4 f5 f6 f 7) O OU--Z7\ 123 456 789 +/ 0 l- U'MODE SELECT MENU Figure 6. Figure 7. 1032 stop AUTO EXECUTING hold clear (fl f 2 13 f4 4K ii %J f6 f7) 2| 3 4 L?J 6 ~7 PH ~9 01 Figure 8. Respirators and Dust Controls 1033 Respirators and Dust Controls Figure 10. 1034 Respirators and Dust Controls RESPIRATORY PROTECTION EQUIPMENT PERFORMANCE STANDARDS IN DEVELOPING COUNTRIES D.P.WILMES P.E. Olsen L. Hendricks 3M Occupational Health and Safety Products Division, Building 2603-02, St. Paul, MN 55144, USA Respirators are a very important factor in the line of defense against pneumoconioses. In less developed countries where resources are very limited to control die disease producing dusts and mists, respirators are probably the only viable method available for worker protection. Unfortunately, in these same countries, there are few standards or regulations governing the performance or use of respirators. Standards and regulations need to be developed to assure an adequate level of respirator performance and their proper use. An effective certification procedure need not be complicated, especially for particulate respirators. Modem technology has made evaluation ofthe performance ofrespiratory protection much easier and more reliable than in die past. Simple pro cedures can be implemented to assure continued compliance with die standards. For respirators offering protection against harmful dusts and mists die following aspects of respirator performance must be addressed: 1. Particulate penetration 2. Breathing resistance 3. Respirator fit $ 1 would like to briefly discuss each ofthese aspects along with my recommendations as to how they can best be addressed in a certification program. The most important aspect of respirator performance is its ability to exclude through its filters and components die harm ful dust from die breathing air ofthe worker in a contaminated environment. In the past, filters or the entire respirator would be challenged with a laboratory generated test agent, such as silica dust. Air would be drawn through the respirator or filter at a specified rate. The amount of dust penetrating die filter or respirator would be collected on a second filter. After a specified period of time the second filter would again be weighed and die performance ofthe respirator reported as the total particulate penetrating die device, or the percent efficien cy ofdie respirator or filter, ifdie challenge concentration was measured. This is the current NIOSH certification test. The results ofsuch tests are highly variable and are often poor predictors of actual respirator performance. For example two respirators that give equivalent results on the NIOSH silica dust test could give differing results if the instantaneous penetration were measured at any given time during the test. The old methods simply do not have die analytical sensitivity necessary to measure the actual performance of respirators. In addition die equipment necessary to perform such a test is very expensive and difficult to operate and would consume a great deal of die testing agency's time. Fortunately technology has simplified particulate respirator performance evaluation. Commercial equipment is now avail able to test particulate respirators in a manner applicable to respirator certification. This equipment uses a small worst case test aerosol so extrapolation to the aerosol found in the workplace is unnecessary. In European certification testing the aerosol is sodium chloride or paraffin oil generated by a controlled atomization. TSI Inc. of St Paul, Minnesota, for instance, manufactures a unit that reliably and accurately measures the filtration per formance of respirators. Their equipment can function with a variety of test aerosols. We have evaluated this test equip ment with very encouraging results. The state ofthe art equip ment was able to reproducibly measure filter performance with a coefficient of variation of less than 4% whereas die silica dust test has a coefficient of variation typically in the range of 60%. The new equipment costs less than 20 % of what a silica dust chamber would cost and is essentially a "turn key" test whereas die dust chamber would take at least 18 months to build and start up. This type of filter efficiency testing cor relates very closely with tests that are performed in Europe and what is currently being proposed for use in the United States. The second important aspect of respirator certification is the determination of acceptable breathing resistance of the respirator. This attribute ofa respirator is important because it affects the user acceptance of die respirator. A respirator not worn when it should be will offer no protection. Deter mination ofbreathing resistance is a simple matter. In fact the state of die art filtration testing equipment automatically measures breathing resistance while determining filter efficiency. The last aspect of respirator performance that requires ad dressing is facefit. In order for a respirator to provide ade quate protection it must seal to the wearer in some manner that excludes die harmful dusts from penetrating die interface be tween die respirator and the wearer. This ability to seal is termed facefit. There are many accepted methods for deter mining how well a respirator fits. Because of limited time I will not discuss these methods but rather discuss approaches 1035 Respirators and Dust Controls ofapplying facefit testing to a respirator certification program. Faces are highly variable. They come in many sizes and shapes and contain highly variable features. Generally, no one model of respirator will fit all faces. No one to date has been successful predicting the fit of a respirator on an individual using any scheme. Yet fit is a very important aspect in respiratory protection. Generally two approaches have been used to address this prob lem. A method that is currendy used in Europe and elsewhere requires that a respirator demonstrate some level ofminimum fit on a substantial percentage of people on a test panel dur ing the certification process. The fit of the respirator on the actual user is then largely ignored during actual use. The other method currendy used in this country is to minimally address fit in the certification process but require through respirator use standards that an acceptable level of fit be determined on each respirator wearer. The first method acknowledges drat some percentage of respirator users will not be protected because their respirator does not adequately fit whereas the second method places a burden on the employer to find a respirator that fits die individual if respiratory protection is required. I believe that the second method is a much more protective standard. The availability of a greater variety of respirator sizes, shapes and models in this country than in Europe is in dicative that this method provides respirators with potential ly better facefit. I believe that a respirator certification scheme should require that a respirator manufacturer in the respirator user instruc tions specify a validated fit test must be performed to assure adequate facefit before the respirator can be relied upon for protection. This would provide assurances that the user has a respirator that adequately fits. These three items are the most important aspects of a respirator certification program. However, a method of en forcement must also be implemented to assure continued com pliance. The best method to accomplish this is for the agency to purchase product from the open market and test for compliance. Before effective respiratory protection can be assured respirator use standards must be developed. If the proper respirators are not selected, if adequate fit cannot be ascer tained and ifthe respirator wearers are not adequately trained in the proper use of die respirator protection will not be assured. With die advancement of technology and existence of prac tical respirator use standards as models, regulations and stan dards should be adopted to assure adequate protection is available against pneumoconioses producing dusts and mists. 1036 Respirators and Dust Controls OPTIMIZATION OF FREELY SUSPENDED EXTERIOR HOODS IN INDUSTRIAL VENTILATION NURTAN A. ESMEN, Ph.D. Dietrich A. Weyel, Sc.D. University of Pittsburgh, Graduate School of Public Health, Pittsburgh, Pennsylvania, USA INTRODUCTION In the design ofan exterior hood, the value ofthe airflow rate through the hood can be found ifspecification ofthe ` `reach" of the hood is given. By the reach of the hood we mean a set ofair speeds induced by the hood, to be achieved or exceed ed at specified locations in front of the hood. If the velocity profile generated by die hood air flow is known, the problem is simply matching the velocity profile with the specifications to obtain the flow rate which will achieve the correct air speeds. There are a number ofexpressions which give velocity profiles with about equivalent accuracy.1-4 Thus, any one of these expressions can be used to design a hood. Clearly, ifthe air speed specifications are given correctly, then the capture efficiency of the hood is expected to be optimal. It must be noted that die optimum for the capture efficiency can be made independent ofcross currents, because die effect of cross cur rents can be included into the specification ofthe air speed. This seemingly direct and simple method of computation, which determines the minimum flow rate to accomplish the desired result, is flawed with respect to the mechanical effi ciency of the hood. This flaw is due to the a priori selection of the hood geometry and orifice size without a quantitative investigation of die possibilities of achieving the same end result with a hood of different geometry and/or orifice size. Although the experience of the designer may be invoked as an influencing factor in the design, even for an experienced designer it is unlikely that the consequences of such alter natives have ever been a consideration. In order to simplify the theoretical development, it will be assumed that a specific value of air speed on all points of a regular geometric shape defined on a plane located in front of a hood is given as die design criterion for die hood. It is important to note that the restriction of specification surface to a plane rather than a curved surface will not give a general solution. Therefore, it may be considered to be a limitation of die theoretical development. However, such a specifica tion would be sufficiently common in the industrial applica tions and more importantly, the methodological approach can be presented without undue complexity of the mathematical formulation so that the results would be useful to a ventila tion system designer. THEORETICAL CONSIDERATIONS In the investigation of the implications of hood orifice geometry and in the selection ofproper size ofdie orifice, die development of the theory is facilitated if the specification geometry is chosen in a way that the distances measured from the point on the hood is readily accomplished. This will sug gest that the shape of the specification surface is symmetric with respect to both of the axes of the plane. An oblong or a circle would satisfy this criterion. Since a square has four extremal points, then the structuring ofthe optimization prob lem can be reduced to matching die air speed generated by the hood to the specified air speed at die extrema. This pro cess would be sufficiendy general, in the sense that die specification can be in terms of a component of a vector. Suppose it is necessary to generate air speed ofVc at the sur face of an oblong located on a plane parallel to the hood sur face and centered on the x-axis with its sides parallel to the xz and yz planes. Furthermore, suppose that it is necessary to keep the hood face velocity equal to or below a specified value VQ. Let A and B be the maxima of the y and z coor dinates respectively. For an oblong hood, with sides a frac tion c of A and B placed with its center at the origin (Figure 1) minimization ofthe flow rate Q might be sought by the ob ject function: Q = L2 f(a,b,h) Vc (1) Subject to: Vc f(a,b,h)/ 4abc2 < VD (2) where, a = Dimensionless specification oblong side, A/L b = Dimensionless specification oblong side, B/L h -- Dimensionless distance to the specification surface, H/L For an oblong orifice, die function f(a,b,h) may be shown to be represented by the non-dimensionalized velocity scaling function (1) multiplied by the hood orifice area: f(a,b,c,h) = x(a+b)cr+2xr2+4abc(c+h(a+b)/ (a2+b2))^ (3) with, r2 = h2+(l-c)2 (4) Equations 1 through 4 can be extended directly to a circular orifice by taking c.L to be the radius of the orifice. In such an extension. Equations 2 and 3 will have to be modified to conform to the description of the flow field in front of a cir cular orifice. The modified equation for a circular orifice hood 1037 Respirators and Dust Controls may be shown to be 3: fc(a,b,c,h) = r^cr+r2)t2+Tcfc2+Kh2)^ (5) K = 4/(*a-2x) and, Vc a,b,h)Ma2+b2)c2 < VQ (6) The, minimum sought may he found directly hy differentiating either equation 3 or equation 6 with respect to c and finding die root ofdie resulting equation which is between zero and one. For an oblong orifice, the non linear equation to be solved is: i(a+b) &+1-3C+2C1 2c2 +hfr+b) +4{c-I)+4abc =0 (7) 0i2+1-2c+c2) % (^-Htfa+b)) * and similarly for a circular orifice: r_ # h2+l-3c+2c2 2c2+Kh =0 2 (h2+l-2c+c2) * +(c_1)+ (cZ+fii) * (8) Ifdie specification surface, instead ofoblong, is a circular one then calculation process may be modified by taking two dif ferent values for square or circular hoods. It may be shown 1038 that for a square orifice bood the square hood A = B and L = A ^2 and for a circular orifice hood L = A. With these altered specifications equations 1 through 8 apply to optimiza tion without further change. (Table I) In general, die process ofcalculation is straight forward and with the use ofa computer presents no significant problems. However, in certain cases no root may exist in the zero to one interval. This suggests that the global optimum design does not exist for that condition. This situation will arise when die dimensionless frontal distance h is sufficiently large. Conse quently, the local optimum which is defined by the maximum face velocity specified in equation 2 or 6 and the correspond ing orifice size may be used. For infrequent design problems where the use ofa computer is not warranted or for those who do not have ready access to a computer, there are a number of simplifications, albeit limited, that reduce the calculations to simple use of tables. To develop these simplifications, consider die specification surface to be bounded by a square, i.e. the sides are such that A = B. Then die optimization can be carried out utilizing the values shown in Table n. The simplest use of this table may be illustrated by an example. Suppose die specification sur face is located 10 cm from die hood plane with A -- .0.25 m. Ifthe air speed desired on this surface is 1 m/sec and the max imum face velocity allowed is 25 m/sec then die optimum hood size for a square hood is calculated as follows: L = A-s/2 = 0.35355 thus h = H/L = 0.283. Therefore, interpolating the proper values from Table II, f(h) = 3.6191 and c = 0.784; consequently, die optimum value of die side of die square hood is 19.6 cm and from equation 1 the a volumetric flow rate is 0.45 m3/sec. Similarly, for a circular hood, the optimum radius is 22.5 cm and the flow rate is Respirators and Dust Controls 0.49 m3/sec. Thus for this simple illustration, a square orifice hood would be an optimum choice. Ifdie example above is recalculated using a circular specifica tion, die optimum square hood would be the same, but the op timum circular hood would have L = 0.25, h -- 0.40 which results in a hood radius of 13.0 cm and flow rate of 0.31 m3/sec. In this case a circular hood would be superior. It is important to note that die theoretical results developed Table I Optimization Parameters for Squares and Circles Dimensionless Distance Circle C f(a,h) Square C f(a,h) 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50 0.9351 0.8926 0.8594 0.8291 0.8018 0.7754 0.7598 0.7266 0.6992 0.6758 0.6562 0.6328 0.6104 0.5869 0.5635 0.5400 0.5166 0.4932 0.4688 0.4434 0.4209 0.3965 0.3721 0.3467 0.3203 0.2949 0.2695 0.2441 0.2148 0.1914 2.2007 2.4464 2.7265 3.0372 3.3768 3.7440 4.1381 4.5588 5.0057 5.4785 5.9770 6.5012 7.0511 7.6263 8.2270 8.8531 9.5044 10.1810 10.8828 11.6098 12.3619 13.1391 13.9414 14.7688 15.6211 16.4984 17.4007 18.3278 19.2799 20.2567 0.7734 0.7344 0.6953 0.6641 0.6211 0.5859 0.5508 0.5156 0.4805 0.4414 0.4062 0.3672 0.3203 0.2634 0.2266 0.1719 0.1094 0.0312 3.1161 3.2874 3.4966 3.7355 3.9989 4.2843 4.5893 4.9126 5.2530 5.6094 5.9811 6.3672 6.7667 7.1790 7.6030 8.0375 8.4809 8.9307 Circular orifices with maximum face velocity: 2 L" fc(a,b,h) VQ - Tr(a2 +b2 )c VQ = 0 Oblong orifices with maximum face velocity: f{ab,h) V - 4 abc' v0 = 0 1039 Respirators and Dust Controb Design CASE I Traditional Square Optimum Square CASE II Traditional Oblong Optimum Oblong CASE III Traditional Oblong Optimum Oblong CASE IV Traditional Square Optimum Square CASE V Traditional Square Optimum Square Circle Table n Comparison of Traditional and Optimized Designs (Unit Control Speed) B vert A Hor. H cm cm cm Diameter or Height cm Width cm 15 15 15 30 27 20 30 25 -- 40 60 33 10 20 30 49 20 40 12 20 20 25 24 40 - 20 20 10 25 40 19 15 - - . - Flow 3. m /sec 0.354 0.254 1.12 1.01 0.902 0.880 0.889 0.830 0.421 0.358 0.359 1040 above are not inherently limited to applications which involve specification surfaces assumed in die development. Obvious ly, if the specification surface is not nearly a square circular or square orifice hoods will be inherendy inappropriate but must be replaced by oblong orifice hoods. Finding die roots ofthe derivative ofthe objective function may be carried out by hand but such a calculation would be cumbersome. Although the computerized solution is simple, when a com puter is not available, the optimization of each dimension of the orifice may be carried out approximately, one at a time by treating each side as an independent imaginary square hood. Although the orifice dimensions determined in this man ner may not predict die exact optimum design values, the resulting dimensions are expected to be near the optimum values. The flow rate for such an orifice cannot be calculated directly from Equations 1 to 4. EXPERIMENTAL RESULTS The direct experimental verification of the optimization procedure given above is at best cumbersome. Such an ex periment would involve the construction of a very large number ofhoods. However, an indirect experimental verifica tion of the procedure may be accomplished by showing that a few representative hoods may be constructed and studied. Respirators and Dust Controls In the experimental study carried out to verify the theoretical calculations indirectiy, three oblong hoods were constructed. These hoods were 5 cm by 5 cm square, 3 cm by 5 cm ob long and 4 cm by 8 cm oblong. With hood opening fixed, con ditions under which these hoods will be optimum were calculated for different values of frontal distance and for each condition, the optimum flow rate was predicted. The air speed was measured at each, the theoretically determined specification point and the flow rate was adjusted until the air speed specification is fulfilled. This experimentally deter mined flow rate was then compared to die theoretical flow rate. All air flow and air speed measurements were carried out by hot wire anemometry. The hot film sensor in X con figuration was calibrated in our laboratory and it is capable of measuring velocities with good accuracy and reproduci bility. The hood airflow measurement was carried out by measuring the air speed by a traverse as close to the orifice plane as possible. The comparison of die calculated optimum and die measured flow rates are given in Figure 2. The results suggest that the optimization procedure is satisfactory and perhaps slighdy pessimistic in die indication ofthe flow rate required. On the average, about 10 percent less flow was required than it was calculated as necessary. Figure 2. Comparison of theoretically and experimentally obtained flow rates for three hoods. 1041 Respirators and Dust Controls DESIGN APPLICATIONS AND DISCUSSION Hie application of the results presented above to die design of freely suspended hoods with single square, circular or oblong orifices is a straight forward process but it must be recognized that the success ofthe hood design based on such calculations will ultimately depend upon the correct specifica tion ofdie velocities to be generated at specific locations. The estimation ofthese velocities is beyond the scope ofthis paper and may be found in manuals dealing with currently accepted practice. Ifthe specification surface isjudged to be a curved surface rather than a plane or ifthe vector components ofthe velocity at specified points are sought, new objective func tions following the theoretical development above can be found. Alternately, the hood size may be selected at an ex ternal point by considering that point to be one of the ver tices of an oblong specification surface and the proper flow rate through die system can be calculated by point matching between the generated flow field and die required flow field. In order to show die efficacy of die optimization procedure developed here, five hypothetical cases were compared to the traditional design procedure. The results ofthis comparison are shown in Table II. For the cases shown in Table n, the efficiency gain through optimization is about 13 percent with a range from 2 to 30 percent. These cases were not constructed with a forethought to show die effectiveness ofthe optimiza tion procedure, but rather they were arbitrarily selected. Since the optimization process is based on the velocity profile in front ofthe hood, and the traditional design procedure which is based on die adjustment of the centerline velocity of die hood, then die hood designed by die optimization procedure ensures that the air speeds specified on the specification plane are satisfied. On the other hand such a statement would not necessarily be correct for die design based on centerline velocity. Consequently, the hoods designed through the pro cess described above would always have a superior total ef ficiency as compared to the traditionally designed hoods. REFERENCES 1. Esmen, N.A., Wcyd.D.A.: Aerodynamics ofmultiple orifice hoods. Ventilation 1985, Elsevier H.D. Goodfellow (edit) New York, p. 735-743, (1986). 2. Esmen, N.A., WeyeJ, D.A., McGuigan, F.P.: Aerodynamic proper ties ofExhaust Hoods. Amer. bid. Hyg. Assoc. /. 47:446-454,(1986). 3. Esmen, N.A., Weyel, D.A-, Pirns, A., Don, A.G.: Aerodynamics of Arbitrarily shaped orifice exterior hoods II: Experimental study. Ann. Occup. Hyg-, (in press). 4. Flynn, M.R., EQenbecker, MJ.: The potential flow solution for airflow into a flanged circular hood. Amer. bid Hyg. Assoc. J. 46:380-389, (1985). This research was supported by The National Institute for Occupational Safety and Health under a research grant mmiher of 1-RO-1-OHO2132-03. 1042 Respirators and Dust Controls SIGNIFICANT REDUCTION OF QUARTZ DUST CONCENTRATIONS IN THE NATURE STONE INDUSTRY DUE TO THE INTRODUCTION OF VENTILATION SYSTEMS VfiRRINGERUNG VON SCHADSTOFFKONZENTRATION DURCH LUFTUNGSTECHNISCHE MApNAHMEN IN DER NATURSTEININDUSTRIE ROBERT FEIGHOFEN, Dipl.-Ing. Steinbruchs-Berufsgenossenschaft, Hannover, F.R. Germany EIMLEITCING Die wirksame Erfassung luftfremder Stoffe und ihre gefahrlose Niederschlagung stellt eine der zentralen Arbeitsschutzma^nahmen dar. Beim Umgang mit diesen Stoffen konnen diese in Form von Stauben, Gasen Oder Dampfen in den Arbeitsbereich der Beschaftigten gelangen. Im Bereich der Steinbruchs-Berufsgenossenschaft haben wir es vor allem mit silikogenen Stauben zu tun. In der Natursteinindustrie, heir insbesondere in der Granitindustrie, war es dringend notwendig, Ma^nahmen zur Emissionsminderung zu ergreifen. Eine der Ma/?nahmen zur Emissionsminderung war die Erfassung luftfremder Stoffe an der Emissionsquelle. Die hierzu notwendigen Einrichtungen waren in ihrer Wirkung zu optimieren. Fur die Berechnung lagen selten geschlossene Losungen vor, vielmehr war man aufPraxiserfahrung angewiesen. Moglichkeiten der Verringerung von Schadstoffkonzentration durch luftungstechnische Ma/Jnahmen sollen an Beispielen der Staubbekampfung in der Granitindustrie aufgezeigt werden. TECHNISCHE SCHUTZMA/3NAHMEN Allgemeines Die Absaugeinrichtung soli den bei den Bearbeitungsvorgangen entstehenden Feinstaub an der Ausbreitung uber die Entstehungsstelle hinaus hindern. Der nicht flugfahige Grobstaub sedimentiert schnell und lagert sich ab. Der Feinstaub dagegen breitet sich mit jeder Luftstroraung aus. Er gelangt in die Atemzone und sein Anted kleiner als 5 pm in die Atemorgane. Die Erfassung des Staubes an der Entstehungsstelle kann z. B. bei der Verwendung von Druckluftwerkzeugen durch eine das Werkzeug weitgehend umschlie/Jende Kapselung oder durch punktformige Absaugung erfolgen. Bei uberwiegender Handarbeit oder auch bei Verwendung von Schleif--oder Trennwerkzeugen in geschlossenen Hallen werden als Erfassungselemente vielfach Saugtrichter in den unterschiedlichsten Formen eingesetzt. Bei maschineller Bearbeitung werden Kapselung, Absaugdiisen oder auch die Absaugung durch eine Bohrung im Werkzeug angewandt. Stauberfassung bei der Bearbeitung mit Werkzeugen 1. Kapselung In der Granit-Werksteinindustrie befmden sich eine gro0e Anzahl der Arbeitsplatze im Freien oder in halboffenen Steinhauerhutten. In diesen Hutten werden liberweigend Rand-, Leisten-, Grenz- und Mauersteine hergestellt. Fur die Bearbeitung werden Druckluftwerkzeuge verwendet. Eine Erfassung des bei der Bearbeitung entstehenden Staubes kann an diesen Arbeitsplatzen nur durch eine moglichst weitgehend das Werkzeug umschliej3ende Kapselung erfolgen. In den ffiiheren Jahren hatte man sich bei der Staub bekampfung an diesen Arbeitsplatzen tiberwiegend auf den Arbeitsvorgang "Stocken" konzentriert, da hierbei die gropte Staubentwicklung auftrat. Es wurde als Stauberfassungs-Einrichtung fur diesen Arbeitsvorgang zunachst der Schardinger Topf entwickelt. Der "Topf' wird uber den Mei^elhals gesteckt und ist an diesem festgelegt. Der "Topf' selbst liegt auf der zu bearbeitenden Flache und wird mit dem Keillochhammer zusammen uber die Flache gefiihrt. Bedingt durch die Bewegung uber die rauhe Oberflache des Werkstiickes wird er stark abgenutzt. Auch ergeben sich gelegentlich Schwierigkeiten beim Bearbeiten an den Kanten der Werkstiicke. Beim sogenannten Hauzenberger Topfwurde eine neuer Weg beschritten. Der Absaugkopf ist an einem Rillenstiick, welches die Haltemutter des Hammers ersetzt, drehbar angebracht. Mit einem Handgriff kann der Absaugkopf auf die jeweilige Lange des Werkzeuges eingestellt werden. Der untere Rand des Topfes soil sich stets im geringstmoglichen Abstand uber dem Werkstiick befinden. Bedingt durch das zusatzliche Gewicht mussen die mit dem Hauzenberger Topf 1043 Respirators and Dust Controls ausgestatteten Hammer von einer besonderen Fiihrung gehalten werden. Ein freihandiges Aibeiten ist nicbt moglich. Eine Weiterentwicklung des Hauzenberger Topfes ist eine Gummihaube mit seitlichem Saugstutzen. Diese Gummihaube wild fest mit dem Stockhammer verbunden und beim "Stocken" mit Hartmetallwerkzeugen verwendet. Der Ham mer kann auch von Hand gefiihrt werden. Schwierigkeiten bei der Benutzung dieser Absaugeinrichtungen treten beim Bossieren, Spitzen und Keiilochmachen, d.h. bei Arbeiten mit dem Spitzeisen auf. Bei der groben Bearbeitung von Flachen ist es notwendig, den Hammer in mehrere Richtungen zu bewegen. Fur diese Arbeitsvorgange, die au/?erdem noch mit Spitzeisen unterschiedlicber Lange durchgeftihrt werden, waren die starren Absaugtopfe nicbt geeignet. Ein Heranfiihren der Absaugduse an die Bearbeitungsstelle war nicbt moglich. In den letzten 10 Jahren ist es gelungen, auch Einrichtungen zum Erfassen des Staubes fbr diese Arbeitsvorgange zu schaffen und zu verbessern. Die StauberfassungsEinrichtungen bestehen aus einer Gummikappe mit seitlichem Saugstutzen, die uber die Haltemutter des Keillocbbammers gezogen wild. In eine in dieser Grandhaube angebrachte Nut werden die mit einem Falz versehenen Absaugdusen von unterschiedlicher Lange und Form fur die verschiedenen Arbeitsvorgange eingesteckt. Man ging auch bier wieder davon aus, den Staub moglichst nabe an der Entstehungsstelle zu erfassen. Je naher die Erfassung des Staubes an der Entstehungsstelle erfolgt, desto geringer kann die erforderliche Absaugluftmenge gehalten werden. Das bedeutet wiederum, da/? die Absaugvorrichtung am Hammer klein und gering im Gewicht und der er forderliche Absaugschlauch auch klein im Durchmesser bleiben konnen. Im unmittelbaren Zusammenhang mit einer Absaugluftmenge steht auch die Gro/?e der Anlage und damit deren Kosten. 2. Punktformige Absaugung Fur verschiedene Arbeiten mit schlagenden Druckluftwerkzeugen, iiberwiegend in geschlossenen Hallen, wird die Punktabsaugung verwendet. Die Absaugung erfolgt mit einem flexiblen Saugrohr oder Schlauch. Der Schlauch oder das Saugrohr sind am Dnicklufthammer befestigt. Das Ende des Schlauches bzw. des Rohres ist so nahe wie moglich an die Entstehungsstelle des Staubes nachzuftihren, damit eine ausreichende Erfassung des Staubes erfolgt. Bei der Punktab saugung wird ebenfalls mit einer geringen Absaugluftmenge gearbeitet. 3. Absaugung mit dem Saugtrichter Es ist allgemein bekannt, da/? auch bei der Steinbearbeitung mit Handwerkzeugen eine erhebliche Staubentwicklung auftritt. In diesen Fallen ist eine Erfassung des Staubes nur durcb Saugtrichter moglich. Diese Art der Absaugung erfordert jedoch wesentlich hohere Absaugluftmengen als bei 1044 Kapselung oder Punktabsaugung. Bei Verwendung von Druckluftwerkzeugen oder elektrisch angetriebenen Werkzeugen ist besonders darauf zu achten, da/? die Flugrichtung des Staubes zur Haube hin zeigt. 4. Absaugung mit Absaugtischen In Jura-Marmorbetrieben werden bei der Steinbearbeitung auch Absaugtische eingesetzt. Bei trockener Bearbeitung von Kanten mit Elektroweikzeugen wird hier der Staub uber einen unter dem Tisch eingebauten Entstauber abgesaugt. Bei Arbeiten mit dem Absaugtisch ist darauf zu achten, da/? die Halterung fur das zu bearbeitende Werkstuck entsprechend nachgestellt wird. Die zu bearbeitende Kante mu/? moglichst nahe der Ansaugoffimng liegen. Nur so kann eine einwandffeie Erfassung des Staubes erfolgen. Hilfseinrichtungen Au/?er bei den Stockarbeiten mit Gestangeftihrung des Druckluftwerkzeuges bereitete das Nachfiihren der Erfassungseinrichtungen und der Schlauche stets Schwierigkeiten. Dieses Problem ist jedoch weitgehend gelost. Bei Druckluft werkzeugen, bei denen die Erfassungseinrichtungen unmittelbar am Werkzeug angebracht sind, werden Druckluft- und Saugschlauch gemeinsam uber einen Gelenkarm zum Werkzeug gefuhrt. Der Gelenkarm mit aufgesetztem Pendelarm hat eine Lange von ca. 3 m, so da/? ein ausreichend grower Schwenkbereich vorbanden ist. Eine Zugentlastung sorgt fur den Gewichtsausgleich. Bei Anlagen mit Saugtrichter wird dieser an eine nach alien Seiten bewegliche und in der Hohe verstellbare Rohrleitung angebaut oder der Trichter befindet sicb an einem flexiblen Schlauch bzw. an flexibel uber Schlauchstucke verbundenen Rohren, die an Gelenkarmen verschiedenster Bauart befestigt sind. Die Leichtgangigkeit der Gelenkarme mu/? stets gewahrleistet sein, da die Saugrussel sonst nicht standig nachgefuhrt werden. Eine ausreichende Staubabsaugung ist dann nicht mehr gegeben. Sind die Hilfseinrichtungen umstandlich zu handhaben oder schwergangig, so wird die gesamte Staubabsaugung in der Regel von den Arbeitem abgelehnt. Staubabsaugung bei Bearbeitung mit Maschinen 1. Pflasterstein-Spaltmaschine Der beim Spalten entstehende Staub wird durch seitlich neben dem Obermesser und unter dem Tisch angeordnete Diisen abgesaugt. 2. Randstein-Stockmaschine Mit der Randstein-Stockmaschine werden die von Hand grob vorbereiteten Steine durch im Innem der Einkapselung angeordnete Stockhammer bearbeitet. Der dabei anfallende Grobstaub wird mit einer Forderschnecke, der Feinstaub durch Absaugung aus dem Gehause entfemt. 3. Trog-Frasmaschine Bei der Trog-Frasmaschine erfolgt die Absaugung des Staubes durch das einem Holhbohrer ahnlich gestaltete Fraswerkzeug. STACIBABSCHEIDER Als Staubabscheider werden meistens Gewebefilter, neuerdings auch Sinterlamellenfilter verwendt. Als Antriebsenergie benutzt man tiberwiegend Strom oder Druckluft. Um den Energieverbrauch fur die Entstaubung bei der teinbearbeitung mit Druckluftwerkzeugen und Stauberfassung am Werkzeug moglichst niedrig zu halter, werden in verschiedenen Betrieben sogenannte Einzelentstauber verwendet. Jeder Arbeitsplatz hat fiir sich ein Absauggerat. Es handelt sich hier um Injektor-Gerate. Ein Steuerventil sorgt dafiir, dap das Entstaubungsgerat nur Respirators and Dust Controls lauft, wenn mit dem Drucklufthammer gearbeitet wird. Der Druckluftverbrauch wird bei dieser Arbeitsweise erheblich gesenkt. SCH LU0BETRACHTUNG Fur alle bei der trockenen Bearbeitung von Werkstein vorkommenden Arbeiten gibt es entsprechende Staubabsaugungen. Voraussetzung fiir eine einwandffeie Entstaubung der Arbeitsplatze ist jedoch die bestimmungsgema/te Verwendung und sorgfaltige Wartung der Erfassungseinrichtungen und Anlagen. Bei der Steinbearbeitung mit handgefuhrten Geraten oder Handwerkzeugen bedeutet die Verwendung der Absaugeinrichtungen stets eine leichte Behinderung. Nach einer Einarbeitungszeit werden die Einrichtungen von den Beschafigten im allgemeinen angenommen, da die meisten von ihnen erkannt kaben, da/3 die Anlagen der Erhaltung ihrer Gesundheit dienen. 1045 Respirators and Dust Controls EXPLORATIONS TO SOME PROBLEMS IN ESTABLISHING DOST ALLOWABLE CONCENTRATIONS LIU ZHANYUAN Zhang Weichang Fang Yuxiang Xiao Xingyuan Liaoning Institute of Labour Hygiene, Shenyang, China, PRC Certain difficulty exists, either theoretically or methodologi cally, in studies on dust allowable concentration. Before the 1950s, allowable concentration only existed for silicon dioxide and, later, that for asbestos was added. In die past decade of years, the establishing of dust allowable con centration has developed rapidly, but is still far from meeting die practical need. To improve method for study and to speed up its development, therefore, has become an urgent problem to be solved at pre sent. The present article is exploring some problems in establishing dust allowable concentration as follows: TREND IN DEVELOPMENT OF DUST ALLOWABLE CONCENTRATION Along with increase in number of newly-established dust allowable concentration, classification naturally appears. The ACGIH of die United States divides mineral dust TLV into four major categories.2 hi the Soviet Union, in addition to 53 kinds of mixed dust allowable concentrations established separately,1 the maximum dust allowable concentrations are classified into silicate, carbon, metal and organic matter ex cept that ofsilicon dioxide. The dust allowable concentration published by Japanese Industrial Society falls info three ma jor categories: silicon dioxide, ``various dusts" and asbestos,3 while in China, dust allowable concentration may be divided info six major categories: silicon dioxide, silicate, carbon and coal, metal, organic dust, and others.4 A tendency toward grading has turned up. As for free silicon dioxide dust, in some countries, it is classified into two grades, while in some other countries it is classified info four grades and in some countries, it is calculated by equation (see Table I). In Japan, the "various dusts" with free silicon dioxide con tent less than iq% are divided info three grades.3 hi Soviet Union, no apparent grading is done, but in effect, die 65 kinds ofother various dusts with free silicon dioxide less than 20% are classified info six grades as 1, 2, 4, 6, 8, and 10.2 In China, the various dusts except silicon dioxide are divided into five grades as 3,4,5, 6, and 10.4 GENERAL STRUCTURAL CONSTRUCTION OF DUST ALLOWABLE CONCENTRATION Having analyzed historical development tendency, we pro pose to establish structure with classification and grading for dust allowable concentration. 1046 1. Seven categories are classified according to dust characteristics: a) silicon dioxide dust b) silicate dust c) metal dust d) coal dust and various carbon dust e) organic dust f) various mixed dust g) other dust. One of the purposes of classification is to work as reference for identical dust allowable concentration developed. 2. Four categories are classified according to extent of harm done by dust (see Table II)- One ofthe purposes ofclassification is to simplify the method, to speed up establishing concentration, as well as to benefit monitoring. In recent years, some countries have adopted die method ofcalculating die Si02 dust allowable concentration with formula, which gives an impression of accurate quanti ty, but in effect, by present available method and means it is difficult to reflect accurately the changing factors of pneumoconioses' occurrence due to the complex nature ofthe disease's developing course and die unstableness ofworkers exposed to dust in production. This method gives rise to a series of problems to monitoring. According to die study results ofpneumoconioses in die province in die past twenty years, we think that to divide dusts info four major grades ac cording fo occupational harm they have done may generally distinguish die extent of harm done by various dusts. ON THE STUDY METHOD OF DUST ALLOWABLE CONCENTRATION Data on epidemiology disease is doubtless the key basis for establishing dust allowable concentrations as well as a must data, but pneumoconioses is a chronicle developing process, especially die new industrial dust for which its allowable con centration cannot be established after long periods of time waiting for the data ofepidemiology disease. Then, is it possi ble fo take it as a basis for establishing dust allowable con centrations with animal experiments? We think it is. As is known, pneumoconioses is a disease that can be studied with certain pathological models established on animal experiments. Analysis of animal experiments on about twenty kinds of dusts, conducted in contrast with data Respirators and Dust Controls Table I Grading of Free Silicon Dioxide Dust Allowable Concentration in Various Countries (mg/m3) Country China Soviet Union Japan U.S.A. Other Content o free silicon dioxide (*) dusts -1 1-2 1-10 -"30... 11 ---40- 1--50 -i -70 j1 n-50r >80 10 2 1 10 4 2 1 2.9 12 1.5 3.0 6.0 R=------------- T=--------------- 0.22Q+1 0.22Q+1 10 0.05-^0.1 Notet R = The inhalant dust T = Total dusts Q = Content of free SiO, in dust (*) Table H Grading of Dust Allowable Concentration Extent of ham Very serious Serious Moderate Slight Grading 1 II III IV Max. allowable concentration (eg/e*) 1 2 5 10 Dust Pure quartz dust with free SiO, over 80* Various dusts with free SiO, between 10^80*. Asbestos dust. Various dusts with free SiO, between 5--10*;partial silicate dust (as talcum dust); partial metal dust (as metalic aluminium dust). Various dusts with free SiO, less than 5*; partial silicate dust (as pearlite and dolomite); carbon and coal dust; partial metal dust (as tin); and organic dust, etc. 1047 Respirators and Dust Controls Table m Cases of Grading of Harm Done by Dust (According to Length of Time for Appearence of Fibering) Grading Length of tine of appearence of fibering of pulmonary tissue when animal is contaminated (month) Nane of dust experimented r 3 Pure quartz dust (with 85^-90* of free SiO,) ii 6 Ceraaic nixed dust, caly (A) dust (15^35* of free SiO,) in 12 Mixed clay (B) dust (5.9** of free SiO,) IV 18 Pe&rlite dust, clay (C) dust ( 0. 5--3. 6* of free SiO,) Fibering standards appearence of gelatinizing fiber on the basis of hyperplasia of netted fiber ofepidemiology, may basically reflect the extent ofoccupa tional harm done by various dusts with animal experiments. The pneumoconioses with high occurrence, short work age, rapid development and high mortality (such as that caused by quartz dust) appears rapid fibering of pulmonary tissue and serious extent ofpathological change in animal experiments, while in reverse, die pneumoconioses with low occurrence, long work age ofoccurrence, slow development and low mor tality (such as pneumoconioses caused by clay dust) appeared slow in fibering of pulmonary tissue and slighter extent of pathological exchange in animal experiments. With die time for rat lung to show fibering as die basis of grading, results of grading at various dusts are shown in Table HI. These results provide a possibility to use animal experimental data for establishing dust hygienic standard. The united animal ex periment method can be determined by the National Hygiene Standard Commission. The standard dust for contrast may be supplied by die National Labour Hygiene Study Center and it is for all the local labour hygiene study centers to direct the experimental method. All labour hygiene and scientific research departments can engage in study and development ofdust allowable concentration. Checked and approved by the Hygiene Standard Commission, die study results can be published and put into force as a provisional standard, hi die second stage, die standard can be revised according to data ofepidemiologic investigation. Thus it is possible to speed up the establishment of (hist allowable concentration. The pathological grading ofanimal experiments can be based on the speed ofthe appearence offibering for the time being. Obviously, there are many problems to be further explored such as, die biological effect of dust cannot be attributed to whether there is fibering effect. Therefore, it is very impor tant to set up a systematic study method for pulmonary tox icity experiments. It is, however, advisable, from technical development strategy, to select a practical and feasible method. REFERENCES 1. CaHHTapHue Bpasaaa npeKTNpaaa HMfl apoMtia eHUx npeAopHflTMit < r 0-CTYI2.1005-76>, 1976. 2. ACG1H, Threshold limit values for chemical substances in workroom air adopted by ACGIH for, 1981. 3. Japanese Industrial Hygiene Society, Allowable CoocaXralion (1) Report (1980), Industrial Medical Science 22(5), 421, 1980. 4. Hygiene Standard for Industrial Enterprise Design, Beijing, 1979. 3. Sbong Tengyuan: SomeProblems oo Allowable Concentration. Labour Science 56(6), 335, 1980. 6. WHO: Methods used in the USSR forestablishing biologically safe levd of toxic substances, Geneva, 1975. 1048