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Tt Performance Characteristics of Dust Respirators, Bureau of Mines Approved and Non-approved Types WILLIAM H. REVOIR and VINCENT A. YURGILAS Respirator Development Laboratory, American Optical Company, Southbridge, Massachusetts 01550 g The performance characteristics of six Bureau of Mines approved and six non* approved respirators were evaluated against seven different dust aerosols* Silica, silicate polishing compound, cement, sulfur, lead, iron and one aerosols were used. Approved respirators permitted less particulate penetration of the filters, however some approved respirators failed to meet tests carried out in accordance with the Bureau of Mines approval schedules. Approved respirators were fairly uniform in performance, with few exceptions, but non-approved respirators varied widely in per formance. The respirators rested represented a wide range of filter materials and filtering areas. Introduction countered in industrial occupations. The ear DobmlfaecsartniunsUpesgrahSa.srittunTeiDccgdlh,ueISassgatnrssidainusnsdtdpthihnieaseegnped,errdoereaissdssbeoipnridlnaitrecdaiaongitnointrrgoarsyw,tisiaodhthininriarcigzlhlbapinyroraodgfrcme,emsseagosocnelesihdndsta nicRfaib"liinaenfluoaalsetmdhthtradsioaslrerenor"dcswfNuotthsliraeomdto.at"uecdolsroiva.fvoTelexahdrPHieddtlfreiihsrenuoteysotmoatrfayrterpch"2eere3semstpovtaoEieornftanlhdy7tmteoe9irrirnne,uAhefdsea.raearDstleaeo.naR,stfcinooredfelnmorsfooerasmeoirnnesf frequently encountered in industry'. Although the best procedures to prevent inhalation of the literature, extending from ancient times to the present, pertaining to the employment harmful dusts by personnel are the removal of the particulates at their source of genera of dust respirators to protect miners, meal refiners, quarry workers, stone cutters, grain tion or the reduction of the particulate con millers, tool grinders, etc. Although dust centration to levels sufficiently low so as not respirators were widely used in the nineteenth to cause bodily harm, there are situations century, no proper study of these devices where, for one reason or another, these was made, and consequently the efficiency procedures are inapplicable, impractical, im of the particulate filtering materials was low, possible, or not adequately effective. In the breathing resistance was usually high, such situations, personal respiratory protec and the fit on the face was poor. tive devices are utilized to protect personnel. In the United States, the matter of ade The dust respirator, a device which covers quate functional characteristics for dust res the nose and mouth and which contains a pirators based on scientific and engineering porous material that removes dust from in principles was not established until as late spired air, is the most widely used instru as the 1930's. On August 20, 1934, the U. S. ment for protection against dust. Bureau of Mines issued a test and approval Dust respirators were used in ancient times schedule pertaining to particulate filtering- to protect men against injurious dusts en type respiratory' protective devices including 322 TX TINER RMC0058004 American Industrial Hygiene Association Journal Table I Description of Dust Respirators Respirator Type Respirator Designation Approved, angle filter ASI AS2 AS3 Approved, double filter .ADI AD2 AD3 Nuisance dust Ml N2 N3 N4 NS N6 Type of Filter Medium Effective Filtering Area (cm*) Electrostatic felt Electrocute felt Nonwoven web of synthetic fiber* and asbestos 48 42 66 Electrostatic felt Soft paper Nonwoven web of synthetic fiber* and asbestos 73 266 73 Open-cell elastomeric foam Thin nonwoven web of eellulosic fibers Cellulosic fiber batt Open-ceil elastomeric foam Thin nonwoven web of cellulosic fibers Nonwoven web of synthetic fibers 41 137 40 ,, 154 76 36 323 .1 .1 fl i Table II Characteristics of Dust Particulates Dust Particulate Silica* Lead* Polishing compound* Cement Sulfur Iron Zinc Geometric Mean Size (microns) 0.51 0.67 0J3 0.74 1.03 1.2 10 Standard Geometric Deviation 1.90 1.94 2.42 1.97 2.30 1.96 2.40 Specific Gravity 2.65 9.98 2.5 2.3 2.07 7.9 7.14 U. S. Bureau of Mine* silica dint particulate. MJ. S. Bureau of Mine* lead dust particulate (75% litharge, 25% lead). Chiefly silicates. dust respirators.1 This test and approval schedule and its subsequent revisions2,3 do not require that all dust respirators must be sub mitted to the Bureau for testing and approv al. The Bureau has no regulatory power re quiring that all respirators must be tested and approved. Submitting respirators to the Bu reau for approval is entirely voluntary on the part of the respirator manufacturers. Ap proved respirators should ensure users of adequate efficiency of removing airborne con taminants from inspired air, sufficiendy low breathing resistance, and an economically feasible period of service. The first dust res pirator was approved by the U. S. Bureau of Mines in 1935. Dust respirators, approved by the U. S. Bureau of Mines and nonapproved, made by a number of different manufacturers are available. These respirators differ widely in design, construction, materials, and functional characteristics. The nonapproved devices, popularly known as nuisance dust respirators, generally are recommended for protection against nontoxic dusts. Many industrial hy gienists and physicians feel that there is no such thing as a nontoxic dust, since inhaling copious quantities of so-called inert dust par- i i t\ t TX TINER RMC0058005 324 July^August, 1968 Table III Performance Characteristics of Dust Respirators for Silica Dust Range of Dust Concentration: 56.1-60.3 mg/tn* Range of Dust Load: 164.3-173.7 mg Respirator Type Approved, single filter Respirator AS1 AS2 AS3 Approved, double filter Nuisance dust ADI AD2 AD3 NI N2 N3 N4 N5 N6 Inhalation Resistance at 85 Lpm Dust Penetration <*> Initial (ms HrU) Final (mm MrO) lJ 173 44.9 2.7 2U 48.5 3.2 21.1 46.3 2.0 27.2 50.3 0.3 24.1 38.1 0.6 24.4 50.0 0.4 8.4 18.0 0.1 8.9 18.5 0.9 36.3 69.6 0.3 46.3 84.3 1.1 13.0 7.9 1.2 12.2 23.4 20.8 31.1 16.7 16.9 32.9 33.3 5.7 4.0 36.2 29.3 28.1 31.5 6.1 5.6 1.8 1.8 2.0 2.3 41.2 72.4 2.8 2.5 9.7 9.1 25.9 19.8 84.9 91:2 6.6 7.1 199.4 241.2 373 66.8 22.4 16.5 ticulate, especially for long periods of time, can result in adverse physiological effects. Although the literature contains informa* tion concerning the performance characteris tics of dust respirators, much of the informa tion is old, pertains to only one specific res pirator, or cites the functional characteristics of dust respirators for only one particular type of dust particle.'**12 Inasmuch as dust respirators are extensively used in industry', the authors felt it important to investigate and report the performance characteristics of modem, commercially available dust respira tors, U. S. Bureau of Mines, approved de vices and nonapproved devices, for a wide variety of dusts. This information should be helpful to industrial hygienists and safety en gineers in aiding them to select the proper dust respirators for protection of workers. Respirators Twelve different dust respirators, each made by a different manufacturer, were evaluated. Six of the respirators were ap proved by the U. S. Bureau of Mines for use against dusts, and the other six were nonapproved nuisance dust type respirators. The respirators employed in the study dif fered greatly in style, filtering material, and filtering area. All the respirators were pur chased on the open market, so they repre sent what users obtain when they purchase respirators for protection of workers. Three of the approved respirators employ single filter elements, while the other three use double filter elements. All the approved respirators utilize relatively inexpensive, re placeable filter elements. The approved res pirators contain facepieces composed of rub ber, plastic, or metal, and the face-sealing edge of all facepieces is either soft rubber or flexible plastic so as to conform to the facial features of the wearer. The approved de vices utilize both inhalation and exhalation valve systems. The respirators are approved by the U. S. Bureau of Mines for protection TX TINER RMC0058006 American Industrial Hygiene Association Journal Table IV Performance Characteristics of Dust Respirators for Lead Dust Range of Dust Concentration: 18.6-22.7 mg/m' Range of Dust Load: 53.5-65.5 mg Respintor Type Approved, jinfle filter Respirator AS1 AS2 ASS Approved, double filter ADI AD2 AD3 Nuisance dust N! N2 N3 N4 NS NS Inhalation Resistance at 83 Lpn Dust Penetration Initial (%) fmmHsO) Final (an HsO) 0.67 0.37 0.13 0.38 0.07 0.02 19.6 21.1 25.6 26.7 23.9 25.4 21.3 21.6 26.9 2S.9 26.2 26.9 0.03 0.02 0.05 0.02 0.23 0.53 6.9 8.9 48.0 50.8 11.7 10.4 9.4 9.4 50.0 33.9 12.7 11.7 14.1 16.6 21.4 13.3 14.0 17.0 1.8 1.2 20.6 26.5 26.7 19.6 6.9 6.6 1.8 1.8 2.5 2-5 79.8 116.8 2.8 2.8 7.1 9.6 7.1 7.4 2.3 2.0 3.3 2.6 107.6 153.7 2.9 4.3 7.6 10.2 325 of personnel against pneumoconiosis-produc ing and nuisance dusts (dusts having a TLV not less than 2.4 million particles per cubic foot of air) and dusts not significantly more toxic than lead (dusts having a TLV not less than 0.1 milligram of particulate per cubic meter of air). Some of the respirators are approved under Bureau Schedule 21,1 while others are approved under Bureau Schedule 21A,* or 21B.3 The Bureau does not require that a respirator be upgraded when a test and approval schedule is re vised. Once a respirator is approved by the Bureau under a specific schedule, it can be manufactured and sold as long as it con forms to the requirements of the schedule under which it was tested and approved. All the nonapproved respirators use single filtering elements. Some of the nonapproved devices employ a facepiece, while others do not but instead utilize the filtering element for sealing against the wearer's face. Only one of the nonapproved respirators has both an inhalation and exhalation valve system, two of these respirators contain an exhala tion valve system, and the other three respi rators have neither an inhalation nor an ex halation valve system. The absence of an exhalation valve system in a respirator means that the wearer must exhale through the fil tering element. As the filtering element con tinues to retain particulate, its resistance to breathing increases--this can be dangerous, inasmuch as it can cause fatigue, since ex halation is not a muscular effort but is in stead due to a passive muscular relaxation. The respirators employed in the study are described in Table I. The effective filtering areas reported were obtained from measure ments of areas of respirator filtering elements containing dust particulate deposited during evaluation tests. 326 July-August, 1968 Table V Performance Characteristics of Dust Respirators for Fine Polishing Compound Range of Dust Concentration*. 55.9-60.2 mg/m' Range of Dust Load: 161.0-173.0 mg Respirator Type Approved, tingle filter Respintor AS1 AS2 AS3 Approved, double filter ADI AD2 AD3 Nuisance dust Nl N2 S3 N4 N5 N6 Inhalation Rcsistancie at 85 Lpa Dun Penetration Initial {%) (am H.-0) Final (an HeO) 2.8 20.1 2.0 20.1 60.7 53.3 2.1 27.4 54.6 2.2 26.9 51.6 0.8 23.1 1.1 23.1 52.5 50.3 0.6 8.9 19.0 0.2 9.9 21.3 4.8 42.7 75.2 0.6 47.7 91.4 1.3 13.7 26.9 1.1 13.0 25.2 32.1 26.1 14.7 15.6 24.1 24.9 6.4 8.8 23.4 48.7 29.1 27.9 5.6 7.1 2.3 2.0 2.8 3.0 125.7 64.7 3.0 3.3 9.4 9.7 17.5 21.6 90.4 70.6 13.0 9.7 381.0 203.2 73.4 31.0 16.5 15.2 Dust Particulates Seven different particulates were used to evaluate the performance characteristics of the dust respirators. Both nonmetallic and metallic particulates were utilized. The dusts varied widely in particle size and specific gravitv. Particle size information was ob tained by sampling the dust aerosols with membrane filters and then employing stan dard optical and electron microscopy meth ods for particle size measurements. The characteristics of the particulates are given in Table II. Procedures A chamber having a volume of 18 cubic meters was used to evaluate the performance characteristics of the dust respirators. Fil tered air was passed continuously through the chamber, and provision was made to continuously inject and disperse into the atmosphere of the chamber the particu lates. Regulating the flow of air through the chamber and precisely controlling the rate of particulate injection resulted in ob taining die desired concentration of airborne dust particulate in the test atmosphere. The particulate injector employed is known as the U. S. Bureau of Mines dust freed ap paratus.13 This apparatus utilizes a rising vertical glass tube containing the dust par ticulate connected to an air ejector. The glass tube containing the particulate is pulled up around a fixed glass tube connected to the ejector. The moving tube is raised at a controlled rate and the particulate is picked up by a whirling airstream and is carried through the fixed tube into the ejector. Particulate-laden air passes from the in jector into an air micronizer which breaks up aggregates of particulate and disperses separate and discrete dust particles into the atmosphere of the test chamber. The air micronizer used is a form of fluid energy mill.**'18 In this device, compressed air is TX TINER RMC0058008 * * Vi F sr I American Industrial Hygiene Association Journal 1 Table VI Performance Characteristics of Dust Respirators for Cement Dust Ranye of Dust Concentration: 56.7-61.6 mg/m' Range of Dust Load: 163.2-177.2 mg Respirator Type Approved, single filler Respirator AS1 AS2 AS3 Approved, double filter ADI AD2 AD3 Nuisance dust .VI N2 N3 N4 N5 N6 Inhalation Resistance at 85 Lpw Dust Peaetratioo Initial (%) (mm HiOl Final (mm Hrl>) 3.1 18.5 41.9 2.1 20J 43.8 1.3 27.4 48.3 1-7 26.4 46.8 0.2 24.6 42.2 0.3 23.1 40.2 0J3 7.6 16.3 0.3 8.9 18.8 1.5 48.5 79.2 1.9 44.4 75.7 2.1 11.4 19.8 1.8 12.2 20.8 24.2 21.1 15.7 14.5 16.9 16.1 5.5 3.9 18.6 22.6 17.2 13.3 6.9 7.1 2.0 2.3 2.5 2.8 54.6 81.3 3.0 2.8 7.6 9.1 17.3 18.8 30.2 32.3 6.3 7.1 315.0 377.2 20.1 22.6 13.0 18.3 1 327 M :1 i i fed into a small cylindrical-shaped chamber by jets arranged tangentially to the peripheral wall of the cylindrical chamber. This re sults in a high-velocity swirling airstream at substantially atmospheric pressure inside the cylindrical chamber. Particulate-laden air from the injector also enters the raicronizer chamber tangentially where shearing forces break up aggregates of particulates. The swirling air stream exits from the micronizer at a central opening at its axis, and the airstream disperses separate and discrete dust particles into the atmosphere of the test chamber. Respirators being tested are sealed to spec ial holders located inside the test chamber. Each holder is connected to a high-voltage alternating-current electric precipitator which collects on a glass tube the particles that penetrate the respirator. An electric pre cipitator also is used to collect samples of dust particulate in the atmosphere in the chamber for the determination of the concen tration of dust in the chamber and for the determination of the dust load passed into a respirator during a test. The principle of operation of the alternating-current electric precipitation is well-known.17 The precip itators employed are modified versions of those designed and used by the U. S. Bu reau of Mines in the testing of particulate filtering-type respirators.19 A box-shaped baf fle projecting from the wall of the test chamber which surrounds the respirators be ing tested is used to ensure a uniform dust concentration at each of the sampling loca tions. Air exiting from a precipitator is passed through a bed of activated carbon granules to remove ozone created in the precipitator, then through a rotameter which indicates the airflow rate, next through a needle valve used to control the airflow, and, finally, through an air pump. The test chamber contains four sampling units, and each samp- 'i .{ i U TX TINER RMC0058009 328 July-August, 1968 Table VII Performance Characteristics of Dust Respirators for Sulfur Dust Range of Dust Concentration: 55.5-60.8 mg/ms Range of Dust Load 159.9-175.2 mg Respirator Type Approved, single filter Respirator ASl AS2 AS3 Approved, double filter ADI AD2 AD3 Nuisance dust N1 N2 N3 N4 N*5 N6 Inhalation Resistance at 85 Lpm Dust Penetration Initial We) (an HiO) Final (an HiO) 0.4 19.3 35.8 1.1 20.3 32.0 0.6 25.4 37.3 0.4 25.9 35.1 0.2 24.1 30.2 0.2 24.6 30.5 0.2 8.9 12.4 0.3 9.4 15.2 0.5 49.8 63.3 0.7 43.2 54.3 0.6 12.4 16.5 0.5 11.9 15.7 13.4 13.5 5.5 8.0 9.3 9.1 0.4 1.2 9.2 10.4 2.6 7.1 7.1 5.6 2.3 2.0 2.8 2.8 67.1 85.0 2.5 2.5 9.4 7.6 17.5 18.3 23.9 22.1 14.5 15.2 159.8 209.9 13.5 11.9 15.2 9.6 ling unit has its own air pump. A mano meter is connected to each respirator holder downstream of the respirator to measure the resistance to airflow being offered by the res pirator during the test. During a test, the test atmosphere is passed into a respirator at a steady airflow rate of 32 liters per minute for a test period of 90 minutes. The dust particles penetrating the respirator are collected by the glass sample tube of the precipitator, and the mass of penetrating particulate is determined either gravimetrically or by chemical analysis, de pending on the particulate composition. A precipitator not connected to a respirator is operated similarly and is used to collect samples of dust in the test chambers at mosphere throughout the 90-minute test period. The manometer connected to the downstream side of the respirator measures the resistance to inhalation offered by the respirator to the continuous airflow of 32 liters per minute through the respirator dur ing the entire test period. In addition, just prior to the test and just after completion of the test, the inhalation resistance offered by the respirator to a steady airflow of 85 liters per minute is measured. These are the test conditions of dust respirator approval tests carried out by the U. S. Bureau of Mines.1*3 Each of the dust respirators was tested against silica dust in the manner employed by the U. S. Bureau of Mines for approval testing of dust respirators for use against pneumoconiosis-producing and nuisance dusts (dusts having a TLV not less than 2.4 million panicles per cubic foot of air! .1*3 Each of the dust respirators was evaluated against lead dust in the way that the Bureau carries out approval tests of dust respirators for use against dusts not significandv more toxic than lead (dusts having a TLV not less than 0.1 milligram of particulate per cubic meter of air).1*3 The silica dust tests were carried TX TINER RMC0058010 American Industrial Hygiene Association Journal Table VIII Performance Characteristics of Dust Respirators for Iron Dust Range of Dust Concentration: 56.2-62.8 mg/rn* Range of Dust Load: 161.7-181.0 mg Respirator Type Approved, single filter Respirator AS1 AS2 AS3 Approved, double filter ADI AD2 AD3 Nuisance dust N'l N2 N3 N4 N5 N6 Inhalation Resistance at 85 Lpm Dust Penetration Initial {%) (mm HrO) Final (mm HiO) 0.9 19.8 20.8 1.2 20.6 24.1 0.8 26.9 28.4 0.5 27.4 29.5 0.2 23.9 30.0 0.3 23.1 25.6 0.6 8.6 10.4 0.6 8.9 9.6 0.6 48.3 57.7 0.2 41.2 45.9 0.7 12.7 15.8 0.6 14.5 16.3 18.8 5.6 7.6 13.3 6.1 8.6 10.6 2.3 6.3 2.3 5.8 7.8 2.5 5.1 16.1 2.3 3.3 2.5 95.8 204.5 2.1 99.0 210.8 11.1 2.8 18.8 12.8 2.8 9.9 14.1 8.1 9.4 15.2 8.4 9.6 ! 329 out so that the concentration of particulate reau schedules do not permit the inhalation *A in the atmosphere in the test chamber would resistance offered by a dust respirator to ex be approximately that of the maximum con ceed 50 millimeters of water for a steady air centration of 60 milligrams of particulate per flow rate of 85 liters per minute. cubic meter of air prescribed by the Bureau. When the dust respirators were tested The lead dust tests were performed so that against the other five dust aerosols, the pro the concentration of particulate in the test cedures employed were those prescribed for atmosphere in the chamber would be ap U. S. Bureau of Mines dust tests. These tests proximately the maximum concentration of were carried out so that the dust concentra 20 milligrams of particulate (analyzed as tions in the test atmosphere would be approx metallic lead) per cubic meter of air as or imately 60 milligrams of particulate per cubic c> dained by the Bureau. meter of air. p1 A respirator approved by the Bureau under Schedules 21 and 21A is permitted a silica Results dust particulate penetration of 3.0 milligrams, Each of the twelve dust respirators was while a respirator approved under Schedule tested twice against each of the seven dust 2 IB is allowed a silica dust particulate pene aerosols. The test results are given in tabular tration of only 1.5 milligrams. A respirator form in Tables III through IX. approved by the Bureau under Schedules 21, Figure 1 graphically illustrates how the sili 21A, and 21B is allowed a lead dust par ca dust particulate penetration of the non- ticulate penetration of 0.43 milligram (ana approved nuisance dust respirators varied as lyzed as metallic lead). The mentioned Bu the mass of silica dust particulate passed :( .i f J .1 i T TX TINER RMC0058011 330 July-August, 1968 Table IX Performance Characteristics of Dust Respirators for Zinc Dust Range of Dust Concentration: 58.2-60.3 mg/m* Range of Dust Load: 167.7-173.5 mg Respirator Type Approved, single filter Respirator AS1 AS2 ASS Approved, double filter ADI AD2 AD3 Nuisance dust SI N2 S3 N4 NS N6 Inhalation Resistance at 85 Lpn Dust Penetration Initial <%) (mm HjO) Final (mm HtO) 1.6 20.6 23.1 1.6 19.8 21.6 0.7 26.4 28.5 0.8 25.4 27.9 0.7 24.4 26.7 0.4 23.4 25.4 0.7 9.4 10.2 0.8 8.6 9.7 4.5 46.8 49.0 2.9 48.7 56.2 0.5 12.4 13.2 0.8 12.7 ' 14.0 10.9 12.3 7.3 5.5 7.2 8.8 1.7 1.4 25.0 21.3 7.0 8.2 7.1 6.1 2.0 2.5 2.8 2.3 70.3 86.3 3.0 3.3 8.4 9.7 7.6 6.9 2.8 4.1 3.0 2.8 99.7 120.7 4.8 5.8 9.1 11.2 into the respirators increased. A graphical illustration of this type for the dust respira tors approved by the U. S. Bureau of Mines was not made, since these respirators allowed only a very small quantity of silica dust par ticulate to penetrate. Figure 2 is a graphical illustration on how the inhalation resistance of the Bureau-ap proved dust respirators varied as the amount of silica dust particulate passed into said respirators increased. Likewise, Figure 3 graphically shows how the inhalation resist ance of the nonapproved nuisance dust res pirators changed as the quantity of silica dust passed into these respirators increased. Discussion A review of the test results shows that the nonapproved nuisance dust respirators per mitted particulate penetrations that are substantially greater than the penetrations of Bureau-approved dust respirators. In fact, the particulate penetrations of Bureau-ap proved respirators are only very small frac tions of those of the nonapproved respira tors. As expected, penetrations of respirators by particles of larger size and greater specific gravity are generally, but not always, less than the penetrations by particles of smaller size and lower specific gravity. The graphical illustration of the variation of particulate penetration of nonapproved nuisance dust respirators with increase in par ticulate load into the respirators indicates that the percentage of particulate pene tration of these respirators often is very great during the first portion of the test period. This can be dangerous, inasmuch as during this period a respirator offers a relatively low resistance to breathing--thus, the wearer of the respirator may tolerate it only during the time that it offers low breathing resistance and permits a substantial particulate penetra- TX TINER RMC0058012 American Industrial Hygiene Association Journal jj, CE 331 SILICA DUST INTO RESPIRATOR (") FtcuRE 2. Variation of increasing inhalation re sistance offered by Bureau-approved dust respirators for 324pm airflow with increasing mass of silica dust particulate passed into respirators. Figure 1. Variation of increasing silica dust paniculate penetration of nonapproved nuisance dust respirators with increasing mass of particulate passed into respirators. tion, and he discards it when the breathing resistance increases and replaces it with a fresh unit that again allows a substantial portion of the dust to be inhaled. A review of the silica dust aerosol tests and the lead dust aerosol tests for the dust respirators approved by the U. S. Bureau of Mines indicates that two of these respira tors had particulate penetrations greater than that allowed by the older Bureau Schedules 2l and 21A. These test results also show that one of the respirators had final inhala tion resistances at the end of both the silica dust tests and the lead dust tests greater than the maximum inhalation resistance permitted by the Bureau. The test data show that the one nonap proved nuisance dust respirator that allowed much lower dust particulate penetrations than the other respirators of this class had both initial and final inhalation resistances that far exceeded those of the other respirators. In fact, this respirator had final inhalation resistance values that are intolerable. A review of the test results indicates that, while most types of Bureau-approved respi rators are fairly uniform in performance, some types have a significant variation in performance. Also, the test results show that most types of nonapproved nuisance dust res pirators vary widely in performance. Summary An investigation was carried out to deter mine the performance characteristics of com mercially available dust respirators, both res pirators approved by the U. S. Bureau of Mines and nonapproved respirators popularlyknown as nuisance dust respirators. Twelve respirators, six approved types and six non approved types, were employed in the study. The performance characteristics of these res pirators were evaluated for seven different dust aerosols. Both aonmetallic and metallic particulates were utilized, and the particu- 332 July-August, 1968 o etrauons allowed by the Bureau-approved respirators are only small fractions of the penetrations permitted by the nonapproved respirators. The investigation indicates that, while most types of Bureau-approved dust respirators are fairly uniform in performance, some vary significantly in performance, and most types of nonapproved nuisance dust res pirators vary widely in performance. Figure 3. Variation of increasing inhalation re sistance offered by nonapproved nuisance dust re spirators for 32-ipm airflow with increasing mass of silica dust particulate passed into respirators. lates varied widely in both size and specific gravin-. The study shows that the particulate pen- References 1. Pnocmvtt roa Testing Futm-Tyfe Dust. Fume. *no Mist Respirators por Permissibility. V. S. Bunak of Mine: Schedule 21 (Aug. 20, 193*). 2. Test for Permissibility op Filter-Type Dust. Fume, and MiST Respirators. U. S. Bureau of Mines Schedule 21A lAoril 19. 1953;. 3. Test por Permissibility op Filter-Type Dust. Fume, and Mist Respirators. V. S. Bureau of Mines Schedule 21B (Jan. 19. 1965). 4. Kat2. S. H.. C. W. Smith, and E. C. Meiter: Dum Respirators--Their Construction and Filtering Efficiency. U. S. Bureau of Mines Technical Paper 394, p. 3t 09261. 5. Katz, S. H.. E. C. MtrrtR. and F. H. Gibson; Efficiencies of Painters' Respirators. U. S. 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H.: Clogging Tests on Dust Respirators u-der Humid Conditions. British Standards I restitution Document 67/4154 (Feb. 6, 1967). 13. Schresk, H. H,: Testing and Design of Respiratory Protective Devices. U. S. Bureau of .Miner Information Circular 7086 (September 1939). 14. Berry. C. E.: Fluid-Energy MUls, Ind. Eng. Chem. 36: 672 (March 19*6). 15. Smith, J. C.: Size Reduction. CAem. Eng. 59; 151 (Aug. 1952). 16. Perry, R. H.. C. K. Chilton, asd S. D. Kirkpatrick (Es.): CAemieef Engineers' Handbook, 4th Ed., pp. 8-42. McGraw-Hill Book Company, Inc., New York, X. Y. (1963). 17. Cosine, J. D.: Caseous Conductors, p. 252. McGrow. Hill Book Company. Ine., New York, X. Y. (19*11, TX TINER RMC005S014