ASTM F2101 – 01

Designation: F 2101 – 01 Standard Test Method for Evaluating the Bacterial Filtration Efficiency (BFE) of Medical Face Mask Materials, Using a Biological Aerosol of Staphylococcus aureus1 This standard is issued under the fixed designation F 2101; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval. INTRODUCTION Workers, primarily those in the health care profession, involved in treating and caring for individuals injured or sick, as well as the patient, can be exposed to biological aerosols capable of transmitting disease. These diseases, which may be caused by a variety of microorganisms, can pose significant risks to life and health. Since engineering controls can not eliminate all possible exposures, attention is placed on reducing the potential of airborne exposure through the use of medical face masks. 1. Scope 1.1 This test method is used to measure the bacterial filtration efficiency (BFE) of medical face mask materials, employing a ratio of the upstream bacterial challenge to downstream residual concentration to determine filtration effi- ciency of medical face mask materials. 1.2 This test method is a quantitative method that allows filtration efficiency for medical face mask materials to be determined. The maximum filtration efficiency that can be determined by this method is 99.9 %. 1.3 This test method does not apply to all forms or condi- tions of biological aerosol exposure. Users of the test method should review modes for worker exposure and assess the appropriateness of the method for their specific applications. 1.4 This test method evaluates medical face mask materials as an item of protective clothing but does not evaluate materials for regulatory approval as respirators. If respiratory protection for the wearer is needed, a NIOSH-certified respi- rator should be used. Relatively high bacterial filtration effi- ciency measurements for a particular medical face mask material does not ensure that the wearer will be protected from biological aerosols since this test method primarily evaluates the performance of the composite materials used in the construction of the medical face mask and not its design, fit or facial sealing properties. 1.5 Units—The values stated in SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance of the standard. 1.6 This test method does not address breathability of the medical face mask materials or any other properties affecting the ease of breathing through the medical face mask material. 1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use. 2. Referenced Documents 2.1 ASTM Standards: E 171 Specification for Standard Atmospheres for Condi- tioning and Testing Flexible Barrier Materials2 F 1494 Terminology Relating to Protective Clothing3 2.2 ANSI/ASQC Standard:4 ANSI/ASQC Z1.4 Sampling Procedures and Tables for Inspection by Attributes 2.3 ISO Standard:5 ISO 2859-1 Sampling Plans for Inspection by Attributes 2.4 Military Standard:6 MIL-STD 36954C (1973) Military Specification: Mask, Surgical, Disposable 1 This test method is under the jurisdiction of ASTM Committee F23 on Protective Clothing and is the direct responsibility of Subcommittee F23.40 on Biological. Current edition approved April 10, 2001. Published June 2001. 2 Annual Book of ASTM Standards, Vol 15.09. 3 Annual Book of ASTM Standards, Vol 11.03. 4 Available from American Society for Quality Control, 611 East Wisconsin Ave., Milwaukee, WI 53202. 5 Available from American National Standards Institute, 11 W. 42nd Street, 13th Floor, New York, NY 10036. 6 Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700 Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS. 1 Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. 3. Terminology 3.1 Definitions: 3.1.1 aerosol, n—a suspension of solid or liquid particles in a gas. 3.1.2 agar, n—a semi-solid culture medium used to support the growth of bacteria and other micro-organisms. 3.1.3 airborne exposure pathways, n—inhalation routes of exposure to the medical face mask wearer. 3.1.4 bacterial filtration effıciency (BFE), n—the effective- ness of a medical face mask material in preventing the passage of aerosolized bacteria; expressed in the percentage of a known quantity that does not pass the medical face mask material at a given aerosol flow rate. 3.1.5 biological aerosol, n—a suspension of particles con- taining biological agents which have been dispersed in a gas. 3.1.6 blood-borne pathogen, n—an infectious bacterium or virus, or other disease inducing microbe carried in blood or other potentially infectious body fluids. 3.1.7 body fluid, n—any liquid produced, secreted, or ex- creted by the human body. 3.1.8 protective clothing, n—a product which is specifically designed and constructed for the intended purpose of isolating parts of the body from a potential hazard. 3.1.9 medical face mask, n—an item of protective clothing designed to protect portions of the wearer’s face, including at least the mucous membrane areas of the wearer’s nose and mouth, from contact with blood and other body fluids during medical procedures. 3.1.9.1 Discussion—Medical face masks also function to partly limit the spread of biological contamination from the mask wearer (health care provider) to the patient. 3.2 For definitions of other protective clothing-related terms used in this test method, refer to Terminology F 1494. 4. Summary of Test Method 4.1 The medical face mask material is clamped between a six-stage cascade impactor and an aerosol chamber. The bacterial aerosol is introduced into the aerosol chamber using a nebulizer and a culture suspension of Staphylococcus aureus. The aerosol is drawn through the medical face mask material using a vacuum attached to the cascade impactor. The six-stage cascade impactor uses six agar plates to collect aerosol droplets which penetrate the medical face mask material. Control samples are collected with no test specimen clamped in the test apparatus to determine the upstream aerosol counts. 4.2 The agar plates from the cascade impactor are incubated for 48 h and counted to determine the number of viable particles collected. The ratio of the upstream counts to the downstream counts collected for the test specimen are calcu- lated and reported as a percent bacterial filtration efficiency. 5. Significance and Use 5.1 This test method offers a procedure for evaluation of medical face mask materials for bacterial filtration efficiency. This test method does not define acceptable levels of bacterial filtration efficiency. Therefore, when using this test method it is necessary to describe the specific condition under which testing is conducted. 5.2 This test method has been specifically designed for measuring bacterial filtration efficiency of medical face masks, using Staphylococcus aureus as the challenge organism. The use of S. aureus is based on its clinical relevance as a leading cause of nosocomial infections. 5.3 This test method has been designed to introduce a bacterial aerosol challenge to the test specimens at a flow rate of 28.3 L/mm. (1 ft3/min). This flow rate is within the range of normal respiration and within the limitations of the cascade impactor. 5.4 This test method allows the aerosol challenge to be directed through either the face side or liner side of the test specimen, thereby, allowing evaluation of filtration efficiencies which relate to both patient-generated aerosols and wearer- generated aerosols. 5.5 Degradation by physical, chemical, and thermal stresses could negatively impact the performance of the medical face mask material. The integrity of the material can also be compromised during use by such effects as flexing and abrasion, or by wetting with contaminants such as alcohol and perspiration. Testing without these stresses could lead to a false sense of security. If these conditions are of concern, evaluate the performance of the medical face mask material for bacterial filtration efficiency following an appropriate pretreatment tech- nique representative of the expected conditions of use. Con- sider preconditioning to assess the impact of storage conditions and shelf life for disposable products, and the effects of laundering and sterilization for reusable products. 5.6 If this procedure is used for quality control, perform proper statistical design and analysis of larger data sets. This type of analysis includes, but is not limited to, the number of individual specimens tested, the average percent bacterial filtration efficiency, and standard deviation. Data reported in this way help to establish confidence limits concerning product performance. Examples of acceptable sampling plans are found in references such as ANSI/ASQC Z1.4 and ISO 2859-1. 6. Apparatus and Materials 6.1 Apparatus: 6.1.1 Autoclave, capable of maintaining 121-123°C. 6.1.2 Incubator, capable of maintaining 37 6 2°C. 6.1.3 Analytical Balance, capable of weighing 0.001 g. 6.1.4 Vortex Mixer, capable of mixing the contents of 16 mm 3 150 mm test tubes. 6.1.5 Orbital Shaker, capable of achieving 100-250 rpm. 6.1.6 Refrigerator, capable of maintaining 2-8°C. 6.1.7 Six-Stage Viable Particle Cascade Impactor. 6.1.8 Vacuum Pump, capable of 57 L/m (2 ft3/mm). 6.1.9 Air Pump/Compressor, capable of 15 PSIG minimum. 6.1.10 Peristaltic Pump, capable of delivering 0.01 mL/min. 6.1.11 Nebulizer, capable of delivering a mean particle size of 3.0 µm 6 0.3 µm and a challenge level of 2200 6 500 viable particles per test, as determined according to step 12.3. 6.1.12 Glass Aerosol Chamber, 60 cm 3 8 cm diameter tube. 6.1.13 Colony Counter, manual or automatic, capable of counting up to 400 colonies/plate. 6.1.14 Timers, capable of 0.1 s accuracy. F 2101 2 6.1.15 Automatic Pipetor, capable of delivering 1.0 mL 6 0.05 mL. 6.1.16 Flow Meters, capable of 28.3 L/min. 6.1.17 Aerosol Condenser. 6.1.18 Pressure Gauge, capable of 35 kPa 6 1 kPa accu- racy. 6.1.19 Air Regulator. 6.2 Materials: 6.2.1 Flasks, 250-500 mL Erlenmeyer. 6.2.2 Petri Dishes, sterile 15 3 100 mm. 6.2.3 Pipettes, 1 mL, 5 mL, and 10 mL. 6.2.4 Test Tube Rack, stainless 6.2.5 Bottles, sterile, glass, 100-500 mL capacity. 6.2.6 Inoculating Loop. 6.2.7 Stoppers/Closures, of appropriate size to fit test tubes. 6.2.8 Test Tubes, 16 mm 3 150 mm. 7. Reagents 7.1 Tryptic Soy Agar [TSA]7. 7.2 Tryptic Soy Broth [TSB]7. 7.3 Peptone Water7. 7.4 Staphylococcus aureus, ATCC #6538 8. Hazards 8.1 Sterilize all apparatus and supplies which come into contact with the bacterial challenge suspension, by autoclaving at 121-123 °C for a minimum of 15 min. Extreme care must be taken to avoid contamination of the laboratory spaces by complete sterilization or high level disinfection of all apparatus and supplies. This will reduce the possibility of laboratory contamination. 8.2 Staphylococcus aureus is common to the normal flora of the body, however, it is a leading cause of nosocomial infections and is a human pathogen. Technicians conducting the testing must have proper microbiological training. Gloves and other protective clothing equipment should be worn during testing to prevent contamination. 8.3 All aerosols must be contained to prevent exposure and reduce laboratory contamination. 9. Media Preparation 9.1 Prepare media using standard microbiological tech- niques. 9.2 Prepare agar plates for cascade impactor as specified by the manufacturer of the cascade impactor. 10. Test Specimen 10.1 Test specimens shall be taken from manufactured medical face masks, with all layers arranged in proper order. 11. Conditioning 11.1 Condition each specimen for a minimum of 4 h by exposure to a temperature of 21 6 5 °C (70 6 10°F) and relative humidity of 85 6 5 % as described in Specification E 171 using a controlled temperature and humidity chamber or space. 12. Preparation of the Bacterial Challenge 12.1 Inoculate an appropriate volume of tryptic soy broth with and incubate with mild shaking at 37 6 2°C for 24 6 2 h. 12.2 Dilute the culture in peptone water to achieve a concentration of approximately 5 3 105 CFU/mL. 12.3 The challenge delivery rate will be maintained at 2200 6 500 viable particles per test. The challenge delivery rate is determined each day of testing and is based on the results of the positive control plates when the aerosol is collected in a six-stage viable particle cascade impactor, with no test speci- men clamped into the test system. The dilution of the challenge suspension will need to be adjusted to deliver the proper challenge level during testing. 13. Test Procedure 13.1 The aerosol challenge apparatus is outlined in Fig. 1. 13.2 Deliver the challenge to the nebulizer using a peristal- tic or syringe pump. Connect tubing to nebulizer and peristaltic pump and into the challenge suspension; purge tubing and nebulizer of air bubbles. NOTE 1—The peristaltic pump or syringe pump must be calibrated to deliver a consistent challenge volume throughout the testing interval. 13.3 Perform a positive control run without a test specimen clamped into the test system to determine the number of viable aerosol particles being generated. The mean particle size (MPS) of the aerosol will also be calculated from the results of these positive control plates. 13.4 Initiate the aerosol challenge by turning on the air pressure and pump connected to the nebulizer. 13.5 Immediately begin sampling the aerosol using the cascade impactor. Adjust the flow rate through the cascade impactor to 28.3 L/m. 13.6 Time the challenge suspension to be delivered to the nebulizer for 1 min. 13.7 Time the air pressure and cascade impactor to run for 2 min. 13.8 At the conclusion of the positive control ran, remove plates from the cascade impactor. Label each plate with the corresponding stage number. 13.9 Place new agar plates into the cascade impactor and clamp the test specimen into the top of the cascade impactor, with either the inside or outside oriented toward the challenge as intended. 13.10 Initiate the aerosol challenge as outlined above. 13.11 Repeat the challenge procedure for each test speci- men. 13.12 Repeat a positive control sample after completion of the test sample set. 13.13 Perform a negative control sample by collecting a 2 min sample of air from the aerosol chamber. No bacterial challenge should be pumped into the nebulizer during the collection of the negative control sample. 13.14 Incubate agar plates at 37 6 2°C for 48 6 4 h. 13.15 Count each of the six-stage plates of the cascade impactor.7 Available from Difco, Detroit, MI 48232. F 2101 3 13.16 Total the counts from each of the six plates for the test specimens and positive controls, as specified by the manufac- turer of the cascade impactor. The filtration efficiency percent- ages are calculated using the following equation: C – T C 3 100 5 % BFE (1) where: C = average plate count total for test controls, and T = plate count total for test sample. 13.17 Calculate the mean particle size using the specifica- tion of the manufacturer of the cascade impactor. The mean particle size of the bacterial aerosol shall be maintained at 3.0 µm 6 0.3 µm. 14. Report 14.1 State that the test was conducted as directed in Test Method F 2101. 14.2 Report the area of the test specimen tested. 14.3 Report the flow rate during testing. 14.4 Report the mean particle size of the challenge aerosol. 14.5 Report the percent bacterial filtration efficiency for each test specimen. 14.6 Report the average plate count results of the positive controls. 14.7 Report the average plate count results of the negative controls. 14.8 Report the plate count total for each stage. 14.9 Report which side of the specimen was oriented toward the challenge aerosol. 15. Precision and Bias 15.1 Precision—The repeatability of the procedure in Test Method F 2101 for measuring the bacterial filtration efficiency of medical face mask materials was determined for a single laboratory and a single operator using three materials. The results of these tests are summarized in Table 1. The reproduc- ibility of this test method is being determined and should be available by January 2004. 15.2 Bias—No information can be presented on the bias for the procedure in Test Method F 2101, for measuring the bacterial filtration efficiency of medical face mask materials, because no material having an accepted reference value is available at this time. 16. Keywords 16.1 aerosol; bacterial filtration efficiency (BFE); medical face mask materials FIG. 1 Bacterial Filtration Efficiency Test Apparatus TABLE 1 Bacterial Filtration Efficiency Performance of Various Materials—Repeatability Material x Sr t A 99.54 0.1753 0.1035 B 99.30 0.3521 0.2081 C 94.48 1.0400 0.6146 x = mean of each material. Sr = repeatability standard deviation for each material. t = 95 % repeatability limit for each material. F 2101 4 The American Society for Testing and Materials takes no position respecting the validity of any patent rights asserted in connection with any item mentioned in this standard. 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