nova safety committee 2004.11.24

• When OSHA has a substance specific standard (e.g., lead, methylene chloride).
• When employees notice symptoms (e.g., irritation, odor) or complain of respiratory health effects.
• When the workplace contains visible emissions (e.g., fumes, dust, aerosols).

• Why the respirator is necessary and how improper fit, use, or maintenance can compromise its protective effect
  
• Limitations and capabilities of the respirator
  
• Effective use in emergency situations
  
• How to inspect, put on and remove, use and check the seals
  
• Maintenance and storage
  
• Recognition of medical signs and symptoms that may limit or prevent effective use
  
• General requirements of OSHA's respirator standard,  Respiratory Protection Advisor - Major Requirements of OSHA's Respiratory Protection Standard 29 CFR 1910.134

Particulate Respirators Combination Respirators Gas & Vapor Respirators capture particles in the air, such as dusts, mists, and fumes do not protect against gases or vapors generally become more effective as particles accumulate on the filter and plug spaces between the fibers filters should be replaced when user finds it difficult to breath through them (see Selection Criteria for Particulate Filters) are normally used in atmospheres that contain hazards of both particulates and gases   have both particulate filters and gas/vapor filters may be heavier are normally used when there are only hazardous gases and vapors in the air   use chemical filters (called cartridges or canisters) to remove dangerous gases or vapors do not protect against airborne particles are made to protect against specific gases or vapors provide protection only as long as the filter's absorbing capacity is not depleted the service life of the filter depends upon many factors and can be estimated in various ways (see Respirator Change Schedules)

Appendix B-2 to § 1910.134: Respirator Cleaning Procedures (Mandatory)

These procedures are provided for employer use when cleaning respirators. They are general in nature, and the employer as an alternative may use the cleaning recommendations provided by the manufacturer of the respirators used by their employees, provided such procedures are as effective as those listed here in Appendix B- 2. Equivalent effectiveness simply means that the procedures used must accomplish the objectives set forth in Appendix B-2, i.e., must ensure that the respirator is properly cleaned and disinfected in a manner that prevents damage to the respirator and does not cause harm to the user.

I. Procedures for Cleaning Respirators

A. Remove filters, cartridges, or canisters. Disassemble facepieces by removing speaking diaphragms, demand and pressure- demand valve assemblies, hoses, or any components recommended by the manufacturer. Discard or repair any defective parts.

B. Wash components in warm (43 deg. C [110 deg. F] maximum) water with a mild detergent or with a cleaner recommended by the manufacturer. A stiff bristle (not wire) brush may be used to facilitate the removal of dirt.

C. Rinse components thoroughly in clean, warm (43 deg. C [110 deg. F] maximum), preferably running water. Drain.

D. When the cleaner used does not contain a disinfecting agent, respirator components should be immersed for two minutes in one of the following:

1. Hypochlorite solution (50 ppm of chlorine) made by adding approximately one milliliter of laundry bleach to one liter of water at 43 deg. C (110 deg. F); or,

2. Aqueous solution of iodine (50 ppm iodine) made by adding approximately 0.8 milliliters of tincture of iodine (6-8 grams ammonium and/or potassium iodide/100 cc of 45% alcohol) to one liter of water at 43 deg. C (110 deg. F); or,

3. Other commercially available cleansers of equivalent disinfectant quality when used as directed, if their use is recommended or approved by the respirator manufacturer.

E. Rinse components thoroughly in clean, warm (43 deg. C [110 deg. F] maximum), preferably running water. Drain. The importance of thorough rinsing cannot be overemphasized. Detergents or disinfectants that dry on facepieces may result in dermatitis. In addition, some disinfectants may cause deterioration of rubber or corrosion of metal parts if not completely removed.

F. Components should be hand-dried with a clean lint-free cloth or air-dried.

G. Reassemble facepiece, replacing filters, cartridges, and canisters where necessary.

H. Test the respirator to ensure that all components work properly.

[63 FR 1152, Jan. 8, 1998]

How long can a particulate respirator be used before it must be discarded?

How long will a HEPA filter last?
Envirco offers a variety of High Efficiency Particulate Air (HEPA) and Ultra Low Penetration Air (ULPA)
ducted ceiling modules
 and panel filters
to complete your cleanroom design
 A HEPA filter can last three to five years or more in a standard cleanroom environment. Life of the HEPA also depends on ambient conditions and maintenance of the prefilters. Since airflow capacity decreases and static pressure increases over time, HEPA filters actually become more efficient as the filter loads. The filter should be changed once it has reached its capacity. For example, if a HEPA unit is set to for 90 ft/min (0.45 m/sec) on the <High> setting, but is only achieving 70 ft/min (0.35 m/sec) on <High>, then the HEPA filter should be changed.

How often do I need to change the prefilter?
In dirtier environments, the prefilter may need to be changed as often as every one to three months. Frequency will depend on ambient conditions.

	A change schedule is the part of the written respirator program which says how often cartridges should be replaced and what information was relied upon to make this judgment.  A cartridge's useful service life is how long it provides adequate protection from harmful chemicals in the air.  The service life of a cartridge depends upon many factors, including environmental conditions, breathing rate, cartridge filtering capacity, and the amount of contaminants in the air.  It is suggested that employers apply a safety factor to the service life estimate to assure that the change schedule is a conservative estimate. If you know what the chemical is and how much of it you are exposed to, then you are ready to estimate out how long your respirator cartridges will work and apply the safety factor.
	3  valid ways for you to estimate a cartridge's service life: 1. Conduct Experimental Tests   Can save money by providing a more accurate service life value instead of relying on conservative assumptions made by other methods     Most reliable method, especially for multiple contaminants     Can be used to validate an existing change schedule     Will likely take time and money to perform the tests   2. Use the Manufacturer's Recommendation   Can result in a more accurate estimate for your particular brand of respirator   Relies on the manufacturer's broad knowledge and expertise     May not be possible if the manufacturer is unable to provide a recommendation     May not account for all workplace and user factors adequately   3. Use a Math Model   Inexpensive and takes little time     Requires no math calculations if you use the Advisor Genius     Not as accurate as experimental testing. May result in a service life estimate that is shorter than it needs to be due to conservative assumptions     Generally limited to single contaminant situations
	Keep In Mind
	You may not rely on odor thresholds and other warning properties as the primary basis for determining the service life of gas and vapor cartridges and canisters. You should account for environmental and user factors and use a conservative approach when evaluating service life testing data. You should apply a safety factor to any estimate to account for uncertainty. Mixtures, intermittent use and concentrations, storage practices and other variables may require the use of an administrative time limit, e.g. one day, even though the estimated life would be longer. There is a published "Rule of Thumb" that may provide a rough estimation of cartridge service life.  However, you should NOT use this as the sole method of determining service life.

Keep In Mind

• There is no widely accepted, standard protocol for performing service life testing.
• OSHA has devised a field testing approach which will demonstrate the validity of an established change schedule.
• The EPA has published draft Interim Recommendations for cartridge testing.
• A field testing approach is provided by Cohen, H. J., Development of a Field Method for Calculating the Service Lives of Organic Vapor Cartridges – Part IV. Results of Field Validation Trials, American Industrial Hygiene Association Journal, (1991), pages 263-270.
• Ideally, respirator cartridges should be tested under worst case conditions either in the workplace or in the laboratory.
• The determination of breakthrough from workplace testing does not require the determination of the full breakthrough curve for the respirator cartridge.

	Experimental procedures that determine, under actual workplace conditions, whether respirator cartridges are effectively protecting the worker are perhaps the best measure of cartridge performance. Two procedures which have been included in the American Industrial Hygiene Association seminar "Respirator Cartridges: How to Set a Replacement Schedule" are outlined below. You should use these procedures on a systematic and frequent-enough basis to verify your change schedule estimates. Your change schedule estimates must be re-evaluated whenever operations change, or when work place conditions are different than those used by equipment manufacturer's to determine change schedules. Determine the change schedule per manufacturer’s recommendations or by using one of the methods listed on OSHA’s Web page. Immediately before changing the cartridges being used based on the procedures determined in step 1, test for breakthrough using any sampling method with sufficient sensitivity to detect the chemical of interest below the Occupational Exposure Limit (OEL). These procedures should be performed immediately after leaving the work area, and should not be performed during the next work day. Methods that you may use include detector tubes, direct reading instruments such as a photoionization detectors, and charcoal tubes which require laboratory analysis. The OEL is normally the health based workplace permissible exposure limit (PEL) or short term exposure limit (STEL) required by OSHA standards. In cases where there is no OSHA workplace exposure limit, use other exposure limits published by the American Conference of Governmental Industrial Hygienists (ACGIH), the American Industrial Hygiene Association, or the National Institute of Occupational Safety and Health. You can test by using one of the following procedures provide your evaluate the respiratory hazard(s) to which the employee is exposed, and use the procedure frequently enough to ensure that workers are being protected by their respirators under the actual workplace conditions. Procedure 1: Using a leak free cartridge holder, adaptors, inert tubing and tee such as teflon or stainless steel, sampling tube, and a sampling pump as shown in Figure 1, draw air through the cartridge being replaced. Perform sampling in a high exposure area so that an adequate detection limit can be obtained. You can perform sampling by attaching the sampling tube to the tee using a short piece of tubing to minimize the "dead space" in the tubing. If possible, insert the sampling tube directly into the contaminant air stream in the tee. If breakthrough occurs, the cartridge is no longer performing as designed and the change schedule should be shortened. Therefore, shorten the change schedule by one hour and repeat the test. Figure 1. Procedure 2: Place a quantitative fit-testing (QNFT) sampling adapter between the cartridge and the face piece (Fig. 2). These adapters are often available through your respirator supplier.   Figure 2. You can connect the direct reading instrument using a short piece of tubing made of teflon or other inert material to the outer hose connection on the adapter which, in turn, connects to a small inert sample tube on the inside of the adaptor. Keep the length of tubing as short as possible to minimize the "dead space" in the tubing. The sample tube passes through the respirator’s inhalation valve and is firmly positioned via a small suction cup and clip so that a sample can be drawn directly from the breathing zone of the respirator (i.e., between the cartridge and the respirator). If breakthrough occurs, the cartridge is no longer performing as designed and the change schedule should be shortened. Therefore, shorten the change schedule by one hour and repeat the test. A reading on the instrument may not be due to breakthrough, but may be due to other reasons such as a poor respirator fit, or exhalation of chemicals that have been absorbed into through the skin. Check the respirator fit using a positive and negative pressure test to verify that leakage is not occurring and verify that any personnel protective equipment, such as gloves, is being effectively used and that no skin absorption is occurring. Since use of the QNFT adapter temporarily voids the respirator’s NIOSH approval, it may be put in place only temporarily during a short equilibration period before sampling to evaluate the change schedule. Reevaluate change schedules if employee exposure may increase due to: (1) change in operations such as using more raw materials or higher concentrations, (2) working without local exhaust ventilation or other ventilation changes occur, (3) employee tasks or durations of tasks change, or (4) employees experience symptoms of breakthrough such as odor, taste, or irritation. For compounds without adequate warning properties, re-evaluate the change schedule any time an odor is detected. Normally you should sample the toxic agent of interest. Sometimes, adequate direct reading sampling procedures are not available for the contaminant. In this case, a sampling method requiring a laboratory analysis may be required. Or, in some cases, a surrogate may be used. For example, a solvent carrier may be monitored if a direct reading instrument is not available for the contaminant of interest. You should use this variation only when calculations or manufacturer’s recommendations indicate that the toxic compound of interest has a longer breakthrough time than the solvent, and therefore the solvent will break through first.

	The recommendations have not been subjected to formal Agency peer review, although peer involvement and informal peer review have occurred. Any policy issues discussed within this document have not been reviewed by the Agency and do not reflect official Agency policy. These recommendations are subject to change as new information is developed that warrants modification of the testing protocol. Background. Under Section 5 of the Toxic Substances Control Act (TSCA), the Environmental Protection Agency (EPA) may require the use of respiratory protection to protect against inhalation exposure to substances submitted as Premanufacture Notifications (PMNs), or new chemical substances. For new chemicals which are volatile, EPA requires the use of NIOSH/MSHA approved supplied-air respirators unless the company can demonstrate that a NIOSH approved air-purifying respirator with organic vapor cartridges is appropriate. This determination is based on EPA approval of the results of cartridge service life testing performed in a laboratory. EPA requires companies to select, maintain and use respiratory protection in accordance with NIOSH and OSHA requirements at 30 CFR 11, and 29 CFR 1910.134, respectively. There is often little or no information available with which to determine whether adequate warning properties exist for new chemical substances. In addition, there is often considerable uncertainty regarding the potential human health effects for new chemicals. Finally, odor threshold data as reported in the literature has been found to vary considerably due to the type of data source, the characteristics of human olfactory response, and differences in experimental methodology(1), Due to these uncertainties, the Agency has determined that odor threshold or other testing to identify warning properties is not warranted. Instead, service life testing of organic vapor cartridges or canisters for the new chemical substance during the anticipated conditions of exposure and a cartridge change out schedule determined on the basis of the testing, is required. There are many factors that affect cartridge service life, such as temperature, relative humidity, challenge concentration, and other environmental and use factors(2-6). In addition, other contaminants can greatly influence the performance of the cartridge and should be considered when conducting cartridge service life testing. While there is no standard test methodology for determination of organic vapor cartridge service life, a testing protocol was published in a peer reviewed technical journal(7). The performance of an organic vapor respirator cartridge in removing a selected airborne substance via adsorption or chemical reaction can be determined by measuring the breakthrough time of the substance through the cartridge under various test conditions. Summary of Method. These Interim Recommendations for performing organic vapor cartridge service life testing are based on recommendations presented in the published article(7), a draft Decision Logic prepared by NIOSH for the EPA(8), and professional judgment. The current recommendations require at least 8 tests during the PHASE I testing. Depending on the use conditions, additional testing may be required in PHASE II to investigate desorption characteristics at elevated temperatures. Specific requirements for PHASE II testing will be established by EPA on a case-by-case basis, although it is anticipated that testing at elevated temperatures will be necessary for many new chemicals substances. The testing protocol represent reasonable worst case environmental testing conditions and minimum testing requirements; companies are encouraged (but not required) to perform additional testing to more fully characterize the sorbent/contaminant breakthrough characteristics(7). The safety factor of 60% of the cartridge service life for field application has been retained from Revision 1 to account for variability between laboratory measurements and actual field performance. These recommendations apply only to cartridges and canisters approved by NIOSH/MSHA under 30 CFR 11. As NIOSH modifies the certification standards and adopts 42 CFR 84, these requirements will be reevaluated. In April, 1994, the Industrial Hygiene Task Group of the Chemical Manufacturers Association (CMA) submitted suggested changes to the Revision 1 Interim Recommendations (dated May 1, 1991)(9). The CMA Industrial Hygiene Task Group in February, 1995 again stated their preference for a protocol consisting of a single set of tests at the maximum use concentration for the cartridge under the reasonably anticipated worst case environmental conditions(10). Testing would be done in triplicate, with a demonstrated excess service life of 50%. Furthermore, the CMA stated that the EPA protocol was excessive and was more reflective of a research protocol. EPA carefully reviewed the recommendations, consulted with experts at Los Alamos and NIOSH, reviewed the available literature, and responded to the CMA comments in a joint letter with NIOSH dated May, 1994(11). EPA revised the Interim Recommendations accordingly. While EPA strongly supports reducing testing costs while still maintaining acceptable worker protection, EPA believes that it is necessary to test at more than one concentration, humidity, and temperature to determine the reasonably anticipated worst case conditions. For example, low relative humidity, rather than high, may be worst case conditions for some substances, and the same is true with temperature. The CMA suggestions are a viable option only if it can be demonstrated that the selected environmental conditions are indeed worst case; EPA knows of no reliable means of demonstrating this without testing. The EPA Interim Recommendations are subject to modification on a case by case basis, and companies are encouraged to carefully evaluate the protocol as it applies to their case and consult with EPA as needed. Testing Protocol. Section 1. Initial Screening for Cartridge or Canister Service Life. Several models have been developed for predicting organic vapor cartridge service life(12-23). However, their applicability for predicting cartridge service life for untested compounds is limited, especially for new chemical substances where data useful in predicting service life (e.g. vapor pressure, capacity and adsorption rate, etc.) is generally limited or unavailable. Recently, a model was published based on the modified Wheeler equation and incorporated advancements in predicting organic vapor cartridge service life for untested compounds, provided minimal information on the challenge compound and on the adsorption carbon were available(24). However, the model currently only considers dry conditions (relative humidity < 50%). Predictive models can be useful to initially screen whether a cartridge might be appropriate for a new chemical substance. If the model predicts service life at less than 20 minutes for the new chemical substance, then an organic vapor cartridge may not be appropriate for the substance, and the company may want to reconsider the use of a supplied-air respirator instead of performing cartridge service life testing on cartridges or canisters. Section 2. High Heats of Reactions with the Sorbent. The company shall document that the new chemical substance will not result in high heats of reaction (> 20°C above ambient temperature) with the sorbent material of the cartridge or canister. For substances which generate high heats of reaction, only non-oxidizing sorbent materials shall be used. Section 3. Preparation of Cartridges or Canisters for Testing. Cartridges and canisters shall be tested as received (dry bed conditions). Cartridges used in pairs on an air-purifying respirator should be tested in parallel in pairs, or the airflow rates should be halved for testing them singly. Section 4. Testing Parameters for Cartridge or Canister Service Life Testing. The minimum required replicates and testing parameters for performing cartridge and/or canister service life testing are: PHASE I Testing Requirements Flow Rate (L/min) Concentration (ppm)a Temperature (°C) Relative Humidity (%) Number of Replicatesb 50 10(x) 25 ± 2.5 80 ± 5 2 50 100(x) 25 ± 2.5 80 ± 5 2 50 500(x) 25 ± 2.5 80 ± 5 2 50 500(x) 25 ± 2.5 20 ± 5 2 PHASE II testing requirements will be established on a case-by-case basis. At a minimum, if the cartridge and/or canister will be used as protection against inhalation exposure at elevated temperatures (> 35°C) , the following additional testing is required: PHASE II Testing Requirements Flow Rate (L/min) Concentration (ppm)a Temperature (°C) Relative Humidity (%)c Number of Replicatesb 50 10(x) 35 ± 2.5 80 ± 5 2 50 500(x) 35 ± 2.5 80 ± 5 2 a Where x = New Chemical Exposure Limit (NCEL), or the predicted airborne concentration if no NCEL exists. b More than two replicates shall be tested if the variability between results for each set of replicates exceeds 10%. c If the results of PHASE I testing demonstrate that the service life under low (e.g. 20%) relative humidity conditions is less than the service life at 80% relative humidity, then PHASE II testing shall be conducted under low (20 ± 5%) relative humidity conditions instead of the higher relative humidity conditions specified. Section 5. Cartridge Change Out Schedule. The company shall establish a cartridge/canister change out schedule based on the results of the service life testing for reasonable worst case testing conditions, any administrative controls that will be used, and incorporating the safety factor of 60% of the measured service life to account for variability in environmental conditions. Cartridges or canisters shall be changed prior to the end of service life, or at the end of the shift, whichever comes first. The cartridge change out schedule and other administrative actions shall be incorporated into the Respiratory Protection Program, as required by 29 CFR 1910.134. If extended cartridge change out schedules (longer than 1 work shift) are desired, the company should consult with EPA as additional testing will be required to demonstrate that desorption and migration of contaminant vapor between shifts and during repeated storage and reuse does not occur. There has been little or no research in this area, and standard testing protocols are currently unavailable. Section 6. Reporting of Data. The following data and information shall be submitted to EPA for review and approval of cartridge and/or canister service life testing data: i) the actual breakthrough curve and the tabulated concentration versus time for each set of testing parameters; ii) at a minimum, the breakthrough times at 1% and 10% of the vapor concentration shall be reported; iii) information on the analytical method including, but not limited to the limit of detection, range of applicability, a description of the method, accuracy and precision, etc. shall be reported; iv) the canister or cartridge specifications should be reported in as much detail as is available; v) the cartridge change out schedule and any administrative actions incorporated into the Respiratory Protection Program shall be reported; and vi) documentation that the new chemical substance will not result in high heats af reaction (> 20°C above ambient temperature) with the sorbent material of the cartridge or canister. Section 7. EPA Approval. Upon receipt of EPA approval of the cartridge service life data and the cartridge change out schedule, the company may use NIOSH/MSHA approved air-purifying respirators equipped with an organic vapor cartridge or canister for protection against inhalation exposure to the new chemical substance instead of NIOSH/MSHA approved supplied-air respirators. The organic vapor cartridge used shall provide equivalent or greater sorption capacity to the cartridge or canister tested. Section 8. Other Use Conditions. The cartridge and/or canister is approved only for use in use conditions similar to those reflected by the testing parameters (e.g. single contaminant (the new chemical substance) at a range of airborne concentrations, low to high relative humidity, and selected ambient temperature(s)). Organic vapor-acid gas cartridges and/or canisters may be used for protection against the new chemical substance provided the sorption capacity of the organic vapor-acid gas cartridge or canister is equivalent or greater than that of the tested cartridge or canister. However, if there is potential for inhalation exposure to multiple contaminants (e.g. the new chemical substance and an acid gas), additional service life testing would be necessary to demonstrate that the cartridge or canister selected is appropriate. Only limited evaluation of the breakthrough characteristics of multiple contaminant systems has been conducted to date(25-26).   REFERENCES 1. American Industrial Hygiene Association: Odor Thresholds for Chemicals with Established Occupational Health Standards. American Industrial Hygiene Association: Fairfax, VA. (1989). 2. Nelsen, G.O., and C.A. Harder: Respirator Cartridge Efficiency Studies: V. Effects of Solvent Vapor. Am. Ind. Hyg. Assoc. J. 35:391-410 (1974). 3. Moyer, E.S.: Review of Influential Factors Affecting the Performance of Organic Vapor Air-Purifying Respirator Cartridges. Am. Ind. Hyg. Assoc. J. 44:46-51 (1983). 4. Nelson, G.O. and A.N. Correia: Respirator Cartridge Efficiency Studies: VII. Summary and Conclusions. Am. Ind. Hyg. Assoc. J. 37:514-525 (1976). 5. Hall, T., P. Breysse, M. Corn, and L.A Jonas: Effect of Adsorbed Water Vapor on the Adsorption Rate Constant and the Kinetic Adsorption Capacity of the Wheeler Kinetic Model. Am. Ind. Hyg. Assoc. J. 49:461-464 (1988). 6. Nelson, G.O., A.N. Correia, and C.A. Harder: Respirator Cartridge Efficiency Studies: VII. Effect of Relative Humidity and Temperature. Am. Ind. Hyg. Assoc. J. 37:280-288 (1976). 7. Wood, G.O. and Ackley, M.W.: A Testing Protocol for Organic Vapor Respirator Canisters and Cartridges. Am. Ind. Hyg. Assoc. J. 50:651-654 (1989). 8. Bollinger, N. and Coffey, C.: Decision Logic for Organic Vapor Cartridge Respirators for Premanufacture Notification (PMN) Substances. DRAFT (May 25, 1988, unpublished). 9. Chemical Manufacturers Association. Letter to Mr. Gerry Wood, Los Alamos National Laboratory from Thomas J. Nelson, 3M, and Karen M. Cragg, CMA. (April 11, 1994). 10. Chemical Manufacturers Association. DRAFT Comments submitted to Mr. Roy Seidenstein, EPA from Mr. R. Holmes, on the proposed Generic Section 5(e) Order with New Chemical Exposure Limits, as a supplement to comments previously submitted. (February 6, 1995). 11. National Institute for Occupational Safety and Health. Letter to Ms. Karen M. Cragg and Mr. Thomas J. Nelson, Chemical Manufacturers Association from Ernest S. Moyer, Ph.D. and Cathy Fehrenbacher, EPA. 12. Smoot, D.M., Smith, D.L., and Scheh, T.A.: Development of Improved Respirator Cartridge and Canister Test Methods. U.S. Dept. of Health and Human Services, Public Health Service. Center for Disease Control. National Institute for Occupational Safety and Health. Publication No. 77-209. 13. Ackley M.W.: Residence Time Model for Respirator Sorbent Beds. Am. Ind. Hyg. Assoc. J. 46:679-689 (1985). 14. Yoon, Y.H. and J.H. Nelson: Application of Gas Adsorption Kinetics: I. A Theoretical Model for Respirator Cartridge Service Life. Am. Ind. Hyg. Assoc. J. 45:509-516 (1984). 15. Yoon, Y.H. and J.H. Nelson: Application of Gas Adsorption Kinetics: II. A Theoretical Model for Respirator Cartridge Service Life and Its Practical Applications. Am. Ind. Hyg. Assoc. J. 45:517-524 (1984). 16. Wood, G.O.: A Model for Adsorption Capacities of Charcoal Beds: II. Challenge Concentration Effects. Am. Ind. Hyg. Assoc. J. 48:703-709 (1987). 17. Yoon, Y.H. and J.H. Nelson: A Theoretical Study of the Effect of Humidity on Respirator Cartridge Service Life. Am. Ind. Hyg. Assoc. J. 49:325-332 (1988). 18. Wood, G.O.: A Model for Adsorption Capacities of Charcoal Beds. I. Relative Humidity Effects. Am. Ind. Hyg. Assoc. J. 48:622-625 (1987). 19. Moyer, E.S.: Organic Vapor (OV) Respirator Cartridge Testing - Potential Jonas Model Applicability. Am. Ind. Hyg. Assoc. J. 48:791-797 (1987). 20. G.O. Wood and E.S. Moyer: A Review of the Wheeler Equation and Comparison of Its Applications to Organic Vapor Respirator Cartridge Breakthrough Data. Am. Ind. Hyg. Assoc. J. 50:400-407 (1989). 21. Wood, G.O. and E.S. Moyer: A Review and Comparison of Adsorption Isotherm Equations Used to Correlate and Predict Organic Vapor Cartridge Capacities. Am. Ind. Hyg. Assoc. J. 52:235-242 (1991). 22. Wood, G.O.: Activated Carbon Adsorption Capacities for Vapors. Carbon 30:593-599 (1992). 23. Wood, G.O.: Organic Vapor Respirator Cartridge Breakthrough Curve Analysis. J. Int. Soc. Resp. Prot. Winter :5-17 (1992-93). 24. Wood, G.O.: Estimating Service Lives of Organic Vapor Cartridges. Am. Ind. Hyg. Assoc. J. 55:11-15 (1994). 25. Yoon, Y.H., J.H. Nelson, J. Lara, C. Kamel, and D, Fregeau.: A Theoretical Interpretation af the Service Life of Respirator Cartridges for the Binary Acetone/m-Xylene System. Am. Ind. Hyg. Assoc. J. 52:65-74 (1991). 26. Yoon, Y.H., J.H. Nelson, J. Lara, C. Kamel, and D. Fregeau.: A Theoretical Model for Respirator Cartridge Service Life for Binary Systems: Application to Acetone/Styrene. Am. Ind. Hyg. Assoc. J. 53:493-502 (1992).