What are the options?
By Thomas J. Nelson, C.I.H.
and Larry L. Janssen, C.I.H.
Larry Janssen is a Certified Industrial Hygienist with the 3M OH&ESD Laboratory
revised respiratory protection standard
29 CFR 1910.134
3M W8100 Abrasive Blasting Respirator
Historically, the use of air-purifying respirators for protection against gases and vapors was permitted if the chemical had adequate odor or irritation warning properties to alert the user that the air-purifying elements had reached their capacity. In its revised respiratory protection standard, the Occupational Safety and Health Administration (OSHA) now requires the use of a supplied air respirator for gas or vapor exposures unless:1
The objective data used to set a change schedule must be documented in a written respiratory protection program. It is not necessary to develop a cartridge change schedule for gas and vapor contaminants regulated by OSHA's substance specific standards, since cartridge change schedules are specified in each regulation.
In most situations, employers will choose to use a change schedule since obtaining air supplies may not be feasible and ESLIs are not available for most chemicals. This article will review the methods that are currently available to develop and document change schedules. While the methods apply to both cartridges and canisters, only the term cartridge will be used from this point forward. Forms to develop and document the change schedules are also provided at the end of this article.Definitions
A change schedule is a predetermined interval of time after which a used cartridge is replaced with a new one. In order to determine an appropriate change schedule, the breakthrough time for the gas or vapor in question must be known or estimated. Breakthrough means that a stated concentration of the chemical can be detected on the downstream side of the cartridge. The amount of time required to reach breakthrough is sometimes referred to as the service life of the cartridge. An appropriate cartridge change schedule is one that is both convenient and assures that the concentration of the chemical downstream does not exceed the exposure limit. For example, a cartridge may have a breakthrough time of 15 hours for a given vapor. Changing cartridges at the end of a normal work shift is convenient, and this period of use is less than the breakthrough time.Methods for estimating service life
Several methods can be used to estimate breakthrough times (i.e., service life). These vary in cost, complexity and precision. All methods require professional judgement to establish an appropriate change schedule and all require the same basic information. This information includes the specific respirator and cartridge to be used, airborne concentration of the contaminant(s), temperature and humidity in the workplace, the pattern of respirator use (e.g., hours per shift, shifts per week) and the expected work rate. Each of these can affect cartridge service life.Methods for estimating service life include:
The rules of thumb can be summarized as follows:2
1. Cartridge service life should be at least eight hours if:
2. If the concentration is reduced by a factor of 10, the service life increases by a factor of 5.
3. Service life is inversely proportional to flow rate.
4. Relative humidities above 85% reduce the service life by 50%.
These rules of thumb are simple to apply and cost nothing. However, they do not provide specific information for the cartridges in use. Still, they can be used to estimate the service life of cartridges used for organic vapor exposures when specific data are not available.
Mathematical models provide estimates of service life based on the physical properties of the chemical and the carbon used in the cartridges. A model developed by Wood uses readily-available data to predict breakthrough times for cartridges designed to remove organic vapors.3 This model was tailored to the specific carbons used in each of the 3M cartridges and incorporated into 3M Service Life Software. The software is available at no charge on the 3M OH&ESD web site. The program is able to calculate the expected breakthrough time for approximately 200 chemicals with occupational exposure limits. It requires the following input from the user:
The program returns an estimate of the breakthrough time for the input conditions. This information can be used to help establish a cartridge change schedule.
Two applications of the Wood model are available at OSHA's website . The first is a table of breakthrough times for 120 chemicals at several concentrations. The breakthrough estimates in the table were calculated using "generic" values for the cartridge and workplace input parameters. Therefore, the table does not provide the most accurate breakthrough estimates. OSHA's "Advisor Genius" allows the user to enter specific values for the input parameters to improve the accuracy of the service life estimate. Default values may be used if the actual values are unknown. In addition, the "Advisor Genius" allows calculation of breakthrough times for any organic compound that is a liquid at room temperature and for which the following information is known:
The programs based on Wood's model are easy to use, provide breakthrough estimates for many organic vapors at varying concentrations and workplace conditions, and can provide information specific to the cartridge in use. They can also be used for powered air purifying respirator cartridges where little experimental data are available. The user must determine a suitable change schedule using the breakthrough information, appropriate safety factors and professional judgement. The programs are generally not recommended for high humidities (>65% RH), do not predict breakthrough times for mixtures of materials and cannot be used for inorganic gases.
Laboratory testing has been done with some chemicals by respirator manufacturers, private testing laboratories and research scientists. Laboratory testing involves measuring the actual breakthrough time for a specific cartridge when tested with a specific chemical. The cartridge is mounted in a test apparatus, and a known concentration of the chemical is drawn through it at a specific flow rate, temperature and humidity. The time it takes to detect a stated concentration of the chemical on the downstream side of the cartridge is measured.
Laboratory testing gives an actual measurement of breakthrough time for the test conditions. Because laboratory studies are usually conducted at high concentrations to save time, professional judgement or rules of thumb must be used to apply this information to workplace conditions. It is also possible to conduct a series of tests at different concentrations and humidities in order to develop a mathematical model to predict the performance of the cartridge at a wide range of conditions. Laboratory testing can be done with mixtures, but problems of generating and controlling a complex test atmosphere must be overcome. The cost for laboratory testing is rather high, approximately $2,000 for a single chemical.
Much of the breakthrough data published in the literature were collected using cartridges manufactured more than 20 years ago. Because respirator and carbon technology have improved over the years, modern cartridges are likely to perform better than published data indicate. OSHA and the chemical industry are in the process of assembling available breakthrough data and determining their applicability. OSHA plans to make the information available at its web site when the study is completed.Example:
How can laboratory data be used to establish a change schedule for cartridges exposed to 100 ppm toluene at a normal breathing rate (30 Lpm), 70 degrees F and 50% relative humidity?
Information from a laboratory study published in 1974 indicates a 1% breakthrough time of 94 minutes for toluene, measured under the following conditions:4
-Challenge concentration: 1,000 ppm
Using the second rule of thumb, a ten-fold reduction in concentration should result in a five-fold increase in breakthrough time or 470 minutes. A breathing rate of 53.3 Lpm represents moderately heavy work that could not be sustained over an entire work shift. A moderate work rate of 30 Lpm would result in a proportional increase in service life. Therefore, changing the cartridges at the end of a normal shift would be appropriate. An additional margin of safety is incorporated because activated carbon almost certainly performs better today than the carbon used in the early 1970s.Field testing
Field testing determines breakthrough time in the workplace. Air from the workplace is drawn through the cartridge, and the downstream air is monitored to determine when breakthrough occurs. Pumps capable of drawing 20 to 60 Lpm are required, which typically means that the pump must be in a fixed location. Consequently, the challenge to the cartridge may not accurately represent workers' actual exposures.
A surrogate for the cartridge known as a respirator carbon tube (RCT) has been developed.5 The RCT is a small glass tube packed with a small amount of carbon from a specific cartridge. Air from the workplace is drawn through the RCT with a personal air sampling pump. The RCT is worn by the worker, so the challenge atmosphere is representative of the actual exposure. Equations are used to predict breakthrough time for the actual cartridge based on the breakthrough time measured with the RCT.
Field testing overcomes many of the disadvantages of mathematical models and laboratory testing. Relative humidity and the presence of several vapors in the atmosphere are automatically incorporated into the breakthrough measurement. However, either field testing method has the disadvantage of being relatively equipment- and labor-intensive. In addition, since workplace concentrations of each vapor vary considerably, samples may need to be collected over several days.Determination of remaining service life
An alternate field testing procedure can be used to determine the remaining service life of cartridges after use in the workplace. This type of test is used to demonstrate that the gas or vapor has not broken through. It is easily accomplished by sampling behind the cartridge near the end of the use period. The following procedure is used: A quantitative fit-testing (QNFT) adapter such as the 3M 601 Quantitative Fit Testing Adapter (see Figure 1, below) is mounted between the cartridge and the facepiece.
The tubing that is normally passed through the respirator's inhalation valve to draw a sample from inside the facepiece is removed (see Figure 2, below).
This allows the space between the inhalation valves on the 3M 601 Adapter and the respirator (i.e. between the cartridge and the respirator) to be sampled. A short piece of tubing is attached to the outer hose connection on the adapter to allow connection of a sampling device. The tubing is held closed with a pinch-style paper clip until the sampling device is connected (see Figure 3, below).
Any sampling method with sufficient sensitivity to detect the chemical of interest at a concentration below the exposure limit can be used to take the sample (see Figure 4, below).
Since use of the QNFT adapter temporarily voids the respirator's NIOSH approval, it may be put in place for only a short (~30 minute) equilibration period prior to sampling.Example:
What is an appropriate change schedule for 3M 7251 cartridges used in an atmosphere containing 37 ppm carbon disulfide at a moderate work rate, 68 degrees F and 80% relative humidity?
3M Service Life Software predicts more than 21 hours to reach 50% of the exposure limit breakthrough (5 ppm). A decision was made to replace cartridges at the end of each regular work shift because it is convenient and allows a large margin of safety to account for the high relative humidity. Sampling behind the cartridge was conducted at the end of three work shifts using a 3M 7930 QNFT adapter and colorimetric detector tubes. No carbon disulfide was detected in any of the samples. Therefore, the change schedule is appropriate.
Sampling behind the cartridge has been used for a limited number of materials and exposures. It is a simple method that allows breakthrough to be measured in the workplace at the actual contaminant concentration, environmental conditions and work rate. It enables verification of service life predictions from mathematical models or change schedules based on limited information. This method is also suitable for atmospheres containing several vapors. Its primary disadvantage is its labor intensity, particularly if no service life estimate is available.Estimates of service life for mixtures
There is no accepted method for estimating the service life of cartridges used in an atmosphere containing a mixture of vapors. OSHA's Compliance Directive CPL 2-0.120 suggests that:6
• If the breakthrough times for the individual vapors in a mixture are within one order of magnitude, the individual vapor concentrations should be added together. It can then be assumed that entire mixture behaves like the contaminant with shortest breakthrough time.
• If breakthrough times for the individual components vary by two orders of magnitude or more, the service life estimate should be based on the contaminant with the shortest breakthrough time.
It is not known how well these simple rules predict cartridge service life in a mixed vapor atmosphere.
Research suggests that service time for individual vapors in a mixture is related to their mole fractions in the mixture.7, 8 The mole fraction for each chemical in a mixture is equal to the concentration of that material (in ppm) divided by the total concentration of the mixture. The service life for each component in the mixture is calculated by multiplying its mole fraction by its predicted "single substance" service time. Simply stated, this method estimates when the first component of a mixture will break through. The following example illustrates the use of OSHA's method and the "mole fraction method" for predicting the service life of cartridges exposed to a mixture of air contaminants.Example:
Employees in a coating line have 8-hour time-weighted average exposures to an atmosphere containing the following mixture of solvents:
-Toluene: 100 ppm
The job is classified as light work and relative humidity in the plant is 50%. 3M 6001 organic vapor cartridges are used. What is an appropriate cartridge change schedule?
-Toluene: 3,770 minutes
These values represent the times to reach 10% of the inlet concentration if the cartridges were exposed to each contaminant individually.
Since breakthrough times are within one order of magnitude, the concentrations of the individual contaminants are added and the total concentration is used to predict the breakthrough time:
100 ppm + 100 ppm + 75 ppm = 275 ppm
Since ethyl acetate has the shortest breakthrough time, it is assumed that the entire mixture behaves like ethyl acetate. 3M Service Life Software predicts a service time of 989 minutes for 275 ppm ethyl acetate. Changing cartridges after each normal shift appears to be appropriate.
Mole fraction method:
The mole fractions for the components of the mixture are calculated as follows:Total ppm of mixture = 275 ppm.
-Toluene mole fraction = 100 ppm ÷ 275 ppm = 0.36
Breakthrough times for the components as they exist in the mixture are then calculated:
This method predicts earlier breakthrough than OSHA's method (670 minutes vs. 989 minutes). Changing cartridges after each 8-hour shift still appears to be appropriate, but the margin of safety is smaller. Since there is presently little data to support either of the methods used for mixtures, sampling behind the cartridge near the end of the predicted use period is advisable to confirm that the change schedule is correct.Inorganic gases
Change schedules must also be developed for cartridges used with inorganic gases. It must be recognized that the rules of thumb and computer models discussed earlier in this article generally do not apply to these materials. For example, humidity typically has a positive effect on the service life of acid gas cartridges. Also, preliminary information indicates that service time increases at least linearly when exposure concentration is reduced.
Mathematical models are being developed and validated for inorganic gases. In the interim, manufacturers' laboratory data and NIOSH certification test criteria can be useful in developing service life estimates for these exposures. The previously-discussed field testing methods, including sampling behind the cartridge, are applicable to these materials. In addition, inorganic gases generally have good warning properties, which provide an extra margin of safety if breakthrough occurs before the end of the scheduled use period.
A documented change schedule must be developed for most respiratory protection programs that involve gas or vapor exposures. Setting an appropriate change schedule requires professional judgement to interpret information and apply appropriate safety factors. This is especially true when rules of thumb, laboratory data or mathematical models are used. An acceptable margin of safety between a service life estimate and a change schedule is influenced by:
Respirator manufacturers, the chemical industry and OSHA are working to develop better service life information and methods to make developing change schedules easier.
1. "Respiratory Protection," Code of Federal Regulations Title 29 (5), Part 1910.134. 1998, pp. 412-437.
2. Nelson, G. O.: "Rules of Thumb for Cartridge Service Life," July 29, 1996, [Private communication]. Miller-Nelson Research, 8 Harris Court, Suite C-6, Monterey, CA 93940.
3. Wood, G. O.: "Estimating Service Lives of Organic Vapor Cartridges," Am. Ind. Hyg. Assoc. J. 55(1): 11-15 (1994).
4. Nelson, G.O. and C.A. Harder: "Respirator Cartridge Efficiency Studies: V. Effect of Solvent Vapor," Am. Ind. Hyg. Assoc. J. 35: 391-410 (1974).
5. Cohen, H. J. and R. P. Garrison: "Development of a Field Method for Evaluating the Service Life of Organic Vapor Cartridges: Results of Laboratory Testing Using Carbon Tetrachloride," Am. Ind. Hyg. Assoc. J. 50(9): 486-495 (1989).
6. U. S. Department of Labor/OSHA: Inspection Procedures for the Respiratory Protection Standard, (Directive Number CPL 2-0.120). Washington D.C., 1998.
7. Jonas, L. A., E. B. Sansone and T. S. Farris: "Prediction of Carbon Performance for Binary Mixtures," Am. Ind. Hyg. Assoc. J. 44: 10,716-10,719 (1983).
8. Robbins, C. A. and P. N. Breysse: "The Effect of Vapor Polarity and Boiling Point on Breakthrough for Binary Mixtures on Respirator Carbon," Am. Ind. Hyg. Assoc. J. 57(8): 717-726 (1996).
The new software offers an easy method for estimating the service life of 3M organic vapor respirator cartridges. Service life is the measured or estimated period of time before breakthrough of a gas or vapor contaminant for a specific chemical cartridge under specified conditions of the test or estimate. A service life estimate can be helpful in establishing a cartridge change schedule, which is a specified time period after which the chemical cartridge will be replaced.
The Occupational Safety and Health Administration (OSHA) believes that chemical odor may not serve as a sufficient indicator for all workers to change chemical cartridges. Therefore, the recently revised OSHA respiratory protection standard, 29 CFR 1910.134, requires users of chemical cartridge respirators to implement a cartridge change schedule based on "objective information or data." In this way, used cartridges would be replaced before the chemical breaks through the cartridge at a level that could result in worker overexposure.Approximately 200 organic contaminants
3M Service Life Software is based on a model presented by Wood1 that requires information about carbon properties, cartridge design, environmental and use conditions, and chemical vapor properties. The model was modified for the characteristics of 3M organic vapor chemical cartridges and some of the experimentally-determined values were refined.2 Since the predicted service lives are based on properties of the carbon used in 3M organic vapor cartridges, the software should be used only for 3M cartridges.
The software contains a database of vapor properties for approximately 200 of the organic contaminants listed in the 3M Respirator Selection Guide, as well as a database for several 3M organic vapor cartridges. All contaminants in the database are liquids at ambient temperatures. Organic compounds that have boiling points less than 0 degree C have been excluded, and this model does not consider relative humidity greater than 65% or mixed vapor effects. Since liquid densities are required for service life calculations by the software, materials that are solid at ambient conditions are not included in the database. Gases and vapors for which OSHA has established substance-specific standards are also excluded. For these chemicals, the specific OSHA standards should be consulted.Change schedule parameters
A change schedule may be established after consideration of the service life estimate as well as workplace conditions such as contaminant concentration, relative humidity, temperature, work activities, respirator use pattern (e.g., continuous or intermittent use), presence of other materials, potential for contaminant migration/desorption, health effects of the gas or vapor, and the quality of any warning properties.References
1. Wood, G.O., "Estimating Service Lives of Organic Vapor Cartridges," American Industrial Hygiene Assocation Journal, Vol. 55, No. 1, pp.11-15, 1994.
2. Johnson, E.W. and L.A. Brey, "Prediction of Respirator Cartridge Service Life Against Organic Vapors at Workplace Concentrations," Paper presented at the American Industrial Hygiene Conference and Exposition, Atlanta, GA, May 1998.
Fit-testing requirements under the revised respiratory protection standard 29 CFR 1910.134 Back to Top
On January 8, 1998, the Occupational Safety and Health Administration (OSHA) revised its respiratory protection standard, 29 CFR 1910.134. The fit-testing provisions of the revised standard consolidate the requirements that OSHA had in its substance-specific standards. In addition, several new requirements have been added.
In summary, the standard requires:
Fit-testing of negative pressure respirators has been required for many years. The new regulation also requires fit-testing of positive pressure respirators. Specifically, this means the following respirators must now be fit-tested:
Fit-testing of positive pressure respirators is performed to check for "gross" faceseal leaks. The test must be done while the respirator is in a negative pressure mode. This is typically accomplished by converting the facepiece to a negative pressure configuration for the fit test. The revised regulation permits both QLFT and QNFT methods for fit-testing positive pressure respirators. 3M OH&ESD's Technical Data Bulletin #140, (January 1999) describes the methods that can be used to test the facepieces on 3M positive pressure respirators.Frequency of fit-tests
Annual fit-testing is required under the revised respiratory protection standard. This provision replaces the semi-annual requirement formerly found in some of OSHA's substance-specific regulations, such as those for lead and asbestos.
In addition to annual fit-tests, fit-testing must be repeated if:
The standard requires that a single QLFT or QNFT be passed by each worker. This replaces the requirement found in some of OSHA's substance-specific standards, such as the benzene standard, which required three fit-tests per worker when QNFT was used.Fit-test methods
Mandatory procedures for conducting fit-tests are listed in Appendix A of 29 CFR 1910.134. Four QLFT and three QNFT methods are permitted. QLFT methods rely on the test subject to respond to the odor, taste, or irritation of a test agent in order to identify unacceptable faceseal leakage. Permissible QLFT agents include isoamyl acetate, saccharin, Bitrex™ and irritant smoke. QNFT methods use instrumentation to measure faceseal leakage. Results are expressed as a numerical fit factor. Acceptable QNFT methods include the generated aerosol, ambient aerosol and controlled negative pressure methods.
It is important to recognize that fit factors measured during QNFT are nothing more than indicators of acceptable fit. They differ from assigned protection factors (APFs), which are estimates of how much protection (i.e., reduction of exposure) is expected from a class of respirators when properly selected, fitted and used in the workplace. Table 1 indicates when QLFT and QNFT are permitted, minimum factors required for QNFT and assigned protection factors for each respirator type.
(It is important to recognize that OSHA plans to complete rulemaking on APFs and maximum use concentrations later this year. It is likely that changes to the APFs listed in Table 1 will occur.)
General requirements applicable to all fit-test methods include:
Once an employee has passed a fit-test, maintaining a record of the test results is required. The record must contain the person's name or other identification; the type of test performed; the specific make, model, style and size of respirator tested; the test results; and the date of the test. This record must be retained until the next fit-test.
"Bitrex" is a trademark of Macfarlan Smith, Ltd.
In a recent memorandum to its Regional Administrators, the Occupational Safety and Health Administration (OSHA) granted the 3M W8100 Abrasive Blasting Respirator an assigned protection factor (APF) of 1,000 when used in operations regulated by the Interim Final Rule for Lead in Construction, 29 CFR 1926.62. This regulation has limited the APF for abrasive blasting helmets to 25 since it was published in 1993.Background
An APF of 25 indicates the respirator can only be used in lead concentrations up to 25 times the permissible exposure limit (PEL). Because abrasive blasting on structures painted with lead-bearing paints is often done in an enclosure to minimize environmental contamination, exposures to abrasive blasting operators may be several hundred times the PEL. Given the restrictive APF, abrasive blasting helmets were no longer appropriate in these operations. Consequently, operators were forced to wear abrasive blasting respirators of the pressure demand facepiece type, which can restrict vision and which many wearers find less comfortable than helmets.
OSHA agreed to grant individual abrasive blasting helmets an APF of 1,000 if their manufacturers had simulated workplace protection factor (SWPF) testing performed which supported a higher APF. OSHA required that the testing be performed by independent laboratories and that it demonstrate the respirators achieved an SWPF of at least 20,000 and maintained positive pressure throughout the tests.Limitations
To date, abrasive blasting airline respirators from three manufacturers have been tested according to OSHA's protocol and granted the APF of 1,000. These are:
In each case, OSHA's Directorate of Compliance Programs issued a memorandum to its Regional Administrators listing the same restrictions and limitations on the APF of 1,000:
The APF of 25 in the Lead in Construction regulation was adopted from the National Institute for Occupational Safety and Health (NIOSH) Respirator Decision Logic. NIOSH based this low level of expected performance on workplace protection factor (WPF) studies conducted on powered air purifying respirators with loose-fitting facepieces. No data considered by either OSHA or NIOSH indicated that airline respirators with hoods and helmets perform at the same level as loose-fitting facepieces. In fact, WPF data have shown for many years that an APF of 1,000 is appropriate for hoods and helmets. The SWPF testing performed on the 3M W8100 Abrasive Blasting Respirator further supports the APF of 1,000.
Several other OSHA regulations assign an APF of 25 to hoods and helmets: the Cadmium regulations, 29 CFR 1910.1027 and 1926.1127; the 1,3-Butadiene regulation, 1910.1051; and the Methylene Chloride regulation, 1910.1052. OSHA has not granted relief from the APF of 25 in these regulations. In other substance-specific regulations, APFs for airline respirators with hoods and helmets range from 100 to 2,000. For exposures to contaminants that are not covered by a specific standard, OSHA does not have an APF listed for hoods and helmets.
There is no logical reason to believe that the protection provided by an airline respirator with a hood or helmet should vary based on the contaminant for which it is used. 3M believes the APF of 1,000 for hoods and helmets listed in the American National Standard Practices for Respiratory Protection, ANSI Z88.2-1992 is appropriate.
"Apollo" is a trademark of Clemco Industries Corp.
Are you interested in learning the latest available information on establishing a cartridge change schedule? Do you want hands-on experience in analyzing breathing air quality? Are you an experienced respirator program administrator who just needs to know "3M Canada Occupational Health and Safety What's New" in respiratory protection regulations and technology? 3M has a unique program to respond to these and many more professional development requirements.
Two training courses are offered to provide individuals involved with a respirator program the information they need to operate their program effectively. The courses are unique among those offered by respirator manufacturers in that they are based on the technical and regulatory aspects of a sound respirator program rather than specific products. In fact, a large equipment display from a number of respirator manufacturers is used to supplement the classroom and workshop presentations.
Respiratory Protection is a comprehensive 41/2 day course intended for anyone involved with managing all or part of a respiratory protection program. All respirator types and each element of a respirator program are thoroughly discussed. Workshop sessions are used extensively to reinforce the course material. Current Topics in Respiratory Protection is a two-day course designed to provide the latest in technical and regulatory information to experienced program managers. The 1999/2000 schedule of course locations and dates is listed below. To find out more about these courses, do one of the following:
* Contact your 3M Sales Representative: Phone 1-800-659-0151, ext. 275
* Visit our web site at www.3M.com/occsafety;
* Dial the 3M Fax On Demand system at 1-800-646-1655.
Current Topics in Respiratory Protection
Information on 3M OH&ESD products, as well as on current issues in respiratory protection, can be obtained by visiting our web site.