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Respirator Cartridge Change Schedule

Quick Tips #196


Respirators are among the most important pieces of safety equipment available. With chemical cartridges, they can be used to filter out and protect workers from many hazards. The media used in these chemical cartridges is typically activated carbon, which adsorbs a number of chemicals. However, the adsorption capacity is limited. In 1998, OSHA addressed this issue in its revised respiratory standard. It is no longer acceptable to rely on odor thresholds and other warning properties as the primary way of determining cartridge life. Fortunately for employers, there are three options available to help them comply with this standard.


The revisions to the OSHA standard, 29 CFR 1910.134, became effective April 8, 1998.

29 CFR 1910.134(d)(3)(iii)(B)(2) states that If there is no end-of-service-life indicator appropriate for conditions in the employer's workplace, the employer must implement a change schedule for canisters and cartridges based on objective information or data that will ensure the canisters are changed before the end of their service life.

Simply stated, chemical cartridges must be equipped with a NIOSH-approved end-of-service-life indicator or ESLI. This is an area on the cartridge that changes color when it's time to replace the cartridge. If the cartridge does not have this indicator, employers must develop and enforce a change schedule based on reliable information. Currently, there are very few cartridges equipped with NIOSH-approved ESLIs. To comply with the standard, employers must develop their own change schedules, but they do not have to search for and analyze test data themselves. Employers can simply acquire information from other sources that have the expertise to develop change schedules. The employers must then include the source for this information in their written respiratory program. If no information can be obtained to develop an accurate respirator cartridge change schedule, the employees must use a supplied-air system.

Steps to Develop a Respirator Cartridge Change Schedule

  1. Gather material safety data sheets for all the chemicals in the workplace.
  2. Determine which, if any, hazardous chemicals may be present in the workplace.
  3. Determine the products and the by-products of chemical processes and/or reaction. ** If unknown contaminates are possible, you must use supplied air.
  4. Conduct sampling to determine the concentration levels of contaminants.
  5. Determine the breathing rate of the employees using the respirators.
  6. Determine the workplace temperature and humidity.

Once these pieces of information are gathered, develop a respirator cartridge change schedule by using one of the following methods.

1. Conduct Experimental Tests

An end user, outside consultant or outside laboratory can perform experimental testing to determine cartridge service life once all pertinent information has been gathered about the workplace and the contaminants. A safety factor must then be applied to this service-life information to account for variances in actual workplace conditions. Currently, there is no set protocol for performing this service-life testing. For more information, go to

Many employers do not have the capability or the resources to perform their own tests. However, those employers that do will find this to be the most reliable method to determine cartridge life, especially when dealing with multiple contaminants.

2. Use Manufacturer's Recommendations

A manufacturer's service-life recommendations could come from the chemical supplier or, more likely, the respirator manufacturer. This method is not as reliable as conducting your own tests but is still a good alternative. Unfortunately, respirator manufacturers might not have information for your specific chemicals or compounds.

3. Use Mathematical Models

Mathematical models can assist testing through computer programs or complex mathematical formulas. The computer programs are available online or by using a CD-ROM from some manufacturers. If the computer programs aren't available, use predictive or descriptive mathematical models.

  • Predictive model: A copy of the predictive model developed by G.O. Wood can be found at OSHA's website. This model looks at chemical and physical properties of compounds to determine cartridge life. However, this model is the least accurate method because it does not look at actual experimental data.
  • Descriptive model: A copy of the descriptive model for cartridge testing also can be found at OSHA's website. The descriptive model looks at existing experimental data to set up a basic model. Once this model has been set up, it can be used to calculate values for points where experimental data is not available.

The descriptive model looks at actual experimental data, making it somewhat more accurate than the predictive model. But both models have drawbacks. Neither model relies heavily on experimental data, thus reducing accuracy, and both equations are very complex, opening them to human error. These models also only work well when you deal with single-contaminant situations.

One tool that can be used to help estimate organic vapor cartridge life is the "Rule of Thumb" method. This method is from chapter 36 of the AIHA publication "The Occupations Environment — Its Evaluation and Control". The rule of thumb is:

  • If the concentration of the chemical is less than 200 ppm and the chemical's boiling point is greater than 70°C, you can expect a service life of eight hours at a normal work rate
  • Service life is inversely proportional to work rate
  • Reducing concentrations by a factor of 10 will increase the service life by a factor of five
  • Humidity above 85 percent will reduce service life by 50 percent

**Note: This should not be the sole method of determining service life. It can only be used as a guide.**

Although it is no longer acceptable to use the warning properties of the chemicals as the only means of determining when to change cartridges, if odor is detected at any time, the cartridges must be replaced.



Manufacturer Cartridge Service-Life Information:

OSHA Links:

(Rev. 6/2014)

Find even more information you can use to help make informed decisions about the regulatory issues you face in your workplace every day. View all Quick Tips Technical Resources at

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The content in this newsletter is intended for general information purposes only. This publication is not a substitute for review of the applicable government regulations and standards, and should not be construed as legal advice or opinion. Readers with specific compliance questions should refer to the cited regulation or consult with an attorney.

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