Determining Cartridge Change Schedules

Do not trust odor threshold. Use a systematic methodology to implement an effective change schedule for cartridges/canisters.

EACH day, hazardous chemicals and potential risk of worker exposure is becoming a more complex challenge for many environmental, health and safety professionals. Statistics show that the respiratory condition in the workplace is one of the main cause of illness cases on the job (18,865 cases in 2003; 17,679 cases in 2004; and 20,128 cases in 20051). Employers need to pay attention to these numbers and implement an effective respiratory protection program where all critical elements are included.

According to the Bureau of Labor Statistics, nonfatal respiratory illness cases increased slightly during the period of 2003-2005, from 7.0 percent in 2003 to 8.3 percent in 2005, as shown in the pie charts below.


The incident statistics show us the need for employers to develop a program that includes all elements that ensure continuous improvement in workers' protection from hazardous vapors.

The following are critical elements that must be part of the respiratory protection program:
* Selecting healthier chemicals available in the marketplace.
* If feasible, developing an aggressive engineering controls program as the primary method of eliminating the chemical hazards.
* Performing Job Safety Analysis of all tasks in the facility to determine the risk level and type of respirators and/or cartridges to be used by the employees
* Medical screening follow-up
* An industrial hygiene monitoring program
* A training program (fit testing, MSDSs, etc.)
* Respirators maintenance (change schedule for cartridges/canisters, storage, repairs, inspection).

An additional requirement included in the revision of the OSHA standard, 29 CFR 1910.134, states: "If there is no ESLI [end-of-service-life indicator] appropriate for conditions in the employer's workplace, the employer implements 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."

Usually, a change schedule program for cartridges/canisters is not incorporated in the employer's respiratory protection program. This condition can lead to chemical vapors passing through the cartridges/canisters and harming the worker, Several respirator manufacturers are installing ESLIs to their cartridges. With this system, employers don't need to implement a change schedule program.

OSHA's Requirements
OSHA provides this synopsis of its requirements for Cartridge Change Schedules:
1) "Employers to develop cartridge/canister change schedules based on available data or information. Such information includes the exposure assessment and information based on breakthrough test data, mathematically based estimates, and/or reliable use recommendations from the employer’s respirator and/or chemical suppliers."
2) "Reliance on odor thresholds and other warning properties will not be permitted as the primary basis for determining the service life of gas and vapor cartridges and canisters."
3) "OSHA emphasizes that a conservative approach is recommended when evaluating service life testing data. Temperature, humidity, air flow through the filter, the work rate, and the presence of other potential interfering chemicals in the workplace all can have a serious effect on the service life of an air-purifying cartridge or canister."
Do not trust odor threshold. Use a systematic methodology to implement an effective change schedule for cartridge/canisters. OSHA has published on its Web page (in the eTools section, at www.osha.gov/SLTC/etools/respiratory/index.html) all necessary information that employers must know regarding the change schedule for a respirator's cartridge/canisters. Those methods can help employers develop a very comprehensive and effective program to be in compliance with OSHA regulations and reduce/eliminate employees exposure to hazardous chemicals in the workplace, following a systematic analysis of the hazards instead of trusting odor threshold for determining the cartridge change schedule.

Three Models
In the OSHA eTools section, we can find the following methods for cartridge/canister change schedules:

a) MATH MODEL:
Mathematical equations have been used to predict the service lives of organic vapor respirator cartridges when used for protection against single contaminants. Using an equation developed by G. Wood (American Industrial Hygiene Association Journal, January 1994), it is suggested that you reduce the service life estimate by some safety factor to give a change schedule that you should document in your written respiratory program.

The steps of the Math model are:
1. Determine the concentration level of airborne contaminants in the work area.
2. Obtain access to a predictive table that is based on research.
3. Use the table to come up with a cartridge service life estimate.
4. Account for differences in the real work environment and those assumptions used by the math model:
--Humidity and temperature
--Breathing rate
5. Create a written change schedule for the cartridges.

The mathematical formula is:

 





Where:
tb= breakthrough time (min)
We = equilibrium adsorption capacity (g/g carbon)
W = weight of carbon adsorbent
rb = bulk density of the packed bed (g/cm³)
Q = volumetric flow rate (cm³/min)
Co = inlet concentration (g/cm³)
Cx = exit concentration (g/cm³)
 
b) MANUFACTURER'S RECOMMENDATIONS
1. Obtain the following information:
* concentrations of those airborne contaminants (in parts per million)
* humidity in work area
* work rate
2. Contact the manufacturer of the respirators you plan to use.
3. Provide the manufacturer with the following information:
* name of the respirator model
* information from step 1
4. Request the cartridge service life, as well as the exact objective information the manufacturer relied upon to project the service life.
5. Create a written change schedule for the cartridges.

c) EXPERIMENTAL TEST
1. Obtain the following information:
* names of all airborne contaminants
* breathing rate of workers, or
* maximum flow rate of powered air-purifying respirator
* estimate of worst case exposure levels
2. Determine who will conduct the experimental tests.
* Your company's industrial hygienist
* An outside consultant or laboratory
3. Provide the tester with the following:
* information from step 1
* actual cartridges for the respirators
* the opportunity to test at the work site under typical conditions, or
* the range of variable factors or conditions to be given to the lab
4. Obtain the results and create a written change schedule for the cartridges.

This article originally appeared in the May 2007 issue of Occupational Health & Safety.

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