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Respirator Change Out Schedules
Document Number: 196
Introduction
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 different hazards. The media used in
these chemical cartridges is typically activated carbon which adsorbs
a number of different chemicals. However, the adsorption capacity is
limited. Recently, OSHA has 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 new standard.
Background
The revisions to the OSHA standard, 29 CFR 1910.134, became
effective as of April 8, 1998.
29 CFR 1910.134(d)(3)(iii)(B)(2) 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."
Simply stated, chemical cartridges must be equipped with a
NIOSH-approved end of service life indicator (ESLI). This is an area
on the cartridge that changes color when its 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
these NIOSH-approved ESLI's. To comply with the new standard,
employers must develop their own change schedules, but they do not
have to search for and analyze test data them-selves. 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 change schedule,
the employees must use a supplied air system.
Steps to Develop Change Schedules
- Gather MSDS's for all he chemicals in the workplace.
- Determine which, if any, hazardous chemicals may be present in
the workplace.
- Determine the products and the by-products of chemical processes
and/or reaction. **If there is a possibility of unknown
contaminates, you must use supplied air.
- Conduct sampling to determine the concentration levels of
contaminants.
- Determine the breathing rate of the employees using the
respirators.
- Determine the workplace temperature and humidity.
Once these pieces of information are gathered, a change schedule can
be developed by using one of the following methods.
Methods For Developing Change Schedules
There are three valid methods employers can use to determine the
change schedules for chemical cartridges.
1. Conduct Experimental Tests
Once all pertinent information has been gathered about the
workplace and the contaminants, experimental testing can be performed.
This can be done by either the end user or an outside consultant or
laboratory. The experimental testing will determine the service life
of the cartridges. 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, see:
www.osha-slc.gov/SLTC/respiratory_advisor/testing/testing.html.
For most employers, conducting their own experimental tests on
compounds is simply not a realistic alternative. Many employers do not
have the capability or the resources to perform these tests. However,
for those employers that do, this is the most reliable method to
determine cartridge life, especially when dealing with multiple
contaminants.
2. Use Manufacturer's Recommendations
These recommendations could come from either the chemical
supplier or, more likely, the respirator manufacturer. This method is
not as reliable as conducting your owns tests but is still a good
alternative. Unfortunately, respirator manufacturer's may not have
information for your specific chemicals or compounds.
3. Use Mathematical Models
There are two ways one can approach the mathematical model. It
can either be performed by using computer programs or complex
mathematical formulas. The computer programs are available on-line or
by using CD-ROM's from some manufacturers. If those resources aren't
available to employers, the mathematical models can still be used by
following complex formulas. The mathematical models are broken down
into two categories; predictive models and descriptive models. Each
model has it's own mathematical formula.
- Predictive Model: A copy of the predictive model
developed by G.O. Wood can be found on the internet at
www.osha-slc.gov/SLTC/respiratoryprotection/woodmodel.html.
This model looks at chemical and physical properties of different
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 can be
found at
www.osha-slc.gov/SLTC/respiratoryprotection/yoonmodel.html.
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
still have a several drawbacks. First, they rely heavily on
experimental data, thus reducing the level of accuracy. Secondly,
these equations are very complex, making human error a large concern.
And lastly, these models only work well when you are dealing 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 8 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 5.
- Humidity above 85% will reduce service life by 50%.
**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.
Sources for More Information
Manufacturers with Cartridge Service Life Information:
Miscellaneous Web sites for More Information
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Please Note: The information contained in this
publication 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 questions should refer to the cited
regulation or consult with an attorney.
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