Determination of the Impact of Environmental Variables on the Change-Out Frequency for Respirator Cartridges Utilized in SPF Applications

Kevin Blair, Mary Bogdan, Lynn Feiner, William Robert

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Topics

• Introduction• What is breakthrough?• Variables impacting change-out schedule:

– Cartridge type– Breakthrough percentage– Safety factor– Contaminant concentration– Air flow– Humidity– Temperature

• Real world examples• Other factors• Summary/conclusion

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Introduction

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Introduction

• OSHA Respiratory Protection Standard [1910.134(d)(3)(iii)(B)(2)]:If there is no ESLI appropriate for conditions in the employer's workplace, the employer implements a change schedule for canisters and cartridges that is based on objective information or data that will ensure that canisters and cartridges are changed before the end of their service life. The employer shall describe in the respirator program the information and data relied upon and the basis for the canister and cartridge change schedule and the basis for reliance on the data.

• SPFA guidance for high pressure spray foam applications recommends use of air purifying respirators for exterior applications only.

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Limitations

• Calculations based on North® by Honeywell APR cartridges:– As there are differences between cartridge size, type of carbon, etc.,

estimates will vary depending upon the specific cartridge selected.

• Only considered MDI/PMDI and HFC-245fa exposures:– Other components of SPF formulations, such as catalysts,

surfactants and flame retardants, should be evaluated.• As a result, cartridge service life estimates are presented as a

ratio to the initial baseline and not absolute numbers.

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Basis for Comparisons

• North® by Honeywell Organic Vapor (OV) APR respirator cartridges.

• Inputs to the baseline model:– MDI/PMDI concentration: 0.05 ppm– Breakthrough factor: 10%– Safety factor: 0%– Ambient temperature: 70 ºF (21 ºC)– Relative humidity: < 65%– Worker breathing rate: 50 lpm (moderate exertion)

• The impact of changing each input will be discussed in detail.

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Contaminant Physical Properties

Parameter MDI/PMDI HFC-245faCAS Number 101-68-8 / 9016-87-9 460-73-1OSHA PEL / AIHA WEEL (ppm)

PEL 0.02 (MDI) WEEL 300

Molecular Weight 250 / 360 134Density (g/ml) 1.23 1.32Boiling Point (ºC) 314 15Vapor Pressure (mm Hg) 0.00005 / 0.000005 922

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What is Breakthrough?

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What is Breakthrough?

• Defined here as the percentage of the inlet concentration exiting the respirator cartridge.

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Variables Impacting Change-Out Schedule

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Cartridge Type

• Two common types of cartridges for organic vapors:– OV (Organic Vapor) cartridge

– OV/AG (Organic Vapor/Acid Gas) combination cartridge

• Actual SPF use requires the use of a particulate pre-filter.• Selecting an OV/AG cartridge results in a shorter service life.

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Cartridge Type Service Life (Ratio)OV (Organic Vapor) 1OV/AG (Organic Vapor/Acid Gas) 0.8

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Breakthrough Percentage

• The Respiratory Protection Program Manager selects the breakthrough percentage:– Typical percentages are 10%, 50% and 90%.– Must consider where the PEL falls on the breakthrough curve.– Lower numbers are more conservative and result in a greater margin

of safety.• Increasing the breakthrough percentage increases the service

life.

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Breakthrough Percentage Service Life (Ratio)10% of total breakthrough 190% of total breakthrough 1.1

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Safety Factor

• The Respiratory Protection Program Manager selects the safety factor to be used:– Typical factors are 0%, 10%, 20% and 50%.– Safety factors are often used when there is variability

in environmental conditions and worker breathing rates.– Higher numbers are more conservative and result in

a greater margin of safety.• Increasing the safety factor decreases the service life.

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Safety Factor Service Life (Ratio)0% 150% 0.5

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Contaminant Air Concentration

• Contaminant concentration can impact the service life.• Increasing the concentration in the air of MDI/PMDI from 0.05

ppm to 0.075 ppm reduces the service life.

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Contaminant Concentration Service Life (Ratio)0.05 ppm 10.075 ppm 0.7

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Air Flow

• The air flow rate through the cartridge can also impact the service life.

• For powered air purifying respirators (PAPR) this is a constant.• For air purifying respirators (APR), the air flow varies depending

upon the breathing rate of the worker:– Low exertion: 30 lpm– Moderate exertion: 50 lpm– Heavy exertion: 70 lpm

• Need to also account for differences in workers’ physical fitness.• Increasing the breathing rate decreases the service life.

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Worker Breathing Rate Service Life (Ratio)Moderate (50 lpm) 1Heavy (70 lpm) 0.7

OR

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Additional Contaminant

• In SPF applications, there will be potential exposures to multiple contaminants.

• Adding a second contaminant to the model reduces the service life significantly:– HFC-245fa concentration: 20 ppm

• Consideration of additional contaminants will further reduce the estimated service life.

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Contaminant Levels Service Life (Ratio)MDI : 0.05 ppm 1MDI: 0.05 ppm + HFC-245fa: 20 ppm < 0.01

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Humidity

• Humidity of the ambient air can impact the ability of carbon to adsorb the gas or vapor.

• For most chemicals, increasing the humidity decreases the service life:– Certain chemicals, such as ammonia and acid gases, that bond to

water can have longer a service life with increasing humidity.

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Humidity Service Life (Ratio)< 65% RH 1> 80% RH 0.8

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Temperature

• As with humidity, the ambient temperature can impact the ability of carbon to adsorb the gas or vapor.

• Exterior SPF applications can occur under a variety of conditions with significant temperature differences.

• Increasing the temperature only had a slight impact on the service life in our example:– Other chemicals may have much

larger differences.

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Temperature Service Life (Ratio)70 ºF (21 ºC) 1100 ºF (38 ºC) 1

Real World Examples

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Real World Examples

• Three scenarios:– A: Northern US during spring or fall

• 50 ºF (10 ºC), < 65% RH

– B: Southeast US during summer• 100 ºF (38 ºC), > 80% RH

– C: Southwest US during summer• 120 ºF (49 ºC), < 65% RH

• Other model variables:– MDI/PMDI exposures: 0.05 ppm (applicator), 0.02 ppm (helper)– HFC-245fa exposures: 20 ppm (applicator), 15 ppm (helper)– Worker breathing rate: 50 lpm (moderate), 70 lpm (heavy)– Breakthrough percentage: 10%– Safety factor: 0%

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Scenario Results

Scenario Temperature Humidity Applicator HelperA 50 ºF (10 ºC) < 65% 2.0 2.3B 100 ºF (38 ºC) > 80% 0.3 0.4C 120 ºF (49 ºC) < 65% 0.3 0.3

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Moderate Breathing Rate

Scenario Temperature Humidity Applicator HelperA 50 ºF (10 ºC) < 65% 1.4 1.6B 100 ºF (38 ºC) > 80% 0.3 0.3C 120 ºF (49 ºC) < 65% 0.2 0.2

Heavy Breathing Rate

All results expressed as ratio to baseline model service life estimate.

Other Factors

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Other Factors

• Non-environmental concerns:– Chemicals with no or low odor thresholds– Chemicals that are desensitizers– Chemicals with low boiling points

• Particulate pre-filters:– Pre-filters may require changing independent of the service life of the

OV cartridge– Need detected by increased breathing resistance (APR) or low-flow

alarm (PAPR)

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Summary/Conclusion

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Summary

Variable Change ImpactBreakthrough Factor 10% 90% 8% Temperature 70 ºF 100 ºF 3% Cartridge Type OV OVA 20% Humidity < 65% RH > 80% RH 20%Breathing Rate 50 lpm 70 lpm 30%Concentration 0.05 ppm 0.075 ppm 33%Safety Factor 0% 50% 50%Additional Contaminant MDI MDI + 245fa > 99.9%

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Conclusion

• Many factors that vary from job to job affect the service life of a cartridge, some significantly:– Temperature– Humidity– Breathing rate– Contaminant concentration– Number of contaminants

• Evaluation of all potential variables was outside the scope of this paper:– Need additional exposure data on other SPF components.

• The Respiratory Program Manager should work closely with their SPF and respiratory protection equipment suppliers to determine an appropriate cartridge change schedule.

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