Determination of Known Exhalation Valve Damage Using a Negative

Pressure User Seal Check Method on Full Face Respirators

Lisa J. Delaney, M.S., NIOSH

Roy T. McKay, Ph. D., University of Cincinnati

Andrew Freeman, M.D., University of Cincinnati

Respirator Leakage Pathways

• Improper respirator-to-face seal

• Inefficient air filtration device

• Leak sites in the respirator body

• Improperly functioning exhalation valves

• Source: Brueck, Scott et.al. Method Development for Measuring Respirator Exhalation Valve Leakage. Am.Ind. Hyg. Assoc. 7(3): 174-179 (1992).

Exhalation Valves

• Consists of valve seat, valve, and valve cover

• Allows for unidirectional airflow out of respirator

• Prevents unfiltered air from entering respirator

Regulations and Recommendations

• OSHA

• NIOSH

• ANSI

Negative Pressure User Seal Check (NPUSC)

• Procedure– Cover filter/cartridge opening with palm of hand, – Inspire as to create a negative pressure to cause

the respirator to collapse slightly, and – Hold breath for a designated amount of time

• Criteria for Passing– Facepiece remains slightly collapsed AND– No inward air leakage is detected

Respirator Leak Checker™

• Measurement device developed by Drs. Freeman and McKay, Univ. of Cincinnati

• Measures in-mask pressure differentials

• Assesses ability of respirator wearers to properly conduct a USC

Hypotheses

1. Test subjects can identify respirator leakage due to damaged exhalation valves by performing NPUSCs.

2. The RLC can detect respirator leakage due to damaged exhalation valves.

Materials

• Full facepiece elastomeric respirator with oral/nasal cup

• Exhalation Valves1. Undamaged (control)

2. Warped

3. Slit

4. Adhesive

Materials con’t.

• Ambient aerosol (AA) condensation nuclei counter- T.S.I. PortaCount Plus

• Controlled negative pressure (CNP)- Dynatech Nevada 3000

• In-mask pressure differential- Respirator Leak Checker

Test Protocol

• Respirator size selected and donned• Test subject trained • The following tests were performed for each

valve (beginning and ending with the control exhalation valve):– NPUSC– RLC measurement– TSI PortaCount measurement– Dynatech Nevada Fit Tester 3000 measurement

Select and don respirator

Perform NPUSC and obtain RLC measurement

Perform PortaCount fit test

Perform Dynatech Nevada fit test

Replace with next exhalation valve?

NoYesStop

Modifications from OSHA Protocol

• NPUSC– Held breath for 7 seconds instead of the OSHA

required 10 seconds

• TSI PortaCount– Test subject remained facing straight ahead

during all measurements– Fit factor calculated from third maneuver

Modifications from OSHA Protocol con’t.

• Dynatech Nevada Fit Tester 3000– Fit factor calculated from first maneuver,

normal breathing, head facing straight ahead

Data Analysis

• Fit factors analyzed using a repeated measure analysis of variance (ANOVA) to determine differences between valves

• Maximum pressure generated and time above threshold during NPUSC were analyzed using ANOVA to determine differences between valves

Test Subject Characteristics

• 26 test subjects included in study

• 54% male/46% female

• 50% were experienced respirator wearers

Number of Failing Quantitative Fit Tests

0

2625

26

0

26 26 26 26

0

10

20

30

Undam

aged

War

ped Slits

Adhes

ive

Undam

aged

Valve Type

Fai

lure

Fre

quen

cy

AmbientAerosol

ControlledNegativePressure

Responses of Test Subjects to NPUSCs by Valve Order

01

6

9

2625

19

16

0

10

20

30

Undamaged Warped Slits Adhesive

Valve Type

Tes

t Sub

ject

Res

pons

e

Failing/ Unsure

Passing

Relationship Between Fit Factors and Percent Failing/Unsure NPUSCs

Valve Type AAMeanFF

CNPMeanFF

PercentFailing/UnsureNPUSCs

Undamaged 25,046 11,490 0

Warped 20 <14 4% (n=1)

Slits 283 129 23% (n=6)

Adhesive 58 33 35% (n=9)

In-Mask Pressure Differential Measurements During NPUSC

• 98% (102/104) met the criteria set for passing the NPUSC

• Failed tests occurred with the undamaged and slit valves

• No significant difference between maximum pressure generated and time above threshold between the damaged and undamaged valves

Passing Pressure-Time Tracing of NPUSC

05

1015202530

0 1 2 3 4 5 6 7 8 9 10 11 12

Time (Seconds)

Pres

sure

(c

m o

f w

ater

)

Pressure-Time Tracing of NPUSC with Two Breaths Taken

05

1015202530

0 1 2 3 4 5 6 7 8 9 10 11 12

Time (Seconds)

Pre

ssu

re

(cm

of

wat

er)

Conclusions

• NPUSCs rarely identified leakage due to exhalation valve damage

• RLC was useful for assessing ability to conduct NPUSC

• Inspection, fit testing, and NPUSC is needed to maintain proper protection

Acknowledgements

• Support for this research was received in part through the NIOSH ERC Grant to the University of Cincinnati (T42 CCT510420) and from the University of Cincinnati

• Dr. Roy McKay