Transcript Determination of Known Exhalation Valve Damage Using

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 Valves
1.
2.
3.
4.
Undamaged (control)
Warped
Slit
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
Yes
Replace with next
exhalation valve?
No
Stop
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
30
25
26
26 26
26
20
Ambient
Aerosol
10
Controlled
Negative
Pressure
0 0
m
ag
ed
nd
a
Valve Type
U
dh
es
iv
e
A
Sl
its
ar
pe
d
W
nd
a
m
ag
ed
0
U
Failure Frequency
26 26
30
Responses of Test Subjects to NPUSCs by
Valve Order
26
Test Subject Response
25
19
20
16
9
10
6
0
0
Undamaged
Passing
1
Warped
Slits
Valve Type
Failing/
Unsure
Adhesive
Relationship Between Fit Factors and
Percent Failing/Unsure NPUSCs
Valve Type AA
Mean
FF
Undamaged 25,046
CNP
Mean
FF
11,490
Percent
Failing/Unsure
NPUSCs
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
Pressure
(cm of water)
Passing Pressure-Time Tracing of
NPUSC
30
25
20
15
10
5
0
0
1
2
3
4
5
6
7
8
Time (Seconds)
9 10 11 12
Pressure
(cm of water)
Pressure-Time Tracing of NPUSC with
Two Breaths Taken
30
25
20
15
10
5
0
0
1
2
3
4
5
6
7
8
Time (Seconds)
9 10 11 12
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