COMPARING REAL-TIME FIT
FACTORS TO TRADITIONAL FIT
FACTORS BY OSHA EXERCISE
FOR N95 RESPIRATORS
MARGARET SIETSEMA, MS
LISA BROSSEAU, SCD
UNIVERSITY OF ILLINOIS AT CHICAGO
ISRP – SEPTEMBER 25, 2014
DEFINITIONS
• FF – Fit Factor – fit achieved by an individual for a specific respirator
• APF – Assigned Protection Factor – level of protection you would expect to
receive for a class of respirators (95% of population)
• 10 for half facepiece air purifying respirators
• SF - Safety Factor – usually 10 to account for differences between people and
how the respirator will work in a variety of industries
• Multiply APF x SF to obtain the Fit Factor Pass Level
𝐶𝑜
𝐹𝐹 =
𝐶𝑖
APF
SF
Pass Level
10 x 10 = 100
QNFT – QUANTITATIVE FIT TEST
• Traditional QNFT is performed using a TSI Portacount.
• Portacount designed to count particles inside the facepiece of a respirator then uses
a switch valve to count ambient particles.
• Goes back and fourth for each exercise
• Exercises usually included:
• Normal Breathing
• Head side to side
• Head up and down
• Bending over
• A harmonic mean is computed for all exercises to determine overall fit factor
OBJECTIVES
• Compare traditional OSHA Fit Test with Real Time Fit Test using
N95 Respirators
• Determine which exercises have the most influence on overall fit
of N95 respirator
PREVIOUS WORK WITH REAL-TIME FIT
• Proposed methodology to measure simulated fit using two
portacounts (Hauge et al., Gjib et al. )
• Respirator Ensemble Research at the Royal Military College of Canada
• We don’t know how these real-time measurements compare to the
traditional way of measuring respirator fit – the OSHA fit test
FUTURE RESEARCH GOALS
• Use real-time methodology with video exposure monitoring
in a simulated environment to determine what motions or
tasks healthcare workers perform that cause the respirator
to leak
INSTRUMENTATION SET-UP
- Chamber is 1.5 m x 1.5 m x 3 m.
Vol = 6.75 m3
- 3 aerosol salt generators
- 1 fan
RESEARCH PROTOCOL
• 16 subjects
• Randomly selected real-time or traditional fit test
• Completed the first fit test using the 8 OSHA fit test
exercises (1.5 minutes each)
• Normal Breathing
• Deep Breathing
• Head Side-to-Side
• Head Up-and-Down
• Talking
• Grimace
• Bend Over
• Normal Breathing
• Immediately, without removing or adjusting the respirator
performed the opposite fit test
CALCULATIONS
• For each fit test exercise, an average concentration inside the facepiece and
ambient concentration was calculated.
FFe =
𝐶𝑜
𝐶𝑖
• Overall Fit is calculated by taking a harmonic mean of all of the exercises
combined
RESULTS – REAL TIME VS. TRADITIONAL
Medians are similar throughout
Variability increases after talking
NB – Normal Breathing
DB – Deep Breathing
SS – Head Side-to-Side
UD – Head Up-and-Down
T – Talking
G – Grimace
BO – Bend Over
NB2 – Normal Breathing 2
O – Overall
Real-Time Fit Factor
Traditional Fit Factor
Real-Time Fit Factor
Traditional Fit Factor
RESULTS – 1ST VS. 2ND TEST
Medians are more similar throughout
Variability increases after talking
NB – Normal Breathing
DB – Deep Breathing
SS – Head Side-to-Side
UD – Head Up-and-Down
T – Talking
G – Grimace
BO – Bend Over
NB2 – Normal Breathing 2
O – Overall
2nd Fit Factor
1st Fit Factor
2nd Fit Factor
1st Fit Factor
DISTRIBUTION OF NORMAL BREATHING
A repeated measure ANOVA that controlled for
variability within subjects was used to compare
means.
No difference was found.
Boxplot shows increase in variability
REGRESSION MODEL
REAL-TIME
TRADITIONAL
Exercise
Intercept
Normal
Breathing
Deep
Breathing
Side to Side
Up and Down
Talking
Grimace
Bending Over
Normal
Breathing 2
Coefficient
9.93
P-Value
0.76
Exercise
Intercept
Coefficient
P-Value
17.40
0.76
0.77
Normal
Breathing
-0.04
0.87
0.47
0.41
Deep
Breathing
0.08
0.66
-0.34
0.28
-0.03
0.91
-0.03
0.94
0.12
0.57
-0.20
0.55
0.20
0.27
0.13
0.36
0.26
0.37
0.63
0.02*
0.58
0.15
-0.04
0.89
0.11
0.18
0.12
Side to Side
Up and Down
Talking
Grimace
Bending Over
Normal
Breathing 2
TRADITIONAL
REAL-TIME
Exercise
Coefficient P-Value
Exercise
Coefficient
P-Value
Intercept
-16.85
0.422
Intercept
29.91
0.44
Deep
0.49
Breathing
Side to Side -0.15
0.002
Talking
0.55
<0.001
0.005
Bending Over
0.33
<0.001
Bend Over
0.50
0.001
Normal
0.14
Breathing 2
0.066
CONCLUSIONS
• Wear time is significant
• Doesn’t always re-seat in the same way
• Method would be useful in future studies
• Produces similar results to OSHA fit test
REFERENCES
• Gijp S. v. d. and L. Steenweg: Respirator Performance during Military Field Trials. ISRP21(III&IV):135-136141 (2004).
• Hauge J., M. Roe, L. M. Brosseau, and C. Colton: Real-time fit of a respirator during simulated health
care tasks. J. Occup. Environ. Hyg.9(10):563-571 (2012).
ACKNOWLEDGEMENTS
• This research was supported in part by the National Institute of Occupational Health and Safety grant
# T42\OH008672