effect of hood size on a qualitative fit test - hsl.gov.uk size powerpoint.pdf · hse operational...
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Health and SafetyExecutive
© Crown Copyright, HSE 2018
Effect of hood size on aqualitative fit test
25th April 2018
Alison Bowry
© Crown Copyright, HSE 2018
Respiratory Protection
• Provide adequate protection
• Fit the wearers face
• To ensure the mask fits carry out a fit test
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Qualitative fit test (QLFT) kits
• Hood
• Two nebulisers to produce aerosols of the– Sensitivity solution– Test solution
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Standard QLFT sensitivity test
• Bitrex sensitivity solution used
• Place the hood on the wearer
• Introduce sensitivity aerosol using nebuliser
• Count the number of squirts needed for thewearer to taste the solution
HSE Operational Circular 282/28
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Standard qualitative fit test
• Don mask
• Place hood over wearers head
• Introduce initial number of squirts of testsolution
• Perform each exercise for 1 minute
• Introduce half the number of initial squirts at30 second intervals
• If the wearer can taste the Bitrex then thetest has failed and the mask doesn’t fit
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Initial number of squirts
Sensitivity result Initial number ofsquirts
1-10 1011-20 2021-30 3030+ -
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Standard QLFT 7 exercises
• Normal breathing
• Deep breathing
• Head side to side
• Head up and down
• Talking out loud
• Bending at waist
• Normal breathing
HSE Operational Circular 282/28
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Hood dimensions - standard hood
• 300mm (12”) in diameter
• 355mm (14”) in height
• Forms a cylindrical shape
• Internal hood space volume 20l
HSE Operational Circular 282/28
ANSI Z88.10:2010
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QLFT Kits available
• Range of kits available on the UK market
• Range of hoods
• Differ in– Construction– Shape– Size– Volume
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Identification of QLFT kits
• 10 commonly available QLFT kits purchased
• Three different designs of hood across the 10manufacturers
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Concerns over differing volumes
• How different are the volumes?
• Does this affect the concentration of aerosolin the hood space?
• Does this have a bearing on the quality andconsistency of the fit test?
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Hood volumes
• Total volume of hood, calculated from itsexternal dimensions when placed on amannequin torso
• Volume of standard Sheffield head calculatedby water immersion technique
• Volume of empty space calculated
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Percentage increase of hood volumes
Hood TypeVolume of hood
spacewhen worn (L)
% increase fromstandard hood
Standard 20 -A 20 0
A Upright 30 50B 23 15
C Flat 48 140C Shaped 44.5 122.5
+/- 5%ANSI recommended hood space volume 20L
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Experimental set up
• Standard Sheffield head attached to torso
• Connected to breathing machine– 1.5 l @ 20 strokes per minute– Regular breathing at low work rate (ISO,
2004)
• Tee shirt fitted to stop the hood slipping
• Alpha Solway 3030V disposable FFP3 maskfitted (used throughout testing)
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Measurement
• TSI PortaCount– Measures ambient particles/cm3
• TSI AM150 Sidepack aerosol monitor (SPAM)– Measures ambient particles mg/m3 (mass)– Calibrated flow rate 0.7l/min
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Tests
• PortaCounts and SPAMs allowed toequilibrate for 2 minutes
• 10 squirts of Bitrex test solution introducedbefore start of test
• 5 squirts introduced at 30 second intervalsfor 7 minutes – duration of fit test
• No attempt to simulate head movements orexercises during the test
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Tests
• Each test was carried out on the 3 styles ofhood in all configurations
• The aerosol concentration was measured
• Each hood configuration was tested 3 timesand a mean concentration calculated
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PortaCount results in hood volumeorder
Hood Type Particle/cm3 Volume(L)Standard 65782 20
A 54523 20B 39673 23
A Upright 53341 30C Shaped 23876 46
C Flat 18582 47
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PortaCount results in hood volumeorder
0
10000
20000
30000
40000
50000
60000
70000
0 10 20 30 40 50
Part
icle
s/cm
3
Hood space volume (l)
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SPAM results in hood volume order
Hood Type mg/m3 Volume(L)Standard 3.76 20
A 4.52 20B 2.43 23
A Upright 3.35 30C Shaped 1.42 46
C Flat 0.99 47
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SPAM results in hood volume order
00.5
11.5
22.5
33.5
44.5
5
0 10 20 30 40 50
mg/
m3
Hood space volume (l)
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Results
• There is a general trend in reduction ofconcentration of aerosol with increasinghood size
• A lower concentration of aerosol in the hoodmay lead to a fit test that is not as sensitiveas required
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Manufacturers
• Produce hoods which have a larger volumethan that specified in 282/28 andrecommended in the ANSI standard
• Instructions of correct assembly of the hoodis sometimes unclear
• Instructions on the delivery of the aerosol issometimes confusing
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