Industrial Ventilation Silica - WorkSafe Queensland ... Industrial Ventilation Silica Dr David...

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  • Industrial Ventilation Silica

    Dr David Bromwich BSc(Hons), MAppSc(Med Phys, QIT), MSc(Occ Hyg, Lond), FAIOH, COH, PhD(Griffith)

    Consulting Occupational Hygienist

    Adjunct Associate Professor Centre for Environment, Population and Health School of Medicine Griffith University

    dbohs.com

  • © David Bromwich 2019 2

    My Industrial Ventilation

  • © David Bromwich 2019 3

    Sources of Respirable Crystalline Silica (RCS)

     Construction  Sandblasting

     Jack hammering

     Rock drilling, cutting, chipping or polishing

     Brick or tile cutting and sawing

     Concrete drilling, sawing, grinding and polishing

     Tunnelling

     Demolition

     Asphalt milling

     Tuckpointing

     Stone countertop fabrication

     Diatomaceous earth processing

     Pottery production

     Foundries

     Work on linings of rotary kilns and cupola furnaces

     Mining

     Hydraulic fracturing

  • © David Bromwich 2019 4

    Risk

    0.25%0.5% 2.5%

    20%

    0

    2

    4

    6

    8

    10

    12

    14

    16

    18 20

    0 0.1 0.2 0.3

    Ri sk

    ( %

    )

    Respirable Crystalline Silica (mg/m3)

    Lifetime risk of silicosis

    ACGIH 2010 Australia

    1993

    ACGIH 1986

    NIOSH Australia

    2005 UK control

    2002,

    Hawke's Nest Tunnel

    UK max 2002

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    Topics  Historical context  Toxicology

     Dust Size

     Free Radicals – age of dust

     Hierarchy of Control & Industrial Ventilation  Industrial Ventilation concepts  Effectiveness of dust suppression with water  Effectiveness of respiratory protection

     Applying Industrial Ventilation concepts

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    Historical  Silicosis and Workers Compensation 1930’s in USA

     Hawk’s Nest Tunnel (1927) USA  About 1000 deaths (3000 workers)

     Sydney Harbour Bridge (1923-1932)  Many died from silicosis (250 stone workers)

     Only 16 died from injuries

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    Historic -1930

    https://www.sciencespo.fr/silicosis/ sites/sciencespo.fr.silicosis/files/ILO _Silicosis_Conference_1930_report_o f_proceedings.pdf

    https://www.sciencespo.fr/silicosis/sites/sciencespo.fr.silicosis/files/ILO_Silicosis_Conference_1930_report_of_proceedings.pdf

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    ILO 1930 Silicosis “The Relative Value of the Use of Water and of Ventilation in the Prevention of Silicosis”

     To keep dust out of the air at the site where the stone was broken; water was very efficient, but the finest dust would pass any form of water

    Ventilation is never 100% effective

    Nor are water sprays for the very toxic fine silica particles

  • © David Bromwich 2019 9

    Hierarchy of Control for Silica  Elimination

     Substitution

     Isolation – control cabins

     Engineering Controls  New technology – water jet cutting

     Water Sprays

     Industrial Ventilation

     Administrative Controls

     Personal Protective Equipment  Respiratory Protection

    https://www.breton.it/

    https://www.breton.it/

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    Visible particulates

    http://amienvironmental.com/

    http://amienvironmental.com/

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    Particle size Nose

    Mouth

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    Industrial Ventilation concepts

     Sucking and Blowing

     Air flow away from face

     Extraction close to source

     Changing particle size

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    Sucking and blowing

    Many industrial ventilation systems (sucking air) are designed by people with an airconditioning background (blowing air) They often get it wrong

    Adapted from McDermott 1976

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    Imagine a black hole vacuum

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    Imagine a black hole vacuum

     Air flows from all directions

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    Imagine a black hole vacuum  Enlarge the hole

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    Imagine a black hole vacuum  Now join a pipe to the hole

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    Imagine a black hole vacuum  Capture zone

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    Imagine a black hole vacuum  Often contaminants escape…

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    Shaping the airflow - flanges

    https://www.nap.edu/read/4911/chapter/1

    https://www.nap.edu/read/4911/chapter/1

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    Suction is not directional

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    Industrial Ventilation concepts

     Sucking and Blowing

     Air flow away from face

     Extraction close to source

     Changing particle size

  • © David Bromwich 2019 23

    Ideal flow is away from face

    https://www.ccohs.ca/oshanswers/prevention/ventilation/hoods.html

    Intended

    Desired

    https://www.ccohs.ca/oshanswers/prevention/ventilation/hoods.html

  • © David Bromwich 2019 24

    Industrial Ventilation concepts

     Sucking and Blowing

     Air flow away from face

     Extraction close to source

     Changing particle size

  • © David Bromwich 2019 25

    Wet grinding benchtop

    Source /www.cdc.gov/features/preventing-silicosis

    HOOD

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    Good design

     90% of Industrial Ventilation design is with hood

     If capture of toxic air is ineffective then  Person breathes more toxic air

     Larger vacuum / extraction fan needed – greater cost

     Noisier

     Many systems badly designed, even on tools

  • © David Bromwich 2019 27

    HSE research (UK)  RR926 - On-tool controls to reduce exposure to

    respirable dusts in the construction industry - A review (2012) https://www.hse.gov.uk/research/rrhtm/rr926.htm

    • On-tool LEV – reduces exposures by 90% • Hood design, suction • On-tool controls never completely eliminated exposure

    •supplementary respiratory protective equipment (RPE)

    https://www.hse.gov.uk/research/rrhtm/rr926.htm

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    Industrial Ventilation concepts

     Sucking and Blowing

     Air flow away from face

     Extraction close to source

     Changing particle size

  • © David Bromwich 2019 29

    Water Sprays

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    Traditional water suppression

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    Better water suppression

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    Better water suppression

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    Benchtops – saw silica dust control

    Jared H. Cooper, David L. Johnson, Margaret L. Phillips, Respirable Silica Dust Suppression During Artificial Stone Countertop Cutting, The Annals of Occupational Hygiene, Volume 59, Issue 1, January 2015, Pages 122– 126, https://doi.org/10.1093/annhyg/meu083

    44.4

    4.9 3.8 0.6

    0 5

    10 15 20 25 30 35 40 45 50

    Dry Wet Wet + curtain Wet + LEV

    Re sp

    ir ab

    le S

    ili ca

    ( m

    g/ m

    3)

    https://doi.org/10.1093/annhyg/meu083

  • © David Bromwich 2019 34

    Tunnelling  Brisbane has a number of new tunnels

     Standard Practice is to supply fresh air to the cutting face

     Air is filtered and returns along the tunnel

     This is opposite of good practice, as filtration is never 100%

     Other tunnel workers are exposed to respirable silica

    https://accionacorp.blob.core.windows.net/

    portofmiamitunnel.com

    https://accionacorp.blob.core.windows.net/ http://www.portofmiamitunnel.com/press-room/image-gallery/construction-of-tunnel-cross-passage-5/

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    Applying Industrial Ventilation to Respiratory Protection

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    Air flow - inhalation

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    Facial hair and RPE  1.3 cm/month = 150 microns/shift

     Respirable dust 10 microns (0.01 mm)

     Getting a good face seal on a respirator after a day's facial growth is as likely as a fence made of 6 m high powerlines will contain a mouse

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    PPE Fit

     Inhalation – air flows over surface of face (sucking)

     Exhalation – air flows in a plume (blowing)

     A face mask makes even more air flow over the surface of the face

     Facial growth – holds face mask off face

     A beard makes any face mask much less effective

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    PPE

    Source: https: