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Industrial VentilationSilica

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

Consulting Occupational Hygienist

Adjunct Associate Professor Centre for Environment, Population and HealthSchool of MedicineGriffith University

dbohs.com

© David Bromwich 2019 2

My Industrial Ventilation

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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

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Risk

0.25%0.5%2.5%

20%

0

2

4

6

8

10

12

14

16

1820

0 0.1 0.2 0.3

Risk

(%

)

Respirable Crystalline Silica (mg/m3)

Lifetime risk of silicosis

ACGIH2010 Australia

1993

ACGIH1986

NIOSHAustralia

2005UK control

2002,

Hawke's Nest Tunnel

UK max2002

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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_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

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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/

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Visible particulates

http://amienvironmental.com/

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Particle sizeNose

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

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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

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Ideal flow is away from face

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

Intended

Desired

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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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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

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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)

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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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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 3.80.6

05

101520253035404550

Dry Wet Wet + curtain Wet + LEV

Resp

irab

le S

ilica

(m

g/m

3)

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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

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Applying Industrial Ventilationto 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://www.abc.net.au/news/2018-10-12/what-is-the-dust-lung-disease-silicosis/10365604

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Seal to neck is important

Managing respirable crystalline silica dust exposure in the stone benchtop industry Code of Practice 2019 (Queensland)

https://www.worksafe.qld.gov.au/injury-prevention-safety/workplace-hazards/managing-respirable-crystalline-silica

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Silica dust control

Agglomerate dust with fine water spray

Remove this dust with well designed extraction ventilation Also use good respiratory protection

Quantitative Fit testing and training

Professional Respiratory Protection Program (not cheap!)

Thank YouDavid Bromwich

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