21- careers, information sources and conclusion · healthy cilia damaged cilia defence mechanisms...

1

SILICA SEMINAR

www.aioh.org.au

Linda Apthorpe & Ian Firth

AIOH Seminars

• AIOH runs technical seminars throughout the year

• Purpose:

Encourage professional development for members and others working in the industry

Find out about latest industry trends in health and safety

Determine what you can do to achieve effective positive behaviour change in your workplace

Hear what others are doing by networking with peers with similar interests

2

Presenters

• Ian Firth

IC Firth OHs Solutions PTY LTD

• Linda Apthorpe

3

2

Your Turn!

• Please introduce yourself and tell us why you are here!

4

Crystalline Silica

• Present in many workplaces

• Recent publicity -> engineered stone industry

• SafeWork Australia

• State Jurisdictions

5

Topics

• RCS Occurrence and Types

• RCS Health effects

• RCS Exposure Standards

• Exposure Risk and Disease Incidence

• Sampling & Analytical Methods

• Control

• The future for RCS

6

3

SILICA SEMINAR

www.aioh.org.au

RCS - Introduction

Session Outcomes

• Describe different forms of silicon dioxide

• Discriminate between types/phases of quartz

• List workplaces where crystalline silica can be found

8

RCS Occurrence and Types

9

4

Silica

SiO2

Crystalline Amorphous

10

Silicon Dioxide – Quartz

• SiO2 – oxide of silicon

• Most abundant mineral on earth

• Commonly found: sand, rocks &

diatoms

• Hard abrasive mineral

• Also present in soils & clays

11

Quartz Properties

• Quartz is slightly soluble in body fluids and soluble in HCl

• It is insoluble in water, organic solvents, most mineral acids.

• Molecular weight: 60.09

• Specific density: 2.65

• Melting point: 1,600 deg C

• Boiling point: 1,723 deg C

12

5

Used for…

13

Crystalline Types

• Quartz

• Cristobalite & Tridymite (high temperature)

Source: touch of modern

14

Crystalline Types

• Coesite & Stishovite (dense, meteorites)

• Free silica

Source: Britannica.comSource: individual.utoronto.ca

15

6

Phase Diagram

16

Other Types of Silica

• Microcrystalline silica (opal, flint, tripoli, silica flour, chalcedony)

Source: via Google

17


• Amorphous silica

18

7


• Fumed Silica

• Lechatelierite, rare amorphous glass

Source: Wikimedia commons

19


• Silica fume (microsilica)

Average diameter: 150 mm

20

Terminology

• Terms for the same thing?

Respirable crystalline silica (RCS)

Respirable crystalline quartz

Respirable silica

Respirable quartz

Respirable alpha quartz

Crystalline quartz

Crystalline silica

21

8

Workplace Silica

22

Crystalline Silica

SiO2

α-Quartz Cristobalite

Tridymite

Quartz in Workplaces

• What types of workplaces would RCS be found?

• Mining, rock-drilling, sandblasting, construction, foundry work, stonecutting, drilling, quarrying (hard rock & sand), building and general construction work, road work and road construction, cement products manufacturing, demolition operations, sweeping, masonry, tunnelling, ceramics & brick manufacture, demolition, abrasive blasting, agricultural earth works, asphalt production, abrasives, glass & paint manufacture...

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24

9

25

26

27

10

28

29

30

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31

32

33

12

% Quartz

Type ~% Quartz

Granite 25-50

Shale 22

Natural quartzite 65-90

Natural sandstone 65-90

Engineered stone Up to 90 (+ cristobalite)

Natural Sand 80-90

Manufactured Sand 0-90

Concrete (as sand/quartz) 20-25

Concrete 20-60 (as SiO2)

34

Exposure Sources

• Exposure to RCS is widespread across Australia

(mainly from mining & construction industries)

• Cristobalite & Tridymite

formed in high temperatures

• Remember to consider possibility of presence of cristobalite (& tridymite) in workplaces

35

Session Recap

• Different forms of silicon dioxide

crystalline & amorphous

• Discrimination between types/phases of quartz

quartz, cristobalite, tridymite

• Workplaces where crystalline silica can be found

36

13

References

• ACGIH Documentation of the Threshold Limit Values &

Biological Exposure Indices, 7th Edition

• Pattys Industrial Hygiene & Toxicology, 3rd (rev) edition

• ILO Encyclopaedia of Occupational Health & Safety, 3rd (rev) edition

• IARC monographs (No 68-6)

• OSHA website (www.osha.gov)

• NIOSH website (www.cdc.gov/NIOSH)

• SafeWork Australia (www.safework.gov.au)

37

SILICA SEMINAR

www.aioh.org.au

RCS – Health Effects

Session Outcomes

• Describe the health effects of RCS

• Specify the elements of a health surveillance program

• Explain the factors that affect the disease potential of RCS

39

http://www.osha.gov/

http://www.cdc.gov/NIOSH

http://www.safework.gov.au/

14

Health Effects of RCS

• Silicosis

• Bronchogenic carcinoma

• COPD

• Pulmonary tuberculosis

• Industrial bronchitis

• Auto-immune diseases

• Renal disease

40

The Respiratory Tract

41

Gas Exchange Region of the Lung

42

15

Defence Mechanisms

The respiratory system has a number of ‘dust filters’ that must be passed before dust can reach a point in the lung where it can cause damage.

Clearance of dust is by:

Hairs in the nose

Transport via the mucociliary ladder

Removal by scavenger cells (macrophages) in the alveolar region

Health effects can eventuate when these mechanisms become overloaded.

43

Defence Mechanisms

44

Healthy cilia Damaged cilia

Defence Mechanisms

45

Macrophage Action in Alveolar Region

Julie A. Champion and Samir Mitragotri, Role of target geometry in phagocytosis, Proc Natl Acad Sci U S A. 2006 March 28; 103(13): 4930–4934.

16

Lung Function Testing - Spirometry Graphs

2 ways of looking at a Spirometry result

46

FLOW VOLUME VOLUME TIME

Shapes of Spirometry Curves

47

Volume VolumeVolume

RestrictionObstruction Mixed

Abnormal Ventilatory Function

Normal (?)

From: DP Johns, R Pierce. Pocket

Book of Spirometry. Sydney:

McGraw-Hill, 2003.

Flo

w

Flo

w

Flo

w

Lung disease - Obstructive symptom (COPD)

Asthma, Bronchitis, Emphysema

Increased resistance of airways

Narrowing of the airways from brochospasm

Swollen tissues

Excessive mucous

Increased thickness of airway wall (collagen) due to remodelling

Loss of elastic recoil (due to alveoli collapse - emphysema)

48

17

Lung disease - Restrictive symptom

Diffuse Lung Diseases

decreased respiratory muscle strength

stiff lungs (increased elastic recoil –fibrosis)

shrunken and non-homogeneous lung without obstruction of larger airways

total lung volume reduced (forced vital capacity, FVC)

the ratio of FEV1/FVC is normal (forced exhaled volume in 1 second, FEV1)

49

Interpretation Algorithm

50

No

Yes

Yes No

Is FVCbelow lower limit of normal?

Normal Spirometry

RestrictionReferral for

confirmation & diagnosis

ObstructionSeverity: Use % predicted FEV1

Is FEV1/FVCless than 70%

51

18

Grinders disease

Silicosis among the grinders of razors, forks, knives, saws and other edge tools in Sheffield, England

THE ILLUSTRATED LONDON NEWS,

January/March, 1866

52

Potter’s Rot - 1840

The "scourers", chiefly young women, necessarily inhale, the room being literally filled with dust, the fine particles of flint, which produce similar effects to what is provincially denominated, in the Sheffield trade, " the grinder's rot; " something might be done, perhaps, to lessen this evil, if judicious precautionary measures were adopted.I have suggested the use of a wet sponge, so adapted to the mouth and nostrils that the air of respiration must necessarily pass through it…... "

http://www.thepotteries.org/jobs/scourer.htm

53

Pneumonoultramicroscopicsilicovolcanoconiosis

• Name given to silicosis when caused by the specific exposure to fine silica dust found in volcanoes

• Longest word in the English language (45 letters)

54

http://www.thepotteries.org/jobs/scourer.htm

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Notice chalked up in a foundry in Coventry

(1934)

55

Silicosis

• Progressive fibrotic lung disease (pneumoconiosis)

• Frequently not the primary cause of death

• Classification is made according to the disease's severity, onset and rapidity of progression:

chronic silicosis (includes simple and complicated silicosis)

accelerated silicosis

acute silicosis

56

Silicosis

Symptoms:

• Shortness of breath

• Cough

• Rapid breathing

• Loss of appetite

• Chest pain

57

Source: ATS Silica Awareness

20

Silicosis

Diagnosis using:

• Patient history

• Physical check up

• Lung function test

• Chest X-ray

• CT scan

• Autopsy

Silica Essentials Presentation, BOHS April 17th 2007, Colin Davy HSE, HM Specialist Inspector

58

ILO Categorisation of Silicosis

ILO

Category

Qualitative description

0/0 No small (up to 1 cm) silicotic opacities (nodules) are present

0/1Probably no nodules, but some areas of radiograph are suspect (possible silicosis)

1/0

Small silicotic nodules are most likely present, but not certainly (probable silicosis)

HSE – only a minor radiographic abnormality, not necessarily indicative of silicosis development, no functional impairment

59

ILO Categorisation of Silicosis

ILO

Category

Qualitative description

1/1

Small silicotic nodules are definitely present

HSE – particularly high degree of inter-reader variability so

difficult to determine where to place on exposure-response curve

1/2Small silicotic nodules are definitely present; other areas of the radiograph may indicate more advanced lesions including large opacities (> 1 cm), pleural thickening.

2/1, 2/2, 2/3, 3/2, 3/3

More advanced stages of silicosis/increasing certainty of the presence of lung abnormalities

HSE – 2/1+ is the most reliable basis for identifying true cases of silicosis, low reader variability, more specific but less sensitive (than 1/0 or 1/1) indicator of silicosis

60

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ILO classification for silicosis – lung

scarring profusion (source: Daniel Powers M.D. Radiology)

61

ILO classification for silicosis – lung

scarring profusion (source: Daniel Powers M.D. Radiology)

62

Silicosis

63

Healthy lung Silicosis

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Mechanism of disease

• The critical factor in the onset of silica disease appears to be

cessation of clearance of silica particles and the onset of inflammation (Tran 2005)

• This inflammation culminates in the development of nodules

which characterise the diagnosis of silicosis (Rao et al. 2004)

• Latency period largely independent of cumulative dust

exposure (Hnizdo & Sluis-Cremer 1993)

• Risk of silicosis increases exponentially with cumulative dust

dose (Hnizdo & Sluis-Cremer 1993, Steenland and Brown 1995, Chen et al 2001, Churchyard et al

2004 2003, Hughes et al 1998)

64

Relative fibrogenicity risk

• It was thought that cristobalite was more fibrogenic than quartz based on invitro studies

65

• However the UK HSE was unable to find any evidence that quartz and cristobalite should be treated differently when assessing human exposure (Meldrum et al 2001)

http://globalinvestmentwatch.com/2009/03/31/sparkle-finger-dead-stonecutter-china/

Lung cancer

• International Agency for Research on Cancer (IARC) 1997

crystalline silica inhaled in the form of quartz or cristobalite from occupational sources is considered carcinogenic to humans (Group 1)

reassessed and confirmed in 2012

• ACGIH classifies quartz as an A2 (confirmed animal, suspect human) carcinogen

• Safe Work Australia classifies quartz / RCS as cat. 1A (known human) & STOT (repeated exposure) cat. 1

66

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Lung cancer

• IARC working group noted that carcinogenicity was not

detected in all industrial circumstances studied

• Determination specifically relates to occupational exposure and not environmental exposure

• Findings of relevance to lung cancer and RCS exposure arose

from five main industrial settings:

ceramics, diatomaceous earth, ore mining (not coal

mining), quarries, and sand and gravel

• Strongest evidence supporting carcinogenicity of RCS in the lung comes from pooled and meta-analyses of selected

epidemiological studies

67

Lung cancer

• EU Scientific Committee for Occupational Exposure Limits

(SCOEL):

There is sufficient information to conclude that the relative lung cancer risk is increased in persons with silicosis (and,

apparently, not in employees without silicosis exposed to silica dust in quarries and in the ceramic industry).

• This continues to be studied

• Others have concluded that the weight of evidence from occupational epidemiology does not support a causal

association of lung cancer and RCS exposure (Gamble 2011)

68

Lung cancer

• Effect of several carcinogens can lead to additive or more complicated reactions – e.g. silica exposure and smoking = increased cancer risk

• Exposure periods of at least ten years with a latent period of several decades up to the appearance of the illness has been observed

• Mechanism is impaired particle clearance leading to macrophage activation and persistent inflammation -inflammation-driven secondary genotoxicity (IARC 2012)

69

24

Lung cancer

70

Healthy lung Lung cancer

Lung cancer X-ray

http://article.wn.com/view/2009/02/08/Whither_lung_cancer/?section=SectionResults&template=cheetah-meta%2Fmeta-related-stories.txt

71

Chronic obstructive pulmonary disease (COPD)

• COPD describes chronic airflow limitation that is usually irreversible

• Includes four interrelated disease processes

chronic bronchitis

emphysema peripheral airways disease

• Cigarette smoking is a major cause of COPD, but community air pollution and occupational exposure to dust, particularly among smokers, also contribute

• Studies indicate exposure to gold mine dust is an important cause of COPD, particularly in smokers

• Risk of COPD appears greater for gold miners than for coal miners

72

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Chronic obstructive pulmonary disease (COPD)

Destruction of alveolar walls in silica dust exposed subjects can

lead to emphysema which is the main cause of COPD

73

Decrements in lung function

• Initial studies of granite workers (0.1 mg/m3 exposure)

indicated decrements in pulmonary function parameters (Therialt et

al 1974)

• Follow-up studies of the same workers failed to detect pulmonary function loss when smoking history was included (Graham et al 1994)

• Cigarette smoking is associated with approximately twice the

lung function loss attributable to silica dust exposure

• Significant decrements in pulmonary function do not occur

early in simple silicosis and radiological changes may be a better diagnostic tool

74

Pulmonary tuberculosis

• Silica particles can destroy or alter the metabolism of the pulmonary macrophage, thereby reducing its capacity for anti-bacterial defence

• Occupational exposure to silica dust renders a subject susceptible to developing pulmonary tuberculosis - 10–30 fold increased incidence

• The risk of developing pulmonary tuberculosis while exposed, and also after exposure ends, depends on the cumulative amount of silica dust exposure

• Presence of silicosis in the lung further increases the risk of developing pulmonary tuberculosis

• Rate of tuberculosis in workers exposed to silica is related to the rate of tuberculosis in the general population (SORDSA, 1999).

76

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Industrial bronchitis with airflow limitation

• Generally accepted that this condition can be caused by occupational exposure to dust

• Can lead to COPD

• Individual susceptibility is important

• Smoking is a significant cause

• May be caused by larger particles than those responsible for disease in the deep lung

77

Auto-immune diseases

• Scleroderma (an autoimmune disorder) - hardening or

sclerosis in the skin or other organs

• Evidence to date not sufficient to conclude that RCS is a causative factor for systemic sclerosis - no exposure-response

data available

• Rheumatoid arthritis - significantly higher among granite

workers than in general male population of the same age -possible aetiological or pathophysiological role of granite dust

may be based on the effects of quartz on the immune system

78

Renal disease

• Increased risk of renal disease has been implicated with

elevated exposures to RCS

• A US study found a doubling of risk of non-malignant renal disease but no increase in renal cancer

• While studies of cohorts exposed to RCS have found elevated

standard mortality ratios (SMRs) for renal disease, there was

no clear evidence of a dose–response relationship

• Pathogenesis of renal effects in RCS exposed workers is not clear - elevated risk is perhaps attributable to diagnostic and

methodological issues

79

27

Health surveillance

• Pre-employment medicals

• Ongoing medicals

• Termination medicals

• Annual employee testing for respirable dust and crystalline silica exposure.

80

Health surveillance

• Demographics, occupational and medical history

• Health advice - workers informed of the potential health effects

• Standardised respiratory questionnaire

• Standardised respiratory function test including, for example, FEV1, FVC and FEV1/FVC

• Chest X-ray, full size posterior-anterior view

• Records of personal exposure

• Physical examination if indicated by occupational or medical history. Emphasis on respiratory system

• ACOEM and AIOH recommend health surveillance where exposure to RCS is > 0.05 mg/m3

81

Health surveillance

• If at any point, the worker is suspected of having silicosis during a surveillance evaluation, remove from exposure and refer immediately for definitive diagnosis

• Frequency of health surveillance (ACOEM):

Follow-up evaluation within 12 months: Evaluate need for repeat chest X-ray at this time

if exposure is < 0.05 mg/m3, assess need for frequency of future follow-up evaluations

if exposure is > 0.05 mg/m3 for less than 10 years, 3 years

if exposure is > 0.05 mg/m3 for 10 or more years, 2 years

• SWA focus on questionnaire and lung function tests to reduce use of X-rays - every 5-10 years in first 20 years of work unless exposures > WES. BUT need for low threshold for early radiological screening

82

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Health surveillance

• The employee should be informed of the results of the health

surveillance

• The employer should be informed when abnormal findings are detected so that control measures can be checked

• Termination health surveillance:

date of termination

reason for termination

• if ill-health give details

• date and cause of death if in service

examination

83

Factors thought to affect the potential for RCS

to cause disease

• Polymorphic type of crystalline silica

• Presence of other minerals

• Particle number, size and surface area

• Freshly fractured and “aged” surfaces

84


to cause disease

• Polymorphic type of crystalline silica: cristobalite, tridymite and quartz appear more reactive and more cytotoxic than coesite and shishovite

• There is however no evidence from human experience for any differences in the toxic properties of cristobalite and quartz (HSE 2002)

85

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to cause disease

The presence of other minerals

• the toxic effects of quartz are reduced in the presence of aluminium containing clay materials

• the protective effect of aluminium containing materials is not permanent, as the quartz dust may be “cleaned” in the lungs, and this eventually begins to express its pathogenic properties

• iron enhances quartz toxicity

86


to cause disease

The particle number, size and surface area:

• regardless of type of dust, total surface area of the dust retained in the lungs is an important determinant of toxicity

• surface area is related to particle size – smaller particles of RCS would be expected to produce more lung damage than equal masses of larger respirable size fractions

87


to cause disease

Freshly fractured and “aged” surfaces:

• cleavage leads to formation of reactive radical species

• leads to an increase in cytotoxicity• the activity of the free radicals decays with time -

‘aging’• occurs slowly in air, but rapidly (within minutes) in

water• freshly fractured silica with iron contamination

results in enhanced generation of reactive radicals

88

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Session recap

• Describe the health effects of RCS

• Specify the elements of a health surveillance program

• Explain the factors that affect the disease potential of RCS

89

Source: ATS Silica Awareness

References

• AIOH (2018). Respirable Crystalline Silica and its Potential for Occupational Health Issues– Position Paper - https://www.aioh.org.au/resources/publications1/epublications

• American College of Occupational and Environmental Medicine (ACOEM)

http://www.acoem.org/

• HSE (2002). Respirable Crystalline Silica - Phase 1: Variability in Fibrogenic Potency and Exposure-Response Relationships for Silicosis. Hazard Assessment Document: Guidance

note, environmental hygiene/EH75/4, Health and Safety Executive, UK. http://www.hse.gov.uk/pubns/books/eh75-4.htm

• IARC (2012). Monographs on the evaluation of carcinogenic risks to humans Vol 100C, Silica Dust, Crystalline, in the form of Quartz or Cristobalite. https://monographs.iarc.fr/iarc-monographs-volume-100c-silica-dust-crystalline-in-the-form-of-quartz-or-cristobalite/

• NIOSH (2002). Hazard Review – Health Effects of Occupational Exposure to Respirable Crystalline Silica. DHHS (NIOSH) Publication Number 2002-129.

https://www.cdc.gov/niosh/docs/2002-129/default.html

• Parker, JW & R Gregory (2011). Silicosis. International Labor Organisation (ILO) Encyclopaedia of Occupational Health and Safety. http://iloencyclopaedia.org/part-i-47946/respiratory-system/21-10-respiratory-system/silicosis

• Safe Work Australia (2013). Crystalline silica health monitoring.

https://www.safeworkaustralia.gov.au/doc/crystalline-silica-health-monitoring

90

SILICA SEMINAR

www.aioh.org.au

RCS – Exposure Standards

https://www.aioh.org.au/resources/publications1/epublications

http://www.acoem.org/

http://www.hse.gov.uk/pubns/books/eh75-4.htm

https://monographs.iarc.fr/iarc-monographs-volume-100c-silica-dust-crystalline-in-the-form-of-quartz-or-cristobalite/

https://www.cdc.gov/niosh/docs/2002-129/default.html

http://iloencyclopaedia.org/part-i-47946/respiratory-system/21-10-respiratory-system/silicosis

https://www.safeworkaustralia.gov.au/doc/crystalline-silica-health-monitoring

31

Session Outcomes

• Explain respirable size fraction

• Describe relevant Exposure Standards

• Consider WES adjustments

Exposure Standards

• Snowy mountains scheme

• NSW silicosis hot spots in 1970

• Development of ES in Australia

1905 hard rock mining investigation - WA

1914 Royal Commission at Broken Hill

Silicosis board of NSW

1920’s dust control regulations (NSW & WA)

Particles greater than 100 µm

Particles less than 100 µm - inhalable

Particles less than 10 µm – respirable dust & quartz

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Lung Diagram

Inhalable dust:

• <100 µm

•Toxic particles

effect upper

respiratory tract

Respirable dust:

• <10 µm

•Toxic particles effect

alveolar region

Penetration of Dust

96

Equivalent Aerodynamic Diameter Respirability

Micrometres (µm) %

0 100

1 100

2 97

3 80

4 56

5 34

6 20

7 11

8 6

10 2

12 0.5

14 0.2

16 0.1

18 0

AS 2985-2009

(ISO/CEN/ACGIH)

Size Fractions

50% cut point

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Exposure Standards

• WES values set by SafeWork Australia

• WES based on an 8-hour day

• For longer shifts the ES can be adjusted as:-

Longer time to be exposed per day

Shorter times for recovery (non exposed time)

• WES development history

Time Weighted Average

100

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

1 2 3 4 5 6 7 8

Respirable quartz

mg/m3

One 8 hour day

Short term sampling & excursions

Average = 0.03 mg/m3

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WES - HCIS

101

Crystalline Silica

α-Quartz

0.1 mg/m3

Cristobalite

0.1 mg/m3

Tridymite

0.1 mg/m3

102

WES - HCIS

103

Amorphous Silica

Diatomaceous earth

10 mg/m3

Fumed silica

2 mg/m3

Silica gel

10 mg/m3

Precipitated silica

10 mg/m3

Note: • there is no WES value for silica fume

35

International RCS (α-quartz) ES ValuesCountry ES (mg/m3)

Austria 0.15

Belgium 0.1

Canada 0.1

UK 0.1

Finland 0.05

France 0.1

Ireland 0.05

Netherlands 0.075

New Zealand 0.1

US (ACGIH-non regulatory) 0.025

US (OSHA & NIOSH) 0.05

Australia 0.1

Source: GestisDatabase, ACGIH, Worksafe NZ, SafeWork Australia

RCS ES History

1983-84 OES (mg/m3)

Quartz 0.2

Cristobalite 0.1

Tridymite 0.1

• 1983-84 NHMRC recommended ES

RCS ES History

1983-84 ES (mg/m3)

1988 ES (mg/m3)

Quartz 0.2 0.1

Cristobalite 0.1 0.05

Tridymite 0.1 0.05

• 1988 Worksafe (NOHSC) recommended ES (following ACGIH)

• Between 1988-96 no formal ES existed

• Some mining & OHS authorities assumed their own ES

• 1996 Worksafe reinstated NHMRC quartz value of 0.2 mg/m3

• After further review, new ES of 0.1 mg/m3 in effect from 2005

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ES Adjustment

• For shifts longer than 8 hours (e.g. 10 or 12 hours)

• Safe Work Australia guidelines

Brief and Scala

(OSHA & pharmacokinetic)

• WA mining industry guidelines

• AIOH – based on Quebec model

• Choose which method best suits the workplace and is conservative

Industry Specific OES

• Pursue ALARA principle

• Action Levels to investigate/remediate

• Industry specific action levels at reduced fractions of ES

• Coal industry (e.g. crib to crib sampling times)

Session Recap

• Respirable fraction explanation

• Current & Historical OES information & descriptions

• WES adjustments

37

References

• Safe Work Australia HCIS website: hcis.safeworkaustralia.gov.au

Exposure Standards – search facility

Hazardous Chemicals – search facility

• ISO 7708:1995 – particle size fraction definitions

• AS 2985:2009 –sampling & gravimetric determination of respirable dust

• AIOH Position Paper: RCS and its potential for occupational health issues

SILICA SEMINAR

www.aioh.org.au

RCS – Exposure Risk & Disease Incidence

Session Outcomes

• Evaluate the risk of disease

• Classify acceptable levels of risk

• Select an appropriate level of exposure

112

RC drilling

http://hcis.safeworkaustralia.gov.au/

38

Exposure Risk and Disease Incidence

• The two most important diseases associated with RCS are silicosis and lung cancer

• A lot of epidemiological work has been done on the risk of developing these two diseases

• There are varying views on the risk of health effects at RCS exposure concentrations of 0.1 mg/m3 and below (AIOH 2018)

113

Risk of developing silicosis from 2 and 4

mg/m3.years* (HSE 2002)

PopulationILO silicosis

category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years

Scottish coal miners 2/1+ 5 15

* 2 & 4 mg/m3.years is 0.1 and 0.2 mg/m3 respectively for 20 years.

114




category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years


South African gold miners

1/1+ 5 52


115

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category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years


South African gold miners 1/1+ 5 52

Hong Kong granite workers

1/1+ 6 15


116




category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years




1/1+ 6 15

US gold miners 1/1+ 8 53


117




category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years




1/1+ 6 15


Chinese tin miners 1/1+ 11 45


118

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category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years




1/1+ 6 15



Colorado hard rock miners

1/1+ 11 53


119



PopulationILO

silicosis category

% with

silicosis

2 mg/m3.years

% with

silicosis

4 mg/m3.years




1/1+ 6 15




1/1+ 11 53


120




category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years

UK pottery industry 1/0+ 0 2


121

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category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years


Ontario hard rock miners

1/1+ 0.4 1.2


122




category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years


Ontario hard rock miners 1/1+ 0.4 1.2

UK heavy clay industry 1/0+ 0.9 -


123




category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years




Diatomaceous earth workers

1/0+ 1.1 – 3.7 4 - 12


124

42




category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years





1/0+ 1.1 – 3.7 4 - 12

Iron foundry workers 1/0+ 2 10


125




category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years





1/0+ 1.1 – 3.7 4 - 12


Vermont granite workers

1/0+ 4 -


126




category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years





1/0+ 1.1 – 3.7 4 - 12


Vermont granite workers 1/0+ 4 -


127

43

Uncertainties in studies with higher risk

estimate (HSE 2002)

PopulationSelection

BiasFollow-up

Other minerals

Freshly fractured

Exposure assessment

Scottish coal miners

South African gold miners


US gold miners

Chinese tin miners


128

X X Yes ?

- ? Yes X

X ? Yes X ?

X X - Yes X

- ? Yes X

X ? Yes X ?

Uncertainties in studies with lower risk estimate(HSE 2002)

PopulationSelection

BiasFollow-

upOther

mineralsFreshly

fracturedExposure

assessment

UK pottery industry

Ontario hard rock miners

UK heavy clay industry


Iron foundry workers


129

- X X No X ?

- - X ? Yes X

- X ? No X

- X X No X ?

- X X Yes X

- X - Yes X ?

Summary of study assessment

• Lower risk studies lack adequate follow-up and/or involved co-exposure to aluminium-containing minerals and/or exposure to aged rather than freshly cut surfaces

• Higher risk studies have poor exposure data, sometimes selection bias and poor diagnosis. Also, risk levels relate to workplace situations where exposure is to freshly cut surfaces of RCS and no exposure to aluminium

130

44

Strongest studies

Two study populations stand out from the pack as the

benchmarks:

• Scottish coal miners – 0.5% risk with 15 year exposure to 0.04 mg/m3 (0.6 mg/m3.years)

• Vermont granite workers – 0.85% risk with 20-40 year

exposure to 0.06 mg/m3 (1.2-2.4 mg/m3.years)

131


category

% with silicosis

2 mg/m3.years

% with silicosis

4 mg/m3.years



1/0+ 4 -


Risk of death from silicosis from 2 and 4 mg/m3.years*

Population % with exposure of 2.25 mg/m3.years

% with exposure of 4.5 mg/m3.years

6 occupational cohorts (ACGIH) 0.6 1.2

132

Sandstone block cutting• OSHA (2010) conducted a comprehensive review of

RCS health effects from a range of studies

• Lifetime silicosis risk estimates over 45 years associated with exposure to RCS generated using high-energy processes

• Estimated most reliable risks to be 30 cases per 100 workers for exposure to 0.1 mg/m3 and 5.5 cases per 100 workers for exposure to 0.05 mg/m3.

Lung Cancer – Strongest studies (HSE 2003)

133

Population SMR* / SIR**

Granite workers (US)

Shed workers 1.27*

Quarry workers 1.0* (0 extra cases)

Early hire workers >1.67* (8 extra cases)

Granite workers (Finland) 1.7** (18 extra cases)

Industrial sand workers1.5* (28 extra cases based on national

mortality rates)

1.39* (23 extra cases based on local mortality rates)

10 pooled occupational cohorts 2.8% (above background of 3-6%)

* Standardised mortality ratio is the observed number of cases divided by the number of expected cases

** Standardised incidence ratio is the number of new cases in the exposed population divided by the number of new cases in the control population

45

Lifetime risks of mortality from lung cancer from RCS (Goldsmith

2006)

RCS concentration (mg/m3) Predicted lung cancer deaths per 1000 workers a,b

0.001 0.3

0.005 1.5

0.010 2.9

0.020 5.9

0.030 8.8

0.040 12.0

0.050 15.0

0.060 18.0

0.070 20.0

0.080 23.0

0.090 26.0

0.100 29.0

a. Assumes constant 45 years exposure between age 20 and 65 and thereafter accumulating annual risks to 85 years; and

b. Excess risk estimates/1000 workers exposed (i.e. the excess lifetime risk for lung cancer at 0.1 mg/m3 silica is 29 deaths per 1000 workers)

134

Lung Cancer

• There is increased lung cancer risk with increasing cumulative exposure and/or duration of exposure

• Relative risk for those in the highest exposure categories tend to be twice that of those in the lowest categories

• Unlikely that the increased risk is due to other factors such as smoking, asbestos or socio-economic differences

• Appear limited to those groups with the highest cumulative exposures, suggesting the existence of a threshold

• Limited to early hire workers who commenced employment before the introduction of adequate dust controls

135

Lung Cancer

• Heavy and prolonged occupational exposure to RCS can cause

an increased risk of lung cancer

• RCS is a relatively weak carcinogen

• It appears that lung cancer mortality in RCS-exposed workers is restricted to those with silicosis

• The weight of evidence suggests that exposures to RCS,

insufficient to cause silicosis, would be unlikely to lead to an

increased risk of lung cancer, although the evidence is not definitive

136

46

Lung Cancer

• A recommendation from the EU Scientific Committee for

Occupational Exposure Limits (SCOEL) was adopted in June 2003. The main conclusions were as follows:

The main effect in humans of the inhalation of respirable

silica dust is silicosis. There is sufficient information to

conclude that the relative lung cancer risk is increased in persons with silicosis (and, apparently, not in employees

without silicosis exposed to silica dust in quarries and in the

ceramic industry). Therefore preventing the onset of silicosis will also reduce the cancer risk. Since a clear

threshold for silicosis development cannot be identified, any

reduction of exposure will reduce the risk of silicosis.

137

Threshold effect

• Exposure-response model for RCS and risk of silicosis / lung cancer using an inflammatory mode of action implied a "tipping point"

threshold (Cox, 2011)

• Applied to epidemiological data - levels on order of 0.1 mg/m³ are

probably below the threshold for triggering lung diseases in humans (Cox, 2011)

• Study indicated an RCS dust exposure (8-hour TWA) concentration threshold greater than 0.1 mg/m3 and possibly as high as 0.25

mg/m3 (Morfeld et al, 2013)

138

What does it all mean??

139

• A threshold for silicosis development has been determined but is not acknowledged by all

• The risk is not linearly related to cumulative exposure – it rises more steeply as absolute exposure concentrations increase

• If we can control silicosis we can control the other diseases

Sandstone block cutting

47

Acceptability of risk (Hester & Harrison 1998)

140

Acceptable risk

Intolerable risk

– it does not imply that the risk will be acceptable to everyone, i.e. that everyone

would agree without reservation to take the risk or have it imposed on them

• ‘tolerable’ does not mean ‘acceptable’

– it refers instead to a willingness by society as a whole to live with a risk so as to

secure certain benefits in the confidence that the risk is one that is worth taking

and that it is being properly controlled


• HSE upper limits of tolerable risk – deaths per year (annual

risk):

Workers – 1 in 1,000 person.years

General public – 1 in 10,000 person.years

Individual – 1 in 1,000,000 person.years

• HSE believes:

that an individual risk of death of one in a million per annum corresponds to a very low level of risk

should be used as a guideline for the boundary between

broadly acceptable and tolerable regions

141

Acceptability of risk

• Lifetime risk (80 year life)

Workers – 8,000 in 100,000

General public – 800 in 100,000

Individual – 8 in 100,000

142

48


• NOAEL – no observed adverse effect level

• If a NOAEL cannot be established, use a LOAEL

• USEPA NOAEL

The highest exposure level at which there are no statistically or biologically significant increases in the frequency or severity of an adverse effect between the exposed population and its appropriate control

• WHO NOAEL

No detectable adverse alteration of morphology, functional capacity, growth, development or lifespan of the target

143


Uncertainly factors used for setting WESs were far smaller than those used in other areas of standard setting, such as exposure to pesticides, food contamination residues, and environmental contaminants

144

Comparison of risk estimates (Tran et al. 2005)

ACGIH NOAEL for silicosis (implied)

DFG NOAEL for silicosis

DFG LOAEL for silicosis

0.025 mg/m3

0.007-0.1 mg/m3

0.02-0.25 mg/m3

ACGIH NOAEL for lung cancer 0.046 mg/m3

Risk estimates from Scottish coal miners study

(Silicosis Category 2/1 or greater)

Risk 1/1000 (Occ NOAEL) 0.01 mg/m3

Risk 2.7/1000 0.025 mg/m3

Risk 17/1000 0.1 mg/m3

De Klerk (silicosis risk)

Risk <1/100 0.13 mg/m3

Human NOAEL estimated from animal studies

0.0011 mg/m3

ACGIH recommended TLV 0.025 mg/m3

145

49

Comparison of risk estimates (Tran et al. 2005)

146

• The average NOAEL based on extrapolation from the

animal studies is some 9 to 45 times lower than those based on epidemiological studies

• May be overly conservative due to the application of

conventional uncertainty factors recommended by the

US EPA

Relative risk

147

Risk Level SituationLifetime risk per

100,000

Extra highSmoking (all causes)

Smoking (lung cancer)

21,900

8,800

High 1,500

Elevated Frequent airline passenger 730

Motor vehicle 600

Moderate Light drinker 150

Low Cycling 75

Very low Vaccination 22

Lightning 3

Extremely lowEnvironmental asbestos exposure

1

Relative risk – HSE upper tolerable limits

148


100,000



21,900

8,800

Upper tolerable limit Workplace 8,000

High 1,500

Upper tolerable limit General public 800


Motor vehicle 600


Low Cycling 75


Acceptable Individual 8

Extremely low

Lightning

Environmental asbestos exposure

3

1

50

Relative risk – lung cancer mortality

149


100,000



21,900

8,800


RCS: cancer mortality?? 2,900

High 1,500

Upper tolerable limit General public 800


Motor vehicle 600


RCS: cancer mortality?? 100

Low Cycling 75


Acceptable Individual 8

Relative risk – silicosis mortality

150


100,000



21,900 (22%)

8,800 (9%)


High 1,500

Upper tolerable limit General public 800 (0.8%)

Elevated Frequent airline passenger 730 (0.7%)

Motor vehicle 600 (0.6%)

RCS: silicosis mortality 600 (0.6%)


RCS: lung cancer mortality 100

Low Cycling 75


Relative risk – silicosis morbidity

151


100,000



21,900 (22%)

8,800 (9%)


High RCS: silicosis (Scottish study) 1,700 (1.7%)

RCS: silicosis (de Klerk) 1,000 (1%)






RCS: lung cancer mortality 100

Low Cycling 75


51

Relative risk – acceptable level of exposure?

152


100,000



21,900 (22%)

8,800 (9%)


High 0.1 mg/m3 1,700 (1.7%)

RCS: silicosis (de Klerk) 1,000 (1%)





0.025 mg/m3 270 (0.27%)

Moderate Light drinker 150 (0.15%)

RCS: lung cancer mortality 100 (0.1%)

0.01 mg/m3 <100 (<0.1%)

Session Recap

• Evaluate the risk of

disease

• Classify acceptable levels

of risk

• Select an appropriate

level of exposure

153

RC drilling

References

• AIOH (2018). Respirable Crystalline Silica and its Potential for Occupational Health Issues

– Position Paper - https://www.aioh.org.au/resources/publications1/epublications

• de Klerk, NH, GL Ambrosini & AW Musk (2002). A Review of the Australian Occupational

Exposure Standard for Crystalline Silica. The University of Western Australia, December

2002.

• DFG (2000). Silica, crystalline: quartz dust, cristobalite dust and tridymite dust (respirable

fraction). MAK Value Documentation, Deutsche Forschungsgemeinschaft (DFG) -

https://onlinelibrary.wiley.com/doi/10.1002/3527600418.mb0sio2fste0014

• HSE (2002). Respirable Crystalline Silica - Phase 1: Variability in Fibrogenic Potency and

Exposure-Response Relationships for Silicosis. Hazard Assessment Document:

Guidance note, environmental hygiene/EH75/4, Health and Safety Executive, UK.


• HSE (2003). Respirable Crystalline Silica – Phase 2: Carcinogenicity. Hazard

Assessment Document EH75/5: Health and Safety Executive, UK.


• OSHA (2010). Occupational Exposure to Respirable Crystalline Silica – Review of Health

Effects Literature and Preliminary Quantitative Risk Assessment. Occupational Safety

and Health Administration, Docket OSHA-2010-0034.

https://www.osha.gov/silica/Combined_Background.pdf

154

https://www.aioh.org.au/resources/publications1/epublications

https://onlinelibrary.wiley.com/doi/10.1002/3527600418.mb0sio2fste0014



https://www.osha.gov/silica/Combined_Background.pdf

52

SILICA SEMINAR

www.aioh.org.au

RCS - Sampling & Analysis

Session Outcomes

• Select correct sampling equipment

• Choose suitable analytical technique

• Explain detection limits

Historical Sampler

• MRE-113A horizontal elutriator

53

Konimeter

Owens Dust Jet

Thermal Precipator

Impinger

Respirable Dust & Quartz Sampling

• AS 2985:2009 Method for sampling and gravimetric determination respirable dust

• Gravimetric analysis for respirable dust

• Personal and static (fixed location) samples

• Minimum sampling duration is 4 hours (or ½ shift)

159

Sampling

• Comparison of results with relevant WES values

• Representative and non biased

• Size selecting cyclone sampler used for sampling

160

54

Respirable Dust Samplers

• AS 2985:2009 lists requirements for size selecting samplers

• Examples are:-

BCIRA cyclone

(SIMPEDS) Modified Higgins & Dewell cyclone

Aluminium cyclone

• No SIMPEDS terminology!

162

Cyclone Diagram

‘Modified’ Higgins & Dewell cyclone

55

Breathing Zone

Sample Filters

• Sample filters are generally 25 mm

• Pore size is 5 µm or less

• PVC GLA 5000 filters are normally used for RCS

• Filters are normally pre & post weighed to estimate respirable dust concentrations via gravimetric analysis

Analysis of Sample Filters

• NATA accredited laboratory (ISO 17025)

• NATA accredited labs for RCS analysis

• Two techniques:-

Infrared (FTIR) analysis

X-Ray Diffraction (XRD) analysis

• Based on Australian NHMRC & US NIOSH methods

56

Remember!!

• Conduct quartz analysis only on valid filters from respirable dust samplers

FTIR Analysis

• Infrared absorbance at specific wavelengths

• Absorbance or transmission of infrared

• Interferences

• Organic materials - ashed

FTIR Instrumentation

57

798 cm-1

779 cm-1

694 cm-1

796 cm-1

58

912 cm-1

Twin peaks at 795 & 750 cm-1

800 cm-1

X-Ray Diffraction (XRD)

• Expensive instrument

• Needs a radioactive source

• Can determine (singularly or together):-

quartz

cristobalite

tridymite

amorphous silica

59

Crystal Lattice & Bragg’s Law

XRD Schematic

177

XRD Instrumentation

60

10 15 20 25 30 35 40 45 50 552Theta (°)

100

200

300

400

500

Inte

nsity (

cps)

Q100

Q101

Q112

Ag111 Ag200

Theta Degrees

Intensity

FTIR vs XRD

• FTIR

Quick

Cheaper (usually)

Comparable detection limits

Can’t speciate between quartz & cristobalite when both together

Some interferences

180

FTIR vs XRD

• XRD

Longer analysis time

May be more expensive

Comparable detection limits

Can speciate between quartz & cristobalite phases when both together

Some interferences

Can analyse amorphous forms

181

61

Detection Limits

• Detection limits can be variable

• Limit of Detection – lowest practicable detection limit

• Limit of Quantitation – lowest amount determined quantitatively

• Ensure LOD & LOQ are suitable

Detection Limits - Practicality

• Direct on Filter – lower DL than ashed or re-deposited methods

• Based on 500 L sample (4hr @ 2.2 L/min)

FTIR: 0.02 mg/m3

XRD: 0.02-0.04 mg/m3

• In real life, real workplace samples

<0.05 mg/m3 is problematic

• Better to take near shift length samples (8-12 hr)

183

Materials for Analysis

• Sample filters from respirable (size-selecting) dust samplers

• Bulk samples – e.g. road dust, ores, quarry material etc.

• Respirable quartz in the respirable fraction of a bulk material

62

Session Recap

• Sampling techniques (historical & selecting current sampling devices)

• Analytical techniques (FTIR & XRD) description

• Limit of Detection & Limit of Quantitation explanation

AIOH Resources

• AIOH Position Paper – RCS and Occupational Health Issues

• AIOH – Technical papers

Sampling Pumps

Flow Measuring Equipment

Size-selective Samplers for Respirable Dust Sampling

186

References

• AS 2985:2009 –sampling & gravimetric determination of respirable dust

• NHMRC Method of quartz in respirable airborne dust by infrared & XRD, 1984

• ISO 16258-1 (2015) Workplace air – Analysis of RCS by X-Ray Diffraction, Part 1 Direct on filter method

• NATA website: www.nata.asn.au

http://www.nata.asn.au/

63

SILICA SEMINAR

www.aioh.org.au

RCS – Exposure Control

Impact of dust control - Vermont granite

workers (Graham et al 1991, 2001)

Year hired % of miners with silicosis (cases)

1940-44 17.9 (5)

1945-49 7.5 (8)

1950-54 4.2 (4)

1955-59 3.8 (2)

> 1959 1.5 (1)

189

Session Outcomes

• Use the hierarchy of control

• Apply engineering and administrative control

• Set up a respiratory protection program

190

64

Most Effective

LeastEffective

Personal Protective Equipment

Administration/Training

Engineering/Isolation

Substitute

Eliminate Hardcontrols

Softcontrols

191

Hierarchy of Control

Substitution

• Olivine and zircon in moulds and cores in foundries

• Glass beads, metallic shot, slag or grit for abrasive blasting

• Alumina for flint in pottery

• Pre-fabrication

design buildings with pre-built recesses for plumbing, gas,

and electric wiring so there is less need to cut or drill masonry

192

Principles of dust control

1. Prevention of dust formation

2. Prevention of dust spread

3. Prevention of worker dust exposure

193

65

Prevention of dust formation

• Engineering

Tools and equipment

Wet processes

• Administrative

Work processes

Maintenance of equipment

194




Substitute

Eliminate

Prevention of dust formation – tools and

equipment

• Sharp cutting tools minimise the generation of dust at source through less grinding

195

Prevention of dust formation – wet processes

• Dust is eliminated if powdered material is suspended or dissolved in a liquid

• If materials are adequately moistened by capillary action or by condensation, the point is reached where they will cease to generate dust.

moulding sand

sandstone

196

66

Prevention of dust formation – work processes

& maintenance

• Control of dust levels along travelling roads

• Change cutting method

• Reduce cutting speed

• Equipment maintenance

197

Prevention of dust spread

• Engineering control

Design

Segregation

Extraction ventilation

Water suppression

Physical barriers

Packaging systems

• Administrative control

Work processes

Housekeeping

198




Substitute

Eliminate

Prevention of dust spread - design

199

• Concentrate dusty processes in one area

• Ensure contaminated air does not spread to clean areas

• Wall and flooring surfaces and furniture that is easy to keep clean

• Use solid floors (mostly!!)

• Minimise fall distances and slope angles

• Ensure flooring is designed to allow drainage

67

Prevention of dust spread - design

200

• Protect electrical systems against moisture and dust

• Adequate correctly positioned water and vacuum points

• Low maintenance equipment

• Closed circuit television systems

• Equip silos with pressure relief devices, high level alarms and dust extraction systems

• Consider downstream maintenance

Prevention of dust spread - segregation

201

• Where possible full enclosure

should be considered:

grinding mills in vented enclosures

blasting cabinets - operator

controls from outside the

enclosure

enclosed transfer points, crushers, conveyor systems,

bucket elevators & screen

houses

pneumatic transport systems

enclosed automatic bag dumping stations


202

68


203

Three deck screen with dust control (Hanson Quarries)


204

• Pneumatic systems

consider highly abrasive nature of RCS

for horizontal transport angle pipes downward

minimise directional changes (large radius bends)

properly seal pipe connections

• Conveyor belts equipped with cleaning devices

• Consider maintenance access for enclosed systems

• Enclosure normally requires some form of extraction ventilation

Prevention of dust spread – extraction

ventilation

205

• Removes contaminants at the

source of emission

• Enclose the dust source as much as possible

• Incorporates a hood/enclosure or

other inlet to collect dust,

ductwork, a cleaning device, a fan and a discharge duct

• Ensure a clean air supply to the

work area to replace extracted

air

69


ventilation

206

• Hood/enclosure or other inlet to collect dust

away from doors, windows and HVAC system outlets

as close to emission point as possible

deep enough to contain equipment and materials

opening as small as possible

see-through panels and plastic strips do not store items inside the ventilated

area

easy way to check it is working – small flag

Industrial Ventilation A Manual of Recommended Practice. 23rd Edition American Conference of Governmental Hygienists (ACGIH)


ventilation duct design

207

• Short and simple

• Under negative pressure & properly sealed

• Minimise flanges and inspection holes

• Avoid long sections of flexible duct

• Design so dust cannot settle

• Ensure transport velocities are appropriate

• Minimise internal wear – have few bends

• Provide an appropriate number of resealable test points


ventilation

208

Dust extraction cleaning devices

Drop out boxes

Cyclones

Wet scrubbers

Bag filters/houses

Electrostatic precipitators

Design considerations

– the need for pre-separator/pre-cyclone

– particulate & noise emission limits

– maintenance requirements

– need for inclination of more than 60° at the base

– access to the flue and sample ports

70


ventilation maintenance

209

• Test against performance standards

• Never modify the system

• Monitor filters/bags &/or monitor emissions

• Maintain water levels/supply in wet scrubbers

• Temporarily seal leaks with duct sealing tape

• Repair/replace damaged/dented sections of ductwork

• Take extra precautions regarding protection of maintenance workers

Prevention of dust spread – portable extraction

ventilation systems

• Often difficult to install a ventilation system because of moving process and/or equipment - flexible ducts may be the solution

210

• portable extraction systems may be used

Prevention of dust spread – portable extraction

ventilation

211

Small equipment such as laboratory grinders and stone mason tools should have integrated exhaust ventilation

71

Prevention of dust spread – water suppression

• Once a dust cloud has been generated it is not easy to control it by wet methods

difficult to wet fine airborne particles, particularly quartz

• However water suppression remains one of the main dust control techniques

• High-pressure water jets/sprays that produce fog or fine mist spray are most effective

water sprays specifications

• close to breakage point

• sufficient water volumes

• sufficient pressure

• appropriate jets/nozzles/venturis

212


• Wetting agents/surfactants may be added to increase the surface tension of the water and hence enhance its wetting ability

• Examples

Wet cutting

Wet scrubbers

Road watering

Sprays on traffic routes, conveyors & crushers

Water curtains - particularly at conveyor transfer points and chute draw points

Stockpile/muckpile sprinklers/watering

Wet cleaning – mopping, wet brushing, hosing

213

Prevention of dust spread – wet cutting

processes

214

Dry cutting

Wet cutting

72


wetting agents

215

Sprays being used on a cone crusher and conveyor system transfer point (Hanson Quarries)

Prevention of dust spread – water suppression -

Longwall mining

216

Stock pile water suppression

217

Water sprays to control dust off stock piles. (Hanson

Quarries)

73

Road watering with wetting agents

218

Haul road without DustBloc. (Hanson Quarries)

Road watering with wetting agents

219

Haul roads with DustBloc. (Hanson Quarries)

Prevention of dust spread – physical barriers

• Rubber curtains to prevent dust release - conveyor transfer points and chute draw points

• Wind barriers/sails

• Stockpile discharge socks/curtains or retractable vertical chutes

220

74

Prevention of dust spread – packaging

• Enclosed bulk transport systems

keep the loading point under negative pressure

collect displaced air from tanker

if not enclosed tarp load

221

Prevention of dust spread – packaging

• Bag systems

Bulker bags reduce exposure during packaging but may be difficult to handle for the customer

Small bags have the greatest potential for exposure during packaging

• use plastic liners

• seal the bag collar onto the filling spout

• use vibration to prevent hang-ups and

to compact material

222

Prevention of dust spread – administrative

control

223

• Ore passes not emptied

below the brow point and crusher chutes are kept full

• Apply good house-keeping

practices to prevent dust

build-up and dust spread

clean workplace on a regular basis – daily if

necessary

deal with spills

immediately

75

Prevention of dust spread – administrative

control

224

• Dry cleaning - vacuum cleaning systems

ensure system is not overloaded

not generally suitable for damp materials

follow procedures when emptying vacuum of dust

do not use dry brush or compressed air

• Define specific storage areas for silica based products – if outdoors, site area to minimise wind entrainment of dust

Prevention of worker exposure

• Engineering control

Dilution ventilation

Segregation

Automation

• Administrative control

Maintenance systems

Training

Supervision

• PPE

225




Substitute

Eliminate

Prevention of worker exposure – dilution

ventilation

226

• Natural ventilation from windows and doors or fan forced ventilation

• Should ensure the removal of contaminated

air and make it up with clean or filtered replacement air

• Seldom a correct solution in working with a dust problem

• May use ducting to help focus air supply on specific areas

• Consider conditioning air to warm or cool it

• Ensure dilution ventilation does not interfere with local extraction ventilation

76

Variations in dilution ventilation designs

Air curtains

• A type of jet that reduces the exchange of air across an opening.

• Commonly used to reduce the flow of cold air into a heated building or vice-versa.

227

Industrial Ventilation A Manual of Recommended Practice. 20th Edition American Conference of Governmental Hygienists (ACGIH)

Variations in dilution ventilation designs

Overhead Air Supply Island System

(OASIS)

• Uses a wide nozzle or plenum at low velocity to provide a zone of

fresh air around the worker.

• Usually operate on either fresh air

from outside the workplace or filtered air from inside the

workplace.

228


Prevention of worker exposure – dilution

ventilation

• How forced or natural ventilation is applied to a workplace

requires forethought and planning to be effective

• Fresh air should always pass the operator, collect the contaminant, then pass to the outlet. Should the general

ventilation operate in any other way, the air may become

contaminated before reaching the worker’s breathing zone

229


77

Prevention of worker exposure – segregation

• Segregation in enclosed and filtered control rooms and mobile

equipment cabins

have own clean air supply

sealed and physically separated from dusty areas

ventilate using positive pressure systems

provide sufficient widows to monitor the process from within the control room

filters must remove very fine particles

230


231


232

Precleaned, pressurised and

filtered external/recirculated

air mixed in the HVAC

plenum & blown into cabin

Cleaned & Filtered

Air

To Recirculation RESPA

Unit

From Cabin

Standard HVAC UnitExternal air & debris enter primary

RESPA Unit. Debris goes through two

ejective precleaning cycles. Precleaned

air then passes through Merv 16 / 17 filter

sending CLEAN air into HVAC system

Maintaining a pressurised

cabin is essential for effective

air filtration. A sensor can be

installed to monitor cabin

pressure (0.049 kpa).

Air from cabin enters RESPA

Recirculation Unit, where it

passes through second MERV

16/ 17 filter to remove particles

that enter the cabin via the

door, or carried in via boots &

operator clothing

RESPA- HVAC Pre-cleaner Pressuriser +

Filtration Technology

78


233

RESPA- HVAC Precleaner Pressuriser + Filtration Technology

Debris laden air enters the

RESPA Unit

Debris particles

ejected back into

the environment.

Pre-cleaned air

continues into the

filter

Fresh air continues

into the evaporator


234

Prevention of worker exposure – automation

• Remote monitoring of crusher from camera within control room

• Automated longwall mining

• Remote control mucking

235

79

Typical control strategies

Process Enclosure ExtractionWet

process

Drying/calcining minerals

Loading/unloading bulk

material

Lab crushing/drying

Cutting and polishing refractory

Concrete cutting

Core making and moulding in

foundries

Knock-out and shake-out in

foundries

236

Typical control strategies

Process Enclosure ExtractionWet

process

Mobile equipment –

excavation and haulage

Rock drilling

Furnace charging

Crushing, grinding and

screening

Bagging

Grinding, sawing and drilling

ceramic products

Mixing

Firing ceramics

237

Prevention of worker exposure – administrative

controls

• Restrict access to dust generating work areas to authorised personnel

• Position personnel so they are out of the dust or so they are working upwind of dust emission

• Job rotation

• Perform regular visual checks – look for build-up of fine dust that may indicate a control failure

• Maintenance

follow supplier/installer maintenance guidance & keep records

• Training, Supervision

238

80

Administrative control systems - training

• Hazards of RCS

• Dust exposure prevention

• Checking controls are working and using them

• When and how to use respiratory protective equipment –limitations

• What to so if something goes wrong e.g. spillage

• Dust monitoring programs – including results

• Health surveillance

• Refresh every 2 years

239

Dust control systems - supervisors

• Have a knowledge of health hazards

• Understand the potential problem areas of the process

• Understand the control measures - their use and maintenance

• Know the health surveillance requirements

• Check control measures are in place and are being used

• Report faults to supervisors and get them fixed

• Set an example by following procedures

240

Prevention of worker exposure – respiratory

protection

241

Half face disposable

respirator

(P1 or P2)

PAPR – Powered air

purifying respirator

(P2 or P3)

81

Prevention of worker exposure – RPE

• There are three classes of particulate respirator

Class P1 - for use against mechanically generated particulates e.g. asbestos and silica

Class P2 - for use against mechanically or thermally generated particulates e.g. zinc or lead fume

Class P3 - for use with any particulate including highly toxic particulates e.g. beryllium and some microbiological agents.

• Filtering efficiency

P1 - not more than 20% penetration

P2 - not more than 6% penetration

P3 - not more than 0.05% penetration.

242

RPE management program

243

• Set up in accordance with AS1715

• Conduct regular inspections to ensure PPE is being utilised consistently and correctly

• Signage indicating areas where PPE is required

• Store in a clean and fully operational condition, safe from damage, and easily accessible e.g. disposable RPE at building entrances

• Regular checking & maintenance – keep records

• Repair or discard if damaged or defective

RPE management program

• Individual fit-testing for face seal and to ensure comfort (qualitative or

quantitative)

• Personal issue (facial features &

protection factor)

• Training in use and limitations

• Simple written procedures and policy

- e.g. clean shaven policy if negative pressure face seal respirators used

• For more details see: https://www.3m.com.au

244

https://www.3m.com.au/

82

Clean Shaven

• RCS – much smaller than facial hair

• Respirator relies on good facial seal

• Clean shaven –> shave before coming to work!

Need for more than one control

• US engineered stone top bench manufacture – 30-min RCS samples in mg/m3: (Cooper et al 2015)

dry cutting: 44.6

wet blade alone: 1.87–4.85

wet blade + curtain: 0.92–3.41

wet blade + LEV: <0.12–0.20.

• UK stone working sectors - 61% RCS exposures where water suppression used > 0.1 mg/m3

(Baldwin et al 2019)

246

Session Recap

• Use the hierarchy of control

• Apply engineering and administrative control

• Set up a respiratory protection equipment

247

83

References

• NEPSi ‘Good Practice Guide’ - http://www.nepsi.eu/ - with

more than 50 different task sheets that include controls for RCS generation.

• NIOSH Safety and Health Topic page on ‘Silica’ -

https://www.cdc.gov/niosh/topics/silica/constructionControlMa

in.html - examples of engineering controls, including use of LEV to capture dust at source and use of water sprays to

suppress dust.

• OSHA ‘Controlling Silica Dust in Construction Fact Sheets’ page

-https://www.osha.gov/dsg/topics/silicacrystalline/construction.

html.

• UK HSE ‘Control of exposure to silica dust’ page -

http://www.hse.gov.uk/pubns/indg463.htm.

248

SILICA SEMINAR

www.aioh.org.au

RCS – Future Initiatives

Safe Work Australia report that workers in Australia

are 8 times more likely to die from an occupational

illness or disease than an accident at work.

Statistics released by Safe Work Australia indicate that on

average 250 people will die from injury at work, while over

2000 people will die from an occupational disease

Safe Work Australia 2012

http://www.nepsi.eu/

https://www.cdc.gov/niosh/topics/silica/constructionControlMain.html

https://www.osha.gov/dsg/topics/silicacrystalline/construction.html

http://www.hse.gov.uk/pubns/indg463.htm

84

Web based information hub: www.breathefreelyaustalia.org.au

What is available on the BOHS site

AIOH site currently covers: Construction, Welding, Engineered Stone and Mining

85

HI Standard

Self-Assessment

Tool

+ other web-

based resources

Breathe Freely Australia - helping you take control

.

Let’s get going by deciding to treat health like safety.

Then begin to breathe freely.

Join us and be part of the solution

www.breathefreelyaustralia.org.au

http://www.breathefreelyaustralia.org.au/

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