Silica

Larry Joswiak, MPHMarch 31, 2010

Silica 1926.55 – Mineral Dusts

• It’s not just dust…It’s silica

• Silica NEP (National Emphasis Program) January 24, 2008

• Silica LEP (Local Emphasis Program) October 1, 2009 Targets specific General Industry SIC Codes

What is silica?

• Mineral – crystalline or amorphous forms– Crystalline most hazardous

• Crystalline- 3 forms– Quartz, cristobalite, tridymite

• Quartz – most commonMajor component of soils and readily found in rock

Granite ~30% quartzShale ~ 20% quartzBeach sand – nearly pure quartz

Silica Exposure Activities

• Sand/abrasive blasting

• Tuckpointing• Jack hammering

concrete• Brick/block cutting• Concrete cutting &

drilling• Demolition

• Stone cutting• Foundry work• Tunneling• Rock drilling• Quarrying

What is silicosis?

• A disabling and often fatal lung disease caused by breathing very small “respirable” particles of crystalline silica

• >14,000 deaths since 1968

• >200 deaths each year in the U. S.

Silicosis

• Chronic/Classic – Occurs after 15 – 20 years of moderate to low

exposure

• Accelerated– Occurs after 5 – 10 years of high exposures

• Acute– Occurs after a few months or as long as 2 years to

extremely high concentrations

Other Health Effects of Silica Exposure

• Lung cancer– IARC Group 1: Carcinogenic to Humans

• Tuberculosis

• Chronic Obstructive Pulmonary Disorder– Bronchitis, Emphysema

• Immunologic Disorders & Autoimmune Disease

• Renal Disease

• Diseased and healthy lung • Compare these sections cut from a diseased lung with large cavities (left) and a

pink, healthy lung (right). The diseased lung shows a case of miner’s phthisis (also known as silicosis) which has led to tuberculosis. Quartz dust is inhaled by miners, and trapped in the lungs causes silicosis making the victim more susceptible to diseases such as tuberculosis and pneumonia.

Current Respirable Silica Quartz Exposure Limits

OSHA (PEL)Construction

OSHA (PEL)General Industry ACGIH (TLV)

250 mppcf% silica + 5

10 mg/m3

% silica + 2 Quartz: 0.025 mg/m3

Cristobalite: 0.025 mg/m3

AIR SAMPLING EQUIPMENT

Personal Air Pump with Cyclone

PERSONAL SAMPLING

OSHA ConstructionIndustry

OSHA GeneralIndustry

ACGIHConstruction & General

Industry

Employee Name

% Silica Time Sampled(minutes)

8 HRTWAa

(mppcf)e

PELb

(mppcf)e

8 HRTWAa

(mg/m3)d

PELb

(mg/m3)d

8 HRTWAa

(mg/m3)d

ACGIHTLVf

(mg/m3)d

Grinder 1 5.5 464 19.6 23.8 1.96 1.4 1.96 0.025

Grinder 2 4.5 474 20.2 26.3 2.02 1.54 2.02 0.025

Laborer1 3.6 463 3.5 29.1 0.35 1.79 0.35 0.025

Laborer 2Air hose

3.8 478 5.7 28.4 0.57 1.72 0.57 0.025

a 8-hour Time Weighted Average d mg/m3 – milligrams per cubic meter of airb OSHA Permissible Exposure Limit e mppcf – million particles per cubic foot of airc Employee exposure for time sampled f TLV – American Conference of Governmental Industrial Hygienist’ Threshold Limit Values

Concrete Cutting (Dry) Example

• 6 % silica• 2.27 mg/M3 PEL• 16.3 mg/M3 (68 min)• 2.31 mg/M3 8 hr TWA • 8 hour severity

102% of PEL• EXCEEDED PEL • Gas saw dry cuts hole

in concrete manhole• 718 % of PEL for 68

minute sample time

30% Crystalline Silica Quartz

10% Crystalline Silica Quartz

10% Crystalline Silica Quartz

8 % Crystalline Silica Quartz

Silica Conclusions

• Dry operations: High likelihood of silica dust overexposure

• Wet operations: Low potential for silica dust overexposure

• Exposures may be multiplied by factors such as interior workplace and corner location.

Silica Conclusions

• Written Hazard Communication Program– Employee training on silica

• Engineering Controls– Use of water during cutting– Local exhaust ventilation

• Respiratory Protection– NIOSH approved– Air Monitoring– Required or voluntary use

• Eye Protection