1. Silica
Larry Joswiak, MPH
March 31, 2010

2. 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

3. What is silica? Mineral – crystalline or amorphous forms
Crystalline most hazardous
Crystalline- 3 forms
Quartz, cristobalite, tridymite
Quartz – most common
Major component of soils and readily found in rock
Granite ~30% quartz
Shale ~ 20% quartz
Beach sand – nearly pure quartz

4. 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

5. 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.

7. Silicosis Chronic/Classic Accelerated Acute
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

8. 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

9. 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.

10. Current Respirable Silica Quartz Exposure Limits
OSHA (PEL)
Construction
OSHA (PEL)
General Industry
ACGIH (TLV)
250 mppcf
10 mg/m3
Quartz: mg/m3
Cristobalite: mg/m3
% silica + 5
% silica + 2
Can anyone tell me what a Permissible exposure limit (PEL) is? Specific legal guidelines created by OSHA based on an 8-hour (time weighted average) TWA. If you look at the different standards for general industry and construction, sometimes they don’t match. The levels are based on a risk assessment and research in industry. In 1971 OSHA came into effect, OSHA took the American Conference of Governmental Industrial Hygienists (ACGIH), Threshold Limit Values (TLV’s) that had already been established and basically used them as the new PEL-essentially the PELs are the TLVs, but could even be less protective because they haven’t been changed in 30 years. The two different PELs indicated here are written differently because they are based on two different analytical methods. The one with the mmpcf is based on a sampling device no longer used. However, they mean the same thing the units are just reported differently.
The second set of limits are the REL-Recommended Exposure Limits these are based on research and are recommended by NIOSH which is the research branch if OSHA. Their limits are also not legally enforceable. OSHA tried in 1989 to overhaul all of the PELs at once, by the courts rejected them and said that OSHA needs to do one at a time. There is specifically no standard or program for silica. The only thing OSHA has is a PEL. Asbestos however, does have its own standard: with regulated areas and engineering controls.
If you look at the third set of limits called the TLVs, we can compare them to the PELs. (write on board) You can see that if you have 100% silica which = 10mg/m3 / ( ) = 10/102~ 0.1mg/m3, the same would be true for Cristobalite and Tridymite. However, you would need to divide by 2.

11. AIR SAMPLING EQUIPMENT
Personal Air Pump with Cyclone
To collect a sample representational of your day’s exposure you need to use a personal air-sampling pump with a cyclone. This is a cyclone (show) –the way it works is that there is a small inlet on the side, a air whirls around, dust gets caught –does anyone know what happens?- the large/heavy particles fall to the bottom, the ones greater than 10 microns in diameter. The particles less than or equal to 10 microns collect on the filter. The filter you use is a PVC filter, if you order them from the lab who is going to analyze your results which is done by x-ray diffraction, the cassettes will come pre weighed.

12. PERSONAL SAMPLING
You need to collect the sample at a flow rate of 1.7 liters/min. It is especially important that you pre and post calibrate your sampling device. Without calibrating your sampling device the results are meaningless. So I would suggest hiring a consultant to help with the sampling procedure. Unless you take a silica sampling class like ours. If you have worn sampling pumps before, you may remember that you wore the filter over the shoulder. With the cyclone you need to wear it under the arm so that you do not turn it upside down. You also do not want to connect or tape the base onto your shirt because when you lean over everything will fall out! Let it hang loosely. It is designed to orient itself in the right position. (show how to wear it). Area samples can be captured on an instrument called a data ram.

13. Construction & General Industry
OSHA Construction
Industry
OSHA General
ACGIH
Construction & General Industry
Employee Name
% Silica
Time Sampled
(minutes)
8 HR
TWAa
(mppcf)e
PELb
TWAa (mg/m3)d
(mg/m3)d
TLVf
Grinder 1
5.5
464
19.6
23.8
1.96
1.4
0.025
Grinder 2
4.5
474
20.2
26.3
2.02
1.54
Laborer1
3.6
463
3.5
29.1
0.35
1.79
Laborer 2
Air hose
3.8
478
5.7
28.4
0.57
1.72
a 8-hour Time Weighted Average d mg/m3 – milligrams per cubic meter of air
b OSHA Permissible Exposure Limit e mppcf – million particles per cubic foot of air
c Employee exposure for time sampled f TLV – American Conference of Governmental Industrial Hygienist’ Threshold
Limit Values

14. 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 % of PEL
EXCEEDED PEL
Gas saw dry cuts hole in concrete manhole
718 % of PEL for 68 minute sample time

15. 30% Crystalline Silica Quartz

18. 10% Crystalline Silica Quartz

23. 8 % Crystalline Silica Quartz

25. 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.

26. 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