2 Silica 1926.55 – Mineral Dusts It’s not just dust…It’s silica Silica NEP (National Emphasis Program) January 24, 2008Silica LEP (Local Emphasis Program) October 1, 2009 Targets specific General Industry SIC Codes
3 What is silica? Mineral – crystalline or amorphous forms Crystalline most hazardousCrystalline- 3 formsQuartz, cristobalite, tridymiteQuartz – most commonMajor component of soils and readily found in rockGranite ~30% quartzShale ~ 20% quartzBeach sand – nearly pure quartz
7 Silicosis Chronic/Classic Accelerated Acute Occurs after 15 – 20 years of moderate to low exposureAcceleratedOccurs after 5 – 10 years of high exposuresAcuteOccurs after a few months or as long as 2 years to extremely high concentrations
8 Other Health Effects of Silica Exposure Lung cancerIARC Group 1: Carcinogenic to HumansTuberculosisChronic Obstructive Pulmonary DisorderBronchitis, EmphysemaImmunologic Disorders & Autoimmune DiseaseRenal 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)ConstructionOSHA (PEL)General IndustryACGIH (TLV)250 mppcf10 mg/m3Quartz: mg/m3Cristobalite: mg/m3% silica + 5% silica + 2Can 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 CycloneTo 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 SAMPLINGYou 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 ConstructionIndustryOSHA GeneralACGIHConstruction & General IndustryEmployee Name% SilicaTime Sampled(minutes)8 HRTWAa(mppcf)ePELbTWAa (mg/m3)d(mg/m3)dTLVfGrinder 15.546419.623.81.961.40.025Grinder 24.547420.226.32.021.54Laborer13.64633.529.10.351.79Laborer 2Air hose3.84785.728.40.571.72a 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’ ThresholdLimit Values
14 Concrete Cutting (Dry) Example 6 % silica2.27 mg/M3 PEL16.3 mg/M3 (68 min)2.31 mg/M3 8 hr TWA8 hour severity % of PELEXCEEDED PELGas saw dry cuts hole in concrete manhole718 % of PEL for 68 minute sample time
25 Silica ConclusionsDry operations: High likelihood of silica dust overexposureWet operations: Low potential for silica dust overexposureExposures may be multiplied by factors such as interior workplace and corner location.
26 Silica Conclusions Written Hazard Communication Program Employee training on silicaEngineering ControlsUse of water during cuttingLocal exhaust ventilationRespiratory ProtectionNIOSH approvedAir MonitoringRequired or voluntary useEye Protection
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