Presentation on theme: "RESPIRABLE CRYSTALLINE SILICA"— Presentation transcript:
1 RESPIRABLE CRYSTALLINE SILICA New Considerations for Sampling and Analysis
2 SILICA IS A TOPIC IN THE U.S. HOTSKC INC.is pleased to share thelatest updates.
3 BUT FIRST CONSIDER: SILICA THE COMPUND Look at chemical formula for silica (SiO2), and considerthis:Oxygen is the most abundant element in the Earth’s crust and silicon is the second most abundant.Quartz, the most common form of crystalline silica, is the second most common mineral on the earth’s surface.Amorphous silica such as diatomaceous earth is not particularly toxic to humans unless heated to high temperatures.
4 CRYSTALLINE SILICA: WHERE ITS FOUND Crystalline silica is naturally occurring in sand, gravel, and mineral ores.Quartz, the most common form, is found in almost every type of rock.Nearly all mining and quarrying activities involve exposures to crystalline silica.
5 CRYSTALLINE SILICA: WHERE ITS USED Due to its chemical and physical properties, crystalline silica is a prized mineral with a number of industrial applications.Major ingredient in building materials such as concrete, bricks, and stoneUsed as a molding material for metal casting in foundries.Filler in plastics, rubber, and paint.Raw material for glass manufacture along with porcelain and fine china.
6 APPLICATION IN THE HEADLINES: FRACKING Silica sand is used to hold open the fissures created by hydraulic fracturing (fracking) so natural gas or oil can flow out of the shale and into the well.
7 CRYSTALLINE SILICA: WORKPLACE EXPOSURES U.S. OSHA reports that 2.2 million workers are exposed to respirable crystalline silica.The majority (1.85 million) are in the construction industry.Exposures occur when workers cut, grind, crush, or drill silica-containing materials.
9 NEW PROPOSED RULE FROM U.S. OSHA In September 2013, U.S. OSHA published aNotice of Proposed Rulemaking (NPRM) forOccupational Exposure to Respirable CrystallineSilica.This is the first update since the originalPermissible Exposure Limit (PEL) was adoptedin 1971.See this 757-page document athttps://www.osha.gov/silica/nprm.pdfIn September 2013, federal OSHA published the long-awaited Notice of Proposed Rulemaking for respirable crystalline silica.You can see this 757-page document at the URL shown on the slide.During the holidays, I did a quick scan of the entire document and picked out THREE key pages that impact sampling. I did a lab mailing and included these 3 pages. Beth has a copy.In general, however, the proposed rulemaking is very good news for SKC.
10 SUMMARY OF ISSUES IN THE NPRM AFFECTING SAMPLING & ANALYSIS New Permissible Exposure LimitNew Specifications for Respirable Dust SamplersGuidance on Sample Times required to exceed limit of quantification at the proposed levelsGuidance on Analytical Methods that are sensitive enough to measure silica at proposed levels
11 PERMISSIBLE EXPOSURE LIMIT: EXISTING CONSTRUCTION ANDSHIPYARDSA formula based on obsoletemethod of collecting dust intoimpingers with analysis byparticle counting.PEL is approximatelyequivalent to 250 ug/m3.GENERAL INDUSTRYA formula based on the % silicain the air sample. Example:_____10____% Quartz + 2PEL is equivalent to 100 ug/m3when the material is purequartz . PEL approaches 5mg/m3, (the PEL for ParticulatesNot Otherwise Classified) with alow percentage of quartz in thesample..So let’s go through the notable changes that will affect exposure assessments.The first notable change is in the Permissible Exposure Limits. The current OSHA PEL for GENERAL INDUSTRY is not just a number. The PEL must be CALCULATED each time based on the % silica in the air sample.Adding to the hassle, there will be a different PEL for each type of silica in the sample such as quartz, cristobalite, and tridymite.
12 PERMISSIBLE EXPOSURE LIMIT: PROPOSED 50 ug/m3 as an 8-hr TWA for all forms ofsilica including quartz, cristobalite, andtrydymite for all industry sectors covered bythe rule.25 ug/m3 action level (same as current TLV)You may be surprised to learn that the federal OSHA PEL for respirable crystalline silica in construction and shipyards industy is DIFFERENT than the PEL for general industry.Amazingly, the PEL for construction and shipyards is based on particle counting in impinger solutions.This is obsolete and few labs offer the analysis.The PEL for these industries is now equivalent to 250 ug/m3, more than twice that of general industry.The new proposed PEL will be the same in all industries.
13 SPECIFICATIONS FOR SAMPLERS: EXISTING Existing specs for respirable dust samplers werepromulgated in 1971 and are listed in 29 CFR; Table Z-3 for mineral dusts.A respirable dust sampler with a 50% (median)cut-point of 3.5 um is specified.The Dorr-Oliver (nylon) cyclone is the onlysampler used by federal OSHA inspectors to meetthe existing specifications.The second notable changes in the silica rule is the specifications for samplers.Based on the 1971 standard published in the Code of Federal Regulations, federal OSHA inspectors can use only the Dorr-Oliver cyclone at 1.7 L/min or an exact equivalent to achieve a collection efficiency curve with a 50% or median cut point of 3.5 um.Now, OSHA has moved away from specifying a sampler by name and has instead moved to a performance based standard.
14 U.S. OSHA IS TRYING TO UPDATE TO CURRENT AEROSOL SCIENCE Page 539: OSHA acknowledges that the existingcollection efficiency specifications for respirable dustsamplers (50% cut-point of 3.5 um) are obsolete.Page 542: OSHA states that crystalline silicameasurement should be determined by a samplingdevice designed to meet the characteristics for particle-size-selective samplers specified in ISO 7708:1995 AirQuality-Particle Size Fraction Definitions forHealth-Related Sampling.
15 ISO 7708:1995This is the standard that ACGIH, NIOSH, CEN, and most countries around the world have already adopted.The collection efficiency curve for respirable dust samplers in this standard includes a 50% (median) cut-point of 4 um which is more conservative than the existing OSHA specification of 3.5 um.SKC has never mentioned the ISO standard by number in the past. So please be sure you recognize this standard number if customers contact you: ISO 7708.This is what SKC has referred to previously as the ISO/CEN/ACGIH curve. This is the collection efficiency curve followed by most countries in the world and NIOSH in the US.This collection efficiency curve for respirable dust samplers has a 50% cut-point of 4 microns.
16 RESPIRABLE DUST SAMPLERS: TO MEET ISO 7708 SPECIFICATIONS OPTION #1:TRADITIONAL CYCLONES
17 CYCLONE SAMPLERS: TO MEET SPECS IN ISO 7708 NYLON DORR-OLIVER CYCLONE:Listed in OSHA SILICA NPRM on page 267Listed in NIOSH respirable dust methodsDesignated flow rate is 1.7 L/min (same as that used for previous criteria?)On this slide, you can see the cyclones available from our competitors along with government listings of each.Review each
18 DORR-OLIVER CYCLONE ADVANTAGES AND DISADVANTAGES Advantage: Long history of use in the U.S. by compliance officers.Disadvantage: Nylon construction creates static electricity concerns.Disadvantage: Orientation bias. (AIHA Journal 56, November 1995).Disadvantage: Dust sticks to cassette top with closed-face operation. (ASTM, STP 1565, 2013)A BETTER WAY?
19 CYCLONE SAMPLERS: TO MEET SPECS IN ISO 7708 SKC ALUMINUMCYCLONE:Listed in NIOSH respirable dust methodsPublished performance(J. Aerosol Science, 29, 1998).Designated flow rate is 2.5 L/minShown on this slide are the SKC respirable dust cyclones, flowrates, and data sources or listings in government methods and rulemakings.To meet the specifications of ISO 7708 as specified by OSHA, the SKC aluminum cyclone should be operated at 2.5 L/min.SKC has the following evidence that the cyclone meets the requirements: Listed as an option in NIOSH methods. Published journal article.SKC
20 ALUMINUM CYCLONE ADVANTAGES AND DISADVANTAGES Metal construction eliminates static electricity concerns.Open-face sample collection enhances collection.Calibration adapter offers user convenience.DISADVANTAGEAluminum can not be used in underground mines due to spark hazard.Users frequently make the mistake of removing the red cap (grit pot) on the cyclone during sampling.
21 CYCLONE SAMPLERS: TO MEET SPECS IN ISO 7708 SKC G(S)-3:Listed in OSHA SILICA NPRM on page 267Published performance(J. Aerosol Science, 28, 1997).Designated flow rate is 2.75 L/min.SKC
22 GS-3 CYCLONE ADVANTAGES AND DISADVANTAGES Designed to overcome orientation bias of Dorr-OliverConductive plastic construction eliminates static electricity concerns.Not a spark hazard for underground mines.Open-face sample collection enhances collection.DISADVANTAGESNo calibration adapter like with aluminum cyclone. Requires calibration jar or the easier jarless calibration methods.
23 CYCLONE SAMPLERS: TO MEET SPECS IN ISO 7708 BGI GK 2.69Listed in OSHA SILICA NPRM on page 267Designated flow rate is 4.2 L/minNow available from SKC as or -25 for 25-mm version.
24 BGI GK 2.69 CYCLONE ADVANTAGES AND DISADVANTAGES Metal construction eliminates static electricity concerns.Higher flow of 4.2 L/min allows users to sample only 4 hours to collect enough sample for quantitative analysis of even cristobalite at the action level.DISADVANTAGESMay not be suitable for use in underground mines.No calibration adapter like with aluminum cyclone.
25 IMPORTANT NOTE ON FLOWRATE All cyclones are not created equal!Each cyclone has different operating specifications and performance criteria.Be sure you know the flow rate specified to achieve the desired cut-point before using any cyclone.
26 TECH TIP: CASSETTE MATERIAL In a March 2013 JOEH article by NIOSH, cassette wall losses were noted when using cyclones with typical cassettes made of styrene*.NIOSH recommends the use of 37-mm black conductive cassettes made of polypropylene.*Ashley & Harper (2013) Analytical Performance Issues, Journal ofOccupational and Environmental Hygiene, 10:3.
27 RESPIRABLE DUST SAMPLERS: TO MEET ISO 7708 SPECIFICATIONS NEW OPTIONS
28 NEW SAMPLERS: TO MEET SPECS IN ISO 7708 Page 539 of OSHA SILICA NPRM states:Adoption of this (ISO) definition byOSHA would allow for workplace sampling tobe conducted using ANY particulate samplingdevice that conforms to the ISO definition i.e.collects dust according to theparticle collection efficiency curve specified inthe ISO standard.The best news is that the OSHA standard does NOT limit samplers to CYCLONES.Page 539 states…Beth has a copy of page 539 or print one yourself from the link I gave you.I wrote a letter to the OSHA docket for SKC supporting verbiage that allows use of ANY sampler and discouraging the use of only cyclones.
29 NEW SKC SAMPLERS: TO MEET SPECS IN ISO 7708 Impaction based PPI samplers also available for respirable dust.Designed to precisely match the ISO/CEN/ACGIH/NIOSH criteria.Available in reusable or disposable options.
30 SKC RESPIRABLE PPI: FLOWRATE OPTIONS Single-use, disposable PPI models are available for use at either 2, 4, or 8 L/min.Available empty or pre-loaded with filters.A calibration adapter is available for disposable models.2 L/min:8 L/min:4 L/min:
31 WHY THE HIGHER FLOW RATE RESPIRABLE PPI SAMPLERS? NIOSH reported that for a working environment withan airborne concentration of respirable silica nearthe current TLV of 25 ug/m3, the amount of samplecollected with current respirable dust samplers (attypical flow rates of 2 L/min ) might not be enoughfor quantitative analysis. (Harper, et. al. Ann. Occup. Hyg., 2010.)So having solved that problem, let’s move on to the issue of ENHANCED SENSITIVITY for compounds like respirable crystalline silica that have a very low exposure limits or guidelines. .
32 PUMP PARTNERS: HIGH FLOW PPI SAMPLERS Respirable PPI4 L/min model can be partnered with SKC XR5000.8 L/min model can be partnered with the SKC Leland Legacy pump.To solve this problem, a PPI was developed by SKC that matched the respirable convention at 8L/min.Read second bullet.
34 PPI DATA: OSHA DOCKET SKC submitted comments to the OSHA docket on the silica NPRM with data onthe PPI. (Electronic copies are available uponrequest).The data which was published in the Journalof Physics shows that the collection efficiency ofthe PPI is a close match to the ISO standardand the bias is more acceptable than the HDcyclone (listed in the NPRM.)In my submission to the OSHA docket, I also sent data on the PPI documenting the fact that these samplers met the ISO 7708 standard.OSHA would only accept data that was published in a a peer reviewed journal and Saulius had previously done this. The data was published in the Journal of Physics. I have that journal article available electronically upon request.The data on the PPI was “prettier” than that of the Higgins-Dewell cyclone that is listed by name as being acceptable in the OSHA proposal.
35 SAMPLE TIMES REQUIRED FOR QUANTIFICATION BY LAB 4+ HOURSPER OSHA NPRMUsing respirable dustsamplers at flows ofapprox. 2-4 L/min inworkplace concentrationsof quartz down to theproposed action level of25 ug/m3. (TLV levels)2+ HOURSPER SKC SCIENTISTSUsing respirable dustsamplers at flows of8 L/min at these sameworkplace concentrations.
36 ANALYTICAL METHODS: SENSITIVITY CONCERNS U.S. OSHA concluded that both X-Ray diffraction (XRD) and Infrared Spectroscopy (IR) methods are sensitive enough to quantify silica in workplace concentrations at the proposed PEL and action levels. (But precision is lacking at 25 ug/m3)Visible absorption spectrophometry (VIS) methods are NOT sensitive enough.
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