Presentation on theme: "RESPIRABLE CRYSTALLINE SILICA New Considerations for Sampling and Analysis."— Presentation transcript:
RESPIRABLE CRYSTALLINE SILICA New Considerations for Sampling and Analysis
SILICA IS A TOPIC IN THE U.S. SKC INC. is pleased to share the latest updates.
BUT FIRST CONSIDER: SILICA THE COMPUND Look at chemical formula for silica (SiO 2 ), and consider this: 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.
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.
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 stone Used 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.
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.
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.
CRYSTALLINE SILICA: WORKPLACE EXPOSURES High Risk Jobs: Abrasive blasting Foundry work Stonecutting Rock Drilling Mining Tunneling Hydraulic Fracturing
NEW PROPOSED RULE FROM U.S. OSHA In September 2013, U.S. OSHA published a Notice of Proposed Rulemaking (NPRM) for Occupational Exposure to Respirable Crystalline Silica. This is the first update since the original Permissible Exposure Limit (PEL) was adopted in See this 757-page document at https://www.osha.gov/silica/nprm.pdfwww.osha.gov/silica/nprm
SUMMARY OF ISSUES IN THE NPRM AFFECTING SAMPLING & ANALYSIS 1. New Permissible Exposure Limit 2. New Specifications for Respirable Dust Samplers 3. Guidance on Sample Times required to exceed limit of quantification at the proposed levels 4. Guidance on Analytical Methods that are sensitive enough to measure silica at proposed levels
PERMISSIBLE EXPOSURE LIMIT: EXISTING GENERAL INDUSTRY A formula based on the % silica in the air sample. Example: _____10____ % Quartz + 2 PEL is equivalent to 100 ug/m 3 when the material is pure quartz. PEL approaches 5 mg/m 3, (the PEL for Particulates Not Otherwise Classified) with a low percentage of quartz in the sample.. CONSTRUCTION AND SHIPYARDS A formula based on obsolete method of collecting dust into impingers with analysis by particle counting. PEL is approximately equivalent to 250 ug/m 3.
PERMISSIBLE EXPOSURE LIMIT: PROPOSED 50 ug/m 3 as an 8-hr TWA for all forms of silica including quartz, cristobalite, and trydymite for all industry sectors covered by the rule. 25 ug/m 3 action level (same as current TLV)
SPECIFICATIONS FOR SAMPLERS: EXISTING Existing specs for respirable dust samplers were promulgated 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 only sampler used by federal OSHA inspectors to meet the existing specifications.
U.S. OSHA IS TRYING TO UPDATE TO CURRENT AEROSOL SCIENCE Page 539: OSHA acknowledges that the existing collection efficiency specifications for respirable dust samplers (50% cut-point of 3.5 um) are obsolete. Page 542: OSHA states that crystalline silica measurement should be determined by a sampling device designed to meet the characteristics for particle- size-selective samplers specified in ISO 7708:1995 Air Quality-Particle Size Fraction Definitions for Health-Related Sampling.
ISO 7708:1995 This 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.
RESPIRABLE DUST SAMPLERS: TO MEET ISO 7708 SPECIFICATIONS OPTION #1: TRADITIONAL CYCLONES
CYCLONE SAMPLERS: TO MEET SPECS IN ISO 7708 NYLON DORR- OLIVER CYCLONE: Listed in OSHA SILICA NPRM on page 267 Listed in NIOSH respirable dust methods Designated flow rate is 1.7 L/min (same as that used for previous criteria?)
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)
CYCLONE SAMPLERS: TO MEET SPECS IN ISO 7708 SKC ALUMINUM CYCLONE: Listed in NIOSH respirable dust methods Published performance (J. Aerosol Science, 29, 1998). Designated flow rate is 2.5 L/min SKC
ALUMINUM CYCLONE ADVANTAGES AND DISADVANTAGES ADVANTAGES Metal construction eliminates static electricity concerns. Open-face sample collection enhances collection. Calibration adapter offers user convenience. DISADVANTAGE Aluminum 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.
CYCLONE SAMPLERS: TO MEET SPECS IN ISO 7708 SKC G(S)-3: Listed in OSHA SILICA NPRM on page 267 Published performance (J. Aerosol Science, 28, 1997). Designated flow rate is 2.75 L/min. SKC
GS-3 CYCLONE ADVANTAGES AND DISADVANTAGES ADVANTAGES Designed to overcome orientation bias of Dorr- Oliver Conductive plastic construction eliminates static electricity concerns. Not a spark hazard for underground mines. Open-face sample collection enhances collection. DISADVANTAGES No calibration adapter like with aluminum cyclone. Requires calibration jar or the easier jarless calibration methods.
CYCLONE SAMPLERS: TO MEET SPECS IN ISO 7708 BGI GK 2.69 Listed in OSHA SILICA NPRM on page 267 Designated flow rate is 4.2 L/min Now available from SKC as or -25 for 25-mm version.
BGI GK 2.69 CYCLONE ADVANTAGES AND DISADVANTAGES ADVANTAGES 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. DISADVANTAGES May not be suitable for use in underground mines. No calibration adapter like with aluminum cyclone.
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.
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 of Occupational and Environmental Hygiene, 10:3.
RESPIRABLE DUST SAMPLERS: TO MEET ISO 7708 SPECIFICATIONS NEW OPTIONS
NEW SAMPLERS: TO MEET SPECS IN ISO 7708 Page 539 of OSHA SILICA NPRM states: Adoption of this (ISO) definition by OSHA would allow for workplace sampling to be conducted using ANY particulate sampling device that conforms to the ISO definition i.e. collects dust according to the particle collection efficiency curve specified in the ISO standard.
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.
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. 4 L/min: L/min: L/min:
WHY THE HIGHER FLOW RATE RESPIRABLE PPI SAMPLERS? NIOSH reported that for a working environment with an airborne concentration of respirable silica near the current TLV of 25 ug/m3, the amount of sample collected with current respirable dust samplers (at typical flow rates of 2 L/min ) might not be enough for quantitative analysis. (Harper, et. al. Ann. Occup. Hyg., 2010.)
PUMP PARTNERS: HIGH FLOW PPI SAMPLERS Respirable PPI 4 L/min model can be partnered with SKC XR L/min model can be partnered with the SKC Leland Legacy pump.
PPI SAMPLER PERFORMANCE COMPARED TO CRITERIA
PPI DATA: OSHA DOCKET SKC submitted comments to the OSHA docket on the silica NPRM with data on the PPI. (Electronic copies are available upon request). The data which was published in the Journal of Physics shows that the collection efficiency of the PPI is a close match to the ISO standard and the bias is more acceptable than the HD cyclone (listed in the NPRM.)
SAMPLE TIMES REQUIRED FOR QUANTIFICATION BY LAB 4+ HOURS PER OSHA NPRM Using respirable dust samplers at flows of approx. 2-4 L/min in workplace concentrations of quartz down to the proposed action level of 25 ug/m 3. (TLV levels) 2+ HOURS PER SKC SCIENTISTS Using respirable dust samplers at flows of 8 L/min at these same workplace concentrations.
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/m 3 ) Visible absorption spectrophometry (VIS) methods are NOT sensitive enough.