Presentation on theme: "INHALABLE PARTICULATE MASS HISTORY, CURRENT TECHNOLOGY, AND DATA CONSIDERATIONS Presented by."— Presentation transcript:
INHALABLE PARTICULATE MASS HISTORY, CURRENT TECHNOLOGY, AND DATA CONSIDERATIONS Presented by
TOTAL DUST: HISTORY OF THE TERM Except in cases where diseases are caused by fine respirable dust, it has been common practice to sample so-called total dust. This is in general recognition that all inhaled particles could present either a specific or non- specific risk to health. (Mark and Vincent, 1986.) Total dust, however, was never defined by a specific size range and a 50% cut-point (D 50 ) was never established for total dust samplers.
THE FIRST DUST SAMPLERS: U.S.A. The initial work on dust sampling was done by the US Bureau of Mines. In the 1920’s, impingers were used to collect dust which was reported as TOTAL NUMBER OF PARTICLES i.e. millions of particles per cubic foot of air. Since impingers are cumbersome, health and safety professionals in the U.S. replaced them with 37-mm filter cassettes over time. (Harper, 1997)
DUST SAMPLERS: GLOBAL Not all countries have standardized on 37-mm filter cassettes for total dust sampling. Given the vague definition of total dust, a number of personal samplers with various performance characteristics have been used for sampling total dust around the world.
TOTAL DUST SAMPLERS: UNITED KINGDOM Single Hole Lead Head for MDHS 6 Seven Hole Head for MDHS 14 SKC SKC
SURPRISING STATISTICS: SAMPLER PERFORMANCE There is very limited data available on how well these samplers actually measure the true dust exposure. Studies show considerable differences in results from these various samplers when sampling the very same dust under the identical environmental conditions. ≠ ≠
SURPRISING STATISTICS: LIMITATIONS OF 37-MM CASSETTES 37-mm Filter Cassettes : Were never designed to represent a “physiologically relevant exposure” to the respiratory system. Aspiration efficiency is not very similar to the nose and mouth. Are not 100% efficient in collecting all sizes of dust particles. Have a upper size limit (approx. 30 um) where efficiency falls to zero. ( T. Renee Anthony, AIHCE 2011)
SURPRISING STATISTICS: ERRORS WITH 37-MM CASSETTES Sampling errors with 37-mm cassettes can be evidenced from: Ambient wind velocity effects Orientation effects Dust deposition on walls of cassette
SO WHY DO WE USE THEM? In the U.S., we have been using 37-mm cassettes because: “Reductions in exposures as measured with these have been associated with reductions in health effects”. Cheap and Easy Used by compliance officers History-Years of data on file
SEARCHING FOR A BETTER WAY NEW CRITERIA FOR DUST SAMPLING Beginning in the 1980’s, occupational hygiene experts from around the world began to investigate a better way to evaluate particulates in the workplace. First, was the need for standards (guidelines) that reflect closely the nature of human exposure. Secondly, was the need for samplers that collect the “physiologically relevant” size fraction of interest.
WHY CHANGE? Measuring dust concentrations with the same efficiency as we inhale them makes better sense when evaluating the health-related dose.
SEARCHING FOR A BETTER WAY NEW CRITERIA FOR STANDARDS Committees from ISO, CEN, and ACGIH have come to an agreement on new criteria. Many occupational hygiene bodies around the world have now adopted this criteria. Health-related sampling should be based on the following particle size-selective fractions: Inhalable, Thoracic, and Respirable.
NEW CRITERIA: DESCRIPTIONS Inhalable-the fraction that enters the nose and/or mouth during breathing (D 50 of sampler= 100 um) Thoracic-the sub-fraction of inhalable that penetrates into the respiratory tract below the larynx (D 50 of sampler= 10 um) Respirable-the sub-fraction of inhalable that penetrates to the alveolar region of the lung. (D 50 of sampler= 4 um) (AIHA Aerosol Committee Publication)
NEW CRITERIA: ILLUSTRATION Inhalable Thoracic Respirable
ACGIH: ADOPTED NEW CRITERIA In 1993, revisions to the Appendix “Particle Size-Selective Sampling Criteria for Airborne Particulate Matter” were made by ACGIH. At this time, ACGIH adopted and defined inhalable, thoracic, and respirable particulate mass fractions. See page 78 of the 2014 TLV handbook.
NIOSH: STATUS OF NEW CRITERIA NIOSH has NOT formally adopted the new criteria in total. Inhalable-NIOSH Method 5700 for formaldehyde on dust is the only method. Thoracic-NIOSH Method 5524 for metalworking fluids is the only method. Respirable-NIOSH Methods for respirable dust now specify a cyclone with a D 50 of 4 um with several options listed. Ex. See Definition on upper left of NIOSH Method 0600.
OSHA: STATUS OF NEW CRITERIA U.S. OSHA has not officially adopted the new criteria as it requires Congressional action like with PEL updates. OSHA Letter: SKC has a letter on file indicating that the IOM Sampler is “more efficient” in sampling small and large particles than 37-mm cassettes and can be used for compliance sampling of particulates not otherwise regulated.
OSHA: STATUS OF NEW CRITERIA In the OSHA Notice of Proposed Rulemaking on Respirable Crystalline Silica, OSHA indicates that measurement should be determined by a sampling device designed to meet ISO 7708:1995 (page 538). This will harmonize OSHA’s practice with current aerosol science and most other agencies around the world including ACGIH and NIOSH.
INHALABLE PARTICULATE MASS: DEFINED Those materials that are hazardous when deposited anywhere in the respiratory tract Includes particulate matter that enter the head airways region including the nose and mouth Also includes materials that can produce systemic toxicity from deposition anywhere in the respiratory system.
INHALABILITY CRITERION: FURTHER COMMENTS The current criterion for inhalable dust is not perfect, but represents a best-guess based on decades of research. A known flaw: The current inhalability criterion underestimates human intake in calm air and low velocity environments. ( Volckens, AIHCE 2011)
DUST SAMPLERS TO MEET THE NEW CRITERIA After the creation of new criteria for standards researchers began to develop new samplers to meet the new criteria. These new sampling devices were designed to collect a biologically relevant fraction of dust found in the workplace.
THE IDEAL INHALABLE SAMPLER An inhalable sampler is considered ideal “when a personal sampler mounted on the body gives the same measured dust concentration and aerodynamic size distribution as that inspired by its wearer, regardless of dust source location and wind conditions”. (Mark and Vincent, 1986) (Note: Inhalable dust was originally called inspirable dust.) Inhalable samplers have a D 50 of 100 microns.
37-MM FILTER CASSETTES Do not effectively sample the inhalable fraction. They significantly underestimate the concentration of larger dust particles from um. Of particular concern are sample losses that occur from particles that adhere to the interior cassette walls.
JOEH ARTICLE BY NIOSH NIOSH Researchers report: Dust deposits on the walls of filter cassettes were 19% of the total sample for lead and 25% of the total sample for copper. Filter cassettes should be rinsed AND WIPED prior to analysis. Results of wiped 37-mm filter cassettes are a closer match to results from inhalable samplers. (Ashley, Harper, Demange, 2007)
INHALABLE SAMPLERS: DESIGNED FOR THE NEW CRITERIA The first personal sampler specifically designed for inhalable particulate mass was developed by Mark and Vincent in 1986 at the Institute of Occupational Medicine in Scotland. The sampler was named the IOM sampler and SKC Ltd. in the UK was the sole licensee and exclusive manufacturer of this sampler for more than 20 years. The patent has now expired, but SKC is still the only company that can call this device the IOM Sampler.
IOM SAMPLER A GOLD STANDARD Exploded View SKC A
USING THE IOM SAMPLER GRAVIMETRIC ANALYSIS Load a 25-mm filter into the cassette using forceps and wearing gloves. Equilibrate the filter/cassette assembly overnight under controlled humidity conditions then weigh them as a unit. Allow the assembly to stabilize a few minutes before taking a reading. Note: Do not desiccate the filter/cassette.
USING THE IOM SAMPLER GRAVIMETRIC ANALYSIS Place the IOM cassette/filter assembly into the sampler body, screw on the cover cap, and connect to the pump. Calibrate the flowrate to 2 L/min using the IOM calibration adapter or by placing in a calibration jar. Following sample collection, weigh the cassette/filter assembly again. Referenced in HSE Method MDHS 14/3
INHALABLE PLUS RESPIRABLE WITH GRAVIMETRIC ANALYSIS Aerosol physicists at the UK Health & Safety Laboratory have published on the use of polyurethane foam discs (SKC ) inserted into the front of the IOM cassette for size- selective sampling. ( Kenny, Chung, et. al., 2001) The foam scrubs out large inhalable particles. Dust on Filter = Respirable fraction Dust on Filter + Foam = Inhalable fraction
USING THE IOM SAMPLER WITH OTHER TYPES OF ANALYSES The IOM Sampler is also available with a stainless steel cassette. (SKC A) This cassette is typically used for chemical (elemental) analysis where a solvent rinse is done inside the cassette. A stainless steel IOM body along with a stainless steel cassette is available for those using the sampler for bioaerosol sampling. (SKC A) This model allows for autoclaving.
ADVANTAGES OF THE IOM Developed specifically to match the inhalable definition. Best fit with the inhalable curve under many circumstances. Internal wall deposits are included in the sample analysis. Can be combined with a foam insert to collect the respirable fraction simultaneously.
DISADVANTAGES OF THE IOM Tends to oversample in low wind speed and when large particles are present. Large inlet allows sampling of large projectiles (Ex. Blasting operations) Higher limit of quantitation due to weighing of cassette. Designed as a personal sampler only; not for area sampling. (Volckens, AIHCE 2011)
WEIGHING ACCURACY OF IOM SAMPLES CONCERNS March/April 1999 AIHA Journal article discussed problems of water absorption by plastic IOM cassette and resulting instability of the tare weight RESPONSE The type of plastic material was changed to address water adsorption. Do not desiccate Equilibrate under controlled humidity conditions. Consider stainless steel cassettes if necessary.
OTHER INHALABLE SAMPLERS: FROM SKC Button Sampler Developed by Univ of Cincinnati Inlet has a stainless steel inlet screen with numerous, evenly spaced holes. Screen keeps out large, non-inhalable projectiles from impacting or splashing onto the filter. SKC
USING THE BUTTON SAMPLER SAMPLE LOGISTICS Unscrew the sampler inlet and remove the Teflon ® O-ring. Place a 25-mm filter on the stainless steel support screen, replace the 0-ring and the sampler inlet. Calibrate the Button Sampler to a flowrate of 4 L/min using the calibration adapter or by placing in a calibration jar.
USING THE BUTTON SAMPLER SAMPLE LOGISTICS A filter pore size of 1.0 um or higher is recommended due to the backpressure limitations of most personal samplers. After sampling, remove the filter for analysis. Use a conductive plastic filter transport case (SKC ) or Filter-Keeper (SKC ) for shipment to the lab.
ADVANTAGES OF BUTTON SAMPLER Good precision and fit with the inhalable curve Inlet screen keeps out large particles Low sensitivity to wind velocity and direction Uniform collection on the filter Flow rate of 4 L/min for personal sampling increases sensitivity Can be used for personal or area sampling
DISADVANTAGES OF BUTTON SAMPLER Inlet holes can become clogged (i.e. flour dust) Liquid aerosols not collected as efficiently as solid aerosols Dust deposited on sampler walls and O-ring are not included in sample analysis.
OTHER INHALABLE SAMPLERS : FROM SKC IN UK 7-HOLE SAMPLING HEAD Traditional European method using a 25-mm filter and cassette with an end cap with 7 equispaced inlet holes with flows of 2.0 L/min. Listed in HSE MDHS Method 14, but not widely studied. 7-HOLE (DEAD) HEAD ??
INHALABLE SAMPLERS: FROM OTHER SUPPLIERS Conical Inhalable Sampler (CIS) Also known as the GSP Sampler. This German sampler aspirates particles through the inlet at 3.5 L/min onto a 37-mm filter. Limited commercial availability. CIS SAMPLER
INHALABLE SAMPLERS: FROM OTHER SUPPLIERS CIP-10 A French sampler with 2 key components: 1. Impactor/foam pre-separator to retain large particles 2. A rotating cup with a PUF ring that collects the sample for gravimetric analysis CIP-10 SAMPLER
INHALABLE SAMPLING OF BERYLLIUM: REUSE ISSUES SKC consulted with NIOSH for advice on decontamination and reuse of inhalable samplers used to sample beryllium. NIOSH does not clean/reuse these cassettes due to safety and cross-contamination concerns with Be. They recommend using 37- mm cassettes and wiping the walls to account for wall losses. The results will be comparable to those using inhalable samplers.
2014 INTENDED CHANGES TO TLVs ® ISSUED AS INHALABLE Calcium Silicate Ethylene Glycol Lithium hydride Simazine 2,4- or 2,6- Toluene diisocyanate Trimetacresyl phosphate Triorthocresyl phosphate Triparacresyl phosphate For TLVs with IFV notation (Inhalable fraction and vapor) May require 2 separate samples due to flowrate issues for each contaminant phase. Chemically coated filters provide a solution for TDI.
DATA CONSIDERATIONS TOTAL VS INHALABLE KEY REFERENCES Journal article-Werner, et al. (1996) Investigation into the impact of introducing workplace aerosol standards based on the inhalable fraction. Analyst 121: AIHCE 2011 Session-T. Renee Anthony. How to Relate Total and Inhalable Dust Exposures. From the session entitled Inhalable Particles: The State of the Science on a Big Particle Problem. (An electronic copy of this is available upon request.)
DATA CONVERSION?? TOTAL VS INHALABLE Inhalable particulate mass is typically greater than total particulate mass. How much greater will depend upon the SIZE of the particles. With larger particles, inhalable particulate mass will be much greater than total particulate mass. With smaller particles, inhalable and total particulate mass will be comparable.
DATA CONVERSION?? TOTAL VS INHALABLE Type of particulate Ratio of Results IOM/37-mm cassette Dust from powder handling, grinding2.5 Mist from paint spray or oil mist2.0 Hot Processes such as foundries1.5 Fumes from Welding1.0 *Werner, et al. (1996)
DATA CONVERSION?? TOTAL VS INHALABLE Dr. Anthony’s AIHCE 2011 session makes the point that it is really not enough to use a simple conversion factor as given on the previous slide. Ratio of results can also vary with particle size distribution. “Using a standard correction factor without knowing your aerosol distribution may under- or over-estimate inhalable-converted exposure levels.”
DATA CONVERSION?? TOTAL VS INHALABLE So what do you do? Collect both 37-mm cassette and inhalable samples and determine process-specific ratios for YOUR unique operation.
SIDE-BY-SIDE SAMPLING: 37-MM VS INHALABLE SAMPLERS Will bridge your past data using total dust filter cassettes to that using inhalable samplers. Will provide backup data for any compliance related issues.
THANKS FOR YOUR ATTENTION. PLEASE SKC WITH ANY QUESTIONS ON SAMPLING.