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
PLEASE NOTE The word dust will frequently be used as a generic descriptor in lieu of aerosol or particulate mass. Dont be confused by this. References are provided on some of the slides. Complete reference articles are available upon request for most citations.
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. The initial work on dust sampling was done by the U.S. Bureau of Mines. In the 1920s, impingers were used to collect dust which was reported as TOTAL NUMBER OF PARTICLES i.e. millions of particles per cubic feet 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 a 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 Cat. No. 225-52SKC Cat. No. 225-50
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. 20-30 µm) 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 1980s, occupational hygiene experts from around the world began to investigate a better way to evaluate particulates in the workplace. First, was the need for exposure limits (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 through which 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 µm) Thoracic-the sub-fraction of inhalable that penetrates into the respiratory tract below the larynx (D 50 of sampler= 10 µm) Respirable-the sub-fraction of inhalable that penetrates to the alveolar region of the lung. (D 50 of sampler= 4 µm) (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 74 of the 2011 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 µm with several options listed. See Definition on upper left of NIOSH Method 0600
OSHA: STATUS OF NEW CRITERIA OSHA has not officially adopted the new criteria as it requires Congressional action like with PEL updates. OSHA Statement on the IOM Sampler: SKC has a letter on file from OSHA stating that the IOM Inhalable Sampler may be used for measuring compliance with the standard for particulates not otherwise regulated (PNOR).
INHALABLE PARTICULATE MASS: DEFINED Includes 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 the best approach 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 Significantly underestimate the concentration of larger dust particles from 20-100 µm 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 Cat. No. 225-70A
USING THE IOM SAMPLER GRAVIMETRIC ANALYSIS Load a 25-mm filter into the cassette using forceps and wearing gloves. Do not desiccate the filter/cassette. Equilibrate the filter/cassette assembly overnight under controlled humidity conditions then weigh as a unit. Allow the assembly to stabilize a few minutes before taking a reading.
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 flow rate 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 Cat. No. 225-772) 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 Cat. No. 225-79A) 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 Cat. No. 225-76A) 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 Blasting operations Higher limit of quantitation due to weighing of cassette. Designed as a personal sampler only Not designed 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 weight. RESPONSE The type of plastic material was changed to address water adsorption. Do not allow cassette to desiccate. Only equilibrate under controlled humidity conditions. Consider stainless steel cassettes if necessary.
OTHER INHALABLE SAMPLERS: FROM SKC Button Sampler Developed by University 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 Cat. No. 225-360
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 O-ring and the sampler inlet. Calibrate the Button Sampler to a flow rate 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 µm or higher is recommended due to the back pressure limitations of most personal samplers. After sampling, remove the filter for analysis. Use a conductive plastic filter transport case (SKC Cat. No. 225-67) or Filter-Keeper (SKC Cat. No. 225-8301) 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 and 7 equispaced inlet holes with flows of 2.0 L/min. Listed in HSE MDHS Method 14, but not widely studied. 7-HOLE 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 recently consulted with NIOSH for advice on decontamination and reuse of inhalable samplers used to sample beryllium. NIOSH does not clean/reuse samplers used for Be due to safety and cross-contamination concerns. 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.
INHALABLE TLVs 2011 INTENDED CHANGES Diethylene glycol monobutyl ether Manganese, elemental and inorganic compounds o-Phthalodinitrile Piperazine and salts Toluene 2,4- or 2,6- diisocyanate For TLVs with IFV notation (Inhalable fraction and vapor) There is no single sampler that can be used. Requires (2) separate samples: one for each contaminant phase.
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 121:1207- 1214. AIHCE 2011 Session-T. Renee Anthony. How to Relate Total and Inhalable Dust Exposures. From the science symposium titled 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 so-called 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 Fumes from welding1.0 *Werner, et al. (1996)
DATA CONVERSION TOTAL VS INHALABLE Dr. Anthonys 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 inhalable samplers. Will provide backup data for any compliance related issues.
THANKS FOR YOUR ATTENTION. PLEASE EMAIL SKC WITH ANY QUESTIONS ON SAMPLING. SKCTECH@SKCINC.COM