Sampling for Airborne Contaminants

1. Sampling forAirborne Contaminants Industrial Hygiene IENG 341 Carter J. Kerk Industrial Engineering Program SD Tech Spring 2006

2. Reading Assignment • Nims, Chapter 5

3. Outline • Introduction • Why sample the air? • Sampling particulates • Sampling gases and vapors • Standard sampling and analysis methods • Laboratory analytical techniques • Direct-reading methods • Air sampling strategies

4. Introduction • Inhalation in the number one route of entry into the body for airborne materials • We must be able to identify and evaluate air contaminants • Sampling • Analysis methods • Interpretation

5. Why Sample the Air? • Knowledge of conditions so you can apply controls if necessary • Engineering, administrative, PPE • Monitor concentrations • During normal exposures • Before and after controls are implemented • In cleanup operations (asbestos) • Confined Space Entry • For regulatory reasons • To determine required respiratory protection • 29 CFR 1910.134

6. Sampling Approaches • Direct-Reading or Real-Time Sampling • Immediate or rapid feedback • Integrated Sampling • Draw air across a collector (or sampling medium) • Sample is analyzed in a laboratory

9. Sampling Pumps • Individual exposures • Small, light-weight (1-2 lb) • Rates from 1 cc/min to 4 l/min • Low end for gases • High end for particulates • Worn for an entire shift • Area Sampling • Bigger and heavier • Higher rates (2 – 15 l/min) • Fixed location for an entire work area

13. Sampling Particulates • Filters • Commonly used (25% of sampling methods) • Type depends on the contaminant and the method • Thin filters placed in rigid holders (cassettes) with a support pad beneath • Open Face Sampling • Top portion of cassette is removed • When distribution across media is important (asbestos) • Closed Face Sampling • Small plug in top cassette is removed for sampling • As in metal sampling

15. Filter Structure • Not like a regularly-shaped screen or sieve • Maze of interconnected tunnels and pores • Passing air turns, branches, changes speed • Impaction – contaminants collide with surface • Interception – contaminants stick to surfaces • Electrostatic attraction – electrically charged particles stick to attracted to media • Factors: particle size, electric charge of particle/filter, type of filter, flow rate • The capture efficiency of a filter is not limited by the size of the pores

17. Mixed Cellulose Ester Filters • MCEF – a commonly used filter • Manufactured from a polymer that starts as a liquid, is spread out in a thin layer • As it solidifies (or dries) small pores open up • Average size of openings can be controlled by the manufacturing process • 0.4 – 0.8 mm pore sizes • For metal fumes • Entire filter is dissolved in acid and analyzed for metal content • For asbestos • A section of the filter is cut, treated with acetone vapor to make it clear, then viewed through a microscope for fibers

20. PVC (Polyvinyl Chloride) Filters • Have good resistance to acids and bases • Do not absorb much water vapor (hydrophobic) • Used to collect dusts (e.g. silica) • Gravimetric Analysis • Placed in a dessicator and pre-weighed • After sampling, back to the dessicator and post-weighed • Mass of collected dust and sampled air volume determine the airborne concentration • Filters can further be analyzed with x-ray diffraction to identify forms of crystalline structure

21. PVC (Polyvinyl Chloride) Filters • Recall the three fraction ranges of dust: • Inhalable • Thoracic • Respirable • A cyclone filter can be placed on the inlet side of the filter cassette to allow only the desirable fraction(s) to enter

23. Teflon Filters • Polymer filter • Teflon (PTFE) • Polytetraflouroethylene • Like PVC filters, they are chemical-resistant and hydrophobic • Used for aromatic hydrocarbons • Benzopyrene (given off from hot tar or asphalt)

24. Glass Fiber Filters • Layers of fibers arranged in a seemingly tangled mat • Used for collecting particulates and some droplets of contaminants, such as mercury and acid gases • Sometimes used as an upstream, pre-collection device, so that larger particles do not reach a second filter of another type • This allows simultaneous collection of two different physical forms

25. Potential Problems Associated with Filter Collection • Overloading • Too much particulate collection can overload the filter and cause an error • Static Electricity • Filters pick up a charge and can cause an error in gravimetric analysis • Moisture or physical damage • After getting wet, filters can tear or burst • Contamination with interfering substances • Contaminant material causes error in determination of desired material

26. Sampling Gases and Vapors • Sorbent Tubes • Passive Samplers • Impingers • Grab Samples

27. Sorbent Tubes

29. Passive Samplers • Collection accomplished by diffusion into a sampling device • No pump • Passive samplers (sample badges) • Small clip-on devices worn on the collar throughout the work shift • Then sealed in a container and sent to a lab for analysis • Some use a color change agent in presence of a specific contaminant • Simple

31. Impingers • For contaminants that are nonreactive and highly soluble in a specific solution • Impinger is a glass container with a measured volume of the specific solution • A sample pump creates a vacuum drawing air through the solution • Sealed and sent to lab for analysis

33. Grab Samples • Integrated sample from a very brief sampling period, like a snapshot • Useful for evaluating • compliance with a ceiling or peak limit • Screening or basic identification • Sample bags • Teflon or Tedlar bag connected to a pump • Bag is then sealed and shipped to lab for analysis • Evacuated container • Cylinder from which air has been removed and sealed • Seal is broken and contaminated air is drawn in • Container is then sealed and shipped to lab for analysis

36. Standard Sampling and Analysis Methods • Sampling and analysis methods have been developed and validated for many airborne contaminates • OSHA Reference Methods and NIOSH Manual of Analytical Methods • Sampling media to be used • Sampling flow rate • Volume of air to be sampled • Instructions for sample preservation and handling • Detailed procedures for analysis

37. Standard Sampling and Analysis Methods • Before acceptance a NIOSH method must be shown to be able to provide a result that is within 25% of the actual concentration, 95 times out of 100 tries • Flow rates must be calibrated • Laboratory techniques have boundaries of reliability • LOD, Limit of Detection • LOQ, Limit of Quantification • Smallest amount of contaminant that can be reliably detected and quantified, respectively • Study the NIOSH method for sampling and analyzing Ammonia in Table 5-2 of text

38. Gas and Vapor Analysis • Gases and vapors may be collected on sorbent tubes, filters, or in solutions • A titration method adds chemical reagents until an endpoint is reached (color change) • Intensity of the color is proportional to concentration and measured with spectrophotometer

40. Gas Chromatography (GC) • Works like a still • Contains a distillation tower • Different molecules pass through at different speeds • A graph is produced • The area under the peak in the graph is proportional to the amount of material • Graph is compared to known concentrations

43. Mass Spectrometry • Mass Spec or MS • Sample is bombarded with beam of electrons, causing ionization (charged particles, or ions) • Each ion has a specific mass • The mass to charge ratio is unique, m/e • The intensity of each m/e value is proportional to the amount of the ion produced • The highest m/e value is assigned 100 • The MS plot is like a fingerprint unique to each compound

44. Mass Spectrometry: Similar to gas chromotography, the output produced by the mass spectrometer must be compared against a known or reference output to determine the compound that is present. These mass spectra are for n-octane (A) and 2,2,4-trimethylpentane (B).

45. Absorption Spectroscopy • Involves the amount of energy absorbed by a compound • The wavelength where the energy is absorbed indicates the identity of the compound • See Electromagnetic Spectrum (next slide) • Ultraviolet and Infrared Spectrometry • organics • Atomic Absorption (AA) • metals

47. Absorbance of energy at specific wavelengths is a characteristic of organic compounds. These patterns of absorbance are like fingerprints, in the sense that they allow the specific compound to be identified. Shown here are the absorbance spectra of wavelengths in the ultraviolet region for benzene and toluene.

48. Chlorinated hydrocarbons tend to absorb energy in the infrared region. Shown here are IR spectra for five common industrial solvents. Wavelengths are in micrometers.

50. Inductively Coupled Plasma (ICP) • Utilizes ability of electrons to absorb energy • However this technique measures the energy loss • Intensity of emissions is proportional to the amount present • Used for metal scans