Washington Administrative Code › Title 296 - Labor and Industries, Department of › Chapter 296-155 - Safety standards for construction work › Part B-1 - OCCUPATIONAL HEALTH AND ENVIRONMENTAL CONTROL › Section 296-155-17347 - Appendix D to WAC 296-155-173 - Sampling and analytical methods for MDA monitoring and measurement procedures

Current through Register Vol. 24-14, July 15, 2024
Measurements taken for the purpose of determining employee
				  exposure to MDA are best taken so that the representative average eight-hour
				  exposure may be determined from a single eight-hour sample or two four-hour
				  samples. Short-time interval samples (or grab samples) may also be used to
				  determine average exposure level if a minimum of 5 measurements are taken in a
				  random manner over the 8 hour work shift. Random sampling means that any
				  portion of the work shift has the same chance of being sampled as any other.
				  The arithmetic average of all such random samples taken on one work shift is an
				  estimate of an employee's average level of exposure for that work shift. Air
				  samples should be taken in the employee's breathing zone (air that would most
				  nearly represent that inhaled by the employee). There are a number of methods
				  available for monitoring employee exposures to MDA. The method OSHA currently
				  uses is included below. The employer however has the obligation of selecting
				  any monitoring method which meets the accuracy and precision requirements of
				  the standard under her or his unique field conditions. The standard requires
				  that the method of monitoring must have an accuracy, to a 95% confidence level,
				  of not less than plus or minus 25% for the select PEL. DOSH methodology.
Sampling procedure.
Apparatus:
Samples are collected by use of a personal sampling pump that
				  can be calibrated within +/-5% of the recommended flow rate with the sampling
				  filter in line. Samples are collected on 37 mm Gelman type A/E glass fiber
				  filters treated with sulfu-ric acid. The filters are prepared by soaking each
				  filter with 0.5 mL of 0.26N
				  H2SO4. (0.26 N
				  H2SO4 can be prepared by diluting
				  1.5 mL of 36N H2SO4 to 200 mL
				  with deionized water.) The filters are dried in an oven at 100 degrees C. for
				  one hour and then assembled into 3-piece 37 mm polystyrene cassettes without
				  backup pads. The front filter is separated from the back filter by a
				  polystyrene spacer. The cassettes are sealed with shrink bands and the ends are
				  plugged with plastic plugs. After sampling, the filters are carefully removed
				  from the cassettes and individually transferred to small vials containing
				  approximately 2 mL deion-ized water. The vials must be tightly sealed. The
				  water can be added before or after the filters are transferred. The vials must
				  be sealable and capable of holding at least 7 mL of liquid. Small glass
				  scintillation vials with caps containing Teflon liners are recommended.
Reagents:
Deionized water is needed for addition to the vials.
Sampling technique:
Immediately before sampling, remove the plastic plugs from
				  the filter cassettes. Attach the cassette to the sampling pump with flexible
				  tubing and place the cassette in the employee's breathing zone. After sampling,
				  seal the cassettes with plastic plugs until the filters are transferred to the
				  vials containing deionized water. At some convenient time within 10 hours of
				  sampling, transfer the sample filters to vials. Seal the small vials
				  lengthwise. Submit at least one blank filter with each sample set. Blanks
				  should be handled in the same manner as samples, but no air is drawn through
				  them. Record sample volumes (in L of air) for each sample, along with any
				  potential interferences.
Retention efficiency:
A retention efficiency study was performed by drawing 100 L
				  of air (80% relative humidity) at one L/min through sample filters that had
				  been spiked with 0.814 micro-g MDA. Instead of using backup pads, blank
				  acid-treated filters were used as backups in each cassette. Upon analysis, the
				  top filters were found to have an average of 91.8% of the spiked amount. There
				  was no MDA found on the bottom filters, so the amount lost was probably due to
				  the slight instability of the MDA salt.
Extraction efficiency:
The average extraction efficiency for 6 filters spiked at the
				  target concentration is 99.6%. The stability of extracted and derivatized
				  samples was verified by reanalyzing the above 6 samples the next day using
				  fresh standards. The average extraction efficiency for the reanalyzed samples
				  is 98.7%.
Recommended air volume and sampling rate. The recommended air
				  volume is 100 L. The recommended sampling rate is one L/min.
Interferences (sampling):
MDI appears to be a positive interference. It was found that
				  when MDI was spiked onto an acid-treated filter, the MDI converted to MDA after
				  air was drawn through it. Suspected interferences should be reported to the
				  laboratory with submitted samples.
Safety precautions (sampling): Attach the sampling equipment
				  to the employees so that it will not interfere with work performance or safety.
				  Follow all safety procedures that apply to the work area being sampled.
Analytical procedure:
Apparatus:
The following are required for analysis. A GC equipped with
				  an electron capture detector. For this evaluation a Hewlett Packard 5880 Gas
				  Chromatograph equipped with a Nickel 63 High Temperature Electron Capture
				  Detector and a Linear-izer was used. A GC column capable of separating the MDA
				  derivative from the solvent and interferences. A 6 ft x 2 mm ID glass column
				  packed with 3% OV-101 coated on 100/120 Gas Chrom Q or a 25 meter DB-1 or DB-5
				  capillary column is recommended for this evaluation. An electronic integrator
				  or some other suitable means of measuring peak areas or heights. Small
				  resealable vials with Teflon-lined caps capable of holding 4 mL. A dispenser or
				  pipet for toluene capable of delivering 2.9 mL. Pipets (or repipets with
				  plastic or Teflon tips) capable of delivering 1 mL for the sodium hydroxide and
				  buffer solutions. A repipet capable of delivering 25 micro-L HFAA. Syringes for
				  preparation of standards and injection of standards and samples into a GC.
				  Volumetric flasks and pipets to dilute the pure MDA in preparation of
				  standards. Disposable pipets to transfer the toluene layers after the samples
				  are extracted.
Reagents:
0.5 NaOH prepared from reagent grade NaOH. Toluene, pesticide
				  grade. Burdick and Jackson distilled in glass toluene was used.
				  Heptafluorobutyric acid anhydride (HFAA). HFAA from Pierce Chemical Company was
				  used. pH 7.0 phosphate buffer, prepared from 136 g potassium dihydrogen
				  phosphate and 1 L deionized water. The pH is adjusted to 7.0 with saturated
				  sodium hydroxide solution. 4,4'-methylenedi-aniline (MDA), reagent
				  grade.
Standard preparation:
Concentrated stock standards are prepared by diluting pure
				  MDA with toluene. Analytical standards are prepared by injecting micro-L
				  amounts of diluted stock standards into vials that contain 2.0 mL toluene. 25
				  micro-L HFAA are added to each vial and the vials are capped and shaken for 10
				  seconds.After 10 min, one mL of buffer is added to each vial. The vials are
				  recapped and shaken for 10 seconds. After allowing the layers to separate,
				  aliquots of the toluene (upper) layers are removed with a syringe and analyzed
				  by GC. Analytical standard concentrations should bracket sample concentrations.
				  Thus, if samples fall out of the range of prepared standards, additional
				  standards must be prepared to ascertain detector response.
Sample preparation:
The sample filters are received in vials containing deionized
				  water. One mL of 0.5N NaOH and 2.0 mL toluene are added to each vial. The vials
				  are recapped and shaken for 10 min. After allowing the layers to separate,
				  approximately one mL aliquots of the toluene (upper) layers are transferred to
				  separate vials with clean disposable pipets. The toluene layers are treated and
				  analyzed.
Analysis: GC conditions.
Zone temperatures: Column220 degrees C. Injector235 degrees
				  C. Detector335 degrees C. Gas flows, N2 Column 30 mL/min
				  He PurgeColumn 0.9 mL/min. (capillary) with 30 mL/min.
				  ArCH4 (95/5) make up gas Injection volume: 5.0 uL
				  Column: 6 ft x 1/8 in ID glass, 3% OV-101 on 100/120 Gas Chrom Q or 25
				  Retention time of MDA derivative: 2.5 to 3.5, depending on column and
				  flow.
Chromatogram. Peak areas or heights are measured by an
				  integrator or other suitable means. A calibration curve is constructed by
				  plotting response (peak areas or heights) of standard injections versus micro-g
				  of MDA per sample. Sample concentrations must be bracketed by standards.
Interferences (analytical):
Any compound that gives an electron capture detector response
				  and has the same general retention time as the HFAA derivative of MDA is a
				  potential interference. Suspected interferences reported to the laboratory with
				  submitted samples by the industrial hygienist must be considered before samples
				  are derivatized. GC parameters may be changed to possibly circumvent
				  interferences. Retention time on a single column is not considered proof of
				  chemical identity. Analyte identity should be confirmed by GC/MS if
				  possible.
Calculations:
The analyte concentration for samples is obtained from the
				  calibration curve in terms of micro-g MDA per sample. The extraction efficiency
				  is 100%. If any MDA is found on the blank, that amount is subtracted from the
				  sample amounts. The air concentrations are calculated using the following
				  formulae. micro-[MICRO]g/m3 = (micro-[MICRO]g MDA
				  per sample) (1000)/ (L of air sampled) ppb =
				  (micro-[MICRO]g/m3) (24.46)/(198.3) =
				  (micro-[MICRO]g/m3)(0.1233) where 24.46 is the molar
				  volume at 25 degrees C. and 760 mm Hg.
Safety precautions (analytical). Avoid skin contact and
				  inhalation of all chemicals. Restrict the use of all chemicals to a fume hood
				  if possible. Wear safety glasses and a lab coat at all times while in the lab
				  area.
Statutory Authority: Chapter 49.17 RCW. 93-04-111 (Order
					 92-15), § 296-155-17347, filed 2/3/93, effective
					 3/15/93.