California Code of Regulations › Title 8 - Industrial Relations › Division 1 - Department of Industrial Relations › Chapter 4 - Division of Industrial Safety › Subchapter 7 - General Industry Safety Orders › Group 16 - Control of Hazardous Substances › Article 110 - Regulated Carcinogens › Appendix D - Sampling and Analytical Methods for Benzene Monitoring and Measurement Procedures

Current through Register 2024 Notice Reg. No. 28, July 12, 2024
Measurements taken for the purpose of determining
						  employee exposure to benzene are best taken so that the representative average
						  8-hour exposure may be determined from a single 8-hour sample or two (2) 4-hour
						  samples. Short-time interval samples (or grab samples) may also be used to
						  determine average exposure level if a minimum of five measurements are taken in
						  a random manner over the 8-hour work shift. Random sampling means that any
						  portion of the workshift 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). Sampling and analysis must be
						  performed with procedures meeting the requirements of the standard.
There are a number of methods available for monitoring
						  employee exposures to benzene. The sampling and analysis may be performed by
						  collection of the benzene vapor on charcoal absorption tubes, with subsequent
						  chemical analysis by gas chromatography. Sampling and analysis may also be
						  performed by portable direct reading instruments, real-time continuous
						  monitoring systems, passive dosimeters or other suitable methods. The employer
						  has the obligation of selecting a monitoring method which meets the accuracy
						  and precision requirements of the standard under his unique field conditions.
						  The standard requires that the method of monitoring must have an accuracy, to a
						  95 percent confidence level, of not less than plus or minus 25 percent for
						  concentrations of benzene greater than or equal to 0.5 ppm.
The OSHA Laboratory modified NIOSH Method S
						  311 and evaluated it at a benzene
						  concentration of 1 ppm. A procedure for determining the benzene concentration
						  in bulk material samples was also evaluated. This work, reported in OSHA
						  Laboratory Method No. 12, includes the following two analytical
						  procedures:
1. OSHA Method 12 for Air Samples
Analyte: Benzene
Matrix: Air
Procedure: Adsorption on charcoal, desorption with
						  carbon disulfide, analysis by GC.
Detection limit: 0.04 ppm
Recommend air volume and sampling rate: 10 L at 0.2
						  L/min.
1. Principle of the Method.
1.1. A known volume of air is drawn through a charcoal
						  tube to trap the organic vapors present.
1.2. The charcoal in the tube is transferred to a
						  small, stoppered vial, and the analyte is desorbed with carbon
						  disulfide.
1.3. An aliquot of the desorbed sample is injected into
						  a gas chromatograph.
1.4. The area of the resulting peak is determined and
						  compared with areas obtained from standards.
2. Advantages and disadvantages of the method.
2.1. Sampling device is small, portable, and involves
						  no liquids. Interferences are minimal, and most of those which do occur can be
						  eliminated by altering chromatographic conditions. The samples are analyzed by
						  means of a quick, instrumental method.
2.2. The amount of sample which can be taken is limited
						  by the number of milligrams that the tube will hold before overloading. When
						  the sample value obtained for the backup section of the charcoal tube exceeds
						  25 percent of that found on the front section, the possibility of sample loss
						  exists.
3. Apparatus.
3.1. A calibrated personal sampling pump whose flow can
						  be determined within +5 percent at the recommended flow rate.
3.2. Charcoal tubes: Glass with both ends flame sealed,
						  7cm long with a 6-mm O.D. and a 4-mm I.D., containing 2 sections of 20/40 mesh
						  activated charcoal separated by a 2-mm portion of urethane foam. The activated
						  charcoal is prepared from coconut shells and is fired at 600°C prior to
						  packing. The adsorbing section contains 100 mg of charcoal, the back-up section
						  50 mg. A 3-mm portion of urethane
						  foam is placed between the outlet and of the tube and the back-up section. A
						  plug of silanized glass wool is placed in front of the adsorbing section. The
						  pressure drop across the tube must be less than one inch of mercury at flow
						  rate of 1 liter per minute.
3.3. Gas chromatograph equipped with a flame ionization
						  detector.
3.4. Column (10-ft x 1/8 -in stainless steel) packed
						  with 80/100 Supelcoport coated with 20 percent SP 2100, 0.1 percent CW
						  1500.
3.5. An electronic integrator or some other suitable
						  method for measuring peak area.
3.6. Two-milliliter sample vials with Teflon-lined
						  caps.
3.7. Microliter syringes: 10-microliter (10-uL)
						  syringe, and other convenient sizes for making standards; 1-uL syringe for
						  sample injections.
3.8. Pipets: 1.0 mL delivery pipets.
3.9. Volumetric flasks: convenient sizes for making
						  standard solutions.
4. Reagents.
4.1. Chromatographic quality carbon disulfide
						  (CS2). Most commercially available carbon disulfide
						  contains a trace of benzene which must be removed. It can be removed with the
						  following procedure:
Heat under reflux for 2 to 3 hours, 500 mL of carbon
						  disulfide, 10 mL concentrated sulfuric acid, and 5 drops of concentrated nitric
						  acid. The benzene is converted to nitrobenzene. The carbon disulfide layer is
						  removed, dried with anhydrous sodium sulfate, and distilled. The recovered
						  carbondisulfide should be benzene free. (It has recently been determined that
						  benzene can also be removed by passing the carbon disulfide through 13x
						  molecular sieve.)
4.2. Benzene, reagent grade.
4.3. p-Cymene, reagent grade (internal
						  standard).
4.4. Desorbing reagent. The desorbing reagent is
						  prepared by adding 0.05 mL of p-cymene per milliliter of carbon disulfide. (The
						  internal standard offers a convenient means of correcting analytical response
						  for slight inconsistencies in the size of sample injections. If the external
						  standard technique is preferred, the internal standard can be
						  eliminated).
4.5. Purified GC grade helium, hydrogen and air.
5. Procedure.
5.1. Cleaning of equipment. All glassware used for the
						  laboratory analysis should be properly cleaned and free of organics which could
						  interfere in the analysis.
5.2. Calibration of personal pumps. Each pump must be
						  calibrated with a representative charcoal tube in the line.
5.3. Collection and shipping of samples.
5.3.1. Immediately before sampling, break the ends of
						  the tube to provide an opening at least one-half the internal diameter of the
						  tube (2mm).
5.3.2. The smaller section of the charcoal is used as
						  the backup and should be placed nearest the sampling pump.
5.3.3. The charcoal tube should be placed in a vertical
						  position during sampling to minimize channeling through the charcoal.
5.3.4. Air being sampled should not be passed through
						  any hose or tubing before entering the charcoal tube.
5.3.5. A sample size of 10 liters is recommended.
						  Sample at a flow rate of approximately 0.2 liters per minute. The flow rate
						  should be known with an accuracy of at least +5 percent.
5.3.6. The charcoal tubes should be capped with the
						  supplied plastic caps immediately after sampling.
5.3.7. Submit at least one blank tube (a charcoal tube
						  subjected to the same handling procedures, without having any air drawn through
						  it) with each set of samples.
5.3.8. Take necessary shipping and packing precautions
						  to minimize breakage of samples.
5.4. Analysis of samples.
5.4.1. Preparation of samples. In preparation for
						  analysis, each charcoal tube is scored with a file in front of the first
						  section of charcoal and broken open. The glass wool is removed and discarded.
						  The charcoal in the first (larger) section is transferred to a 2-mL vial. The
						  separating section of foam is removed and discarded; the second section is
						  transferred to another capped vial, these two sections are analyzed
						  separately.
5.4.2. Desorption of samples. Prior to analysis, 1.0 mL
						  of desorbing solution is pipetted into each sample container. The desorbing
						  solution consists of 0.05 uL internal standard per mL of carbon disulfide. The
						  sample vials are capped as soon as the solvent is added. Desorption should be
						  done for 30 minutes with occasional shaking.
5.4.3. GC conditions. Typical operating conditions for
						  the gas chromatograph are:
a. 30 mL/min (60 psig) helium carrier gas flow.
b. 30 mL/min (40 psig) hydrogen gas flow to
						  detector.
c. 240 mL/min (40 psig) air flow to detector.
d. 150°C injector temperature.
e. 250°C detector temperature.
f. 100°C column temperature.
5.4.4. Injection size, 1 uL.
5.4.5. Measurement of area. The peak areas are measured
						  by an electronic integrator or some other suitable form of area
						  measurement.
5.4.6. An internal standard procedure is used. The
						  integrator is calibrated to report results in ppm for a 10 liter air sample
						  after correction for desorption efficiency.
5.5. Determination of desorption efficiency.
5.5.1. Importance of determination. The desorption
						  efficiency of a particular compound can vary from one laboratory to another and
						  from one lot of chemical to another. Thus, it is necessary to determine, at
						  least once, the percentage of the specific compound that is removed in the
						  desorption process, provided the same batch of charcoal is used.
5.5.2. Procedure for determining desorption efficiency.
						  The reference portion of the charcoal tube is removed. To he remaining portion,
						  amounts representing 0.5X, 1X, and 2X (X represents target concentration) and
						  based on a 10 L air sample are injected into several tubes at each level.
						  Dilutions of benzene with carbon disulfide are made to allow injection of
						  measurable quantities. These tubes are then allowed to equilibrate at least
						  overnight. Following equilibration they are analyzed following the same
						  procedure as the samples. Desorption efficiency is determined by dividing the
						  amount of benzene found by amount spiked on the tube.
6. Calibration and standards. A series of standards
						  varying in concentration over the range of interest is prepared and analyzed
						  under the same GC conditions that will be used on the samples. A calibration
						  curve is prepared by plotting concentration (ug/mL) versus peak area.
7. Calculations. Benzene air concentration can be
						  calculated from the following equation:
mg/m3 = (A)(B)/(C)(D)
Where: A = ug/mL benzene, obtained from the calibration
						  curve,
B = desorption volume (1 mL),
C = liters of air sampled, and
D = desorption efficiency.
The concentration in mg/m3
						  can be converted to ppm (at 25°C and 760 mm) with the following equation:
						  ppm = (mg/m3)(24.46)/(78.11)
Where: 24.46 = molar volume of an ideal gas at 25°C
						  and 760 mm, and 78.11 = molecular weight of benzene.
8. Backup Data.
8.1. Detection limit--Air Samples.
The detection limit for the analytical procedure is
						  1.28 ng with a coefficient of variation of 0.023 at this level. This would be
						  equivalent to a concentration of 0.04 ppm for a 10 L air sample. This amount
						  provided a chromatographic peak that could be identifiable in the presence of
						  possible interferences. The detection limit data were obtained by making 1 uL
						  injections of a 1.283 ug/mL standard.
Injection
Area
								  Count
..........................1
655.4
..........................2
617.5
..........................3
662.0
X = 640.2
..........................4
641.1
SD = 14.9
..........................5
636.4
CV = 0.023
..........................6
629.2
8.2. Pooled coefficient of variation--Air Samples. The
						  pooled coefficient of variation for the analytical procedure was determined by
						  1 uL replicate injections of analytical standards. The standards were 16.04,
						  32.08, and 64.16 ug/mL, which are equivalent to 0.5, 1.0, and 2.0 ppm for a 10
						  L air sample respectively.
Injection
Area
									 Counts
0.5
								  ppm
1.0 ppm
2.0
								  ppm
..........................1
3996.5
8130.2
16481
..........................2
4059.4
8235.6
16493
..........................3
4052.0
8307.9
16535
..........................4
4027.2
8263.2
16609
..........................5
4046.8
8291.1
16552
..........................6
4137.9
8288.8
16618
..........................1
3996.5
8130.2
16481
..........................2
4059.4
8235.6
16493
..........................3
4052.0
8307.9
16535
..........................4
4027.2
8263.2
16609
..........................5
4046.8
8291.1
16552
..........................6
4137.9
8288.8
16618
X
								  =
4053.3
8254.0
16548.3
SD =
47.2
62.5
57.1
CV =
0.0116
0.0076
0.0034
..........................CV = 0.008
8.3. Storage Data--Air Sample.
Samples were generated at 1.03 ppm benzene at 80%
						  relative humidity, 20°C, and 643mm. All samples were taken for 50 minutes
						  at 0.2 L/min. Six samples were analyzed immediately and the rest of the samples
						  were divided into two groups by fifteen samples each. One group was stored at
						  refrigerated temperature of -25°C, and the other group was stored at
						  ambient temperature (approximately 23°C). These samples were analyzed over
						  a period of fifteen days. The results are tabulated below.
PERCENT RECOVERY
Day
								  Analyzed
Refrigerated
Ambient
0..........................
97.4
98.7
98.9
97.4
98.7
98.9
0..........................
97.1
100.6
100.9
97.1
100.6
100.9
2..........................
95.8
96.4
95.4
95.4
96.6
96.9
5..........................
93.9
93.7
92.4
92.4
94.3
94.1
9..........................
93.6
95.5
94.6
95.2
95.6
96.6
13..........................
94.3
95.3
93.7
91.0
95.0
94.6
15..........................
96.8
95.8
94.2
92.9
96.3
95.9
8.4. Desorption data.
Samples were prepared by injecting liquid benzene onto
						  the A section of charcoal tubes. Samples were prepared that would be equivalent
						  to 0.5, 1.0, and 2.0 ppm for a 10 L air sample.
PERCENT RECOVERY
Sample
0.5
								  ppm
1.0
								  ppm
2.0 ppm
1..........................
99.4
98.8
99.5
2..........................
99.5
98.7
99.7
3..........................
99.2
98.6
99.8
4..........................
99.4
99.1
100.0
5..........................
99.2
99.0
99.7
6..........................
99.8
99.1
99.9
X =..........................
99.4
98.9
99.8
SD =..........................
0.22
0.21
0.18
CV =..........................
0.0022
0.0021
0.0018
X = 99.4
8.5. Carbon disulfide.
Carbon disulfide from a number of sources was analyzed
						  for benzene contamination. The results are given in the following table. The
						  benzene contaminant can be removed with the procedures given in section
						  4.1.
II. OSHA Laboratory Method No. 12 for Bulk
						  Samples
Analyte: Benzene.
Sample
ppm equivalent ug Benzene/ml
(for 10 L air sample)
Aldrich Lot 83017..........................
.......................... 4.20
0.13
Baker Lot 720364..........................
.......................... 1.01
0.03
Baker Lot 822351..........................
.......................... 1.01
0.03
Mallinkrodt Lot WEMP..........................
.......................... 1.74
0.05
Mallinkrodt Lot WDSJ..........................
.......................... 5.65
0.18
Mallindrodt Lot WHGA..........................
.......................... 2.90
0.09
Treated
								  SC2..........................
Matrix: Bulk Samples.
Procedure: Bulk samples are analyzed directly by high
						  performance liquid chromatography (HPLC).
Detection limits: 0.01% by volume.
1. Principle of the method.
1.1. An aliquot of the bulk sample to be analyzed is
						  injected into a liquid chromatograph.
1.2. The peak area for benzene is determined and
						  compared to areas obtained from standards.
2. Advantages and disadvantages of the method.
2.1. The analytical procedure is quick, sensitive, and
						  reproducible.
2.2. Reanalysis of samples is possible.
2.3. Interferences can be circumvented by proper
						  selection of HPLC parameters.
2.4. Samples must be free of any particulates that may
						  clog the capillary tubing in the liquid chromatograph. This may require
						  distilling the sample or clarifying with a clarification kit.
3. Apparatus.
3.1. Liquid chromatograph equipped with a UV
						  detector.
3.2. HPLC column that will separate benzene from other
						  components in the bulk sample being analyzed. The column used for validation
						  studies was a Waters uBondapack C18, 30 cm x 3.9 mm.
3.3. A clarification kit to remove any particulates in
						  the bulk if necessary.
3.4. A micro-distillation apparatus to distill any
						  samples if necessary.
3.5. An electronic integrator or some other suitable
						  method of measuring peak areas.
3.6. Microliter syringes-10 uL syringe and other
						  convenient sizes for making standards. 10 uL syringe for sample
						  injections.
3.7. Volumetric flasks, 5 mL and other convenient sizes
						  for preparing standards and making dilutions.
4. Reagents.
4.1. Benzene, reagent grade.
4.2. HPLC grade water , methyl, alcohol, and isopropyl
						  alcohol.
5. Collection and shipment of samples.
5.1. Samples should be transported in glass containers
						  with Teflon-lined caps.
5.2. Samples should not be put in the same container
						  used for air samples.
6. Analysis of samples.
6.1. Sample preparation. If necessary, the samples are
						  distilled or clarified. Samples are analyzed undiluted. If the benzene
						  concentration is out of the working range, suitable dilutions are made with
						  isopropyl alcohol.
6.2. HPLC conditions.
The typical operating conditions for the high
						  performance liquid chromatograph are:
a. Mobile phase--Methyl alcohol/water, 50/50
b. Analytical wavelength--254 mm
c. Injection size--10 uL
6.3. Measurement of peak area and calibration. Peak
						  areas are measured by an integrator or other suitable means. The integrator is
						  calibrated to report results in % benzene by volume.
7. Calculations.
Since the integrator is programmed to report results in
						  % benzene by volume in an undiluted sample, the following equation is
						  used:
% Benzene by Volume = A x B
Where: A = % by volume on report, and
B = Dilution factor
(B = 1 for undiluted sample).
8. Backup Data.
8.1. Detection limit--Bulk samples.
The detection limit for the analytical procedure for
						  bulk samples is 0.88 ug, with a coefficient of variation of 0.019 at this
						  level. This amount provided a chromatographic peak that could be identifiable
						  in the presence of possible interferences. The detection limit data were
						  obtained by making 10 uL injections of a 0.10% by volume standard.
1..........................
45386
2..........................
44214
3..........................
43822
X = 44040.1
4..........................
44062
SD = 852.5
6..........................
42724
CV = 0.019
8.2. Pooled coefficient of variation--Bulk Samples. The
						  pooled coefficient of variation for the analytical procedure was determined by
						  50 uL replicate injections of analytical standards. The standards were 0.01,
						  0.02, 0.04, 0.10, 1.0, and 2.0% benzene by volume.
AREA COUNT (PERCENT)
Injection
0.01
0.02
0.04
0.10
1.0
2.0
1
45386
84737
166097
448497
4395380
9339150
2
44241
84300
170832
441299
4590800
9484900
3
43822
83835
164160
443719
4593200
9557580
4
44062
84381
164445
444842
4642350
9677060
5
44006
83012
168398
442564
4646430
9766240
6
42724
81957
173002
443975
4646260
..........
X =
44040.1
83703.6
167872
444149
4585767
9564986
SD =
852.5
1042.2
3589.8
2459.1
96839.3
166233
CV =
0.0194
0.0125
0.0213
0.0055
0.0211
0.0174
CV =
0.017
1. New
						  section 5218 and Appendices A-E filed
						  4-20-90; operative 5-20-90 (Register 90, No.
						  23).
Note: Authority cited: Sections
							 142.3,
							 9020,
							 9030 and
							 9040, Labor
							 Code. Reference: Sections
							 142.3,
							 9004(d),
							 9009,
							 9020,
							 9030,
							 9031 and
							 9040, Labor
							 Code.