(3) Ethylene oxide:
(a) Method No.: 30.
(b) Matrix: Air.
(i) Target concentration: 1.0 ppm (1.8
mg/m3)
(ii) Procedure: Samples are collected on two
charcoal tubes in series and desorbed with 1% CS2 in
benzene. The samples are derivatized with HBr and treated with sodium
carbonate. Analysis is done by gas chromatography with an electron capture
detector.
(iii) Recommended air
volume and sampling rate: 1 liter and 0.05 Lpm.
(iv) Detection limit of the overall
procedure: 13.3 ppb (0.024 mg/m3) (based on 1.0
liter air sample).
(v) Reliable
quantitation limit: 52.2 ppb (0.094 mg/m3) (based on
1.0 liter air sample).
(vi)
Standard error of estimate: 6.59% (see backup section 4.6).
(vii) Special requirements: Samples must be
analyzed within fifteen days of sampling date.
(viii) Status of method: The sampling and
analytical method has been subject to the established evaluation procedures of
the Organic Method Evaluations Branch.
(c) Date: August 1981.
(d) Chemist: Wayne D. Potter
(e) Organic Solvents Branch, OSHA Analytical
Laboratory, Salt Lake City, Utah
(f) General discussion:
(i) Background.
(A) History of procedure.
(I) Ethylene oxide samples analyzed at the
OSHA laboratory have normally been collected on activated charcoal and desorbed
with carbon disulfide. The analysis is performed with a gas chromatograph
equipped with a FID (flame ionization detector) as described in NIOSH Method
S286 (Ref. (3)(j)(i)). This method is based on a PEL of 50 ppm and has a
detection limit of about 1 ppm.
(II) Recent studies have prompted the need
for a method to analyze and detect ethylene oxide at very low
concentrations.
(III) Several
attempts were made to form an ultraviolet (UV) sensitive derivative with
ethylene oxide for analysis with HPLC. Among those tested that gave no
detectable product were: p-anisidine, methylimidazole, aniline, and
2,3,6-trichlorobenzoic acid. Each was tested with catalysts such as
triethylamine, aluminum chloride, methylene chloride and sulfuric acid but no
detectable derivative was produced.
(IV) The next derivatization attempt was to
react ethylene oxide with HBr to form 2-bromoethanol. This reaction was
successful. An ECD (electron capture detector) gave a very good response for
2-bromoethanol due to the presence of bromine. The use of carbon disulfide as
the desorbing solvent gave too large a response and masked the 2-bromoethanol.
Several other solvents were tested for both their response on the ECD and their
ability to desorb ethylene oxide from the charcoal. Among those tested were
toluene, xylene, ethyl benzene, hexane, cyclohexane and benzene. Benzene was
the only solvent tested that gave a suitable response on the ECD and a high
desorption. It was found that the desorption efficiency was improved by using
1% CS2 with the benzene. The carbon disulfide did not
significantly improve the recovery with the other solvents. SKC Lot 120 was
used in all tests done with activated charcoal.
(B) Physical properties (Ref. (3)(j)(ii) -
(iv)):
(I) Synonyms: Oxirane; dimethylene
oxide; 1,2-epoxy-ethane; oxane;
C2H4O; ETO;
(II) Molecular weight: 44.06;
(III) Boiling point: 10.7°C
(51.3°);
(IV) Melting point: --
111°C;
(V) Description:
Colorless, flammable gas;
(VI)
Vapor pressure: 1095 mm. at 20°C;
(VII) Odor: Ether-like odor;
(VIII) Lower explosive limits: 3.0% (by
volume);
(IX) Flash point (TOC):
Below 0°F;
(X) Molecular
structure: CH2 --
CH2;
(ii) Limit defining parameters:
(A) Detection limit of the analytical
procedure. The detection limit of the analytical procedure is 12.0 picograms of
ethylene oxide per injection. This is the amount of analyte which will give a
peak whose height is five times the height of the baseline noise. (See backup
data section (3)(i)(i).)
(B)
Detection limit of the overall procedure.
(I)
The detection limit of the overall procedure is 24.0 ng of ethylene oxide per
sample.
(II) This is the amount of
analyte spiked on the sampling device which allows recovery of an amount of
analyte equivalent to the detection limit of the analytical procedure. (See
backup data section (3)(i)(ii).)
(C) Reliable quantitation limit.
(I) The reliable quantitation limit is 94.0
nanograms of ethylene oxide per sample. This is the smallest amount of analyte
which can be quantitated within the requirements of 75% recovery and 95%
confidence limits. (See backup data section (3)(i)(ii).)
(II) It must be recognized that the reliable
quantitation limit and detection limits reported in the method are based upon
optimization of the instrument for the smallest possible amount of analyte.
When the target concentration of an analyte is exceptionally higher than these
limits, they may not be attainable at the routine operating parameters. In this
case, the limits reported on analysis reports will be based on the operating
parameters used during the analysis of the samples.
(D) Sensitivity.
(I) The sensitivity of the analytical
procedure over a concentration range representing 0.5 to 2 times the target
concentration based on the recommended air volume is 34105 area units per
ug/mL. The sensitivity is determined by the slope of the calibration curve (see
backup data section (3)(i)(iii)).
(II) The sensitivity will vary somewhat with
the particular instrument used in the analysis.
(E) Recovery. The recovery of analyte from
the collection medium must be 75% or greater. The average recovery from spiked
samples over the range of 0.5 to 2 times the target concentration is 88.0% (see
backup section (3)(i)(iv)). At lower concentrations the recovery appears to be
nonlinear.
(F) Precision
(analytical method only). The pooled coefficient of variation obtained from
replicate determination of analytical standards at 0.5X, 1X and 2X the target
concentration is 0.036 (see backup data section (3)(i)(v)).
(G) Precision (overall procedure).
(I) The overall procedure must provide
results at the target concentration that are 25% or better at the 95%
confidence level. The precision at the 95% confidence level for the fifteen day
storage test is plus or minus 12.9% (see backup data section
(3)(i)(vi)).
(II) This includes an
additional plus or minus 5% for sampling error.
(iii) Advantages.
(A) The sampling procedure is
convenient.
(B) The analytical
procedure is very sensitive and reproducible.
(C) Reanalysis of samples is
possible.
(D) Samples are stable
for at least fifteen days at room temperature.
(E) Interferences are reduced by the longer
GC retention time of the new derivative.
(iv) Disadvantages.
(A) Two tubes in series must be used because
of possible breakthrough and migration.
(B) The precision of the sampling rate may be
limited by the reproducibility of the pressure drop across the tubes. The pumps
are usually calibrated for one tube only.
(C) The use of benzene as the desorption
solvent increases the hazards of analysis because of the potential carcinogenic
effects of benzene.
(D) After
repeated injections there can be a buildup of residue formed on the electron
capture detector which decreases sensitivity.
(E) Recovery from the charcoal tubes appears
to be nonlinear at low concentrations.
(g) Sampling procedure.
(i) Apparatus.
(A) A calibrated personal sampling pump whose
flow can be determined within plus or minus 5% of the recommended
flow.
(B) SKC Lot 120 Charcoal
tubes: Glass tube with both ends flame sealed, 7 cm long with a 6 mm O.D. and a
4-mm I.D., containing 2 sections of coconut shell charcoal separated by a 2-mm
portion of urethane foam. The adsorbing section contains 100 mg of charcoal,
the backup section 50 mg. A 3-mm portion of urethane foam is placed between the
outlet end of the tube and the backup section. A plug of silylated glass wool
is placed in front of the adsorbing section.
(ii) Reagents.
None required.
(iii) Sampling technique.
(A) Immediately before sampling, break the
ends of the charcoal tubes. All tubes must be from the same lot.
(B) Connect two tubes in series to the
sampling pump with a short section of flexible tubing. A minimum amount of
tubing is used to connect the two sampling tubes together. The tube closer to
the pump is used as a backup. This tube should be identified as the backup
tube.
(C) The tubes should be
placed in a vertical position during sampling to minimize channeling.
(D) Air being sampled should not pass through
any hose or tubing before entering the charcoal tubes.
(E) Seal the charcoal tubes with plastic caps
immediately after sampling. Also, seal each sample with OSHA seals
lengthwise.
(F) With each batch of
samples, submit at least one blank tube from the same lot used for samples.
This tube should be subjected to exactly the same handling as the samples
(break, seal, transport) except that no air is drawn through it.
(G) Transport the samples (and corresponding
paperwork) to the lab for analysis.
(H) If bulk samples are submitted for
analysis, they should be transported in glass containers with Teflon-lined
caps. These samples must be mailed separately from the container used for the
charcoal tubes.
(iv)
Breakthrough.
The breakthrough (5% breakthrough) volume for a 3.0
mg/m3 ethylene oxide sample stream at approximately
85% relative humidity, 22°C and 633 mm is 2.6 liters sampled at 0.05 liters
per minute. This is equivalent to 7.8 µg of ethylene oxide. Upon
saturation of the tube it appeared that the water may be displacing ethylene
oxide during sampling.
(v)
Desorption efficiency.
(A) The desorption
efficiency, from liquid injection onto charcoal tubes, averaged 88.0% from 0.5
to 2.0 x the target concentration for a 1.0 liter air sample. At lower ranges
it appears that the desorption efficiency is nonlinear (see backup data section
(3)(i)(ii)).
(B) The desorption
efficiency may vary from one laboratory to another and also from one lot of
charcoal to another. Thus, it is necessary to determine the desorption
efficiency for a particular lot of charcoal.
(vi) Recommended air volume and sampling
rate.
(A) The recommended air volume is 1.0
liter.
(B) The recommended maximum
sampling rate is 0.05 Lpm.
(vii) Interferences.
(A) Ethylene glycol and Freon 12 at target
concentration levels did not interfere with the collection of ethylene
oxide.
(B) Suspected interferences
should be listed on the sample data sheets.
(C) The relative humidity may affect the
sampling procedure.
(viii) Safety precautions.
(A) Attach the sampling equipment to the
employee so that it does not interfere with work performance.
(B) Wear safety glasses when breaking the
ends of the sampling tubes.
(C) If
possible, place the sampling tubes in a holder so the sharp end is not exposed
while sampling.
(h) Analytical method.
(i) Apparatus.
(A) Gas chromatograph equipped with a
linearized electron capture detector.
(B) GC column capable of separating the
derivative of ethylene oxide (2-bromoethanol) from any interferences and the 1%
CS2 in benzene solvent. The column used for validation
studies was: 10 ft x 1/8 inch stainless steel 20% SP-2100, .1% Carbowax 1500 on
100/120 Supelcoport.
(C) An
electronic integrator or some other suitable method of measuring peak
areas.
(D) Two milliliter vials
with Teflon-lined caps.
(E) Gas
tight syringe -- 500 µL or other convenient sizes for preparing
standards.
(F) Microliter syringes
-- 10 µL or other convenient sizes for diluting standards and 1 µL
for sample injections.
(G) Pipets
for dispensing the 1% CS2 in benzene solvent. The Glenco
1 mL dispenser is adequate and convenient.
(H) Volumetric flasks -- 5 mL and other
convenient sizes for preparing standards.
(I) Disposable Pasteur pipets.
(ii) Reagents.
(A) Benzene, reagent grade.
(B) Carbon disulfide, reagent
grade.
(C) Ethylene oxide, 99.7%
pure.
(D) Hydrobromic acid, 48%
reagent grade.
(E) Sodium
carbonate, anhydrous, reagent grade.
(F) Desorbing reagent, 99% Benzene/1%
CS2.
(iii) Sample preparation.
(A) The front and back sections of each
sample are transferred to separate 2-mL vials.
(B) Each sample is desorbed with 1.0 mL of
desorbing reagent.
(C) The vials
are sealed immediately and allowed to desorb for one hour with occasional
shaking.
(D) Desorbing reagent is
drawn off the charcoal with a disposable pipet and put into clean 2-mL
vials.
(E) One drop of HBr is added
to each vial. Vials are resealed and HBr is mixed well with the desorbing
reagent.
(F) About 0.15 gram of
sodium carbonate is carefully added to each vial. Vials are again resealed and
mixed well.
(iv)
Standard preparation.
(A) Standards are
prepared by injecting the pure ethylene oxide gas into the desorbing
reagent.
(B) A range of standards
are prepared to make a calibration curve. A concentration of 1.0 µL of
ethylene oxide gas per 1 mL desorbing reagent is equivalent to 1.0 ppm air
concentration (all gas volumes at 25°C and 760 mm) for the recommended 1
liter air sample. This amount is uncorrected for desorption efficiency (see
backup data section (3)(i)(ii), for desorption efficiency
corrections).
(C) One drop of HBr
per mL of standard is added and mixed well.
(D) About 0.15 grams of sodium carbonate is
carefully added for each drop of HBr (a small reaction will occur).
(v) Analysis.
(A) GC conditions.
Nitrogen flow rate -- 10mL/min.
Injector temperature -- 250°C
Detector temperature -- 300°C
Column temperature -- 100°C
Injection size -- 0.8 µL
Elution time -- 3.9 minutes
(B) Peak areas are measured by an integrator
or other suitable means.
(C) The
integrator results are in area units and a calibration curve is set up with
concentration vs. area units.
(vi) Interferences.
(A) Any compound having the same retention
time of 2-bromoethanol is a potential interference. Possible interferences
should be listed on the sample data sheets.
(B) GC parameters may be changed to
circumvent interferences.
(C) There
are usually trace contaminants in benzene.
These contaminants, however, posed no problem of
interference.
(D) Retention
time date on a single column is not considered proof of chemical identity.
Samples over the 1.0 ppm target level should be confirmed by GC/Mass Spec or
other suitable means.
(vii) Calculations.
(A) The concentration in µg/mL for a
sample is determined by comparing the area of a particular sample to the
calibration curve, which has been prepared from analytical standards.
(B) The amount of analyte in each sample is
corrected for desorption efficiency by use of a desorption curve.
(C) Analytical results, A, from the two tubes
that compose a particular air sample are added together.
(D) The concentration for a sample is
calculated by the following equation:
where:
|
A
|
=
|
MICROg/mL
|
B
|
=
|
desorption volume in milliliters
|
C
|
=
|
air volume in liters.
|
(E)
To convert mg/m
3 to parts per million (ppm) the
following relationship is used:
ETO, ppm
|
=
|
mg/m3 x 24.45
|
|
44.05
|
where:
|
mg/m3
|
=
|
results from 3.7.4
|
24.45
|
=
|
molar volume at 25°C and 760 mm Hg
|
44.05
|
=
|
air volume in liters.
|
(viii) Safety precaution
(A) Ethylene oxide and benzene are potential
carcinogens and care must be exercised when working with these
compounds.
(B) All work done with
the solvents (preparation of standards, desorption of samples, etc.) should be
done in a hood.
(C) Avoid any skin
contact with all of the solvents.
(D) Wear safety glasses at all
times.
(E) Avoid skin contact with
HBr because it is highly toxic and a strong irritant to eyes and
skin.
(i)
Backup data.
(i) Detection limit data.
The detection limit was determined by injecting 0.8 µL
of a 0.015 µg/mL standard of ethylene oxide into 1% CS2 in benzene. The
detection limit of the analytical procedure is taken to be 1.20 x
10-5
µg per injection. This is equivalent to
8.3 ppb (0.015 mg/m3) for the recommended air
volume.
(ii) Desorption
efficiency. Ethylene oxide was spiked into charcoal tubes and the following
recovery data was obtained:
Amount
spiked (MICROg)
|
Amount recovered (MICROg)
|
Percent
recovery
|
4.5
|
4.32
|
96.0
|
3.0
|
2.61
|
87.0
|
2.25
|
2.025
|
90.0
|
1.5
|
1.365
|
91.0
|
1.5
|
1.38
|
92.0
|
.75
|
6525
|
87.0
|
.375
|
.315
|
84.0
|
.375
|
.312
|
83.2
|
.1875
|
.151
|
80.5
|
.094
|
.070
|
74.5
|
Note:
|
At lower amounts the recovery appears to be
nonlinear.
|
(iii) Sensitivity data. The following data
was used to determine the calibration curve:
Injection
|
0.5 x .75
MICROg/mL
|
1 x 1.5
MICROg/mL
|
2 x 3.0
MICROg/mL
|
1. . . . . . . . . .
|
30904
|
59567
|
111778
|
2. . . . . . . . . .
|
30987
|
62914
|
106016
|
3. . . . . . . . . .
|
32555
|
58578
|
106122
|
4. . . . . . . . . .
|
32242
|
57173
|
109716
|
X. . . . . . . . . .
|
31672
|
59558
|
108408
|
Slope = 34.105.
(iv) Recovery. The recovery was determined by
spiking ethylene oxide onto lot 120 charcoal tubes and desorbing with 1%
CS
2 in Benzene. Recoveries were done at 0.5, 1.0, and
2.0 X the target concentration (1 ppm) for the recommended air volume.
Percent Recovery
Sample
|
0.5x
|
1.0x
|
2.0x
|
1. . . . . . . . . .
|
88.7
|
95.0
|
91.7
|
2. . . . . . . . . .
|
83.8
|
95.0
|
87.3
|
3. . . . . . . . . .
|
84.2
|
91.0
|
86.0
|
4. . . . . . . . . .
|
88.0
|
91.0
|
83.0
|
5. . . . . . . . . .
|
88.0
|
86.0
|
85.0
|
X. . . . . . . . . .
|
86.5
|
90.5
|
87.0
|
Weighted average = 88.2
(v) Precision of the analytical procedure.
The following data was used to determine the precision of the analytical
method:
Concentration
|
0.5 x .75
MICROg/mL
|
1 x 1.5
MICROg/mL
|
2 x 3.0
MICROg/mL
|
Injection
|
.7421
.7441
.7831
.7753
.7612
|
1.4899
1.5826
1.4628
1.4244
1.4899
|
3.1184
3.0447
2.9149
2.9185
2.9991
|
Average Standard Deviation
|
.0211
|
.0674
|
.0998
|
CV. . . . . . . .
|
.0277
|
.0452
|
.0333
|
CV
|
=
|
3(.0277)2 + 3
(.0452)2 + 3
(.0333)2
|
3 + 3 + 3
|
CV + 0.036
|
(vi)
Storage data. Samples were generated at 1.5 mg/m3 ethylene oxide at 85%
relative humidity, 22°C and 633 mm. All samples were taken for twenty
minutes at 0.05 Lpm. Six samples were analyzed as soon as possible and fifteen
samples were stored at refrigerated temperature (5°C) and fifteen samples
were stored at ambient temperature (23°C). These stored samples were
analyzed over a period of nineteen days.
Percent Recovery
Day analyzed
|
Refrigerated
|
Ambient
|
1. . . . . . . . . . . .
|
87.0
|
87.0
|
1. . . . . . . . . . . .
|
93.0
|
93.0
|
1. . . . . . . . . . . .
|
94.0
|
94.0
|
1. . . . . . . . . . . .
|
92.0
|
92.0
|
4. . . . . . . . . . . .
|
92.0
|
91.0
|
4. . . . . . . . . . . .
|
93.0
|
88.0
|
4. . . . . . . . . . . .
|
91.0
|
89.0
|
6. . . . . . . . . . . .
|
92.0
|
|
|
6. . . . . . . . . . . .
|
92.0
|
|
|
8. . . . . . . . . . . .
|
|
|
92.0
|
8. . . . . . . . . . . .
|
|
|
86.0
|
10. . . . . . . . . . .
|
91.7
|
|
|
10. . . . . . . . . . .
|
95.5
|
|
|
10. . . . . . . . . . .
|
95.7
|
|
|
11. . . . . . . . . . .
|
|
|
90.0
|
11. . . . . . . . . . .
|
|
|
82.0
|
13. . . . . . . . . . .
|
78.0
|
|
|
13. . . . . . . . . . .
|
81.4
|
|
|
13. . . . . . . . . . .
|
82.4
|
|
|
14. . . . . . . . . . .
|
|
|
78.5
|
14. . . . . . . . . . .
|
|
|
72.1
|
18. . . . . . . . . . .
|
66.0
|
|
|
18. . . . . . . . . . .
|
68.0
|
|
|
19. . . . . . . . . . .
|
|
|
64.0
|
19. . . . . . . . . . .
|
|
|
77.0
|
(vii) Breakthrough data.
(A) Breakthrough studies were done at 2 ppm
(3.6 mg/m
3) at approximately 85% relative humidity
at 22°C (ambient temperature). Two charcoal tubes were used in series. The
backup tube was changed every ten minutes and analyzed for breakthrough. The
flow rate was 0.050 Lpm.
Tube No.
|
Time
(Minutes)
|
Percent breakthrough
|
1. . . . . . . . . . . . . . . .
|
10
|
(1)
|
2. . . . . . . . . . . . . . . .
|
20
|
(1)
|
3. . . . . . . . . . . . . . . .
|
30
|
(1)
|
4. . . . . . . . . . . . . . . .
|
40
|
1.23
|
5. . . . . . . . . . . . . . . .
|
50
|
3.46
|
6. . . . . . . . . . . . . . . .
|
60
|
18.71
|
7. . . . . . . . . . . . . . . .
|
70
|
39.2
|
8. . . . . . . . . . . . . . . .
|
80
|
53.3
|
9. . . . . . . . . . . . . . . .
|
90
|
72.0
|
10. . . . . . . . . . . . . . .
|
100
|
96.0
|
11. . . . . . . . . . . . . . .
|
110
|
113.0
|
12. . . . . . . . . . . . . . .
|
120
|
133.9
|
(B)
The 5% breakthrough volume was reached when 2.6 liters of test atmosphere were
drawn through the charcoal tubes.
(j) References.
(i) "NIOSH Manual of Analytical Methods," 2nd
ed. NIOSH: Cincinnati, 1977; Method S 286.
(ii) "IARC Monographs on the Evaluation of
Carcinogenic Risk of Chemicals to Man." International Agency for Research on
Cancer: Lyon, 1976; Vol. II, p. 157.
(iii) Sax., N.I. "Dangerous Properties of
Industrial Materials," 4th ed.; Van Nostrand Reinhold Company, New York, 1975;
p. 741.
(iv) "The Condensed
Chemical Dictionary," 9th ed.; Hawley, G.G., ed.; Van Nostrand Reinhold
Company, New York, 1977; p. 361.
(4) Summary of other sampling procedures.
OSHA believes that several other types of monitoring equipment and techniques
exist for monitoring time-weighted averages. Considerable research and method
development is currently being performed, which will lead to improvements and a
wider variety of monitoring techniques. A combination of monitoring procedures
can be used. There probably is no one best method for monitoring personal
exposure to ethylene oxide in all cases. There are advantages, disadvantages,
and limitations to each method. The method of choice will depend on the need
and requirements. Some commonly used methods include the use of charcoal tubes,
passive dosimeters, Tedler gas sampling bags, detector tubes, photoionization
detection units, infrared detection units and gas chromatographs. A number of
these methods are described below.
(a)
Charcoal tube sampling procedures.
(i)
Qazi-Ketcham method (Ex-11-133) -- This method consists of collecting EtO on
Columbia JXC activated carbon, desorbing the EtO with carbon disulfide and
analyzing by gas chromatography with flame ionization detection. Union Carbide
has recently updated and revalidated this monitoring procedure. This method is
capable of determining both eight-hour time-weighted average exposures and
short-term exposures. The method was validated to 0.5 ppm. Like other charcoal
collecting procedures, the method requires considerable analytical
expertise.
(ii)
ASTM-proposed method -- The Ethylene Oxide Industry Council
(EOIC) has contracted with Clayton Environmental Consultants, Inc. to conduct a
collaborative study for the proposed method. The ASTM-Proposed method is
similar to the method published by Qazi and Ketcham in the November 1977
American Industrial Hygiene Association Journal, and to the method of Pilney
and Coyne, presented at the 1979 American Industrial Hygiene Conference. After
the air to be sampled is drawn through an activated charcoal tube, the ethylene
oxide is desorbed from the tube using carbon disulfide and is quantitated by
gas chromatography utilizing a flame ionization detector. The ASTM-proposed
method specifies a large two-section charcoal tube, shipment in dry ice,
storage at less than -5°C, and analysis within three weeks to prevent
migration and sample loss. Two types of charcoal tubes are being tested --
Pittsburgh Coconut-Based (PCB) and columbia JXC charcoal. This collaborative
study will give an indication of the inter- and intralaboratory precision and
accuracy of the ASTM/proposed method. Several laboratories have considerable
expertise using the Qazi-Ketcham and Dow methods.
(b) Passive monitors -- Ethylene oxide
diffuses into the monitor and is collected in the sampling media. The DuPont
Pro-Tek badge collects EtO in an absorbing solution, which is analyzed
colorimetrically to determine the amount of EtO present. The 3M 350 badge
collects the EtO on chemically treated charcoal. Other passive monitors are
currently being developed and tested. Both 3M and DuPont have submitted data
indicating their dosimeters meet the precision and accuracy requirements of the
proposed ethylene oxide standard. Both presented laboratory validation data to
0.2 ppm (Exs. 11-65, 4-20, 108, 109, 130).
(c) Tedlar gas sampling bags-samples are
collected by drawing a known volume of air into a Tedlar gas sampling bag. The
ethylene oxide concentration is often determined on-site using a portable gas
chromatograph or portable infrared spectometer.
(d) Detector tubes -- A known volume of air
is drawn through a detector tube using a small hand pump. The concentration of
EtO is related to the length of stain developed in the tube. Detector tubes are
economical, easy to use, and give an immediate readout. Unfortunately, partly
because they are nonspecific, their accuracy is often questionable. Since the
sample is taken over a short period of time, they may be useful for determining
the source of leaks.
(e) Direct
reading instruments:
(i) There are numerous
types of direct reading instruments, each having its own strengths and
weaknesses (Exs. 135B, 135C, 107, 11-78, 11-153). Many are relatively new,
offering greater sensitivity and specificity. Popular ethylene oxide direct
reading instruments include infrared detection units, photoionization detection
units, and gas chromatographs.
(ii)
Portable infrared analyzers provide an immediate, continuous indication of a
concentration value; making them particularly useful for locating high
concentration pockets, in leak detection and in ambient air monitoring. In
infrared detection units, the amount of infrared light absorbed by the gas
being analyzed at selected infrared wavelengths is related to the concentration
of a particular component. Various models have either fixed or variable
infrared filters, differing cell pathlengths, and microcomputer controls for
greater sensitivity, automation, and interference elimination.
(iii) A fairly recent detection system is
photoionization detection. The molecules are ionized by high energy ultraviolet
light. The resulting current is measured. Since different substances have
different ionization potentials, other organic compounds may be ionized. The
lower the lamp energy, the better the selectivity. As a continuous monitor,
photoionization detection can be useful for locating high concentration
pockets, in leak detection, and continuous ambient air monitoring. Both
portable and stationary gas chromatographs are available with various types of
detectors, including photoionization detectors. A gas chromatograph with a
photoionization detector retains the photoionization sensitivity, but minimizes
or eliminates interferences. For several GC/PID units, the sensitivity is in
the 0.1-0.2 ppm EtO range. The GC/PID with microprocessors can sample up to
twenty sample points sequentially, calculate and record data, and activate
alarms or ventilation systems. Many are quite flexible and can be configured to
meet the specific analysis needs for the workplace.
(iv)
DuPont presented their laboratory
validation data of the accuracy of the Qazi-Ketcham charcoal tube, the PCB
charcoal tube, Miran 103 IR analyzer, 3M #3550 monitor and the DuPont C-70
badge. Quoting Elbert V. Kring:
(v) We also believe that OSHA's proposed
accuracy in this standard is appropriate. At plus or minus twenty-five percent
at one part per million, and plus or minus thirty-five percent below that. And,
our data indicates there's only one monitoring method, right now, that we've
tested thoroughly, that meets that accuracy requirements. That is the DuPont
Pro-Tek badge***. We also believe that this kind of data should be confirmed by
another independent laboratory, using the same type dynamic chamber testing
(Tr. 1470).
Additional data by an independent laboratory following their
exact protocol was not submitted. However, information was submitted on
comparisons and precision and accuracy of those monitoring procedures which
indicate far better precision and accuracy of those monitoring procedures than
that obtained by DuPont (Ex. 4-20, 130, 11-68, 11-133, 130, 135A)
(vi) The accuracy of any method
depends to a large degree upon the skills and experience of those who not only
collect the samples but also those who analyze the samples. Even for methods
that are collaboratively tested, some laboratories are closer to the true
values than others. Some laboratories may meet the precision and accuracy
requirements of the method; others may consistently far exceed them for the
same method.