"Personal Sampling for Air Contaminants" (OSHA Technical Manual)

"Personal Sampling for Air Contaminants" (OSHA Technical Manual)
OSHA TECHNICAL MANUAL - SECTION II: CHAPTER 1
Page 1 of 32
U.S. Department of Labor
Occupational Safety & Health Administration
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Printing Instructions
SECTION II: CHAPTER 1 [New additions and extensively revised]
PERSONAL SAMPLING FOR AIR CONTAMINANTS
Contents:
I.
II.
III.
IV.
V.
VI.
VII.
VIII.
Introduction
General Sampling Procedures
Sampling Media
Special Sampling Procedures
Sampling for Welding Fumes
Equipment Preparation and Calibration
Filter Weighing
Bibliography
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
II:1-1.
II:1-2.
II:1-3.
II:1-4.
II:1-5.
II:1-6.
II:1-7.
Detector Tubes and Pumps
Electronic Flow Calibrators
Manual Buret Bubble Meter Technique
Shelf Life of Sampling Media Provided by SLTC
Sampling for Special Analyses
Sampling and Analytical Errors (SAE's)
List of Substances for Autoweighing Submission
For problems with accessibility in using figures and illustrations in this document,
please contact the Office of Science and Technology Assessment at (202) 6932095.
I. INTRODUCTION.
A. Effective and efficient sampling strategies require planning and foresight to ensure
the most productive and thorough evaluation of air contaminants in the workplace.
Air sampling should be conducted when necessary and laboratory resources should
be used wisely to avoid delays in reporting results of necessary sampling. When
possible, evaluate the potential for employee overexposure by observing work
practices and screening samples before conducting any partial or full-shift air
sampling.
B. Screening with portable monitors, gravimetric sampling, or detector tubes should
be used to evaluate the following:
1. Exposures to substances with exceptionally high permissible exposure limits
(PEL's) in relatively dust-free atmospheres, e.g., ferric oxide and aluminum
oxide;
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2. Intermittent processes involving substances without short-term exposure
limits (STEL's);
3. Engineering controls, work practices, or isolation of process; and the need
for CSHO protection;
4. Substances that have Ceiling exposure limits. (There are validated
direct-reading sampling devices available specifically for these substances.)
C. Take a sufficient number of samples to obtain a representative estimate of
exposure. Contaminant concentrations vary seasonally, with weather, with
production levels, and in a single location or job class. The number of samples
taken depends on the error of measurement and differences in results. Consult the
NIOSH Occupational Exposure Sampling Strategy Manual for further information.
D. If the employer has conducted air sampling and monitoring in the past, review the
records.
E. Bulk samples are often required to assist the Salt Lake Technical Center (SLTC) in
the proper analysis of field samples. (See Section II, Chapter 4, Sample Shipping
and Handling.) Some contaminants in these categories are:
„
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silica
Portland cement
asbestos
mineral oil and oil mist
chlorodiphenyl
hydrogenated terphenyls
chlorinated camphene
fugitive grain dust
explosibility testing
F. Bulk samples can also be taken and analyzed to support any Hazard
Communication inspections (i.e., Material Safety Data Sheet determinations).
II. GENERAL SAMPLING PROCEDURES. NOTE: Radio frequency electromagnetic fields
can interfere with the proper operation of industrial hygiene instruments. This
interference is called electromagnetic susceptibility (EMS). Determine if there is a
potential for such interference. Likely sources of radio frequency interference are
walkie-talkies, vehicles equipped with mobile radio transmitters, RF heat sealers, etc. If
there is a potential for such interference, select sampling instruments that are properly
rated for EMS to avoid faulty data or malfunction.
A. SAMPLING PREPARATIONS. Screen
the sampling area with detector tubes,
if appropriate. Determine the
appropriate sampling technique [see
the Chemical Sampling Information].
Prepare and calibrate the equipment
and prepare the filter media (if sample
weights are necessary, see Section VI.,
Filter weighing, below.). Figure II:1-1a
shows the appropriate assembly for the
three piece sampling cassette used to
collect specific particulates. Other
sampling media usage and preparation
can be found within this chapter, via
Safety and Health Topics Pages
(Chemical Sampling Information or
specific analytical methods).
B. SELECT THE EMPLOYEE to be
sampled and discuss the purpose of the
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sampling. Inform the employee when
and where the equipment will be removed. Stress the importance of not removing
or tampering with the sampling equipment. Instruct the employee to notify the
supervisor or the CSHO if the sampler requires temporary removal.
C. STARTING SAMPLING.
1. Place the sampling equipment on the employee so that it does not interfere
with work performance. Attach the collection device (filter cassette, charcoal
tube, etc.) to the shirt collar or as close as practical to the nose and mouth
of the employee, i.e., in a hemisphere forward of the shoulders with a radius
of approximately six to nine inches. The inlet should always be in a
downward vertical position to avoid gross contamination. Position the excess
tubing so that it does not interfere with the work of the employee.
2. Turn on the pump and record the starting time.
3. Observe the pump operation for a short time after starting to make sure it is
operating correctly.
4. Record the information required by the Air Sampling Data Form (OSHA 91A).
D. MONITORING.
1. Check pump every two hours. More frequent checks may be necessary when
heavy filter loading is possible. Ensure that the sampler is still assembled
properly and that the hose has not become pinched or detached from the
cassette or the pump. For filters, observe for symmetrical deposition of
particulate on the filter, unexpected large particles, or other evidence of
sample tampering with the sample or pump. Record the flow rate and any
relevant observations.
2. Periodically monitor the employee throughout the workday to ensure that
sample integrity is maintained and cyclical activities and work practices are
identified. Turn off or remove sampling pumps immediately prior to an
employee leaving a potentially contaminated area (such as when he/she
goes to lunch or on a break in a clean area). If these areas also appear
contaminated and are considered part of the workplace, continue sampling
and assess the need for surface contamination measurements (see also
Section II, Chapter 2, Sampling for Surface Contamination).
3. Take photographs (as appropriate) and detailed notes concerning visible
airborne contaminants, work practices, potential interferences, movements,
and other conditions to assist in determining appropriate engineering
controls.
4. Prepare blank(s) during the sample period for each type of sample collected.
(Also see Section II, Chapter 4, Sample Shipping and Handling.) One blank
will suffice for up to 20 samples for any given analysis/sampling period
except asbestos, which requires a minimum of two field blanks. The blanks
should be opened but not used to take samples (charcoal tubes, filters etc.).
They should be handled in the same manner as any sampling media used in
sampling air contaminants, with the exception that no air is drawn through
them.
E. FINAL PROCEDURES.
1. Before removing the pump at the end of the sample period, if there is a
pump rotameter, check the flow rate to ensure that the rotameter ball is still
at the calibrated mark. If the ball is no longer at the mark, record the pump
rotameter reading.
2. Turn off the pump and record the ending time.
3. Remove the collection device from the pump and seal it with an OSHA-21
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form as soon as possible. The seal should be attached across sample inlet
and outlet so that tampering is not possible. (See Figures II:1-1b and
II:1-1c.)
FIGURE II:1-1b.
IMPROPERLY SEALED
CASSETTE ALLOWS
ACCESS TO INLET AND
OUTLET AFTER SAMPLE
HAS BEEN TAKEN.
FIGURE II:1-1c.
PROPERLY SEALED
CASSETTE WITH OSHA-21
FORM COVERING INLET
AND OUTLET PORTS
PROVIDES SECURITY.
4. Prepare the samples for mailing to the Salt Lake Technical Center (SLTC) for
analysis. (Also see Section II, Chapter 4.) Mail bulk samples and air samples
separately to avoid cross-contamination. If any sample materials could be
considered hazardous, always consult and follow appropriate shipping
regulations to assure safe handling during shipment. Pack the samples
securely to avoid any rattle or shock damage (do not use expanded
polystyrene packing). Use bubble sheeting as packing. Put identifying
paperwork in every package. Do not send samples in plastic bags or in
envelopes. Use OSHA Form 91A. Print legibly on all forms.
5. Recalibrate pumps after each day of sampling (before charging). Take proper
care of battery packs (see Section II, Chapter 3 - III. Batteries).
6. When calibrating conditions are significantly different from sampling site
conditions such as large temperature and pressure differences, call the Salt
Lake City Technical Center.
III. SAMPLING MEDIA.
A. DETECTOR TUBES. Each pump should be leak-tested before use. Calibrate the
detector tube pump for proper volume at least quarterly or after 100 tubes (See
Appendix II:1-1).
B. TOTAL DUST AND METAL FUME - AEROSOL SAMPLERS.
1. Collect total dust on a preweighed, low-ash polyvinyl chloride (PVC) filter
(See Section VI, Filter Weighing below) at a flow rate of about 2 liters per
minute (L/min), depending on the rate required to prevent overloading.
2. Collect metal fumes on a 0.8-micron mixed cellulose ester (MCE) filter at a
flow rate of approximately 1.5 L/min, not to exceed 2.0 L/min. When the
gravimetric weight needs to be determined for welding fumes, use the
sampling device described in Section VI, Filter Weighing, for gravimetric
determinations.
3. Take care to avoid overloading the filter, as evidenced by any loose
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particulate.
4. Calibrate personal sampling pumps before and after each day of sampling,
using a bubble meter method (electronic or mechanical) or the precision
rotameter method (that has been calibrated against a bubble meter), as
described in Section V, part E-2, below. Assure the calibration equipment
(bubble meter, etc.) is within its prescribed calibration interval, and record
the serial number of the calibration bubble meter (or rotameter) in your
data.
NOTE: Using precision rotameters for pump calibration should be avoided if
at all possible. Tests have indicated significant measurement errors due to
pump pulsations.
5. PVC filters used for gravimetric analysis need to be pre- and post-weighed.
See Section VI, Filter Weighing for further details.
C. RESPIRABLE DUST SAMPLERS. Collect respirable dust using a clean cyclone
equipped with a preweighed low-ash polyvinyl chloride filter at a flow rate of 1.5 to
2.0 L/min. (See Figure II:1-2.). Pre-weighed filters are available from SLTC or CTC
(see Section VI, Filter Weighing, below, for further information). Collect silica only
as a respirable dust, and, if possible, submit a bulk sample also to SLTC.
1. Calibration Procedures
a. Perform the calibration at the pressure and temperature where the
sampling is to be conducted.
b. For respirable dust sampling using a cyclone, or for total dust sampling
using an open-face filter cassette, set up the calibration apparatus as shown
in Figure II:1-9.
c. Place the open-face filter cassette, or cyclone assembly in a 1-liter jar.
The jar is provided with a special cover.
d. Connect the tubing from the electronic bubble meter to the inlet of the
jar.
e. Connect the tubing from the outlet of the cyclone holder assembly or
from the filter cassette to the outlet of the jar and then to the sampling
pump.
f. Calibrate the pump with a light and heavy load, both pre- and
post-sampling. All readings must be within five percent of each other.
2. Alternative Calibration Method - "Jarless Cyclone Calibration."
The following "Jarless Cyclone Calibration" is an alternative method to
calibrating the cyclone with a 1-liter jar. This method will be included in the
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition.
a. Connect the air sampling pump to a TEE fitting, a pressure gauge (0" to
50" H2O vacuum full scale) or water manometer, a light load (typically a
5-µm, 37mm filter), and a calibrated electronic bubble meter (or standard
bubble tube).
b. Adjust the air sampling pump to 1.7 L/min as indicated on the bubble
meter, and adjust the loading, if necessary, to produce a 2" to 5" H2O
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indication on the pressure (vacuum) gauge. c. Increase the loading (typically
five to six 0.8-µm, 37-mm filters) until the pressure (vacuum) gauge
indicates between 25" and 35" H2O, and check the flow rate again. The flow
rate should remain at 1.7 L/min ±5%. d. Finally, replace the load and
bubble meter with the cyclone having a clean filter installed, and verify that
the loading caused by the cyclone assembly is between 2" and 5" H2O.
e. This calibration method actually performs a dynamic test of the pump
under load.
3. Cyclone Cleaning.
a. Unscrew the grit pot from the cyclone. Empty the grit pot by turning it
upside down and tapping it gently on a solid surface. b. Clean the cyclone
thoroughly and gently after each use in warm soapy water or, preferably,
wash in an ultrasonic bath. Rinse thoroughly in clean water, shake off excess
water, and set aside to dry before reassembly. Never insert anything into the
cyclone during cleaning. See Figure II:1-2.
FIGURE II:1-2. CYCLONE ASSEMBLY.
c. Inspect the cyclone parts for signs of wear or damage such as scoring,
rifling, or a loose coupler. Replace the units or parts if they appear damaged.
d. Leak test the cyclone before use unless it has been leak tested within the
past month. A cyclone leak Test Kit and Cyclone Leak Test Procedure are
provided in each office for this purpose. e. Detailed instructions on leak
testing are available from the Directorate of Technical Support, Cincinnati
Technical Center (CTC) and are available through Technical Links on our Web
Page for silica.
D. SOLID SORBENT TUBES.
1. Organic vapors and gases may be collected on activated charcoal, silica gel,
or other adsorption tubes using low-flow pumps (see Figure II:1-3).
FIGURE II:1-3. THE CHARCOAL OR "C"-TUBE WITH
GLASS-SEALED END AND NIOSH-APPROVED CAPS BEFORE
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SAMPLING.
2. Immediately before sampling, break off the ends of the flame-sealed tube so
as to provide an opening approximately half the internal diameter of the
tube. Wear eye protection when breaking ends. Use tube holders, if
available, to minimize the hazards of broken\glass. Do not use the charging
inlet or the exhaust outlet of the pump to break the ends of the tubes.
3. Use the smaller section of the tube as a back-up and position it near the
sampling pump. The tube shall be held or attached in an approximately
vertical position with the inlet either up or down during sampling.
4. Draw the air to be sampled directly into the inlet of the tube. This air is not
to be passed through any hose or tubing before entering the tube.
5. Cap the tube with the supplied plastic caps immediately after sampling and
seal with an OSHA-21 form as soon as possible. (See Figures II:1-4a and b.)
Do not ship tubes with bulk material.
FIGURE II:1-4a. CORRECTLY SEALED C-TUBE. SAMPLE IS
COMPLETELY ENCLOSED IN THE SEAL, AND NO
TAMPERING IS POSSIBLE.
FIGURE II:1-4b. INCORRECTLY SEALED C-TUBE. END
CAPS CAN BE REMOVED AND SAMPLE INTEGRITY
JEOPARDIZED WITHOUT DISTURBING THE SEAL.
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6. Tubes may be furnished by SLTC with either caps or flame-sealed glass
ends. If using the capped version, simply uncap during the sampling period
and recap at the end of the sampling period.
7. For organic vapors and gases, low-flow pumps are required. Refer to the
Chemical Sampling Information for flow rates recommended for specific
chemicals.
8. With sorbent tubes, flow rates may have to be lowered or smaller air
volumes (half the maximum) used when there is high humidity (above 90%)
in the sampling area or relatively high concentrations of other organic vapors
are present.
9. Set up the calibration apparatus as shown in Figure II:1-8 replacing the
cassette with the solid sorbent tube to be used in the sampling (e.g.,
charcoal, silica gel, etc.). If a sampling protocol requires the use of two
charcoal tubes, the calibration train must include two charcoal tubes. The air
flow must be in the direction of the arrow on the tube. Calibrate the pump.
E. MIDGET IMPINGERS AND BUBBLERS.
1. Method.
a. Take care in preparing bubblers and impingers to see that frits or tips are
not damaged and that joints can be securely tightened.
b. Rinse the impinger or bubbler, Figure II:1-5, with the
appropriate reagent (see Chemical Sampling Information and
Appendix II:1-4). Then add the specified amount of this
reagent to the bubbler or impinger flask either in the office or
at the sampling location. If flasks containing the reagent are
transported, caps must be placed on the bubbler or impinger
stem and side arm.
c. To prevent overflow, do not add over 10 ml of liquid to
the midget impingers or bubblers.
d. Collect contaminants in an impinger or bubbler at a
maximum flow rate of 1.0 L/min. Because bubblers tend to
offer better collection efficiency than impingers, they are the
preferred method over impingers for gas and vapor
collection. Impingers are used, if absolutely necessary, for
particle counting. Contact the SLTC prior to collecting any
samples for particle (dust) counting.
e. The impinger or bubbler may either be hand-held by the
industrial hygienist or attached to the employee's clothing
using an impinger or bubbler holster. In either case, it is very
important that the impinger or bubbler does not tilt and
cause the reagent to flow down the side arm to the hose and
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into the pump. NOTE: Attach a trap in line to the pump, if
possible.
f. In some instances, it will be necessary to add additional reagent during
the sampling period to prevent the amount of reagent from dropping below
one half of the original amount.
g. After sampling, remove the glass stopper and stem from the impinger or
bubbler flask.
h. Rinse the absorbing solution adhering to the outside and inside of the
stem directly into the impinger or bubbler flask with a small amount (1-2 ml)
of the sampling reagent. Pour the contents of the flask into a 20-ml glass
bottle (preferably a scintillation vial with inert caps and liners). Avoid using
metal cap liners or other materials that may react with the samples. Teflon
cap liners with polypropylene caps are normally inert to most materials.
Rinse the flask with a small amount (1-2 ml) of the reagent and pour the
rinse solution into the bottle or vial. Tape the cap shut by wrapping the tape
in the direction of cap closure to prevent it from coming loose due to
vibration. If electrical tape is used, do not stretch tape since it will contract
and loosen cap.
2. Calibration.
a. Set up the calibration apparatus as shown in Figure II:1-8 and replace
the cassette with the impinger or bubbler filled with the amount of liquid
reagent specified in the sampling method. (Refer to Chemical Sampling
Information.)
b. Connect the tubing from the electronic bubble meter to the inlet of the
impinger or bubbler.
c. Connect the outlet of the impinger or bubbler to the tubing to the pump.
d. Calibrate the pump up to a maximum flow rate of 1.0 L/min.
F. VAPOR BADGES. Passive-diffusion sorbent badges (also
known as monitors), Figure II:1-6, are useful for
screening and compliance monitoring for certain chemical
exposures, especially vapors and gases. The major
advantage is that no sampling pump is needed to take
the samples. Some badges have been validated for use in
compliance. Badges are available from the SLTC to detect
mercury, nitrous oxide, ethylene oxide, formaldehyde,
and other organic substances. Specific sampling
procedures for each type of badge are also supplied with
the monitors. Interfering substances should be noted
during sampling and recorded. Contact the SLTC for
further information regarding badge availability and use.
FIGURE II:1-6.
VAPOR
BADGE WITH
CLOTHING CLIP.
IV. SPECIAL SAMPLING PROCEDURES
A. ASBESTOS.
1. Collect asbestos on a special 0.8
micrometer pore size, 25-mm
diameter mixed cellulose ester filter
with a back-up pad. Use a fully
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conductive cassette with conductive
extension cowl, Figure II:1-7.
2. Sample open face (the filter/cowl is open to the sampling environment; the
extension cowl is in place but the cowl end piece is removed from the
extension) in the worker's breathing zone.
3. Ensure that the bottom joint (between the extension and the conical black
piece) of the cassette is sealed tightly with a shrink band or electrical tape.
Point the open face of the cassette down to minimize contamination.
4. Use a flow rate in the range of 0.5 to 5 L/min. One liter per minute is
suggested for general sampling. Office environments allow flow rates of up
to 5 L/min. Calibrate pump before and after sampling. Calibration may be
done either as in Figure II:1-8 or Figure II:1-9. Do not use nylon or
stainless-steel adaptors if in-line (Figure II:1-8) calibration is done.
FIGURE II:1-8. FOR CALIBRATION, THE CASSETTE IS ATTACHED TO
AN ELECTRONIC BUBBLE METER.
FIGURE II:1-9. THE CYCLONE IS CALIBRATED BY PLACING THE
CYCLONE IN A 1 LITER VESSEL ATTACHED TO AN ELECTRONIC
BUBBLE METER.
5. Sample for as long a time as possible without overloading (obscuring) the
filter.
6. Instruct the employee to avoid knocking the cassette and to avoid using a
compressed-air source that might dislodge the sample while sampling.
7. Submit 10% blanks, with a minimum of two blanks in all cases.
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8. Where possible, collect and submit to the SLTC a bulk sample of the material
suspected to be in the air.
9. Mail bulk sample and air samples separately to avoid cross-contamination.
Pack the samples securely to avoid any rattle or shock damage (do not use
expanded polystyrene packing). Use bubble sheeting as packing. Put
identifying paperwork in every package. Do not send samples in plastic bags
or envelopes. Use OSHA Form 91A. Print legibly on all forms.
10. For exceptional sampling conditions or high flow rates, contact the SLTC.
More detailed instructions can be obtained from SLTC.
V. SAMPLING FOR WELDING FUMES.
A. When sampling for welding fumes, the filter cassette must be placed inside the
welding helmet to obtain an accurate measurement of the employee's exposure.
NOTE: The policy of placing the inlet of the sampling device inside of personal
protective equipment for the face or eyes applies only to welding hoods. The inlet
of the sampling device shall be placed outside other face or eye personal
protective equipment, such as face shields for projectiles or chemical splashes.
B. Welding fume samples are normally taken using 37-mm filters and cassettes;
however, if these cassettes will not fit inside the helmet, 25-mm filters and
cassettes can be used. Care must be taken not to overload the 25-mm cassette
when sampling.
C. The Assistant Regional Administrator for Technical Support should be consulted in
the case of technical difficulties.
VI. EQUIPMENT PREPARATION AND CALIBRATION.
A. ALKALINE BATTERIES. Replace alkaline batteries as needed. Keep fresh
replacement batteries with the equipment.
B. RECHARGEABLE NI-CAD BATTERIES. Check the rechargeable Ni-Cad batteries
in older pumps under load (e.g., turn pump on and check voltage at charging jack)
before use. (See Section II, Chapter 3, Part III. - Batteries)
C. TIME OF CALIBRATION. Calibrate personal sampling pumps before and after
each day of sampling, using either the electronic bubble-meter method or the
precision-rotameter method calibrated against a bubble meter. Make sure that the
calibration equipment (bubble meter, etc.) is within its prescribed calibration
interval and record the serial number of the calibration instrument in your data.
D. ELECTRONIC FLOW CALIBRATORS. These units are high-accuracy electronic
bubble flow meters that provide instantaneous air-flow readings and cumulative
averaging of multiple samples. These calibrators measure the flow rate of gases
and present the results as volume per unit of time and should be used to calibrate
all air-sampling pumps. Appendix II:1-1 provides more information on this piece of
equipment.
E. CALIBRATION. When a sampling train requires an unusual combination of
sampling media (e.g., glass fiber filter preceding impinger), the same media and
devices should be in line during calibration.
1. Electronic Bubble Meter Method.
a. Allow the pump to run five minutes prior to voltage check and calibration.
b. Assemble the cassette filter holder, using the appropriate filter for the
sampling method. Compress cassette by using a mechanical press or other
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means of applying pressure. Use shrink tape around cassette to cover joints
and prevent leakage. If a cassette adaptor is used, care should be taken to
ensure that it does not come in contact with the back-up pad. NOTE: When
calibrating with a bubble meter, cassette adaptors can cause moderate to
severe pressure drop at high flow rates in the sampling train and affect the
calibration result. If adaptors are used for sampling, they should also be
used when calibrating. CAUTION: Nylon adapters can restrict air flow due to
plugging. Stainless-steel adapters are preferred.
c. Connect the collection device, tubing, pump, and calibration apparatus as
shown in Figure II:1-8 for the cassette sampler and Figure II:1-9 for the
cyclone sampler.
d. Visually inspect all Tygon tubing connections.
e. Wet the inside of the electronic flow cell with the soap solution supplied
by pushing on the button several times.
f. Turn on the pump and adjust the pump rotameter, if available, to the
appropriate flow rate.
g. Press the button on the electronic bubble meter. Visually capture a single
bubble and electronically time the bubble. The accompanying printer will
automatically record the calibration reading in liters per minute.
h. Repeat the step until two readings are within 2%.
i. If necessary, adjust the pump while it is still running.
j. Repeat the procedures described above for all pumps to be used for
sampling. The same cassette and filter may be used for calibrations involving
the same sampling method.
2. Precision Rotameter Method.
The precision rotameter, Figure II:1-10, is a secondary
calibration device. If it is to be used in place of a
primary device such as a bubble meter, take care to
ensure that any error introduced will be minimal and
noted. NOTE: Using precision rotameters for pump
calibration should be avoided if possible. Tests have
indicated significant measurement errors due to pump
pulsations. These pulsations are typically not observable
by the user. a. Replacing the Bubble Meter. The
precision rotameter may be used for calibrating the
personal sampling pump in lieu of a bubble meter,
provided it is:
„ Calibrated regularly, at least monthly, with an
electronic bubble meter or a bubble meter, as
described in Appendix II:1-3.
„
Disassembled, cleaned as necessary, and
recalibrated. (It should be used with care to avoid
dirt and dust contamination, which may affect the
flow.)
„
Not used at substantially different temperature
and/or pressure from conditions present when the
rotameter was calibrated against the primary
source.
„
Used in such a way that the pressure drop across
it is minimized.
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b. Unusual Conditions. If altitude or temperature at
the sampling site are substantially different from those at the calibration
site, it is necessary to calibrate the precision rotameter at the sampling site.
3. Manual Buret Bubble Meter Method. See Appendix II:1-3.
VII. FILTER WEIGHING.
The SLTC is providing pre-weighed filters for gravimetric analysis. These filters should
reduce sample preparation time by CSHO's in the field because the filters are weighed at
SLTC and shipped to the field assembled and ready for use in inspections. The filters will
then be returned to SLTC for gravimetric and any other additional analyses.
A. THE FILTER MEDIA is 37-mm diameter, low-ash polyvinyl chloride. These filters
should be used for silica (quartz) analysis, aluminum, and any other appropriate
substance having a high PEL or requiring gravimetric analysis. The filters may be
used without the cyclone attached for total dust analyses. Please indicate on the
91A form all analytes of interest. If gravimetric analysis yields a result less than
the PEL for the requested substance(s), no further analysis will be provided unless
specifically requested. The filter/cassette unit, shown in Figure II:1-11a, is
expensive; please only use it for samples requiring crystalline silica
gravimetric analysis or other gravimetric analysis. AppendixII:1-7 is a partial
listing of suggested substances that can be sampled and gravimetrically analyzed
using the pre-weighed cassettes.
FIGURE II:1-11a. THE FILTER/CASSETTE UNIT
B. AVAILABILITY. These filters are shipped pre-weighed and assembled in the
cassettes. They are available directly from the SLTC or through the CTC
"Expendables Supplies" li in the "OSHA Property Management Inventory System
(OPMIS)." (Listed as "Cassette, Aerosol, 37MM, Preassembled, **Preweighed at
SLTC**, #FES0000161).
C. INSTRUCTIONS FOR CALIBRATION, SAMPLING AND SUBMISSION OF
SAMPLES. Be sure to follow all appropriate protocols for calibration, sampling and
submission of samples. A blank should be included with every set of samples. Due
to the slightly smaller size of the sampler, check frequently to prevent filter
overloading. This can be accomplished by viewing the inlet sampling port of the
cassette. Visual observation of the airborne dust concentration around the worker
may assist in determining how frequently to check the filter for overloading.
1. Two versions of the pre-weighed cassettes exist. New
cassettes have a stainless steel filter support (shown in
Figure II:1-11b), and older cassettes have a Tyvek®
backup pad. The stainless steel support seems to be
less affected by humidity (providing a more stable
blank weight) than the old pad. Both styles may even
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be used in a single inspection; however, it is very important
that the blanks submitted with a set of samples have the same backu
as the samples.
2. As shown in Figure II:1-11c, the inlet side
of the cassette is marked on the
polystyrene cassette. This is the side of the
filter cassette with the metallic antistatic
shield. The Tyvek® backup pad or the
stainless steel support is visible from the
outlet side of the assembly. Each of the
filter assemblies is bar coded for weighing
purposes. To aid in the tracking of the
filters, please use the barcode number
for the sample submission number
when filling out OSHA form 91A. For your convenience, the barcode numb
printed on a label attached to the outlet side of the cassette.
3. The filter/cassette assembly can be used with both nylon cyclone and holder
assemblies currently in field use; however, the standard MSA coupler (used w
standard 2- or 3-piece cassette) will not fit these cassettes. Another coupler a
from MSA (part #457391), which is plastic instead of stainless steel, can be o
from CTC.
FIGURE II:1-11d.
MSA CYCLONE HOLDER
WITH CASSETTE
FIGURE II:1-11e.
BENDIX HOLDER
WITH CASSETTE
4. If a compliance officer wishes to employ field balance weighing techniques ins
the SLTC weighing program, please consult a prior version of the Technical M
(Sampling Chapter, Section VI) or contact the SLTC for further instructions.
VII. BIBLIOGRAPHY.
American Industrial Hygiene Association (AIHA). 1987. Fundamentals of Analytical Procedures in
Industrial Hygiene. AIHA: Akron, OH.
Hesketh, H.E. 1986. Fine Particles in Gaseous Media. Lewis Publishers, Inc.: Chelsea, MA.
Lioy, P.J. 1989. Air Sampling Instruments for Evaluation of Atmospheric Contaminants. America
Conference of Governmental Industrial Hygienists: Cincinnati.
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Lodge, J.P., Jr. (Ed.) 1988. Methods of Air Sampling and Analysis. Lewis Publishers, Inc.:
Chelsea, MA.
National Institute for Occupational Safety and Health (NIOSH). 1977. Occupational Exposure
Sampling Strategy Manual. DHEW (NIOSH) Publication No. 77-173. U. S. Government Printing
Office, Washington, D.C.
Occupational Safety and Health Administration, U.S. Dept. of Labor. 1995. OSHA Computerized
Information System (OCIS) Chemical Sampling Information. U.S. Government Printing Office:
Washington, D.C.
APPENDIX II:1-1. DETECTOR TUBES AND PUMPS
PRINCIPLE AND DESCRIPTION.
Detector tube pumps are portable equipment which, when used with a variety of commercially
available detector tubes, are capable of measuring the concentrations of a wide variety of
compounds in industrial atmospheres.
Operation consists of using the pump to draw a known volume of air through a detector tube
designed to measure the concentration of the substance of interest. The concentration is
determined by a colorimetric change of an indicator which is present in the tube contents. Most
detector tubes can be obtained locally.
APPLICATIONS AND LIMITATIONS.
Detector tubes and pumps are screening instruments which may be used to measure more
than 200 organic and inorganic gases and vapors or for leak detection. Some aerosols can also
be measured.
Detector tubes of a given brand are to be used only with a pump of the same brand. The tubes
are calibrated specifically for the same brand of pump and may give erroneous results if used
with a pump of another brand.
A limitation of many detector tubes is the lack of specificity. Many indicators are not highly
selective and can cross-react with other compounds. Manufacturers' manuals describe the
effects of interfering contaminants.
Another important consideration is sampling time. Detector tubes give only an instantaneous
interpretation of environmental hazards. This may be beneficial in potentially dangerous
situations or when ceiling exposure determinations are sufficient. When long-term assessment
of occupational environments is necessary, short-term detector-tube measurements may not
reflect time-weighted average levels of the hazardous substances present.
Detector tubes normally have a shelf life at 25 °C of one to two years. Refrigeration during
storage lengthens the shelf life. Outdated detector tubes (i.e., beyond the printed expiration
date) should never be used. The OSHA Training Institute can sometimes use these outdated
tubes for training purposes.
Several different types and brands of detector tubes have been evaluated for screening and
compliance use by SLTC. Information regarding these evaluations can be obtained by
contacting SLTC.
PERFORMANCE DATA.
Specific manufacturers' models of detector tubes are listed in the Chemical Sampling
Information. The specific tubes listed are designed to cover a concentration range that is near
the PEL. Concentration ranges are tube-dependent and can be anywhere from one-hundredth
to several thousand ppm. The limits of detection depend on the particular detector tube.
Accuracy ranges vary with each detector tube.
The pump may be hand-held during operation (weight: 8-11 ounces), or it may be an
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automatic type (weight: about 4 pounds) that collects a sample using a preset number of pump
strokes. A full pump stroke for either type of short-term pump has a volume of about 100 ml.
In most cases where only one pump stroke is required, sampling time is about one to two
minutes. Determinations for which more pump strokes are required take proportionately
longer.
Contact the CTC for information regarding long-term maintenance.
LEAKAGE TEST.
Each day prior to use, perform a pump leakage test by inserting an unopened detector tube
into the pump and attempt to draw in 100 ml of air. After a few minutes, check for pump
leakage by examining pump compression for bellows-type pumps or return to resting position
for piston-type pumps. Automatic pumps should be tested according to the manufacturer's
instructions.
In the event of leakage that cannot be repaired in the field, send the pump to the CTC for
repair. Record that the leakage test was made on the Direct-Reading Data Form (OSHA-93).
CALIBRATION TEST.
Calibrate the detector tube pump for proper volume measurement at least quarterly. Simply
connect the pump directly to the bubble meter with a detector tube in-line. Use a detector tube
and pump from the same manufacturer.
Wet the inside of the 100 ml bubble meter with soap solution. For volume calibration,
experiment to get the soap bubble even with the zero (0) ml mark of the buret.
For piston-type pumps, pull the pump handle all the way out (full pump stroke) and note where
the soap bubble stops; for bellows-type pumps, compress the bellows fully; for automatic
pumps, program the pump to take a full pump stroke. For either type pump, the bubble should
stop between the 95 ml and 105 ml marks. Allow 4 minutes for the pump to draw the full
amount of air (This time interval varies with the type of detector tube being used in-line with
the calibration setup).
Also check the volume for 50 ml (one-half pump stroke) and 25 ml (one-quarter pump stroke)
if pertinent. As in Section 1 above, ± 5% error is permissible. If the error is greater than ±
5%, send the pump to CTC for repair and recalibration. Record the calibration information
required on the Calibration Log (OSHA-93).
It may be necessary to clean or replace the rubber bung or tube holder if a large number of
tubes have been taken with any pump.
ADDITIONAL INFORMATION.
DRAEGER, MODEL 31 (BELLOWS). When checking the pump for leaks with an unopened tube,
the bellows should not be completely expanded after 10 minutes. For the DRAEGER ACCURO
PUMP (BELLOWS), a 15-minute period is used and the end-of-stroke indicator should not be
noticeable after this period.
DRAEGER, QUANTIMETER 1000, MODEL 1 (AUTOMATIC). A battery pack is an integral part of
this pump. The pack must be charged prior to initial use. One charge is good for 1000 pump
strokes. During heavy use, it should be recharged daily. If a "U" (undervoltage) message is
continuously displayed in the readout window of this pump, the battery pack should be
immediately recharged. A leak test is performed by turning the system on, setting the pump
stroke indicator to "2" or greater, inserting an unopened tube into the holder and pressing the
start/stop key. When the second stroke has not started after 30 minutes, the device is
considered sufficiently gas-tight.
MATHESON-KITAGAWA, MODEL 8014-400A (PISTON). When checking the pump for leaks with
an unopened tube, the pump handle should be pulled back to the 100-ml mark and locked.
After 2 minutes, the handle should be released carefully. It should return to zero or resting
position. After taking 100-200 samples, the pump should be cleaned and relubricated. This
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involves removing the piston from the cylinder, removing the inlet and pressure-relief valve
from the front end of the pump, cleaning, and relubricating.
MINE SAFETY APPLIANCES, SAMPLAIR PUMP, MODEL A, PART NO. 46399 (PISTON). The pump
contains a flow-rate control orifice protected by a plastic filter which periodically needs to be
cleaned or replaced. To check the flow rate, the pump is connected to a buret and the piston is
withdrawn to the 100-ml position with no tube in the tube holder. After 24-26 seconds, 80 ml
of air should be admitted to the pump. Every 6 months the piston should be relubricated with
the oil provided.
MINE SAFETY APPLIANCES KWIK DRAW™ SAMPLING PUMP, PART NO. 487500 (BELLOWS). The
pump contains a filter disk that needs periodic cleaning or replacement. The bellows shaft can
be cleaned and lubricated with automotive wax if operation becomes jerky. This pump is tested
for leakage by inserting an unopened tube into the holder, deflating the pump fully and
releasing. After 10 minutes the distance of the bellows to the frame is ½ inch or greater.
NEXTTEQ, LLC (GASTEC MODEL GV-100 PISTON SAMPLING PUMP). When checking the pump
for leaks, first confirm that the inlet clamping nut is firmly tightened. Next, push the pump
handle fully in and align the guide marks on the pump shaft and handle. Then insert a fresh
unbroken tube into the rubber inlet of the pump. Pull out the handle fully until it is locked, and
wait 1 minute. Unlock the handle (by turning it more than 1/4 turn) and guide it back gradually
applying a little force. Otherwise, the handle will spring back due to the vacuum in the cylinder
and may damage the internal parts. Confirm the handle returns to the initial position and the
guideline on the pump shaft is not seen. If this is not confirmed, follow the maintenance
procedures explained in the operations manual for the Model GV-100 pump, or contact your
Nextteq representative for maintenance assistance. The maintenance procedures involve leak
checks on the inlet clamping nut and rubber inlet, and performing pump cylinder lubrication.
Nextteq is Gastec's exclusive U.S. master wholesale distributor. The Gastec Corporation
manufactures Gastec tubes and pumps.
SPECIAL CONSIDERATIONS.
Detector tubes should be refrigerated when not in use to prolong shelf life. Detector tubes
should not be used when cold. They should be kept at room temperature or in a shirt pocket
for one hour prior to use. Lubrication of the piston pump may be required if volume error is
greater than 5%.
APPENDIX II:1-2. ELECTRONIC FLOW CALIBRATORS
DESCRIPTION.
These units are high-accuracy electronic bubble flow meters that provide instantaneous airflow
readings and a cumulative averaging of multiple samples. These calibrators measure the flow
rate of gases and report volume per unit of time.
The timer is capable of detecting a soap film at 80-microsecond intervals. This speed allows
under steady flow conditions an accuracy of ± 0.5% of any display reading. Repeatability is ±
0.5% of any display.
The range with different cells is from 1 ml/min to 30 L/min. Battery power will last 8 hours with
continuous use. Charge for 16 hours. Can be operated from A/C charger.
MAINTENANCE OF CALIBRATOR.
1. Cleaning Before Use. Remove the flow cell and gently flush with tap water. The acrylic flow
cell can be easily scratched. Wipe with cloth only. Do not allow center tube, where sensors
detect soap film to be scratched or get dirty. Never clean with acetone, alcohol or other
cleaning solutions. Use only soap and warm water. When cleaning prior to storage, allow flow
cell to air dry. If stubborn residue persists, it is possible to remove the bottom plate. Squirt a
few drops of soap into the slot between base and flow cell to ease removal.
2. Leak Testing. The system should be leak checked at 6" H2O by connecting a manometer to
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the outlet boss and evacuating the inlet to 6" H2O. No leakage should be observed.
3. Verification of Calibration. The calibrator is factory calibrated using a standard traceable
to National Institute of Standards and Technology, formerly called the National Bureau of
Standards, (NBS). Attempts to verify calibrator against a glass one-liter burette should be
conducted at 1000 ml/min for maximum accuracy. The calibrator is linear throughout the entire
range.
SHIPPING AND HANDLING.
When transporting, especially by air, it is important that one side of the seal tube which
connects the inlet and outlet boss, be removed for equalizing internal pressure within the
calibrator. Do not transport unit with soap solution or storage tubing in place.
PRECAUTIONS AND WARNINGS.
1. Avoid the use of chemical solvents on flow cell, calibrator case and faceplate. Generally,
soap and water will remove any dirt.
2. Never pressurize the flow cell at any time with more than 25 inches of water pressure.
3. Do not charge batteries for longer than 16 hours.
4. Do not leave A/C adapter plugged into calibrator when not in use, as this could damage the
battery supply.
5. Black close fitting covers help to reduce evaporation of soap in the flow cell when not is use.
6. Do not store flow cell for a period of one week or longer with soap. Clean and store dry.
7. The Calibrator Soap is a precisely concentrated and sterilized solution formulated to provide
a clean, frictionless soap film bubble over the wide, dynamic range of the calibrator. The sterile
nature of the soap is important in the prevention of residue build-up in the flow cell center
tube, which could cause inaccurate readings. The use of any other soap is not recommended.
Proper soap solution is available from CTC's expendable supplies program (AESP).
APPENDIX II:1-3. MANUAL BURET BUBBLE METER TECHNIQUE
When a sampling train requires an unusual combination of sampling media (e.g., glass fiber
filter preceding impinger), the same media/devices should be in line during calibration.
Calibrate personal sampling pumps before and after each day of sampling.
BUBBLE METER METHOD
1. Allow the pump to run 5 minutes prior to voltage check and calibration.
2. Assemble the cassette filter holder using the appropriate filter for the sampling method. If a
cassette adaptor is used, care should be taken to ensure that it does not come in contact with
the back-up pad.
NOTE: When calibrating with a bubble meter, the use of cassette adaptors can cause moderate
to severe pressure drop in the sampling train, which will affect the calibration result. If
adaptors are used for sampling, then they should be used when calibrating.
3. Connect the collection device, tubing, pump and calibration apparatus as shown in Figures
II:1-12 and II:1-13.
FIGURE II:1-12. CALIBRATION SET-UP FOR PERSONAL SAMPLING WITH
FILTER CASSETTE.
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FIGURE II:1-13 CALIBRATION OF CYCLONE RESPIRABLE DUST SAMPLER USING
A BUBBLER METER.
4. A visual inspection should be made of all Tygon tubing connections.
5. Wet the inside of a 1-liter buret with a soap solution.
6. Turn on the pump and adjust the pump rotameter to the appropriate flow rate setting.
7. Momentarily submerge the opening of the buret in order to capture a film of soap.
8. Draw two or three bubbles up the buret in order to ensure that at least one bubble will
complete its run.
9. Visually capture a single bubble and time the bubble from 0 to 1000 ml for high flow pumps
or 0 to 100 ml for low flow pumps.
10. The timing accuracy must be within ±1 second of the time corresponding to the desired
flow rate. If the time is not within the range of accuracy, adjust the flow rate and repeat steps
9 and 10 until the correct flow rate is achieved. Perform steps 9 and 10 at least twice.
11. While the pump is still running, mark the pump or record on the OSHA-91 the position of
the center of the float in the pump rotameter as a reference.
12. Repeat the procedures described above for all pumps to be used for sampling. The same
cassette and filter may be used for all calibrations involving the same sampling method.
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APPENDIX II:1-4. SHELF LIFE OF SAMPLING MEDIA PROVIDED BY SLTC
Sampling medium
Shelf life
Comments
Sodium hydroxide (all normalities)
6 months
Hydrochloric acid
Sulfuric acid
Methanol in water
1 year
Same for all concentrations of
all solutions.
Solution for bis-chloromethyl ether
(BCME) and chloromethyl methyl
ether (CMME)
2 months
Prepared on request*
Hydroxylammonium chloride solutions
(for ketene collection)
2 weeks
Prepared on request*
Hydroxylammonium chloride-sodium
hydroxide mixed solutions (for ketene
collection)
Stable only
2 hours
Must be prepared fresh just
prior to use.
Folin's reagent
5 days
Prepared on request*
Passive monitors
Must be used before the
expiration date (if given) printed
on the monitor package.
Nitrogen oxides collection tubes
Should be stored in a
refrigerator.
Sampler for ozone
(Nitrite-treated filter collection device)
28 days
Prepared on request*
Coated filter sampler for di-isocyanates
(MDI, HDI, TDI, etc.)
1 year
Prepared on request*
Treated filter sampler for collection of
anhydrides
30 days
Prepared on request*
* Please notify SLTC of need two days in advance to allow for preparation time.
APPENDIX II:1-5. SAMPLING FOR SPECIAL ANALYSES
CRYSTALLINE SILICA SAMPLES ANALYZED BY X-RAY DIFFRACTION (XRD).
Air Samples.
Respirable dust samples for quartz, cristobalite, and tridymite are analyzed by X-ray diffraction
(XRD). XRD is the preferred analytical method due to its sensitivity, minimum requirements for
sample preparation and ability to identify polymorphs (different crystalline forms) of free silica.
The analysis of crystalline free silica by XRD requires that the particle size distribution of the
samples be matched as closely as possible to the standards. This is best accomplished by
collecting a respirable sample.
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Respirable dust samples are collected on a tared low ash PVC filter using a 10-mm nylon
cyclone at a flow rate of 1.5 to 2.0 L/min. A sample not collected in this manner is considered a
total dust (or nonrespirable) sample. Because of the difficulty in matching sample particle size
with analytical standards, CSHO's are discouraged from submitting total dust samples. If the
sample collected is nonrespirable, the laboratory must be advised on the OSHA-91 form.
Samples are analyzed for cristobalite or tridymite only upon request.
Quartz (also cristobalite and tridymite) is initially identified by its major (primary) X-ray
diffraction peak. A few substances also have peaks near the same location, and it is necessary
to confirm quartz (also cristobalite or tridymite) using secondary and/or tertiary peaks. To
assist the analyst in identifying interference, the CSHO should provide information concerning
potential presence of other substances in the workplace. The following substances should be
noted:
„
„
„
„
„
„
„
„
„
„
„
„
Aluminum phosphate
Feldspars (microcline, orthoclase, plagioclase)
Graphite
Iron carbide
Lead sulfate
Micas (biotite, muscovite)
Montmorillonite
Potash
Sillimanite
Silver chloride
Talc
Zircon (Zirconium silicate).
Total air volume shall accompany all filter samples. If a field balance is used to provide
pre- and post weights instead of SLTC- or CTC-supplied pre-weighed filters, sample weights
shall also accompany the filter samples. Sample weights of 0.5 mg to 3.0 mg are preferred. For
those samples that are still weighed in the field, do not submit a sample(s) unless its weight or
the combined weights of all particulate filters representing an individual exposure exceed 0.04
mg. If heavy sample loading is noted during the sampling period, it is recommended that the
filter cassette be changed to avoid collecting a sample with a weight greater than 5.0 mg.
Laboratory results for air samples are usually reported under one of four categories:
„
Percent Quartz (or Cristobalite). Applicable for a respirable sample in which the
amount of quartz (or cristobalite) in the sample was confirmed.
„
Less Than or Equal to Value in Units of Percent. Less than or equal to values are
used when the adjusted 8-hour exposure is found to be less than the PEL, based on the
sample's primary diffraction peak. The value reported represents the maximum amount
of quartz (or cristobalite) that could be present. However, the presence of quartz (or
cristobalite) was not confirmed using secondary and/or tertiary peaks in the sample since
the sample could not be in violation of the PEL.
„
Approximate Values in Units of Percent. The particle size distribution in a total dust
sample is unknown and error in the XRD analysis may be greater than for respirable
samples. Therefore, for total dust samples, an approximate result is given.
„
Nondetected. A sample reported as nondetected indicates that the quantity of quartz
(or cristobalite) present in the sample is not greater than the detection limit of the
instrument. The detection limit is usually 10 µg for quartz and 30 µg for cristobalite. If
less than a full-shift sample was collected, the CSHO should evaluate a nondetected
result to determine whether adequate sampling was performed. If the presence of quartz
(or cristobalite) is suspected in this case, the Industrial Hygienist may want to sample for
a longer period of time to increase the sample weights.
Bulk Samples.
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Bulk samples should be submitted for all silica analyses, if possible. They have the following
purposes:
„
To confirm the presence of quartz or cristobalite in respirable samples, or to assess the
presence of other substances that may interfere in the analysis of respirable samples.
„
To determine the approximate percentage of quartz (or cristobalite) in the bulk sample.
„
To support Hazard Communication inspections.
A bulk sample must be representative of the airborne free silica content of the work
environment sampled; otherwise, it will be of no value.
The laboratory's order of preference for bulk samples for an evaluation of personal exposure is:
„
A representative settled-dust (rafter) sample.
„
A bulk sample of the raw material used in the manufacturing process (most practical if
used for Hazard Communication inspections).
The type of bulk sample submitted to the laboratory should be stated on the OSHA-91 form
and cross-referenced to the appropriate air samples.
Normally, any reported results for bulk sample analysis for quartz (also cristobalite or
tridymite) will be approximate because of the difficulty in matrix and particle size matching of
the bulk material with the analytical standards used during analysis.
SAMPLE CALCULATIONS FOR CRYSTALLINE SILICA EXPOSURES.
Where the employee is exposed to combinations of silica dust (i.e., quartz, cristobalite, and
tridymite), the additive effects of the mixture will be considered.
For the PEL calculation specified in 29 CFR 1910.1000, Table Z-3, the percent silica will be
determined by doubling the percentage of cristobalite and/or tridymite and adding it to the
percentage of quartz, according to the following formula. The PEL mixture pertains to the
respirable fraction. (Refer to Figure II:1-14.)
Two consecutive samples from the same employee taken for a combined exposure to silica
dusts have the following results, shown below in Figure II:1-14, Sample Calculation for Silica
Exposure.
FIGURE II:1-14. SAMPLE CALCULATION FOR SILICA EXPOSURE
Sample
Sampling
period
(min)
Total
volume
(L)
Respirable
weight
(mg)
Respirable
concentration
(mg/m3)
Laboratory
results
(%)
A
238
405
0.855
2.1
5.2 quartz
2.3 cristobalite
ND tridymite
B
192
326
0.619
1.9
4.8 quartz
1.7 cristobalite
ND tridymite
Total
430
731
1.474
Key: ND = Not detectable.
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Calculation of the TWA from the sampling and analytical data:
Step 1. Calculate the percentage of quartz, cristobalite, and tridymite in the respirable
particulate collected.
Quartz:
5.2 (0.855/1.474) + 4.8 (0.619/1.474) = 3.0 + 2.0 = 5.0%
Cristobalite:
2.3 (0.855/1.474) + 1.7 (0.619/1.474) = 1.3 + 0.7 = 2.0%
Step 2. Calculate the PEL for the mixture.
PELmixture
= 10/[5.0 + 2(2.0) + 2(0) +2] = 10/11.0 = 0.91 mg/m3
Step 3. Calculate the employee's exposure.
Exposure = (Sample wt. A + Sample wt. B)/Total volume = (0.855 + 0.619)/0.731 = 2.0
mg/m3
Step 4. Adjust (where necessary) for less than 8-hour sampling period.
TWA = (2.0 mg/m3)[(430 min)/(480 min)] = 1.8mg/m3 Step 5. Calculate the severity of
the exposure.
(1.8 mg/m3)/(0.91 mg/m3) = 2.0
SAMPLES ANALYZED BY INDUCTIVELY COUPLED PLASMA (ICP)
Metals.
Where two or more of the following analytes are requested on the same filter, an ICP analysis
may be conducted. However, the compliance officer should specify the metals of interest in the
event samples cannot be analyzed by the ICP method. A computer printout of the following 13
analytes may be reported:
„
„
„
„
„
„
„
„
„
„
„
„
„
Antimony
Beryllium
Cadmium*
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Molybdenum
Nickel
Vanadium
Zinc
* Cadmium can be analyzed if air volumes are greater than 200 liters.
If requested, the laboratory can analyze for "solder-type" elements, such as:
„
„
„
„
„
Antimony
Beryllium
Cadmium
Copper
Lead
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„
„
„
Page 24 of 32
Silver
Tin
Zinc
Samples taken during abrasive blasting operations are no longer analyzed by ICP because of
difficulties with heavy loadings. These samples can be analyzed by atomic absorption
spectrometry (AAS) for specific metals (i.e, Pb, Cd, Cr, Fe).
SAMPLES ANALYZED BY X-RAY FLUORESCENCE (XRF).
Filter, wipe, and bulk samples can be qualitatively analyzed by XRF. Requests for XRF analyses
should be preceded by a phone call to SLTC to determine the extent and value of the analysis.
Packaging and shipping of such samples should be done in a manner consistent with directions
previously given in this chapter.
APPENDIX II:1-6. SAMPLING AND ANALYTICAL ERRORS (SAE's)
DEFINITION OF SAE's.
When an employee is sampled and the results analyzed, the measured exposure will rarely be
the same as the true exposure. This variation is due to sampling and analytical errors, or
SAE's. The total error depends on the combined effects of the contributing errors inherent in
sampling, analysis, and pump flow.
Definition of Confidence Limits.
Error factors determined by statistical methods shall be incorporated into the sample results to
obtain the lowest value that the true exposure could be (with a given degree of confidence) and
also the highest value the true exposure could be (also with some degree of confidence).
The lower value is called the lower confidence limit (LCL), and the upper value is the upper
confidence limit (UCL). These confidence limits are termed one-sided since the only concern is
with being confident that the true exposure is on one side of the PEL.
DETERMINING SAE's.
SAE's that provide a 95% confidence limit have been developed and are listed on each
OSHA-91B report form (most current SAE's). If there is no SAE listed in the OSHA-91B for a
specific substance, call the SLTC. If using detector tubes or direct-reading instruments, use the
SAE's provided by the manufacturer.
ENVIRONMENTAL VARIABLES.
Environmental variables generally far exceed sampling and analytical errors. Samples taken on
a given day are used by OSHA to determine compliance with PEL's. However, where the
employer has previously monitored the work area, the CSHO should review the long-term
pattern and compare it with the results. When OSHA's samples fit the long-term pattern, it
helps to support the compliance determination. When OSHA's results differ substantially from
the historical pattern, the CSHO should investigate the cause of this difference and perhaps
conduct additional sampling.
CONFIDENCE LIMITS.
One-sided confidence limits can be used to classify the measured exposure into one of three
categories:
1. If the measured results do not exceed the standard and the UCL also does not exceed the
standard, we can be 95% confident that the employer is in compliance. (See Equation II:1-6E.)
2. If the measured exposure exceeds the PEL and the LCL of that exposure also exceeds the
PEL, we can be 95% confident that the employer is in noncompliance, and a violation is
established. (See Equation II:1-6F.)
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Page 25 of 32
3. If the measured exposure does not exceed the PEL, but the UCL of that exposure does
exceed the PEL, we cannot be 95% confident that the employer is in compliance. (See Equation
II:1-6E.) Likewise, if the measured exposure exceeds the PEL, but the LCL of that exposure is
below the PEL, we cannot be 95% confident that the employer is in noncompliance. (See
Equation II:1-6F.) In both of these cases, the measured exposure can be termed a "possible
overexposure."
A violation is not established if the measured exposure is in the "possible overexposure" region.
It should be noted that the closer the LCL comes to exceeding the PEL, the more probable it
becomes that the employer is in noncompliance.
If measured results are in this region, the CSHO should consider further sampling, taking into
consideration the seriousness of the hazard, pending citations, and how close the LCL is to
exceeding the PEL.
If further sampling is not conducted, or if additional measured exposures still fall into the
"possible overexposure" region, the CSHO should carefully explain to the employer and
employee representative in the closing conference that the exposed employee(s) may be
overexposed but that there was insufficient data to document noncompliance. The employer
should be encouraged to voluntarily reduce the exposure and/or to conduct further sampling to
assure that exposures are not in excess of the standard.
SAMPLING METHODS.
The LCL and UCL are calculated differently depending upon the type of sampling method used.
Sampling methods can be classified into one of three categories:
1. Full-period, Continuous Single Sampling. Full-period, continuous single sampling is
defined as sampling over the entire sample period with only one sample. The sampling may be
for a full-shift sample or for a short period ceiling determination.
2. Full-period, Consecutive Sampling. Full-period, consecutive sampling is defined as
sampling using multiple consecutive samples of equal or unequal time duration which, if
combined, equal the total duration of the sample period. An example would be taking four
2-hour charcoal tube samples. There are several advantages to this type of sampling:
„
If a single sample is lost during the sampling period due to pump failure, gross
contamination, etc., at least some data will have been collected to evaluate the
exposure.
„
The use of multiple samples will result in slightly lower sampling and analytical errors.
„
Collection of several samples allows conclusions to be reached concerning the manner in
which differing segments of the work day affect overall exposure.
3. Grab Sampling. Grab sampling is defined as collecting a number of short-term samples at
various times during the sample period which, when combined, provide an estimate of
exposure over the total period. Common examples include the use of detector tubes or
direct-reading instrumentation (with intermittent readings).
CALCULATIONS.
If the initial and final calibration flow rates are different, a volume calculated using the highest
flow rate should be reported to the laboratory. If compliance is not established using the lowest
flow rate, further sampling should be considered.
Generally, sampling is conducted at approximately the same temperature and pressure as
calibration, in which case no correction for temperature and pressure is required and the
sample volume reported to the laboratory is the volume actually measured. Where sampling is
conducted at a substantially different temperature or pressure than calibration, an adjustment
to the measured air volume may be required depending on sampling pump used, in order to
obtain the actual air volume sampled. The actual volume of air sampled at the sampling site is
reported, and used in all calculations.
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OSHA TECHNICAL MANUAL - SECTION II: CHAPTER 1
Page 26 of 32
For particulates, the laboratory reports mg/m3 of contaminant using the actual volume of air
collected at the sampling site. The value in mg/m3 can be compared directly to OSHA Toxic and
Hazardous Substances Standards (e.g., 29 CFR 1910.1000).
The SLTC normally does not measure concentrations of gases and vapors directly in parts per
million (ppm). Rather, most analytical techniques determine the total weight of contaminant in
collection medium. Using the air volume provided by the CSHO, the lab calculates
concentration in mg/m3 and converts this to ppm at 25°C and 760 mm Hg using Equation
II:1-6A. This result is to be compared with the PEL without adjustment for temperature and
pressure at the sampling site.
Equation II:1-6A
ppm(NTP)=mg/m3(24.45)/Mwt
Where: 24.45 = molar volume at 25°C
(298°K) and 760 mm Hg
Mwt = molecular weight
NTP = Normal Temperature and Pressure,
25°C and 760 mm Hg.
If it is necessary to know the actual concentration in ppm at the sampling site, it can be
derived from the laboratory results reported in ppm at NTP by using the following equation:
Equation II:1-6B
ppm(PT)=ppm(NTP)[(760)/(P)][(T)/(298)]
where:
P = sampling site pressure (mm of Hg)
T = sampling site temperature (°K)
298 = temperature in degrees Kelvin (273°K + 25°)
Equation II:1-6C
Since ppm(NTP)=mg/m3(24.45)/(Mwt)
ppm(PT)=(mg/m3)(24.45/Mwt)(760/P)(T/298)
NOTE: When a laboratory result is reported as mg/m3 contaminant, concentrations expressed
as ppm (PT) cannot be compared directly to the standards table without converting to NTP.
NOTE: Barometric pressure can be obtained by calling the local weather station or airport,
request the unadjusted barometric pressure. If these sources are not available, then a rule of
thumb is: for every 1,000 feet of elevation, the barometric pressure decreases by 1 in. Hg.
CALCULATION METHOD FOR A FULL-PERIOD, CONTINUOUS SINGLE SAMPLE.
Obtain the full-period sampling result (value X), the PEL and the SAE. The SAE can be obtained
from the OSHA 91B or by contacting SLTC.
Divide X by the PEL to determine Y, the exposure severity. That is:
Equation II:1-6D
Y = X/PEL
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Compute the UCL95% as follows:
Equation II:1-6E
UCL95%=Y+SAE
Compute the LCL95% as follows:
Equation II:1-6F
LCL95%=Y-SAE
Classify the exposure according to the following classification system:
„
If the UCL < 1, a violation does not exist.
„
If LCL < 1 and the UCL > 1, classify as possible overexposure.
„
If LCL > 1, a violation exists.
SAMPLE CALCULATION FOR FULL-PERIOD, CONTINUOUS SINGLE SAMPLE.
A single fiberglass filter and personal pump were used to sample for carbaryl for a 7-hour
period. The CSHO was able to document that the exposure during the remaining unsampled
one-half hour of the 8-hour shift would equal the exposure measured during the 7-hour period.
The laboratory reported 6.07 mg/m3. The SAE for this method is 0.23. The PEL is 5.0 mg/m3.
Step 1. Calculate the exposure severity.
Y = 6.07/5.0 = 1.21
Step 2. Calculate confidence limits.
LCL = 1.21 - 0.23 = 0.98
Since the LCL does not exceed 1.0, noncompliance is not established. The UCL is
calculated:
UCL = 1.21 + 0.23 = 1.44
Step 3. Classify the exposure.
Since the LCL < 1.0 and the UCL > 1.0, classify as possible overexposure.
CALCULATION METHOD FOR FULL-PERIOD CONSECUTIVE SAMPLING.
Equation II:1-6G
The use of multiple consecutive samples will
result in slightly lower sampling and analytical
• Obtain X1, X2 ... Xn, the n consecutive
errors than the use of one continuous sample
since the inherent errors tend to partially cancel
concentrations n one workshift and
each other. The mathematical calculations,
their time durations, T1, T2 ... Tn.
however, are somewhat more complicated. If
preferred, the CSHO may first determine if
• Also obtain the SAE in listed in the
compliance or noncompliance can be established
OSHA-91B sample report form.
using the calculation method noted for a
full-period, continuous, single-sample
measurement. If results fall into the "possible overexposure" region using this method, a more
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OSHA TECHNICAL MANUAL - SECTION II: CHAPTER 1
exact calculation should be performed using
equation II:1-6G below.
• Compute the TWA exposure.
Classify the exposure according to the following
classification system:
• Divide the TWA exposure by the PEL to
find Y, the standardized average
(TWA/PEL).
„
If UCL < 1, a violation does not exist.
„
If LCL < 1, and the UCL > 1, classify as
possible overexposure.
„
If LCL > 1, a violation exists.
Page 28 of 32
• Compute the UCL95% as follows:
UCL95% = Y + SAE (Equation II:1-6E)
• Compute the LCL95% as follows:
LCL95% = Y - SAE (Equation II:1-6F)
When the LCL < 1.0 and UCL > 1.0, the results
are in the "possible overexposure" region and the CSHO must analyze the data using the more
exact calculation for full-period consecutive sampling, as follows:
Equation II:1-6H
SAMPLE CALCULATION FOR FULL-PERIOD CONSECUTIVE SAMPLING.
If two consecutive samples had been taken for carbaryl instead of one continuous sample, and
the following results were obtained:
-- Samples -A
B
Sampling rate (L/min)
2.0
2.0
Time (min)
240
210
Volume (L)
480
420
3.005
2.457
6.26
5.85
Weight (mg)
3
Concentration (mg/m )
The SAE for carbaryl is 0.23
Step 1. Calculate the UCL and the LCL from the sampling and analytical results:
TWA = [(6.26 mg/m3) 240 min + (5.85 mg/m3) 210 min]/450 min =
6.07 mg/m3
Y = 6.07 mg/m3/PEL = 6.07/5.0 = 1.21
Assuming a continuous sample: LCL = 1.21 - 0.23 = 0.98
UCL = 1.21 + 0.23 = 1.44
Step 2. Since the LCL < 1.0 and UCL > 1.0, the results are in the possible
overexposure region, and the CSHO must analyze the data using the more exact
calculation for full-period consecutive sampling as follows:
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OSHA TECHNICAL MANUAL - SECTION II: CHAPTER 1
Page 29 of 32
= 1.21 - 0.20 = 1.01
Since the LCL > 1.0, a violation is established.
GRAB SAMPLING.
If a series of grab samples (e.g., detector tubes) is used to determine compliance with either
an 8-hour TWA limit or a ceiling limit, consult with the ARA for Technical Support regarding
sampling strategy and the necessary statistical treatment of the results obtained.
SAE's FOR EXPOSURE TO CHEMICAL MIXTURES.
Often an employee is simultaneously exposed to a variety of chemical substances in the
workplace. Additive toxic effects on a target organ is common for such exposures in many
construction and manufacturing processes. This type of exposure can also occur when
impurities are present in single chemical operations. Permissible exposure limits [or Threshold
Limit Values (TLV's) such as the welding fume TLV of 5 mg/m3] for mixtures address the
complex problem of additive exposures and their health effects. In addition, 29 CFR 1910.1000
contains a computational approach to assess exposure to a mixture. This calculation should be
used when components in the mixture pose an additive threat to worker health. While these
calculations can be used for synergistic exposures, a separate consideration must be
performed. For synergistic mixtures, an individualized assessment of toxicity using the most
current scientific data is conducted to consider the total physiologic burden. [See the OSHA
Field Inspection Reference Manual (FIRM) for further details.] The SAE can still be calculated
for synergistic mixtures; however, Equation II:1-6I is adjusted to reflect any synergistic
effects.
Whether using a single standard or the mixture calculation, the sampling and analytical error
(SAE) of the individual constituents must be considered before arriving at a final compliance
decision. These SAE's can be pooled and weighted to give a control limit for the additive
mixture. To illustrate this control limit, the following example using the mixture calculation is
expressed in the following equation.
Equation II:1-6I
Em=C1/L 1+C2/L2+...+C n/Ln
Where:
Em = equivalent exposure for a mixture
(Em should be < 1 for compliance)
C = concentration of a particular substance
L = PEL
For example, to calculate exposure to three different but additive substances:
Material
8-hr. exposure
8-hr TWA PEL (ppm)
SAE
Substance 1
500
1000
0.089
Substance 2
80
200
0.11
Substance 3
70
200
0.18
Using Equation II:1-6I: Em = 500/1000 + 80/200 + 70/200 = 1.25
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OSHA TECHNICAL MANUAL - SECTION II: CHAPTER 1
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Since Em > 1, an overexposure appears to have occurred; however, the SAE for each
substance also needs to be considered:
„
„
Exposure ratio (for each substance) Yn = Cn/Ln
Ratio to total exposure R1 = Y1/Em ... Rn = Yn/Em
The SAE's (95% confidence) of the substance comprising the mixture can be pooled by:
(Rst)2 = [(R1)2 (SAE1)2+(R 2)2 (SAE2)2+ ... (Rn)2 (SAEn)2]
The mixture Control Limit (CL) is equivalent to: 1 + RSt
If Em < CL, then an overexposure has not been established at the 95% confidence level;
further sampling may be necessary.
If Em > 1 and Em > CL, then an overexposure has occurred (95% confidence).
Using the mixture data above:
Y1 = 500/1000
Y2 = 80/200
Y3 = 70/200
Y1 = 0.5
Y2 = 0.4
Y3 = 0.35
R1 = Y1/Em = 0.4
R2 = 0.32
R3 = 0.28
(Rst)2 = (0.4) 2(0.089)2 + (0.32)2(0.11)2 + (0.28)2(0.18)2
RSt = [(RSt) 2]1/2 = 0.071
CL = 1 + RSt = 1.071
Em = 1.25
Therefore Em > CL and an overexposure has occurred within 95% confidence limits. This
calculation is also used when considering a standard such as the one for total welding fumes. A
computer program that will calculate a control limit for any additive mixture is available for
personal computers. The program will run on any IBM-compatible computer in DOS and is
available on the OSHA CD under the heading "software."
APPENDIX II:1-7. PARTIAL LIST OF SUBSTANCES FOR AUTOWEIGHING SUBMISSION
Oil Mist (Mineral)
alpha-Alumina..........
Total dust...........
0160
15
Respirable fraction..
A201
5
5010
5
Particulates not
otherwise regulated
(PNOR)............
Aluminum Metal (as Al).
Total dust...........
A100
15
Respirable fraction..
A110
5
Total dust...........
9135 15
Respirable fraction..
9130
5
Pentaerythritol........
Ammonium sulfamate.....
Total dust...........
0185
15
Respirable fraction..
A111
5
Total dust...........
1987 15
Respirable fraction..
P157
5
Perlite................
Barium sulfate.........
Total dust...........
B101
15
Respirable fraction..
B104
5
Total dust...........
2035 15
Respirable fraction..
P101
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OSHA TECHNICAL MANUAL - SECTION II: CHAPTER 1
Bismuth telluride
Plaster of paris.......
Undoped..............
Total dust...........
2127 15
P102
Total dust...........
0370
15
Respirable fraction..
Respirable fraction..
B110
5
Portland cement........
Boron oxide............
Total dust...........
0380
15
Total dust...........
0505
15
Respirable fraction..
C130
5
Calcium Carbonate......
15
Respirable fraction..
5
0520
5
Calcium silicate.......
C112
15
Respirable fraction..
C122
5
Calcium sulfate........
Respirable fraction..
Respirable fraction..
P104
5
Total dust...........
2229 15
Respirable fraction..
R102
5
precipitated and gel.
9050
Silica, amorphous,
diatomaceous earth,
1% crystalline silica
S112
Silica, crystalline
cristobalite,
C104
15
C123
5
0527
3.5
Cellulose..............
respirable dust......
9015
Silica, crystalline quartz,
respirable dust.........
9010
Silica, crystalline
Total dust...........
0575
15
Respirable fraction..
C124
5
Coal dust (less than
tripoli (as quartz),
respirable dust......
S114
Silica, crystalline tridymite,
5% SiO(2)),
respirable fraction..
0557 15
containing less than
Total dust...........
Carbon black...........
Total dust...........
Silica, amorphous,
Total dust...........
Total dust...........
5
Rouge..................
Calcium hydroxide......
Calcium oxide..........
Page 31 of 32
respirable dust......
9040
9017
Silica, fused,
Coal dust (greater than
respirable dust......
or equal to 5% SiO(2)),
9013
Silicates (less than 1%
respirable fraction............. C120
crystalline silica)
Cotton Dust (The SLTC will supply special
pre weighed cotton dust filters and
cassettes on request.)
Dicyclopentadienyl iron
Total dust...........
0904
15
Respirable fraction..
D100
5
Total dust...........
1016
15
Respirable fraction..
E102
5
Grain dust (oat, wheat,
barley)........
G109
10
Emery..................
Glycerin (mist)........
Total dust...........
1363
15
Respirable fraction..
G115
5
Graphite, synthetic....
Total dust...........
1366
15
Respirable Fraction..
G100
5
Gypsum.................
Total dust...........
1367
15
Respirable fraction..
G101
5
Mica (respirable dust)........
Soapstone, total dust
9025
Soapstone, respirable
dust.................
S121
Talc (containing no
asbestos),
respirable dust......
9030
Silicon................
Total dust...........
2235 15
Respirable fraction..
S120
5
Silicon carbide........
Total dust...........
2236 15
Respirable fraction..
S123
5
Starch.................
Total dust...........
2263 15
Respirable fraction..
S124
5
Sucrose................
Total dust...........
2285 15
Respirable fraction..
S130
5
Tantalum, metal and
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OSHA TECHNICAL MANUAL - SECTION II: CHAPTER 1
Kaolin.................
oxide dust...........
Page 32 of 32
2325
5
Total dust...........
1568
15
Respirable fraction..
K100
5
Total dust...........
1593
15
Respirable fraction..
L100
5
Total dust...........
M113
15
Zinc oxide.............
Respirable fraction..
1615
5
Total dust...........
Z102 15
Respirable fraction..
Z103
1610
15
Limestone..............
Total dust...........
2440 15
Vegetable oil mist.....
Magnesite..............
Magnesium oxide fume...
Total Particulate....
Titanium dioxide......
Marble.................
Total dust...........
V126 15
Respirable fraction..
V127
5
Zinc oxide fume........
2610
5
Total dust...........
2616 15
Z104
5
2620
5
Total dust...........
1626
15
Respirable fraction..
Respirable fraction..
M114
5
Zirconium compounds
(as Zr)..............
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5
Zinc stearate..........
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