Air Sampling and Industrial Hygiene Engineering - Chapter 3 potx

CHAPTER 3
Calibration Techniques
This chapter contains theoretical and real-world discussions about the intricacies of calibration.
It gives special emphasis to situations where the knowledge of calibration techniques is a prerequi-
site for sampling adequacy.
Calibration is the means used to provide evidence that instrumentation is working
accurately and that results are reliable and repeatable within the tolerance levels prescribed
for these instruments. The calibration of real-time instruments is very specific, and manu-
facturer’s instructions must be followed. Increasingly, instrumentation is calibrated using
electronic circuitry, with empirical tests against standards in accordance with the manu-
facturer’s requirements at prescribed intervals.
Collection efficiency must also be taken into account when calibration curves are
developed. As filters, cartridges, or sorbent tubes load, air intake and calibrated airflow
volumes across the media can be expected to change (Figure 3.1).
3.1 CALIBRATION REQUIREMENTS
Instrument calibration records must be reviewed periodically by the users to assess
accuracy of documentation and to evaluate instrument performance. Assessment is based
on the instrument operating instructions and knowledge of the user.
• Users will check minimum calibration frequency requirements for the instrument
and calibrate according to the applicable operating instruction manual.
• Calibrating the instrument at the worksite under actual field conditions is an
important requirement.
• Air-sampling instrument readings for calibration will be corrected for tempera-
ture and barometric pressure.
Record calibration and challenge results as follows in the field logbook and include the
following information:
• Instrument identification
• Date (if not on page in logbook)
• Precalibration readings as found or as set
• Readings after calibration and span settings, if applicable
© 2001 CRC Press LLC

108642
Figure 3.1 SKC cyclone sampler at 2.6 l/min collection efficiency vs. aerodynamic diameter.
•Calibration gas (challenge) used and lot number
•Signature of person performing calibration
3.1.1Calibration Assurance
The user will transport the instrument to the field in its carrying case or by other means
that will adequately protect the instrument. All devices to be used in the field sampling
train must be in-line during calibration (Figure 3.2).
Relevant information such as the type of instrument to be used, frequency of monitor-
ing, and specific warning and action levels are found in the site safety and health plan or
Activity Hazard Analysis (AHA) written for the specific job site. The user must follow
these requirements:
• Users are expected to follow the specific manufacturer’s operating instruction
manual for the instrument being used. The user takes a field copy of the operat-
ing instruction manual into the field with the instrument.
• Prior to entering a contaminated zone, the user will take appropriate precautions
to prevent contamination of the instrument, e.g., using plastic bags or filters.
• The instrument is used in accordance with the applicable operations and mainte-
nance (O&M) manual and site safety and health plan.
• Data are recorded in the field logbook.
© 2001 CRC Press LLC
AIRCHEK
SAMPLER
SAMPLE PERIOD MINUTES
START
HOLD
FLOW
AND
BATTERY
CHECK

DIGIT
SET
PUMP
RUN
TIME
DIGIT
SELECT
TOTAL
ELAPSED
TIME
SET-UPMODE
FLOW
ADJ
ON
5
4
3
2
1
AIRCHEK SAMPLER
MODEL 224-PCXR8
U
L
¤
LISTED 124U
SERIAL NO.
SKC INC.
EIGHTY FOUR PA 15330
WARNING - SUBSTITUTION OF
COMPONENTS MAY IMPAIR INTRIN

SIC SAFETY. USE ONLY UL LISTED
PORTABLE AIR SAMPLING PUMP
BATTERY PACK MODEL P21661
INTRINSICALLY SAFE
PORTABLE AIR SAMPLING PUMP
FOR USE IN HAZARDOUS LOCA
TIONS CLASS I, GROUPS A B C D
AND CLASS II, GROUPS E F G
AND CLASS III, TEMPERATURE
CODE T3C.
Figure 3.2 A primary standard flowmeter connected to a sampling train. (SKC)
3.1.2Decontamination
Decontamination of instruments is necessary to remove contaminants present at a site.
The user is expected to take the proper steps to assure the instrument is clean prior to leav-
ing a contaminated zone. Aradiation release sticker may be required depending on the cir-
cumstances of radioactive contamination on-site.
Decontamination procedures will vary depending on the individual contaminants and
circumstances involved. Steps may be as simple as wiping down the instrument probe with
soap and water or as involved as disassembly and thoroughly cleaning with decontami-
nation agents.
Decontaminate the instrument in accordance with the site safety and health plan
decontamination procedures or instructions provided by air monitoring professionals.
3.1.3Maintenance
Users should not attempt field repairs other than preventive maintenance, cleaning,
adjustments, or decontamination. Major repairs must be done by a qualified instru-
ment technician or the factory. Refer to the O & M manual for maintenance instruc-
tions. Flow-rate holders also require frequent maintenance to assure consistent operation
(Figure 3.3).
• Battery charging will be done in accordance with the manufacturer’s O&M man-
ual to prevent overcharging or possible damage to the equipment.

© 2001 CRC Press LLC
Figure 3.3 Single, double, triple, and quadruple adjustable low flow holders. (SKC)
•Manufacturer’s preventive maintenance procedures and major repairs by the fac-
tory or instrument technician will be recorded in the field logbook or calibration
logs for that instrument.
•After field maintenance, instrument calibration is invalidated, and recalibration
is necessary prior to use.
The terms primaryandsecondarycalibration devices are used in field calibration.
Primary calibration means that a physical phenomenon whose progression is dictated by
the laws of physics is measured for quantification. Such a physical phenomenon is the time
required for a bubble to move up a glass tube or the time required for a gas to evaluate a
chamber.
Secondary calibration involves the use of equipment previously calibrated against a
primary standard. Such equipment is often the proper choice because primary standards
often cannot be readily transported and relied upon under field conditions.
3.2MANUAL BURET BUBBLE METER TECHNIQUE
(PRIMARY CALIBRATION)
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 calibra-
tion. Calibrate personal sampling pumps before and after each day of sampling (Figure 3.4).
3.2.1 Bubble Meter Method
For the Bubble Meter Method use the following procedures:
1. Allow the pump to run 5 min prior to voltage check and calibration.
2. Assemble the polystyrene cassette filter holder using the appropriate filter for the
sampling method.
3. If a cassette adapter is used, care should be taken to prevent contact with the
backup pad.
4. Note: When calibrating with a bubble meter, the use of cassette adapters can
cause moderate to severe pressure drop in the sampling train, which will affect
the calibration result. If adapters are used for sampling, then they should be used

during calibration.
© 2001 CRC Press LLC
Figure 3.4 This portable standard flowmeter can be used in the office or laboratory, and in
the field. (SKC)
5.Connect the collection device, tubing, pump, and calibration apparatus.
6.Avisual inspection should be made of all Tygon
®
tubing connections.
7.Wet the inside of a 1-l burette with a soap solution.
8.Turn on the pump and adjust the pump rotameter to the appropriate flow-rate
setting.
9.Momentarily submerge the opening of the burette in order to capture a film of
soap.
10.Draw two or three bubbles up the burette so the bubbles will complete their run.
11.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.
12.The timing accuracy must be within ϩ1 s of the time corresponding to the desired
flow rate.
13.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 in any event.
14.While the pump is still running, mark the pump or record (on the calibration
record form) the position of the center of the float in the pump rotameter as a
reference.
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.
Calibration of multiple tubes, whether in series or in parallel, is sometimes required.
Any flow adjustment mechanisms and critical orifices must also be installed in the sam-
pling train during these calibrations. When flexible tubing is used, it must be consistently
used in all applications during sampling events (Figure 3.5).

3.3 ELECTRONIC FLOW CALIBRATORS
Electronic flow calibrators are high-accuracy, electronic bubble flowerets that provide
instantaneous airflow readings and a cumulative averaging of multiple samples.
© 2001 CRC Press LLC
Figure 3.5 Two sorbent sampling tubes in series with a single adjustable low-flow holder. (SKC)
•These calibrators measure the flow rate of gases and present the results as volume
per unit of time.
•These calibrators may be used to calibrate all air-sampling pumps.
•The timer is capable of detecting a soap film at 80-␮s intervals.
•This speed allows under steady flow conditions an accuracy of Ϯ0.5% of any dis-
play reading.
•Repeatability is Ϯ0.5% of any display.
•The range with different cells is from 1 ml/min to 30 l/min.
•Battery power will last 8 h with continuous use. Charge for 16 h. These meters can
be operated from A/C chargers.
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 cali-
bration (Figure 3.6).
3.3.1 Cleaning Before Use
Before using an Electronic Flow Calibrator:
• Remove the flow cell and gently flush it with tap water. The acrylic flow cell can
be easily scratched.
• Wipe with cloth only.
• Protect center tube, where sensors detect soap film, from dirt and scratches.
• Never clean with acetone. Use only soap and warm water.
© 2001 CRC Press LLC
Figure 3.6 The electronic flow calibrator using soap bubbles is easy to use and suitable for field use.
(SKC)
When cleaning a flow cell prior to storage, allow it to air-dry. If stubborn residue per-
sists, it is possible to remove the bottom plate. Squirt a few drops of soap into the slot

between base and flow cell to ease residue removal.
3.3.2 Leak Testing
The system should be leak checked at 6-in. H
2
O by connecting a manometer to the out-
let boss and evacuate the inlet to 6 in. H
2
O. No leakage should be observed.
3.3.3 Verification of Calibration
The calibrator is factory calibrated using a standard traceable to the NIST, formerly
called the NBS.
• Attempts to verify the calibrator against a glass 1-l burette should be conducted
at 1000 ml/min for maximum accuracy.
• The calibrator is linear throughout the entire range.
© 2001 CRC Press LLC
3.3.4 Shipping and Handling
When transporting, especially by air, one side of the seal tube that connects the inlet
and outlet boss must be removed for equalizing internal pressure within the calibrator. Do
not transport the unit with soap solution or storage tubing in place.
3.3.5 Precautions and Warnings
Avoid the use of chemical solvents on the flow cell, the calibrator case, and the face-
plate. Generally, soap and water will remove any dirt.
• Never pressurize the flow cell at any time with more than 25-in. water pressure.
• Do not charge batteries longer than 16 h.
• Do not leave A/C adapter plugged into calibrator when not in use to avoid dam-
age to the battery supply.
• Close-fitting covers help to reduce evaporation of soap in the flow cell when it is
not in use.
• Do not store flow cell for 1 week or longer without removing soap.
• Clean the flow cell and store dry.

Calibrator soap is a precisely concentrated and sterilized solution formulated to pro-
vide a clean, frictionless soap film bubble over the wide, dynamic range of the calibrator.
The sterile feature of the soap is important to prevent residue buildup in the flow cell
center tube, which could cause inaccurate readings. The use of any other soap is not
recommended.
3.4 ELECTRONIC BUBBLE METER METHOD
Various electronic meters are available that mimic the performance of the bubble
burette. Most use shortened bubble tubes and calculate this shortened tube length as
though the bubble burette was the standard size. The protocol for using these meters is as
follows:
• Connect the collection device, tubing, pump, and calibration apparatus.
• Visually inspect all Tygon
®
tubing connections.
• Wet the inside of the electronic flow cell with the soap solution by pushing on the
button several times.
• Turn on the pump and adjust the pump rotameter, if available, to the appropriate
flow rate.
• 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.
• Repeat these steps until two readings are within 5%. If necessary, adjust the pump
while it is still running.
• Repeat the procedures described above for all sampling pumps. The same cas-
sette and filter may be used for calibrations involving the same sampling method.
For sorbent tube sampling, however, the sorbent tube to be used must be used
during the calibration.
© 2001 CRC Press LLC
Note:When calibrating with a bubble meter, cassette adapters can cause moderate to
severe pressure drop at high-flow rates in the sampling train and affect the calibration

result.
•If adapters are used for sampling, they should also be used for calibrating.
•Caution:Nylon adapters can restrict airflow due to plugging.
•Stainless-steel adapters are preferred.
3.5DRY-FLOW CALIBRATION
With the advent of computer chip and microcircuitry technology, dry-flow calibration
of instruments is now possible. Dry-flow calibrators measure the flow across near friction-
less composite pistons (Figure 3.7). For some pumps, an adapter must be used between the
pump and the dry-flow calibration instrument (Figure 3.8).
In addition to measuring flow rates, the calibration devices can also record time,
date, employee names, pump ID, sample ID number, and other programmed information
(Figure 3.9).
3.6PRECISION ROTAMETER METHOD (SECONDARY)
The precision rotameter is a secondary calibration device. If used in place of a primary
device such as a bubble meter, take care that any error introduced is minimal and noted
(Figure 3.10).
Figure 3.7 An electronic flow calibrator is available that does not use soap; instead it uses a
graphite/carbon-composite piston that rises in the chamber like the bubble. (Bios
International Corp.)
© 2001 CRC Press LLC
Figure 3.8 An electronic adapter is available to automatically calibrate an air sampling pump.
(SKC—AirCheck
®
2000 air sampling pump, CalCheck
®
Communicator with DC-Lite
calibrator). (Bios International Corp.)
Figure 3.9 The electronic standardization and communication module provides time/date stamp-
ing; employee, pump, and sample ID numbers; volumetric flow rate readings; and read-
ings at user-defined time intervals for flow stability testing. (Bios International Corp.)

© 2001 CRC Press LLC
Figure 3.10 Secondary standard rotameters are used in the field to calibrate air-sampling pumps.
Rotameters are calibrated to a primary standard. Flow rates must be corrected for stan-
dard temperature and pressure. (SKC)
3.6.1 Replacing the Bubble Meter with a Precision Rotameter
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 bub-
ble meter.
• 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 levels than
when the rotameter was calibrated against the primary source.
• Used in such a way that the pressure drop across the rotameters is minimized.
If altitude or temperature at the sampling site is substantially different from that at the cal-
ibration site, it is necessary to calibrate the precision rotameter at the sampling site.
3.7 SPAN GAS
Span gas of known concentration can be used to calibrate detectors. An example is the
use of span gas in a PID.
A known concentration of a gas that readily ionizes in the PID energy lamp’s electron
voltage is drawn into the ionization chamber. Essentially this gas spans the distance
between the anode and cathode sides of the ionization chamber. The detector must there-
fore detect this span and send an appropriate electrical signal to the readout device.
The electrical output to the detector readout for the PID is then adjusted. The reason
for this adjustment or calibration is that with a known concentration of a gas that will
© 2001 CRC Press LLC
ionize at a known voltage, the PID should detect and read out the same as the concentra-
tion listed on the compressed gas bottle.
Isobutylene has an IPof 9.8 eV and is the usual calibration gas of choice for PIDs.
Historically, benzene was used (same IPof 9.8 eV); however, that use was discontinued due

to benzene’s carcinogenic and toxic effect potential. Remember that after the ionization
cycle, the gases reform and are exhausted from the PID reaction chamber. The other expo-
sure route occurred when the calibration gas was attached to the sampling train.
3.8BUMP TESTING
Bump testing is used to check sensor operation. This sensor check is not a substitute for
the calibration of sensors. However, bump testing can
•Provide an indication of sensor reliability under field conditions.
•Indicate when calibration is required.
•Test all sensors simultaneously.
Bump testing involves the use of a bump test gas cylinder filled with known concen-
trations of various gaseous challenge agents. These gases each provide a known percent-
age or parts per million component. The gas cylinder is attached to an instrument’s inlet
portal or diffusion grid, and the instrument’s detector readouts are compared to the bump
gas known concentration (Figure 3.11).
Figure 3.11 Bump testing needs to be performed regularly to ensure that real-time air monitoring
instrumentation is functioning properly. (MSA)
© 2001 CRC Press LLC