2. Objectives
Describe colorimetric science
Describe common colorimetric detection devices
Describe the process for detection of known materials
Describe the process for detection of unidentified
materials
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3. Colorimetric Sampling
Colorimetric tubes
Detect known and unidentified gases or vapors
Easy method to narrow down an unidentified material
to its chemical family
Can tell you how much of a certain material is present
if you know the material
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4. Colorimetric Sampling
One of the most important concepts of colorimetric
sampling
They may not be able to tell you what is present
But they can certainly tell you what is not present
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5. Colorimetric Science
Reagent filled glass tubes
designed to react with
specific gases and vapors
Bellows or piston style
pump used to draw
contaminated air across
reagent
If target gas or vapor is
present there is a color
change to the reagent
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6. Colorimetric Science
They can usually detect a wide variety of
substances.
Most have some cross-sensitivities and will react in
much the same fashion as the target material.
Instructions provide cross-sensitivities list.
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7. Chip System
In addition to tubes, Dräger
has a Chip Measurement
System (CMS)
Bar coded strips that function
much like the colorimetric
tubes, but a reader performs
analysis of the tube
With the CMS, a reading is
given on a LCD screen and
does not need interpretation
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8. Chip System
CMS
Good that there is no human interpretation
But it is also bad in that there is no human
interpretation
Unable to manipulate the CMS chip, as you can a tube
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9. Detecting of known materials
Most tubes are designed
Always read instructions
to read in parts per
million
Some are in percent by
volume
Some only indicate
presence of a material
For some materials there
are a variety of sampling
ranges available
for tube
You need to know:
Number of pump
strokes
Color changes
Cross sensitivities
Special instructions
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10. Detecting of known materials
Calibrated for a certain
temperature and humidity
Correction factors
provided
Use less pump strokes to
decrease sensitivity of tube
Use more pump strokes to
increase sensitivity of tube
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11. Detection of unidentified
materials
Detection of unidentified materials is not an easy task
Knowledge of colorimetric sampling, chemistry, and
street sense is essential
Most manufacturers provide a flow chart when looking
for unidentified materials
$499
Use a combined system of flow charts, with several types
of detection tools
When looking for unidentified materials, you are not
$595
trying to establish levels of the material
You are only trying to see what may be present
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12. Detection of unidentified
materials
If you get a hit on a tube,
Both Dräger and Mine
there is no need to
continue pumping air
across the tube that is a
positive
Move onto the next tube
in the system
More than one material
may be present
Safety Appliances company
allow for multiple tube use
Tubes are preassembled
and placed in manifold to
draw air across 5 tubes at
one time
Detection times extended
due to extra tubes that are
drawing air
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14. Street Smart Tips
Major key point - Read the Instructions
Cross sensitivities are very useful in identifying a
unidentified material
Book of photocopied instructions works much better
than 20 sheets
Use additional pump strokes to increase sensitivity of
tube
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15. Street Smart Tips
Humidity plays a major
factor in tube response
Atmospheric pressure also
Most tubes are calibrated
for 50 percent humidity
Correction factors can be
calculated using the
instructions
plays a role
Each tube has a specific
temperature
Age, light, and storage
conditions determine
accuracy of tubes
Tubes typically have a 2-3
year shelf life
Consistent storage
temperatures are best
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16. Street Smart Tips
More than one gas may be
present
Remember cross
sensitivities of tubes
Know color of tube you are
sampling and the color it
should change to
Keep an unbroken tube
with you to compare color
changes
Some may be very subtle
Water vapor may be
released from pump
Not uncommon for a tube
to heat up and release
visible vapor
Some chemical tubes
create a very hot chemical
reaction or ignition source
Some tubes release
irritating gases
Clear pump with strokes in
between tubes
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17. Summary
Colorimetric sampling can be a valuable tool if
instructions are followed
Colorimetric tubes can establish a level of
contaminants present
Colorimetric tubes can help identify or at least classify
an unidentified material
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