module 6 colormetric sampling, american fork fire rescue
TRANSCRIPT
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Colormetric Sampling
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ObjectivesDescribe 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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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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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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Colorimetric ScienceReagent 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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Colorimetric ScienceThey 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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Chip SystemIn 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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Chip SystemCMS
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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Detecting of known materialsMost tubes are
designed 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
Always read instructions for tube
You need to know: Number of pump
strokes Color changes Cross sensitivities Special instructions
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Detecting of known materialsCalibrated 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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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 Use a combined system of flow charts, with
several types of detection tools When looking for unidentified materials, you
are not trying to establish levels of the material You are only trying to see what may be present
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$499
$595
Detection of unidentified materials
If you get a hit on a tube, 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
Both Dräger and Mine 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 1212
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Multi-Tube Systems
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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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Street Smart Tips Humidity plays a
major factor in tube response
Most tubes are calibrated for 50 percent humidity
Correction factors can be calculated using the instructions
Atmospheric pressure also 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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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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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