2. Objectives
Describe the ionization process
Describe the various types of ionization detection
devices
Identify the uses for ionization detection devices
Compare types of ionization detection types and use
in emergency response
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3. Photoionization Dectectors
The most common
detector of general toxic
risk is the
photoionization detector
PID are very common in
the scientific community
Several methods to
provide the ionizing
energy through ionization
PID uses an ultraviolet
lamp.
The method of ionization
may vary but the end results
are the same
Vapor is separated and the
resulting change in electrical
activity is measured against a
know gas.
PID detects a variety of
gases.
LEL sensor does not detect
low enough to protect
responders against toxic risk.
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4. Photoionization Dectectors
Can detect organic and some inorganic gases.
Ammonia, Arsine, Phosphine, Hydrogen Sulfide,
Bromine, Iodine.
Has the ability to detect a wide variety of gases in small
amounts
Dose not indicate what the material is
It justifies that something is in the air
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5. Photoionization Detectors (PID)
May be built into a multi-gas meter
Advantage – sensitivity
PID starts to read at 0.1 ppm to 2,000 or 10,000 ppm
LEL typically will start to read at 50 ppm
RAE systems has PPB RAE
Can detect down to 1 PPB
LEL sensor identifies flammability issues
PID determines toxic risk – PEL less than 500 ppm are
considered toxic
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6. Photoionization
PID uses ultraviolet lamp to ionize gas
Gas sample has various molecules
Neutrons (neutral), protons (positive), electrons
(negative)
Ionization–electron is removed resulting in a charged
particle (ion)
PID detects change and makes reading
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7. Photoionization
In order to be read by a PID,
the vapor or gas to be
sampled it must be able to be
ionized (Ionization potential)
Measurement of an IP is
electron volts (eV) Found in
the NIOSH pocket guide
UV lamps
9.8 eV, 10.2 eV
10.6 eV most common
11.7 eV, 13.0 eV
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9. Photoionization
Know the chemical you are dealing with to determine
quantity of material present
Compare readings you get with the PEL or IDLH to
determine your safety
PID has correction factors as well
Most PIDs are calibrated to isobutylene
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10. Photoionization
What is a toxic reading
As a rule of thumb for an
occupancy that has
chemicals is use.
50 ppm may be acceptable
Small: 5-10 ppm could be
harmful or safe depending
on the environment
Large: 1800 could be
harmful or safe depending
on the environment
Reading only indicates that
could be something
potentially toxic in the air.
Best to use PID for a variety
of situations to get used to
the types of reading that
can be anticipated.
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11. Problems with PIDs
Humidity affects this in 2-ways
If you have a dirty lamp and sensing area the water vapor
may create a short which will cause a meter reading.
Is a quenching problem, if there is humidity in the area
of the lamp, much as fog absorbs the energy of
headlights? The meter reads
Lamps are affected by dirt and dust and require
99
cleaning
Diesel exhaust and other particulate matter. Like
mown grass or cement dust
$595
Salt water or hard water environments may affect
the lamp as well
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12. Problems with PIDs
Higher levels of Methane (Natural gas, Swamp gas, landfill gas)
May suppress some of the ionization potential of the lamp.
Use an LEL monitor to read LEL PID will not read
methane (IP 13.0)
PID cannot separate out gas mixtures.
Mixtures can present an identification problem
Some PID requires at least 10 percent oxygen to be present.
RAE systems PID do not require any oxygen to function.
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13. Summary
Understanding use of ionization devices can detect
potentially toxic environments
Understanding how these devices function can assist
in the selection process during an emergency response
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