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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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8. Photoionization
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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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