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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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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.3
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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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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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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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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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Photoionization
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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
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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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 cleaning
Diesel exhaust and other particulate matter. Like mown grass or cement dust
Salt water or hard water environments may affect the lamp as well
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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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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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