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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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