A Comprehensive Overview to Photoionization Detectors

A Comprehensive Overview to Photoionization Detectors

Posted by William Kimmell on 27th Jul 2022

Photoionization detectors (PID) are sensors used to detect a broad range of volatile organic compounds (VOCs) and inorganic compounds from parts-per-billion (ppb) to parts per million (ppm). A photoionization device can come in a variety of models including person, hand-held, and fixed. The goal of using photoionization detectors is to provide an accurate reading of the air quality in a space. These detectors have programming to provide an alarm to signal when the concentration level of toxic gases exceeds the set point.

The following guide provides a comprehensive overview to photoionization detectors, how they work, and what compounds they measure to benefit the safety and health of people.

Common Uses for a PID

Photoionization detectors provide industrial hygiene measurements to prevent workers from being exposed to toxic compounds and other hazardous applications. Photoionization detectors are commonly used in the following sectors:

  • Education
  • Aerospace
  • Oil and gas
  • Laboratories
  • Construction
  • Manufacturing
  • Power generation
  • Food and beverage
  • Government and defense
  • Pharmaceutical and medical
  • Semiconductor manufacturing

How Does a PID Work?

Photoionization-detecting technology uses ultraviolet (UV) light to break down volatile organic compounds (VOCs) in the air into positive and negative ions. Photoionization detectors reads or measures the charge of the ionized gas. The charge of the ionized gas functions as the concentration of volatile organic compounds in the air. Majority of VOCs are detectable by PIDs, except for low molecular weight hydrocarbons.

Th detection mechanism in a photoionization device uses lamps to operate a sensor system. A UV lamp generates high-energy photons that pass through these lamps into the central chamber of the device. When a photoionization detector takes a sample of gas in the atmosphere, it passes over into the sensor chamber and one percent of it diffuses through a membrane filter.

From there, the device generates a current that’s proportional to a gas concentration displayed as a ppm or ppb. Not all molecules become ionized, and the major components of air do not cause a response unlike a host of volatile organic compounds (VOCs).

Defining VOCs and PID

Volatile organic compounds are carbon-containing chemicals that become vaporized at ambient temperatures. VOCs also describe a broad range of natural and synthetic chemicals. The term “volatile” comes from how these chemicals evaporate and release molecules into earth’s atmosphere. Volatile organic compounds play a significant role in a variety of synthetic materials like plastic, rubber, glue, and paint.

Photoionization detectors are the first line of response used for VOC leaks. It’s necessary to measure volatile organic compounds because they can negatively impact human health. VOCs are harmful through breathing, skin exposure, and have the potential to cause an explosion on a worksite if they react to oxygen. Photoionization detectors provide the option for monitoring VOCs in applications without oxygen present.

Types of VOCs Detected

Photoionization detectors can read thousands of VOCs present in an environment. The sensors on a PID can detect examples from the following compounds:

  • Alkanes: Hexane, Isopar solvents, and diesel fuels.
  • Alcohols: Butanol, isopropanol, ethanol, and propylene glycol.
  • Acrylates: Ethyl acetate solvent, methyl methacrylate glues, and propylene glycol (PMGEA).
  • Aldehydes: Glutaraldehyde sterilant, acetaldehyde, and formaldehyde.
  • Aromatics: Benzene, toluene, xylene, pyridine, phenol, and naphthalene.
  • Esters: Ethyl ether solvent, methyl-t-butyl ether gasoline additive, ethyl cellosolve.
  • Olefins: Butadiene, cyclohexene, trichloroethylene, vinyl chloride, and turpentine.
  • Ketones: Acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK).
  • Organic Amines: Methylamine and trimethylamine (not always detectable by PID).
  • Bromides and Iodides: Methyl bromide fumigant, n-bromopropane degreaser, iodine.
  • Sulfides and Mercaptans: Methyl mercaptan natural gas odorant.

What a PID Does Not Measure

Photoionization detectors cannot accurately read the following:

  • Natural gas: Including methane and ethane.
  • Noble gases: Helium, xenon, krypton, and argon.
  • Radioactives: Radon, plutonium, and radon.
  • Mineral acids: Nitric acid, sulfuric acid, and hydrochloric acid.
  • Non-Volatiles: Including waxes and greases.
  • Small Molecules: Ozone, hydrogen, carbon monoxide, hydrogen peroxide, sulfur dioxide.
  • Fluorinated Compounds: Aesthetic gases, sulfur hexafluoride, and refrigerants like vehicle coolant.
  • Components of clean air: Including nitrogen, oxygen, carbon dioxide, and water vapor.

Photoionization detectors are first responders to VOC leaks but they cannot identify the type of leak that’s occurring. It’s necessary to use specific gas detectors to help identify the type of leaks occurring. It’s also important to remember that because photoionization detectors respond to a broad range of VOCs, there’s the possibility of false alarms in an area of application. PID technology can be adversely affected by humid or dirty applications where other nonresponsive gases are present in the atmosphere.

It’s important to remember that chloride compounds also have varying responses when read by a photoionization device. In general, fuels like gasoline, diesel, aromatics, olefins, and alkanes have a much higher rate of providing a strong response.

Since only a small fraction of molecules become ionized, the detection method of PIDs is nondestructive. A nondestructive method of detecting gases means photoionization detectors can be used in conjunction with other detectors to help confirm accurate readings of the environment.

Advantages of Photoionization Detectors

Photoionization devices and other gas detectors serve a wide variety of purposes. The most significant advantages of photoionization detectors are to ensure the safety of workers. Photoionization detectors are ideal sources to use when monitoring oil spills, gas leaks, leaking cylinders, and other hazardous material incidents.

Volatile organic compounds are toxic and combustible materials that can endanger the health and safety of workers, even at low concentration levels. It’s a best practice to install photoionization detectors in an industrial facility as a preventative measure for keeping workers safe from overexposure to toxic materials. Installing photoionization detectors offers significant advantages, including:

  • Cost-effective technology that offers fixed and handheld models.
  • Simple to use and easy to install devices to suit different skill levels.
  • Able to provide almost instantaneous results for advanced protection.
  • Able to detect and signal even low levels of volatile organic compounds.

TG Technical Services is here to provide you with top quality photoionization detecting technology to improve the environment of industrial workers. After exploring this comprehensive overview to photoionization detectors, feel free to explore our broad range of devices to take control of the health and safety of your workplace today!

A Comprehensive Overview to Photoionization Detectors