Photoionization Detector

Last updated: August 11, 2019

What Does Photoionization Detector Mean?

A photoionization detector (PID) is a gas detector that uses ultraviolet (UV) rays to detect the presence of volatile organic compounds (VOCs) and other gases like methane and benzene in a workplace.

A PID can instantly indicate the presence of VOCs even if they are present in low concentration. These sensors are widely used in industrial, mining, and confined working facilities to ensure that the atmosphere is safe and secure for personnel.

Safeopedia Explains Photoionization Detector

A PID is a very sensitive instrument and measures the real-time concentration of both organic and non-organic vapors. It comprises a UV lamp to ionize molecules, which release an electron and form a positive ion. Later, electrodes collect these ions, which are then converted to a digital meter reading in parts per million (ppm).

The most common UV lamps used in field work to detect the VOCs successfully are 10.6eV, 11.7eV, and 11.8eV. The lifespan of all of these detectors vary, and there are unfortunately some associated limitations. A PID cannot detect the presence of semi-volatile compounds. It can indicate if VOCs are present at a workplace but cannot identify the type. Additionally, these instruments can fail to give accurate readings for water vapors. High humidity can reduce sensitivity and cause lamp fog. The impact can be significant especially when soil moisture level is high.

Furthermore, if methane gas is present in a higher concentration, the performance of these detectors can be badly affected, thus contributing to misleading readings. The instrument response can also be skeptical in the case of temperature variations and naturally occurring compounds. One of the significant limitations of these instruments is that they gauge VOCs in a million range and therefore are not suitable for any workspace where these harmful compounds are found in a range of billions.

However, the overall importance of a PID cannot be overlooked. Leak sources are the main cause of a higher concentration of gases. With a PID, workers can immediately rectify leak sources and maintain maximum security. A PID is an extremely valuable tool for all industrial workers in a hazardous environment, as industrial activities produce harmful gases and toxins in large amounts. A continuous monitoring with a PID assessment in confined spaces can ensure that a workspace is free of threats and provide greater protection to personnel.


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