PID Lamps Keep Us Safe

From industrial processes to chemical storage, chemical spill accidents to environmental monitoring and personal safety the need for gas detection is growing and essential. Several technologies are employed to perform this detection including, catalytic and electrochemical sensors, gas chromatography, flame and photo ionisation, and ion mobility spectrometry. The photo ionisation detector, or PID, method offers perhaps the best of all worlds when compared to the other techniques, yielding fast response, low detection levels, ease of use, small size, portability and affordability.

Photo ionisation detection uses a specialised UV lamp that emits high energetic photons. The energy level of the photons depends on the gas fill of the lamp and is measured in electron volts (eV).

When the photons are absorbed by the gas atmosphere to be measured they excite the gas molecules causing the loss of an electron, resulting in ionisation of the gas. The number of ionised gas molecules, which are measured as current generated from the movement of electrons in the detector, is proportional to the concentration of the ionised compound. This allows a quantitative measurement of concentration.

However photo ionisation is not gas selective because all molecules with ionisation potentials less than the photon energy of lamp are ionised. The technique is non-destructive so can be used in conjunction with other detectors for extending the analysis.

Heraeus (Germany) manufactures a range of PID lamps with varying photon energies to enable a degree of compound selection. A recent introduction has been a dedicated 10.0 eV lamp which is particularly useful for measuring benzene, toluene, ethyl benzene and xylene (BTEX compounds).

Measurement of Volatile Organic Compounds (VOCs) using portable Photo ionisation Detectors (PID) enables fast detection with high sensitivity. VOCs comprise numerous chemical compounds such as toluene and isobutylene and are found in many different industries. Exposure limits for these chemicals can be very low, when exposure occurs over a long period of time. Contact to these substances can present a serious health hazard not only in a manufacturing environment but on the streets as they are shipped. For this reason VOC detection is of paramount importance during emergency spill response actions and in industries where worker exposure must be limited.

While many VOCs are also flammable and can be detected with other technologies, such as a catalytic sensor, the levels of concern are typically at the parts-per-million (ppm) or parts-per-billion (ppb) level. For example, toluene has a lower explosive limit (LEL) of 1.2% and a permissible 8-hour exposure of 50 ppm. Exposures to LEL levels are 240 times higher than the shift exposure level (1.2% = 12,000 ppm).

Obviously, a technology capable of higher sensitivity is required to ensure worker or personnel safety. Photo ionisation detectors (PIDs) rely on specific physical properties of the VOCs, and many common VOCs have ionisation potentials lower than 10.6 eV, which is a common energy level for PID UV lamps.

Heraeus Noblelight, a specialist manufacturer of specialty light sources, supplies photo ionisation detector lamps (PID lamps) used in modern portable gas detection units. Using latest electronics and software, PID lamps can be used in durable and easy-to-use mobile gas alarm units delivering reliable detection results.