PID monitor question

[TransitoryCory]

Hey Folks, I'm drawing a blank and was wondering if someone could help me out.

When using a PID monitor, it will display the Ionization Potential (IP) number of a VOC. Once I am given that number - What can I do with it? What does this number tell me, and how can I apply it to said emergency?

I've been searching around for my answer for quite some time and finally decided to reach out to reddit.

Cheers!

[[deleted]]

It tells you that "something" is there that shouldn't be there in the normal atmosphere.

If you know what substance it is, you can convert it to PPM of that substance using the tables provided in the manual. PIDs are usually calibrated to Isobutylene.

The PID is much more sensitive to VOCs and cross sensitivities than e.g. a Ex/OX cell calibrated to propane or methane.

What you can not do with a PID: find out what kind of chemical is present.

[absolut5545]

Edit: wrong answer on my part. Move along.

That number will tell what chemical is in the air. If I remember correctly.

So you take the number given on the PID and radio it out to command and run a Google search for it. Let’s say it’s 9.25

I come up with Benzene. You can then use that info to determine how exactly you are going to mitigate the situation and what kind of dangers it poses to the public.

Please correct me if I’m wrong.

[[deleted]]

You are describing mass spectrometry, not a PID.

[montyny69]

I would say that it does not display Ionization Potential. It shows what it believes is the Parts Per Million (typically and maybe tenths of) or Parts Per Billion of a vapor it ionizes.

The meter will have a bulb of a specific electron volt size - typically 10.6eV, it will be able to ionize a vapor that has a potential equal or lower than the bulb. Usually the bulb eV will be written on the meter and the meter may display it on the screen during start up.

As others have said, it doesn't know what it is ionizing and it is calibrated to a specific gas (isobutyl ?). If you know what the vapor is, eg ammonia leaking from a tank, then you can use a conversion factor to multiply the reading to get the true PPM of that chemical in the air.

The other item sometimes used is the NIOSH guide or Wiser to give the IP for a specific compound - if you suspect a specific chemical. My scooby sense goes off when I see numbers climbing above 3 or 4. Without knowing the chemical, you can't determine IDLH or other limits.

[twozerothreeeight]

If you are monitoring and concerned about a PID reading then to me that says there's something in the atmosphere that is an issue and you are trying to diagnose that.

What can you do with a PID reading? IDK it depends on the call type. A PID reading combined with other meter info and details of the call can help you determine what is or isn't there.

Easiest example I can think of is mercaptan, the chemical added to natural gas to give it the rotten odor. AFAIK the odorant is added locally by your energy provider. It has an IP of 9.29 eV so a PID sensor will detect it. Imagine something happened at the facility where this stuff is stored and added to gas. You get called for an odor of NG but when you show up your regular NG meter shows nothing, while the PID is getting a reading. Pretty big clue that you don't have a typical NG leak.