Wednesday, June 22, 2011

PID Detectors, Humidity, and Smoke

To clarify the incident that first led me to the questions I posted in the last blog, a few months back I was called to a building fire that really made me think about PID's.  Here's the layout- a big storage room with a floor sump cover that collected all the fluids from drains in a laboratory.  No solvents were supposed to go down the drain.  Supposed is always a bad word when dealing with flammables.

In the same room for some incomprehensible reason was also a hot water heater.  Although all the chemists claimed they were innocent of pouring solvent down the drain, one fine sunny day the equation of chemical sump reservoir and hot water equaled a flash fire.

And the overhead exhaust fan that was supposed to eliminate any possible buildup?  It burned out a while before and no one knew.  The suspect solvent was hexane, and that closed door storage room really could have used a functioning overhead exhaust system.

Two quick deflagrations (explosions) in the below ground pipe.  Dust clouds shooting up to the ceiling alerted the personnel of a problem.  Then smoke pouring out from the door to the storage room.

Knowing the nature of the business, I brought in a 5 gas monitor.  After the initial response, we started scanning all drain openings looking for either LEL levels or solvents.  Flammable gas detector for the first reading and the PID for elevated VOC concentrations.

Smoke and a foggy haze filled the environment.  PID is short for Photoionization detector- using a lamp in layman terms to measure variations in absorbance from those in pure air.  Not a specific detector unless coupled with a GC, but sure to pick up solvents like hexane.

So how much did the smoke and chemical extinguisher haze limit my readings?

In checking with companies that sell PID's I was told a variety of answers including "...sure there would be some interference but probably not much," to "... tell you the truth, we just don't know."


When I asked for any research data they had on the topic, no one had any that specifically addressed smoke and/or chemical extinguisher interference with a PID detector. 

I don't think they want to tell us.  How about you?

So this week I'm calling the head research guys at Honeywell Analytics (Sperion Biosystems), RAE Systems, GFG, Industrial Scientific, MSA and Ion Science to see what they have to say.  The two smartest and most straight-up guys I've talked in the gas detection business are Jeff Emonds of Honeywell Analytics and Bob Henderson of GFG.

Time to get some industry pressure in play to get some answers.

I'll report back next week on what I find.

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