Monday, June 27, 2011

Gas Detection Mythbuster!


So what about cleaning the lamps in your PID gas detector?

First, I asked the question I raised in the last post:  the one where I've used my 5 gas detector (H2S, CO, CH4, LEL, O2, and PID)- is the lamp compromised and how would I user know.  I already know the answer to this, but it was interesting to see how many gas technical support people did not.  They were all well meaning and helpful, but not field experienced.

Here's the first response I received and you wouldn't believe what gas detection company it was from- "Well, if you want to know if it's still good, just run a 100 ppm isobutylene calibration gas standard and if it comes up any where within 30 - 40 ppm of where it's supposed to be, it's still okay."

Really?  Does that mean it can still tell the difference between air freshner and horseshit? 

Here's the right answer: after you've been in a hazardous gas detection event that involves smoke or chemical fog, take the lamp out and clean it.  Don't leave chemical fog or smoke on your lamp.  Then calibrate the unit.  If it doesn't meet the normal specs- get a new lamp.  Don't risk your health.

Mythbuster of the Day:  Only RAE Systems PID lamps can be cleaned by the user.  WRONG.  Ask Bob Henderson of GFG or Joe Glorioso of MSA and they'll tell you straight.  Their lamps can be clearned, too.  That's why their companies sell lamp cleaning kits to their customers.

Don't let the anyone tell you otherwise.  Talk to a gas detector calibration expert. 

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.

Friday, June 10, 2011

Smoke, Fog, and Why Your Measurements Are Off

Here's something to ask the companies that manufacture your hazards detection equipment- what is the effect of smoke or fog on their measurements?

Let me give you an example.

Let's say you're depending on a RAE Systems PID to measure your surroundings for VOC's such as benzenes on a foggy day.  How much does the fog affect your reading if at all?  Humidity and PID readings don't mix well, although Ion Science, Inc. seems to have a PID technology that is less affected by humidity.

Or here's my favorite:  we were involved in putting out a chemical fire some months ago and there was the possibility of hexane exposure. 

Of course, we pulled out the PID, this time one from Industrial Scientific.  But there was smoke in the air.  How much did the smoke affect our readings?

Ever wonder how much of an affect humidity has on long distance (say 300 feet) temperature measurement with an IR gun?  Say you're trying to keep your distance from a rail car that might be suspect.  If the humidity is 90%, will it affect your reading?

Next posting we'll see what the manufacturers say about it, then after that will do a reality check.