Last week I talked about some of the potential issues for Emergency Responders re build up on the Fresnel lens system in an infrared temperature gun.  Smoke & ash from fires are one set of issues, and chemical extinguishing agents are another.  Chemical vapor residues from a chemical leak (say methyl bromide, for example) can cause problems, too.  There's a fourth category for all detection & measurement equipment, but I'll address that next posting.

But how often should you clean a top notch temperature gun (say our Top Temp Gun or the Flash Point Temp Gun)?  Here's the answer from our techs:

You're looking at a Fresnel lens sysem that we use for our infrared temperature guns.  Notice the ridges along the tapering cone that lead down the barrel to the lens.

I've been hammering this theme home for a while as regards photoionization detectors, but I promised to bring it around to our infrared temperature guns and today I will,

Even though we handle 100:1 distance to spot infrared temperature guns with Class III laser sights, the situations that hazmat responders have to deal with can involve lots of smoke, dust, chemical leaks and or extinguishants.  If you're not using our Top Temp Gun, it means you'll have to be even closer.  With somebody else's infrared temp gun, say a 50:1 distance to spot ratio, you'll have to be twice as close to get a decent reading.

What is distance to spot ratio?  For a 100:1 infrared temperature gun, it means that at one hundred feet you will be measuring a circle with a 1 foot radius.  That's a tight spec.  It's a real instrument that can save lives.

But what if, during an emergency run, you use your temperature gun in a smokey environment, or while your using it, extinguisher fumes blow your way.  Or chemical fumes from a factory?

The answer is that you have to clean it, just like in the case of the PID.  Swab the ridges and the lens with isopropyl alcohol.  Most people forget to clean the ridges that lead up to the main lens.  That's a cricital mistake.  A bad mistake.  Those ridges aren't there for nothing.  They're part of the instrument's operative principle.  So clean them as often as you clean the lens.

Clean them after every emergency you take the infrared gun to.  That way you'll be sure to get more accurate readings.  How inaccurate can the readings be if the unit's lens package (including the ridges)isn't cleaned?

I'll fill you in on that next time.

There has been some controversy over the impact that humidity has on their readings, with one company- Ion Science- claiming that humidity variations have a significant effect on detection suppression.  In high humidity environments that claim this suppression could be in excess of 50%, which makes humidity and serious consideration when trying to get an accurate reading out of a PID.  However, there are rumors of a new study showing that improvements in PID technology have knocked that down to the range of only 10%.

Of more concern to me is the effect of smoke on PID readings at the time of an emergency event and residual contamination on the detector cell because of the smoke and/or chemical extinguisher vapors.  In earlier postings I have stressed the importance of cleaning PID cells after a chemical event.  Now I raise the question of how much smoke or other particulate and/or condensate fumes have on the accuracy of a PID's readout.

To my knowledge, there have been no studies conducted on this issue by any of the gas detection companies or sensor manufactuerers.  I'm going to keep pushing them to look at this problem, and hope you'll push for the same.  This problem shouldn't be ignored.  After all, the responders actually are at risk in the field.  Gas detector salesman typically don't tend to show up at emergency events where toxic gases are involved.

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. 

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."

Great.

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.