PIDs As HazMat Response Tools

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PIDs As HazMat Response Tools

Application Note AP-123rev 2 cw.01-02Used together, they have a complementary effect, andthey can provide greater confidence in COmeasurement and prevent false alarms. For example,if a homeowner feels that CO is present ,yet thedetector’s digital display reads zero, then a COdetector tube can be used to verify the reading. Ifboth the detector and tube read zero, then it isextremely unlikely that CO is present. To bestunderstand this complementary effect, let’s look atsome more examples.CO in a Printed Circuit Board PlantA portable CO detector read 60 ppm in the cafeteriaof a printed circuit board plant, with no obviousreason for it. When the detector was taken outsidethe plant the CO level on the detector dropped tozero, but a fresh air calibration was performedanyway. Upon reentering the plant the CO detectoragain showed a reading of 60 ppm. The detector wasagain taken out of the plant and 50 ppm COcalibration gas was applied. The meter read 47 ppmwhich showed that it was working properly, but forgood measure it was recalibrated. However, therewas no obvious source of CO, so a CO tube wasused, and it read approximately 50 ppm CO. Withboth the electrochemical CO sensor and the CO tubereading positively for approximately the sameconcentration of CO, it was safe to assume that COwas present. Using the CO detector like a Geigercounter, the source was located at a heat-shrinkpackaging machine that was producing 150 ppm ofCO in the operator’s breathing zone. The companyimmediately had the machine tuned up.CO in a Food WarehouseIn a food warehouse, a portableCO detector showed a COconcentration of 80 ppm.However, the facility used batterypoweredrather than propaneforklifts, so this ruled out the CO from the forklifts,which is a common source of CO in warehouses.The warehouse personnel pointed out that we weremaking the CO measurement in an office locatedwithin the battery charging room. Without animmediate answer to the CO levels, a CO tube wasused to verified the CO concentration. But it did notregister any CO. Lead-acid batteries generatehydrogen gas while charging. Using a crosssensitivitytable supplied by the CO sensormanufacturer showed that 80 ppm on the CO sensormeans that there was approximately 200 ppm ofhydrogen present which is well below its LowerExplosive Limit (LEL) of 4% (40,000 ppm).Engine Company Natural Gas CallsThe calls for “natural gas smell” seem to bealmost as common as CO calls. If enginecompanies are to be tasked with COmeasurement, then perhaps a tool should also beconsidered for natural gas calls because bothseem to run together. Natural gas is a flammablegas consisting primarily of methane and othershort-chain saturated hydrocarbons. Methane isflammable when present in concentrations of 5%volume or greater. 5% methane in air explodesif an ignition source is present. This minimumconcentration of methane that supports combustionis called the Lower Explosive Limit, orLEL. Detectors that are used to measurecombustible gases for safety purposes are oftencalled “LEL meters” and read 0 to 100% of LEL.So if the detector reads 100 that means that theatmosphere is flammable. If the detector isreading 50, it means that the atmosphere is 50%of the way to becoming flammable. The OSHAlimit for entry into confined spaces is 10% ofLEL. For methane, 10% of LEL is 0.5%methane by volume.Odorants Make Natural Gas SmellNatural gas does not smell, so there is no way forsomeone to detect a leak without a propermeasurement tool. Therefore, natural gas is“odorized” with a very smelly compound calledmethyl mercaptan. Methyl mercaptan has anolfactory threshold of between 0.0001 to 0.041 ppm(parts per million) or 0.1 to 41.0 ppb (parts perbillion). This means that one can smell natural gasleaks well below the level that is dangerous. Also,the “sticky” nature of methyl mercaptan means thatit tends to stick to clothes and equipment.Only an LEL Monitor Can Tell You When itis SafeNoses are not very accurate detection devices. Theycan quickly suffer from “olfactory fatigue” as they3RAE Systems Inc.3775 N. First St., San Jose, CA 95134-1708 USAPhone: +1.888.723.8823Email: raesales@raesystems.comWeb Site: www.raesystems.com


Application Note AP-123rev 2 cw.01-02become acclimated to an odor. So one’s sense of smellcan’t be trusted around natural gas leaks. LEL monitorscan help establish whether it is safe to enter a buildingwhen natural gas odor has been noted. The LEL meteroften reads 0, indicating that the area is not flammable,yet the natural gas smell is still there.These numbers are summarized below:Methane %Volume ppm ppb100% LEL 5 50000 5000000010% LEL 0.5 5000 50000001% LEL 0.05 500 5000000.1% LEL 0.005 50 50000OdorThresholdMethylMercaptan0.0000001 0.0001 0.1What this table shows us is that the lowestconcentration of methane that an LEL detector canmeasure is 50,000 ppb, while people can smell theodorant in natural gas at 0.1 ppb. So, people cansmell the odorant at levels 500,000 times below thelimit of detection of any LEL meter. An LELdetector can help increase the safety of enginecompany personnel when natural gas is smelled, andit can help show that building occupants are safe eventhough they might still smell some residual odorant.Choosing the Right Product(s) for Measuring CODetermine how many calls each engine companymakes a year. If they make less than 68measurements per a year, then it might be best tochoose gas detection tubes. If you feel thatcontinuous monitoring is best, then tubes provide anexcellent verification technique.handle and wait for the indicator to change color to readthe tube. RAE offers CO tubes in the ranges of 5-100,20-500 ppm and 0-2-4% and are the most affordabletubes in the market at just $30 per box of 10.ToxiRAE II CO Checker KitThe CO Checker is a complete kit that gives you botha highly accurate CO monitor and the calibration gasnecessary to verify it is reading accurately. The COchecker is a simplified CO detector that onlyprovides continuous CO readings, PEAK hold,battery voltage and run time. It does not provideindustrial hygiene alarms like STEL and TWA thatmight confuse users. The CO checker is alsoavailable without the kit.ToxiRAE LEL DetectorThe ToxiRAE LEL meter is a unique,compact,inexpensive meterthat allows you toreadily measureflammable gasesand give you a readout in % of LEL. A rechargeablemeter, the ToxiRAE LEL meter provides 10 hours ofrun time on its NiCd batteries. If one forgets tocharge the ToxiRAE, it comes with an alkalinebattery pack. One can always use the ToxiRAE aslong as they can pick up 4 AAA alkaline batteries.ReferencesRAE Systems: Sensor Specifications and Cross-Sensitivities (Technical Note TN-114)RAE Systems: Handbook of Gas Detection Tubes& Sampling Pumps (Third Edition, 2005)RAE Systems CO GasDetection TubesA very affordable way tomake CO measurements.The rugged metal syringestyle pump is virtuallyindestructible and requires notraining. Just pull and latch the4RAE Systems Inc.3775 N. First St., San Jose, CA 95134-1708 USAPhone: +1.888.723.8823Email: raesales@raesystems.comWeb Site: www.raesystems.com

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