Calibrate Or Die! While the Title of This White-Paper May Seem Atmosphere Without Checking the Operation of Severe, the Importance of Calibration for Your Detector

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Application Note: 110 Calibrate or Die! While the title of this white-paper may seem atmosphere without checking the operation of severe, the importance of calibration for your detector. Manual calibration helps to handheld gas and vapor detectors cannot be maintain “muscle memory” and user under-emphasized because many gas sensors confidence in their detector. It’s almost like a fail to an unsafe state. A Lower Explosive Limit mini-refresher training. (LEL) combustible gas sensor indicates a safe atmosphere when it reads zero but when it fails Calibration Types it also reads zero. A Chlorine (Cl2) sensor “Bump” indicates a safe atmosphere when it reads zero A qualitative test where the detector is shown but when it fails it also reads zero. While some calibration gas and all the sensors show sensors, like oxygen usually fail to a safe or response and alarm. If one were to apply 25 alarming state, they too can benefit from ppm of Hydrogen Sulfide (H2S) gas to an H2S calibration to restore their accuracy. The only sensor with an alarm set to 10 ppm and it way to assure that many sensors are working responds and goes into alarm, then it passes correctly is to apply a gas to them to “calibrate” the “Bump” test. The number(s) on the them. display is not important for the bump test. OSHA’s Position on Calibration  Checks to show that the sensors AND In 29CFR1910.146 (the “Confined Space” alarms work standard) OSHA requires the use of a  Could be as simple as exhaling into an “calibrated” instrument. OSHA’s guidance oxygen sensor or showing a letter CPL 2.100 OSHA says that the Photoionization Detector (PID) a marker instrument must be maintained and calibrated pen containing a solvent according to manufacturer guidelines.  Pump check if applicable Calibration identifies loss of sensitivity, failing or “Calibration Check” failed sensors. A quantitative test where the detector is Calibration Guards Against Loss of shown calibration gas of a known and Sensitivity traceable value and the user verifies that the readings are within the manufacture’s Sensors can age, dry out and fail. They can be plus/minus specification (typically+/-10%) damaged by shocks, drops or exposure to values. So if one were to apply 50 ppm liquids from immersion or when the detector’s Carbon Monoxide (CO) to a CO detector and pump sucks up liquids. Sensors can be the display showed 49 ppm CO, the detector poisoned by chemicals present in the passes the “Calibration Check” because 49 atmosphere or lose sensitivity from ppm is within 10% of 50 ppm. If one got a innumerable other causes. reading of 42 ppm in the same test the Calibration Improves User detector would not pass because 42 is Confidence greater than 10% out of calibration. 10% of Gas detectors are a “Flashlight” allowing 50 is 5 ppm. So +5 is 55 ppm and -5 is 45 people to “see” toxic gases and flammable ppm. If the accuracy specification of the vapors. You wouldn’t go into a dark basement detector is +/-10% any reading between 45- without 55 is considered to be in calibration if 50 ppm checking the calibration gas is applied. operation of  Pump check if applicable your flashlight. “Full Calibration” Don’t go into a The detector is shown calibration gas and “dark” confined readings are adjusted (automatically or space or other manually) to the certified calibration gas potential value following the manufacturer’s procedure. dangerous  Pump check if applicable Copyright © 8/12/2014 Chris Wrenn Environics USA, Inc. 1308 Continental Drive, Suite J, Abingdon, MD 21009 Tel: (410) 612-1250, Fax: (410) 612-1251 [email protected], www.EnvironicsUSA.com Page 1 of 9

AP-110: Calibrate or Die!

“Factory Calibration” are either taken from or comply with ISEA The detector is returned to a certified factory recommendations: facility for testing and adjustment. Most  The safest course of action is a daily modern detectors do not have this requirement check and any detector that has this requirement will  Fresh air calibration (make sure that the be less available for use than one that does not air is CLEAN) have this requirement.  Expose the sensors to known concentration test gas before each day’s Calibration Check Catches a Bad CO use (“Bump” or “Calibration Check”) Sensor o This test is very simple and takes A fire department took a multi-gas detector that only a few seconds to accomplish had been calibrated that day to a CO call. The  With pumped units ALWAYs check pump wall-mounted CO detector in the apartment flow/alarm during daily check because building went into alarm every time the furnace connections, filters and tubing can fail was turned on, but the fire department CO and leaks can dilute & diminish readings sensor only read 0. The apartment building’s  Adjust span (“Full Calibration”) should be maintenance man’s CO detector show 60 ppm done at regular intervals in accordance when the fire department CO sensor still read with instructions provided by the 0. Upon returning to the station the fire detectors manufacturer, company or department’s CO sensor was “successfully” regulatory agency policy recalibrated. But the detector did not respond o Best practice is AT LEAST once a to CO when it was applied to the detector using month or when necessary a “bump” or “calibration check.” It’s possible that that fire department didn’t fully understand “Busting” the 30 day calibration how to calibrate their detector. But the “Myth” “calibration check” did catch the problem. It seems that “calibrate every 30 days” is the When in doubt, a “bump” or a “calibration most common recommendation. But this is check” is always helpful to establish that a often not a safe enough course of action. detector is functioning properly even AFTER a According to ISEA: “Validation of an calibration has been performed. instrument’s operability should be conducted How Much Calibration is Enough? if any of the following conditions or events occurs during use:” Follow your manufacturer’s written  Chronic exposures to, and use in, recommendations. Don’t rely on unsupported extreme environmental conditions, such verbal assurance from distributors or sales as high/low temperature and humidity, representatives concerning calibration and high levels of airborne particulates. requirements. If anyone says that you can calibrate LESS than once a month (every 6  Exposure to high (over range) months for example) then make sure this is concentrations of the target gases and documented IN WRITING. Calibration vapors frequency should also be driven by the level of o Could be found on any HazMat call threat. The higher or more frequent the risk, or overhaul (post fire clean-up) the more frequent calibration should take place. detection assignment  Chronic or acute exposure of catalytic ISEA Calibration Statements hot-bead LEL sensors to poisons and The International Safety Equipment Association inhibitors including volatile silicones, (ISEA) is the leading organization of hydride gases, halogenated manufacturers of safety and health equipment hydrocarbons, and sulfide gases including environmental monitoring  Chronic or acute exposure of instruments. ISEA has developed a statement electrochemical toxic gas sensors to to ensure definition consistency in all solvent vapors and highly corrosive documentation, and to emphasize the need to gases. validate the operational capability of portable  Harsh storage and operating conditions, gas detectors. The following recommendations such as when a portable gas detector is

AP-110: Calibrate or Die!

dropped onto a hard surface or submerged Pumped units have many more options. in liquid. Normal handling/jostling of the Always check for pump flow on a daily detectors can create enough vibration or basis by clogging the inlet and looking for shock over time to affect electronic a “pump” alarm components and circuitry. Detectors that Generally the preferred method of calibrating live on a vehicle are particularly susceptible a pumped detector is using some form of to wear, requiring more frequent calibration. matched flow calibration. The exception to  Change in custody of the detector, like shift this is that for some highly reactive calibration changes when the detector is “handed off” gases used for electrochemical sensors from one user to another. some manufacturers recommend a flow rate  Any change in work conditions that might in excess of pump flow to “flood” the sensors have an adverse effect on sensors. with enough calibration gases so that the  Any other conditions that would potentially sensor is not “starved” for gas. affect the performance of the detector. Flow matching regulator calibration Detectors are designed for the + A flow matching regulator mechanically industrial TWA environment matches gas flow to the pump’s flow rate Most gas detection equipment was designed + If pump isn’t flowing well the regulator for industrial detection where levels are won’t open and the calibration should fail expected to be at or near the relatively low + Conserves gas TWA (Time Weighted Average) values. − Can be expensive to purchase regulator Calibration recommendations are largely based − Weak pumps may not open the regulator, upon detector use in the industrial TWA sometimes this goes undetected environment. For applications where concentrations can exceed TWA values moving Tedlar bag calibration to IDLH and even higher (like first responders) + A constant flow regulator is used to fill a more calibrations may be required. Non- Tedlar (non-reactive Teflon bag) industrial users of gas detectors should + The pumped product draws from the consider being more rigorous in calibration Tedlar during calibration frequency: + Conserves gas  Calibrate after usage that over-ranged or + You can see if the pumps working by otherwise “stressed” the detector, such as watching the bag deflate a big HazMat call − More time consuming and labor intensive  Calibrate at shift changes so that a detector that was inadvertently stressed by the T-fitting calibration previous shift performs properly for the next + A constant flow regulator is used that shift exceeds the maximum flow-rate of the When Should I Check Calibration? pumped device. If a detector’s pump draws at 250cc/min the regulator should  If you don’t trust detector readings flow at 500 cc/min.  If the detector has been subjected to A “T” tube connection is fitted to the unusually rough handling (drops) + tubing from the constant flow regulator  If the detector has been subjected to unusual environments (high humidity, high + Calibration is done from one side of the chemical concentrations) “T” fitting and excess flow goes out the Calibration gas is confidence in a can! other side of the “T” fitting + Inexpensive How to calibrate − Can use more gas First, ALWAYs follow your manufacturer’s recommendation about calibration requirements. Diffusion products are easy, just flow to the detector with an appropriate manufacturer recommended constant flow regulator. Copyright © 8/12/2014 Chris Wrenn Environics USA, Inc. 1308 Continental Drive, Suite J, Abingdon, MD 21009 Tel: (410) 612-1250, Fax: (410) 612-1251 [email protected], www.EnvironicsUSA.com Page 3 of 9

AP-110: Calibrate or Die!

Cup calibration you remove it from its charge/calibration + A constant flow regulator is used that cradle exceeds the maximum flow-rate of the + Automates calibration, can document pumped device calibration + For example pump draws at 250cc/min − Can be expensive to implement so regulator should flow at 500 cc/min − Tends to lock users into one vendor so + A Cup is fitted to the tubing from the customers don’t select ‘best of breed’ constant flow regulator products in each detection segment. For + Calibration with the inlet of the pumped example one might feel that one device drawing from the cup manufacturers PID is the best while they prefer another multigas detector. + Inexpensive Standardizing on one manufacturers Can use more gas − calibration solution may reduce purchasing flexibility − Discourages uses from touching the detector and developing good “muscle memory” during manual calibration Bad Calibration from a “Docking Station After receiving new detectors and new Flow matched vs. constant flow docking stations a customer called their calibration distributor to say that their new detectors were “acting funny.” When removed from + While a flow matched calibration is their docking cradle the detectors had very preferred, many manufacturers will accept unstable readings, this was unexpected a constant flow regulator for use with their because the customer had a lot of experience pumped units using the previous generation of this detector  For example pump draws at doing manual calibrations. Doing a 250cc/min so regulator should flow “Calibration Check” with a bottle of calibration at 250 cc/min gas demonstrated that the calibration was not  Using a 250cc/min regulator with a correct. After a manual calibration was 500cc/min pump could starve the performed the detector performed as sensors of calibration gas or draw expected. It was found that the docking in ambient air leading to an station was improperly set up and the inaccurate calibration calibration gas was plumbed into the wrong + The pumped device is connected directly to input ports the tubing from the constant flow regulator + Relatively inexpensive Lesson: it is a good idea to do a “Calibration + Easy to execute Check” of detectors after a docking station is − May have accuracy variations if flow rate of set up and after calibration cylinders have pump is radically different from that of the been replaced regulator Virtually any calibration is better Automated calibration than no calibration! + Automated “docking” stations help to One can get caught up in calibration reduce operator error by automating the procedure on things like whether a flow- calibration process matching calibration is best. But don’t lose + Manufacturers have a variety of calibration sight of the fact that virtually ANY calibration procedures, some do a full calibration daily, is better than no calibration! some do a daily “bump” and periodic calibration but all are designed to make sure that the detector is ready for use when

AP-110: Calibrate or Die!

detector is not in an atmosphere with the Calibration Gas Expiration reactive gas in it during the calibration Calibration gas will typically last as long as 24 process (or this would lead to false zeroes). months and as little as 6 months depending on The detector might absorb some of the the gas. One should Never use expired gas reactive gas into its sample components, like 1 ppm. The manufacturer specifies 10 ppm Cl2 calibration gas knowing that they will lose just 10% of the calibration gas to the sample components of the detector. But if one substitutes 5 ppm calibration gas then 1 ppm of lose to absorption is now 20% of the span value which can lead to an unstable calibration. Conversely, if one were to substitute 100 ppm Ammonia (NH3) calibration gas when the manufacturer specified 25 ppm calibration gas for a multigas detector not only could this stress Some gases can be very expensive to own: the NH3 causing it to fail early, but this high value of calibration gas could stress other sensors in the multigas detector leading to their premature failure. Calibration Gas “Hygiene” Users can cause calibration gas to go prematurely “bad.” Repeated introduction of small amounts of moisture, oxygen and other contaminants carried into cylinders by a closed regulator can affect the concentrations of the small amounts of highly reactive gases like Cl2. When a closed regulator is screwed onto a cylinder the air and other contamination between its threads and the closed valve is forced into the cylinder. Combustible gas sensor calibration gas and Oxygen, moisture and other contaminates multi-sensor, all-in-one or “quad gas” can quickly degrade highly reactive calibration gas all have some amount of oxygen calibration gases. It is best to open a (16-20.9% O2) in them or else the combustible regulator prior to attaching it to a cylinder of gas sensors won’t work because it requires gas; this keeps any oxygen. Oxygen concentrations below 20.9% moisture and also allow “spanning” of the oxygen sensor. contamination on the Reactive gases like NH3 and Cl2 are typically regulator from entering balanced with nitrogen because if there were the gas cylinder. any air in the bottle it would react with the gas Regulators and cylinders resulting in very short shelf life. While should be stored in a electrochemical sensors do require oxygen to clean, dry place. work there is typically enough oxygen in the Remove regulators from sensor electrolyte to get through a calibration. cylinders between uses Calibration Concentrations because the valves on Manufacturers have reasons for the calibration the regulators may not values and the flow values that they specify for be fully closed or may their detectors. Low values may give an even leak slightly leaving unstable calibration. Reactive gas sensors like no calibration gas for the next use. Chlorine (Cl2) are particularly sensitive to calibration gas concentrations. Generally the Copyright © 8/12/2014 Chris Wrenn Environics USA, Inc. 1308 Continental Drive, Suite J, Abingdon, MD 21009 Tel: (410) 612-1250, Fax: (410) 612-1251 [email protected], www.EnvironicsUSA.com Page 5 of 9

AP-110: Calibrate or Die!

depressurized is just a hunk of metal that can Not every gas uses the same be thrown out or recycled appropriate. After regulator all residual gas and pressure is bleed off Reactive gases often using the regulator, often all that is required is have special a simple tire valve removal driver to remove regulators AND non- all chance of pressurization prior to disposal. reactive Teflon hoses. Some go an extra step by drilling holes in the Isobutylene gas, used cylinder so it is obvious that it can’t hold to calibrate PIDs, only pressure. needs Tygon calibration tubing but 6 Don’t be afraid of Calibration inches of Tygon tubing  Modern designs make calibration easy will absorb much of 10 and automatic. ppm Cl2 so Tygon  Keep the Calibration Materials With the tubing is not Instrument! appropriate for a reactive gas calibration.  All-In-One Calibration Mixtures Make Therefore it is best practice to dedicate a Functional Testing Easy! regulator to a specific gas cylinder.  Don’t buy a sensor unless you are willing to calibrate it! Calibration hose can affect calibration Calibration: Record keeping Documentation is critical! Without good If a Cl2 sensor “thinks” it’s going to see 10 ppm and the 6” of Tygon tubing on the calibration records you cannot defend or explain your regulator absorbs 6 ppm then the sensor ends procedures (docking stations usually up thinking that 4 ppm is really 10 ppm. This is automate this). If you don’t have the records a primary cause of sensor “noise” and is easily to prove it was being done right -- it wasn’t! fixed by following proper calibration procedure Records can be as simple as the following chart: and using correct hose that will not absorb Cl2. Really what’s happening here is that the distance between zero and span is being accidently compressed by Cl2 absorption into the Tygon tubing. This compression results in a loss of sensitivity. Disposal of Calibration Cylinders The concentration of chemicals in calibration gas cylinders is typically below toxic and Where do I calibrate? Always follow your manufacturer’s flammable levels. Even when gases like Cl2 have 10 ppm in the cylinder and the TWA is recommendations. It is ideal to calibrate just 1 ppm, if the cylinder were to leak the under a fume hood. If lacking a fume hood, concentration of Cl would quickly be diluted use a well-ventilated area so that the 2 calibration gases don’t affect you or others. down to an insignificant level by the ambient air. The real “threat” of calibration gas cylinders is Always calibrate in a clean environment so that they are pressurized cylinders not that they that contaminants don’t affect the calibration. are toxic or flammable. Check with your vendor Some detectors do a “fresh air” or zero when and local regulations for disposal directions, but turned on so they must be turned on in a typically a cylinder that is empty and clean environment!

AP-110: Calibrate or Die!

Calibration “Headaches” A gas detection salesman complained that customer in-service detector trainings were so stressful that they gave him real headaches. But over time the salesman noticed that he only got headaches on classes where there was an actual hands-on calibration. He later found that his headaches were due to H2S exposures. Even at very low levels H2S would give him a head-splitting headache. Calibrating under a fume hood or outside in well-ventilated areas solved the problem. Calibrating cross-sensitive sensors It is possible to combine two cross-sensitive sensors, like ammonia and chlorine, in the same detector when absolutely necessary. Calibrate wherever you need to When calibrating a multi-gas sensor that has regain confidence in your detector two sensors whose gas have significant Docking stations are increasingly used by many cross-sensitivity, be sure to allow adequate to calibrate their detectors, but these fixed time between calibrations to allow the systems may not be immediately accessible sensors to clear. When calibrating sensors when one loses confidence in their detector with cross-sensitivities, calibrate the most (ex: fire dept. HazMat team). Typically the cross-sensitive sensor first, followed by the docking station is in a firehouse or an office that least cross-sensitive sensor. Wait for both is away from where the detector is detecting. sensors to recover to zero, and then expose Mobile users may want to consider carrying both to gas again with most cross sensitive calibration gas on their vehicle to restore first and least cross sensitive second. While confidence in their detector when in the field some manufactures say that you cannot put a away from their docking station. A small Cl2 and NH3 sensor in the same detector it is calibration cylinder and regulator in a case possible if calibration is done properly. (pictured below) can quickly help restore confidence in a detector. Always calibrate in a For example, 65 ppm of NH3 produces 0 ppm well-ventilated area response on a Cl2 sensor and 1 ppm of Cl2 produces about -0.5 ppm of response on a NH3 sensor. Calibrate the NH3 sensor first with 50 ppm of NH3. This should have no effect on the Cl2 sensor. Calibrate the Cl2 sensor on 10 ppm Cl2. This will send the NH3 sensor negative for some period of time. After calibrating the Cl2 sensor, return the detector to clean air and wait until the most cross-sensitive sensor (NH3) fully recovers and/or stabilizes (if it stabilizes to a number other than zero then re-zero the detector). Photo: Luke Sloan After both sensors return to zero apply calibration gas in the same order (NH3 first then Cl2) and note the sensor response. If both sensors are within 10% of the value on the gas cylinder then the calibration of the cross-sensitive sensors was successful. In

AP-110: Calibrate or Die! most cases it’s just easier to separate these the loading dock in a remote part of the plant two sensors in separate detectors pumping out 150 ppm CO in the worker breathing zone. Calibration to help improve your  Clues: Printed circuit board plant confidence in your detector  Toxic Unsafe zero calibration Sensor: 35- A HazMat officer was making an entry into a 45 ppm sewage pump station for preplanning. All the reading on CO right confined space entry operations and  LEL: no permitting were completed. Upon entry to the reading on confined space the officer immediately exited LEL feeling difficulty in breathing and light  PID: no headedness. He thought it was from drinking reading on too much coffee and a long night at the station. PID They then went to the next confined space to  Tubes: 50 preplan, but this time he could tell from ppm reading experience that the atmosphere was most likely on CO tube bad. So he asked him to check it. The Proper Calibration Eliminates a attendant lowered the tubing into the space and Phantom Negative Alarm then turned the confined space detector on. A customer using a PID in a styrene plant The officer was alarmed but waited until the complained of frequent “negative” alarms attendant gave the “everything is normal” sign. when using the PID in the plant. When The officer asked the attendant to take the observed in their calibration lab their tubing out of the space and re-zero the unit in a calibration procedures seemed appropriate. clean atmosphere. With a fresh air calibration When walking through the plant with the PID complete, he lowered the tubing back in the it seemed that the “negative” alarms came space. The unit immediately went into alarm for when a breeze blew through the open air high H S, and low O . If they had entered the 2 2 plant. When checked with a PID calibrated space this time, the odds are they would have outside of the plant it was determined that the collapsed entire plant (including the calibration lab) had  Some detectors zero themselves when a background of 5-10 ppm of styrene. When turned on. If they are turned on while the clean wind blew through the plant the sampling a contaminated atmosphere PIDs tried to read lower than zero prompting they will zero out that atmosphere the “negative” alarm. Charcoal filters were an Printed Circuit Board Plant easy solution to provide clean, zero air for the The CO sensor in a 5-gas detector indicated PIDs. But “zero gas” could also have been 35-45 ppm in a printed circuit board plant with used. styrene, xylene, acetone and other aromatics Calibration Mistakes and ketones expected to be in the air. The user of the detector jumped to false conclusion Negative Alarms that CO sensor was bad or it was responding to Typically negative alarms are caused by hydrocarbons, but the PID showed no zeroing when a background is present and significant reading. When the detector was then going to a cleaner environment. As fresh-aired outside of the plant it still showed there is no such thing a “negative CO” the high CO inside. After the detector was detector usually gives some sort of “NEG” or calibrated with CO gas and still showed the “Negative” alarm. same high CO levels in the plant. When the air was check with a CO colorimetric tube it Startup Zero registered a 50 ppm CO reading which agreed Some detectors zero at start-up, so starting in within 10% to what the detector was reading. “clean” air is always a good idea for all So the user finally started to look for CO. detectors. Investigation found a shrink-wrap machine on

AP-110: Calibrate or Die!

Zeroing near running engines Internal combustion engines that are running Calibration or Die! (like in engine bay) generate CO and The importance of calibration for handheld gas and vapor detectors cannot be under- sometimes SO2. Elevated levels can be found long after an engine has been shut down. emphasized because many gas sensors fail Clean outdoor air is often the best solution for to an unsafe state. The only way to assure this problem. that many sensors are working correctly is to apply a gas to them to “calibrate” them. My detector failed calibration, what next? About the Author If any sensor fails calibration in a detector, and Christopher Wrenn is the Sr. Director of any remedial steps don’t address the problem, Sales and Marketing for Environics USA a then the sensor needs to be replaced or the provider of sophisticated gas & vapor detector repaired and recalibrated before use. detection solutions for the military, 1st Any detector that has failed calibration and has responder, safety and homeland security not been repaired should not be used. Any markets. Previously Mr. Wrenn was a key detector that has failed calibration has been member of the RAE Systems team. Chris repaired and subsequently passed calibration is has been a featured speaker at more than safe for use. If any sensor in a multi-gas 100 international conferences and has written detector has failed, then the entire detector numerous articles, papers and book chapters should be put out of service until it can be fully on gas detection in HazMat and industrial repaired and calibrated because all of the safety applications. sensors may be needed to solve a particular gas detection challenge.  “Only my oxygen sensor failed calibration, can I still use it?” NO