It is a bright Monday morning andyou have just arrived at your officeto start the week. On your desk,there is a package marked to yourattention, the company’s industrialhygienist, which has been placedthere during the weekend. Judgingby its size, you know that it couldonly be one thing. You think toyourself, “It’s here!” The brand newmulti-gas instrument has finallyarrived. You open the box to findthe shiny new instrument within.You pick up the instrument andquickly realize that this is not likeyour son’s game system that simplyhooks up to the television, requiringno review of the instruction manual.You decide it would be best to knowas much about this product as possi-ble. After all, it is a lifesaving pieceof equipment. As you read throughthe manual and caution statements,questions start to pop up in yourmind. Calibrate monthly? Bump testbefore each day’s use? You think toyourself, “How do I do all of this?”As you continue reading, you findthat some extra equipment, such ascalibration gas cylinders and otherrelated equipment, may be needed.You realize that these things thatyou have not purchased may be asimportant as the instrument itself.

Scenarios similar to this one happenevery day in safety departments

within almost every industry. Often,a great deal of time and money arededicated to selecting and purchas-ing a gas detector with little to nothought about the calibration equip-ment that is designed to keep theinstrument operating as the manu-facturer has intended. Regardless ofthe instrument manufacturer, fol-lowing the calibration and bump testrecommendations is imperative toensuring that the unit continues tobe a life-preserving piece of equip-ment. So, how do you know whattype of calibration cylinders andequipment you will need to buy?

Should I buy my calibration gasfrom the instrument manufactur-er or from a local supplier? Before you purchase calibration gas,you must decide whether you aregoing to purchase the instrumentmanufacturer’s calibration gas pri-vate label or purchase it from anoutside local supplier of calibrationgas. In order to make this decision,there are a few things you shouldconsider. Some instruments requirea specific calibration gas concentra-tion and therefore may only beavailable through the instrumentmanufacturer. Although the localsupplier may be cheaper than thequoted manufacturer’s price, it mayalso lack the quality necessary toachieve a good calibration.

One way to verify the quality of thecalibration gas from a local supplieris to ask if the gas cylinder is NIST(National Institute of Standards andTechnology) traceable. In short,NIST traceability provides confi-dence that the proper cylinder con-centration analysis was performedand that a Certificate of Analysis isavailable. Typically the manufactur-er’s private label will be NISTtraceable but it never hurts to verifythis. Do not overlook the impor-tance of NIST traceability. After all,the calibration cylinder is the cor-nerstone of your calibration. If youstart with a flawed calibration gassource, you are going to get aflawed calibration.

Do I use a single-gas cylinder or acylinder blend?The next decision on cylinder selec-tion is whether to use a single-gascylinder or cylinders that have mul-tiple gases blended within.Naturally, single-gas instruments arebest served by using a single-gascylinder, while blended cylindersprovide greater convenience tomulti-gas instrument users.

One of the most common calibra-tion gas blends is known as thefour-gas mix.

This mix of carbon monoxide, hydrogen sulfide, oxygen and combustible gas provides the user of a standard four-gas instrument in this same sensor arrangement, an easier, quicker and cheaper way of calibrating and bump testingtheir instrument. The technology of calibration gas cylinder blending has allowed for almost any four- or five-gasinstrument sensor configuration to be calibrated from just one cylinder. In cases where a blended cylinder is notavailable in that instrument’s sensor configuration, individual single-gas cylinders must be used.

*Data is based on calibrations only. Performing frequent bumptests, as recommended, will reduce the amount of calibrations thata cylinder can provide

What size calibration gas cylinder should I buy?Calibration gas cylinders come in all different sizes ranging from a 17 liter cylinder all the way up to 4,000 liters.Because these cylinders have a shelf life of six months to three years, you have to carefully gauge the amount ofcalibration gas you will use in a given time period. The amount of calibration gas you will use is based on threefactors: number of calibrations and bump tests, amount of time to complete the calibration or bump test and, finally,flow rate. Although this can vary from one manufacturer to the next, a rough estimate of the number of calibrationsyou can expect from a given bottle size is given in the table above.

Which regulator type do I choose?Once you have selected your cylinder(s), the appropriate regulator must be selected. Selection of the regulator isbased on cylinder type, instrument being diffusion or aspirated and whether or not a calibration station is beingused.The simplest of the regulators is the constant flow regulator. This regulator will deliver a constant flow at aspecified rate continuously until the cylinder is either empty or the valve is shut. This type of regulator is useful forcalibrating and bump testing diffusion-type instruments.The demand flow regulator, although more expensive thanthe constant flow regulator, is designed to provide the calibration gas automatically to the instrument via a mechan-ical pump pulling the gas through the regulator. This type of regulator is optimal when calibrating or bump testinginstruments with internal sample draw pumps. This is because it only allows gas to be delivered when the pumppulls the gas and the flow rate will be matched by the pump. If using a calibration station, the demand flow regula-tor is often your best choice. The calibration station will pull the gas automatically through the demand flow regu-lator upon demand, eliminating the need for the user to turn a valve on and off during the calibration or bump test cycle.

Selecting the calibration gas and associated regulator does not have to be as daunting of a task as you thought ifyou follow these simple steps:

(1) Select the calibration gas cylinder manufacturer.(2) Decide if you are going to use single-gas cylinders or the more popular multi-gas blends.(3) Select the cylinder size based on annual usage.(4) Choose the appropriate regulator.

With an instrument manufacturer’s bump test and calibration procedures fully understood, and having the correctcalibration gas and regulator on hand, your life-preserving piece of equipment will continuously work in the waythe gas detection manufacturer had intended which is to help keep your people safe.

Brad Day is a product manager at Industrial Scientific. He can be reached at bday@indsci.com. Forinformation about Industrial Scientific and its products, visit www.indsci.com

Reprinted from the May 2012 issue of Industrial Hygeine News

Cylinder Size Number of34 liter four-gas mix Approximately 30

650 liter four-gas Approximately 600