FAQ: Gas Detection & Calibration Questions Answered

FAQ: Gas Detection & Calibration Questions Answered

Frequently Asked Questions:

What is Gas Detector Calibration?

Gas detector calibration is a requirement for all gas sensors.  It is the act of exposing a sensor to the target gas in a specific concentration, and then adjusting the detector to read that gas concentration properly.  Many sensors also require the use of zero gas to adjust the voltage that is being output when the target gas is not present in the air.  This calibration should always be performed by a competent technician that follows the manufacturer’s instructions properly.  The improper calibration of a gas detector can result in false alarms or a failure to alarm when a hazard is present.

How do you calibrate a CO2 sensor?

Calibrating a CO2 sensor requires span gas ( a bottle with a very specific concentration of carbon dioxide)  and zero  gas (a bottle with no  carbon dioxide).  Some CO2 sensors may allow for a zero calibration that is actually at normal outdoor air levels of 350-400 ppm carbon dioxide, while others require the use of nitrogen gas with no CO2 present.  Knowing the difference between an  air calibration and zero calibration is vital to proper calibration and accuracy of these sensors.


How often should gas detectors be calibrated?

Gas detectors should be calibrated at least as frequency as the manufacturer recommends, or more frequently based on use.  The absolute longest interval between calibration should be 12 months, which is standard for parking garage gas sensors.  Most occupational health and safety sensors should be calibrated every 3 months, and portable gas monitors are often calibrated every 30  days  Often times, out technicians  base the calibration frequency on the levels of exposure expected, such that areas  where gas rarely leaks get calibrated  annually and areas that lea often get calibrated every 30 or 90 days.


How do you calibrate a sensor?

Calibrating a gas sensor requires knowing the brand, model, and type of sensors present.  First you  should read the manual and gather the correct span gas, zero gas, regulator, calibration cap, multimeter, and any specialized controller.  Next the sensor should be inspected for damage.  Finally  the  manufacturer’s  instructions should be followed which includes the application of test gases, span and zero adjustments,  and labeling that the unit has been properly calibrated.


What is calibration gas used for?

Calibration gas is a bottle that contains a pressurized mixture of gases which are specific to the type of sensor being calibrated.  These bottles should be mixed and formulated to NIST requirements, have an expiration date, and be  clearly labeled with the concentration of the target gas and any other gases that are present in the bottle (i.e. air, nitrogen, oxygen, etc.)   Calibration gases can be ordered from Hawk Equipment Services by part number, gas concentration, or specifically formulated  for the brand and model of sensors that you are calibrating.


Is calibration gas dangerous?

Calibration gases, also called span gases, are formulated to a concentration that is typically below the permissible  exposure limit and  lower explosive  limit of the gas being used.  These gases are then placed into a steel or aluminum cylinder under pressure and labeled for safety.  Typically, even if the entire bottle of gas leaked into a room there would be no hazards from fire or exposure, as these gases are in concentrations low enough to prevent these dangers.  Please be sure to fully read the SDS and all safety warnings if you  are unsure of the gas that you are using.


What is zero gas?

Zero gas is a type of calibration gas that has been certified to be free of the toxic of flammable gas that your sensor detects. In general, these gases are wither “air zero” which consists of 20.9% oxygen and 79.1% Nitrogen.  There is also zero gas that is used to calibrate oxygen sensors that consists of 99.9% nitrogen.  When calibrating a gas sensor, it is very important to have properly formulated zero gas to prevent inaccurate readings on your detector.


What is balance gas?

Balance gas is a term used to describe what the remainder of a calibration gas cylinder has been filled with.  If your calibration gas contains 100 ppm carbon monoxide, the balance gas would typically be 999,900 ppm of air or nitrogen.  It is very important to know what balance gas is present in the bottle as sensors that can detect corrosive gases like chlorine may not respond properly to calibration gas that has a balance of nitrogen with no oxygen.


What is the coverage area for a gas sensor?

Each manufacturer will publish the coverage area for their specific sensors.  In general, most toxic gas sensors have a coverage range of 5,000 – 7,500 square feet, while most combustible gas sensors will cover an area of 900  – 1,250 square feet.  Please be sure to  check with your supplier, engineer, distributor, or manufacturer rep  to determine the coverage area that is correct for your specific application.


Who calibrates gas sensors?

The calibration of a gas sensor should always be done by a technician that has been properly trained and has the correct supplies.  This task requires the understanding of how the devices work, what the procedure for that sensor is, and all of the necessary supplies.  Most companies have these sensors calibrated by a gas-detection technician that specializes in this service.  These technicians will have the correct span gases, regulators, tubing, hoses, meters, and tools to certify that the units have been adjusted to the manufacturer’s specification.  Improper calibration of these sensors can create a serious hazard and expose an inexperienced technician to extensive liability.


How much does it cost to calibrate a gas sensor?

While rates and fees may vary between companies, a qualified vendor will normally charge for a site visit and calibration for each sensor.  This calibration should ALWAYS include labeling of each sensor and a full report that shows calibration was accurately performed.  Most gas sensor calibration companies will include the cost of supplies and equipment to the calibration quote, as only a small portion of the calibration gas bottle is used on each sensor, and the majority of the other supplies can be used at multiple jobsites.  If a company were to perform their own calibration, they would incur the costs of the full gas bottles, multiple regulators, and all of the specialty meters and tools necessary to perform this calibration.  Better rates are often provided for companies that schedule in advance, and allow the calibration technician to get all of the sensors at the facilities calibrated at the same time.


Who checks gas sensor calibration?

Gas detector calibration is generally check by the building commissioning agent and the fire marshal at the time a certificate of occupancy issued, and during the annual fire inspections.  These inspectors expect to see proof that the sensors have been tested and calibrated by a trained technician, and that a formal report stating the procedure and results of testing and calibration.  While the manufacturer’s do calibrate the sensors before shipping, changes in temperature, humidity, pressure, and age can cause the sensors to detect inaccurately.  For this reason, most inspectors will refuse to accept a factory certificate and require on-site calibration or testing as part of the building commissioning report.

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