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September 23, 2016

How do You Know if Your Gas Detector is Working Properly?

Written by: Rebecca Erickson

A gas detector is a safety device. It is intended to monitor and measure potentially lethal gases in the workplace and other places where people frequent such as shopping malls, underground parking lots, arenas, swimming pools, etc. It helps protect lives, security, property and the environment. A properly functioning gas detector could be the difference between life and death. With such serious consequences on the line, how do you know your fixed gas detection system is functioning properly?

Did you buy your gas detection system from a reputable company and have it installed by a qualified technician? Incorrect settings can cause your monitor to give false readings and alarms, or more seriously, not alarm when it should. The initial settings and calibration of your equipment should be done by the manufacturer, the dealer or a trained technician to ensure the device is going to operate correctly from the time it is installed.

How well do you know the system and how confident are you that the system is functioning properly? A newly installed system and/or sensor should be closely monitored on a weekly basis (more often if necessary) for a period of time until your expectation in its performance can be set with confidence. Keep records of accuracy readings and any maintenance that was required to develop a history you can refer back to if needed. Any problems associated with having mounted the equipment in an inappropriate location where there might be air flow issues or interference from other gases or issues with sensitivity can be corrected sooner rather than later. Understanding how the system is supposed to respond and how it actually responds will help you quickly determine if it isn’t working properly.

Do you routinely physically checked the equipment, inside and out?Wear and tear on any device can affect its performance and reliability. Gas detection equipment should be checked on a regular basis for accidental damage, deliberate tampering, dirt, cracks, water damage, loose screws and wires, etc.

Is there a qualified person performing routine bump tests?Monthly bump tests are highly recommended, especially for applications involving more dangerous gases, lots of people and any application regulated by Occupational Health and Safety standards. A bump test involves flowing a sample of the target gas over the sensor in question and verifying that the sensor response is strong enough to activate the configured alarm condition. If the detector goes into alarm when shown a target gas concentration that is slightly higher than the configured alarm set point, you know the sensor will respond if there is a gas leak. If a bump test fails or the instrument doesn’t perform as expected, a full calibration should be done to determine if the device is defective or just in need of an adjustment.

A bump test only checks that the detector responds, it does not check the accuracy of the instrument. That is what calibration does. Most often malfunctions are discovered at the time of calibration or bump testing which means at some point between calibrations, the gas detector developed a problem.

Do you have a qualified person calibrating the gas detector on a regular basis?‘How often should I calibrate?’ is one of the most commonly asked questions concerning the use of gas detection instruments. Calibration frequency depends on many factors such as: the type of gas detection system, how it is being used, the required accuracy of the system, manufacturer’s recommendations, application specific health and safety laws and regulations, whether you suspect there are environmental conditions or potential damage that has occurred to the instrument that could affect its performance, whether bump tests are part of your regular maintenance program, etc. At the bare minimum, fixed gas detection systems in underground parking garages and refrigeration applications should be calibrated annually. Applications like swimming pools (chlorine), arenas (ammonia) and others that must meet the Occupational Health and Safety standards should be calibrated every 6 months, or as stated in the regulations.

The calibration procedure uses a specific gas concentration to set a value against which the detector will use to compare the concentration of leaking gas to, should there be a leak. If the leaking gas concentration is higher than the calibrated set value, the alarm will sound and depending on the instrument features and configurations, relays will activate other safety equipment, such as fans or other alarm devices. 

Calibration takes longer and uses more gas then bump tests. However, calibrating the sensor against a known gas standard is the only way to know if the detector will accurately respond to the gases it is designed to detect.

Do you keep a maintenance log? Maintaining a written record of the calibration and bump test results, including adjustments made for calibration drift and any maintenance and repairs carried out, provides a history for reference on how the detector has been performing.

Best Practices:

  • Use the recommended calibration gas concentration.
  • Never use a calibration gas that has passed its expiry date.
  • Follow the manufacturer’s instructions on how to properly calibrate the detector and use the tubing, flow rate, regulators and adapter hood provided by or recommended by the manufacturer of the instrument.
  • Establish a preventative maintenance schedule that includes bump tests, calibrations and physical checks of the equipment.
  • When calibrating sticky gases such as Ozone, Chlorine, Hydrogen Chloride, Ammonia or Nitrogen dioxide, use a Teflon lined hose so the gas doesn’t saturate and adhere to the tubing, weakening the concentration of the flow of gas. Also, keep the length of the Teflon hose to no more than 2 - 3 ft so the gas flow concentration doesn’t lessen over the distance from the cylinder to the sensor.
  • When calibrating a chlorine sensor, use a chlorine gas generator instead of a cylinder of chlorine. Our tests have shown Chlorine cylinder gas to be unstable and it is difficult to get an accurate reading from that source. The quality of the chlorine gas is much higher from a generator, making calibration easier and accurate.
  • Flowing dry gas over a solid state refrigerant or TVOCs sensor can result in a negative a reaction and inaccurate readings. Using a humidification chamber adds humidity and assists in recreating a “real-world” environment for the sensor.
  • When flowing zero or span gas, check the gauge. If it is not showing 30 psi or more, the flow of gas may not be adequate to meet the requirements of the regulator.
  • Be sure to notify the appropriate people before you start any maintenance that may trip relays that set off the alarms, turn on or off fans or notify the fire department directly. There is no reason to send workers and/or patrons into panic mode thinking there is a real emergency. Similarly, the fire department does not look upon false emergency response calls favourably and may charge a hefty fee for wasting their time.
  • Call the manufacturer if you have concerns, questions or require assistance.

 

For suggestions on gas detection systems, indoor air quality monitors, bump tests, calibration, maintenance or service please visit www.critical-environment.comor call us at 1877.940.8741

 

References

Wagner , Dave. (2011, July 13)“Bump Test or Calibration Check? General Gas Education” Industrial Scientific The Monitor Blog, accessed 23 September 2016http://www.askdaveblog.com/general-gas-education/bump-test-or-calibration-check/

Theriot, Francelle. (2011, January 21) “Atmospheric Monitors: Calibration vs. Bump Testing” Roco Rescue OnLine, accessed 23 September 2016http://rocorescue.wordpress.com/2011/01/21/atmospheric-monitors%E2%80%A6%E2%80%9Ccalibration-vs-bump-testing%E2%80%9D/

MacNeal, James R. (2006, October 1) “Air Monitor Calibration, Bump Testing, and Sensor Challenge” OH&S Occupational Health & Safety, accessed23 September 2016http://ohsonline.com/articles/2006/10/air-monitor-calibration-bump-testing-and-sensor-challenge.aspx

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