Tag Archive | "calibration"

Multiple Gas Detectors – Should They all be Calibrated at the Same Time?

Depending on the number and placement of gas detectors in your facility, you might be looking at the task of calibrating them as never-ending. It is true, calibration can be time consuming, especially if it is a large area populated with multiple fixed location sensors with different gas types – some near the ceiling, others near the floor and still others somewhere in between. However, it is a task the needs to be done and dedicating the time to calibrating them all at once is the optimal and responsible course of action. Having some sensors calibrated and others not on a job site leaves room for inaccuracies and poses a potential danger to workers and the public.

How long it takes to calibrate all the sensors will depend on the experience and training level of the person doing the calibration, what type of equipment is used and the number of sensors in the facility. Trained technicians can calibrate up to two different types of gas sensors at one time, which saves labour time. Taking on that challenge is not recommended unless the technician has the equipment, training and experience. Calibrating one sensor at a time may take a little longer, but can be easier for the inexperienced service technician and the end result is still a correctly functioning gas detection system.

Monthly bump testing of sensors is recommended in particular for sensors that are monitoring for gases that pose a serious health and safety risk when they leak, such as Ammonia, Chlorine, and Ozone. A log book must be kept to detail date, time and confirm bump testing results. It benefits the user to bump test all gas sensors in their facility. When bump testing Ammonia, in particular, use only a concentration of span gas just higher than the low alarm set point. Ammonia sensors are consumable and their life span is often measured in “ppm hours”. Using a high concentration of NH3 span gas to bump test will shorten the life of an Ammonia sensor.

How do you know if you are getting a correct reading from the unit?

The only way to guarantee that an instrument will detect gas accurately and reliably is to test it with a known concentration of gas. Exposing the instrument to a known concentration of test gas will show whether the sensors respond accurately and whether the instrument alarms function correctly. Keeping a log and verifying the accuracy of readings on a daily basis for a trial period will reinforce your confidence that the unit is performing correctly.


For suggestions on gas detection systems, indoor air quality monitors and calibration, please visit


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Where are the Gas Detectors in Public Swimming Pool Facilities?

Indoor swimming pools provide exercise and recreational fun for all ages. To ensure swimmers are submerged in crystal clear, sanitary water, a disinfectant maintenance program using Chlorine, or Chlorine & Ozone are commonly followed to treat the pool water. Chlorine is a powerful, corrosive disinfectant and in both gas and liquid forms it is toxic and hazardous to living beings at concentrations as low as 1 ppm. Ozone is created by exposing oxygen to a high voltage or ultraviolet radiation. It is more powerful than Chlorine and when used in conjunction with Chlorine it helps provide an odourless, clear water environment. Less Chlorine is required when Ozone is used as part of a swimming pool sanitization program.

The areas for potential gas leaks of Chlorine and Ozone are found around the equipment in the Chlorine Feed Room and the Ozone Generator Room. In a typical swimming pool application where only Chlorine is being used to disinfect the pool water, we suggest a controller or transmitter with  a display, audible alarm and relay outputs, be mounted outside the Chlorine Feed Room beside the inspection window so it can provide a visual confirmation of the gas level readings prior to entry. If there is a Chlorine leak, the controller or transmitter will alarm and trigger the relays to shut down the ventilation system until it is safe to exhaust the gas from the contaminated area, or activate the ventilation system depending on the local regulation codes. Inside the Chlorine feed room should be mounted a remote transmitter with a Chlorine sensor that provides continues monitoring for leaks and communicates with the controller outside the room. Chlorine is heavier than air and tends to collect in low-lying areas, so the gas detector inside the room should be mounted 6 inches above the floor, close to the area of a potential leak, but away from the ventilation fans and any pockets of air currents.

Similarly, in a typical swimming pool application that uses Chlorine & Ozone to disinfect the pool water, in addition to the aforementioned gas detection system for Chlorine, we suggest a similar set-up for the Ozone Generator Room. A controller with a display, audible alarm and relay outputs should be mounted outside the room to provide confirmation of the gas levels inside the room prior to entry. A remote transmitter with an Ozone sensor should be mounted inside the generator room, near the equipment and between the generator and the destructor. Pure Ozone is slightly heavier than air but does not necessarily settle to the floor. If additional reaction tanks or destructors are more than 16 ft (5 m) away from the existing sensor, an additional sensor may be required. If there is an Ozone leak, the controller will alarm and trigger relays to activate the emergency air exhaust system.

For both applications a remote visual alarm device such as a strobe should be mounted on the ceiling or wall inside the pool area to provide an additional visual alert in the event of a leak inside either room.


View Diagram


There are outside influences that affect the operation of gas detectors and the equipment with which they interface. In addition, sensors change characteristics as they age; they have a set lifespan and deteriorate over time. Regular maintenance of the gas detection system by a qualified technician is as important as a proper installation. For a newly installed system or as part of a very thorough maintenance schedule it is recommended that a bump test be done every 30 days. A bump test basically follows the same procedure as a calibration, but it normally uses less gas and requires less understanding of the intricate workings of the gas detector. A bump test tells you if the detector is malfunctioning or operating normally, if the sensors are responding to the gas as they should and if the low, mid and high alarms are being triggered. This level of upkeep allows you to determine that the daily readings are accurate and the devices are working correctly. If the system malfunctions or goes into fault, patrons and workers would be unprotected if a leak was to occur during that time.

If a bump test fails, a full calibration is required. Calibration is more time consuming than a bump test and should be done by a qualified technician. It is recommend that a full calibration be done every 6 months, regardless of the performance or type of gas detection device. Calibration is like resetting the parameters of the device, in terms of telling what it should be doing at what level. It could be compared to a reset button. As the sensors age, their sensitivity to the gas decreases. Calibration allows you to compensate for that deterioration and keep the sensor detecting the gas at the appropriate levels so that the low, mid and high alarms go off as they should.

It is important to keep a maintenance log with dates and services performed. After a full calibration, a service sticker should be place on the device indicating when the next calibration should be done.

When bump testing or calibrating a Chlorine or Ozone sensor, there are a few things to keep in mind. Both Chlorine and Ozone are considered to be one of the “sticky gases”, meaning they adhere to surfaces and as a result, decrease in concentration. During the flowing of the gas over the sensor, the gas will adhere to the inside of standard tubing and the lengthier the tubing the less gas is left to hit the sensor. Using Teflon lined tubing is recommended, as is a length of tubing no longer than 2 to 3 feet so the gas flow concentration doesn’t lessen over the distance from the gas cylinder to the sensor.

Last but not least, when calibrating a Chlorine sensor, to ensure you get true readings, it is recommended that you use a Chlorine gas generator rather than a cylinder of Chlorine gas. The stability and quality of the chlorine gas is much higher from a generator, making calibration easier and accurate.

For suggestions on gas detection systems, indoor air quality monitors and calibration, please visit www.critical-environment.com


Written by Rebecca Erickson

Ozone Safe Work Practices, 2006 ed. WorkSafe BC 
Chlorine Safe Work Practices, 2002 ed. WorkSafe BC

Posted in Educational, HealthComments Off on Where are the Gas Detectors in Public Swimming Pool Facilities?

How often do gas cylinders need to be replaced?

Gas cylinders are made by many different manufacturers, are available in a variety of sizes, can be disposable or refillable and filled with a low, high or pressurized concentration. Generally speaking, the shelf life of calibration gas, (also known as span gas), is dependent on three factors:

  1. Gas Type
  2. Gas Concentration
  3. Gas Cylinder Quality and Size

1. Gas Type

Calibration gases can be divided into two types: reactive and non-reactive. “Reactive” is a broadly used term for chemicals that have some instability under certain conditions and may react with certain materials, moisture, oxygen or other chemicals. Reactive gas mixtures include gases such as ammonia (NH3), chlorine (Cl2), hydrogen sulfide (H2S), sulfur dioxide (SO2), hydrogen chloride (HCl), hydrogen cyanide (HCN), etc. Reactive gas mixtures are normally filled in aluminum cylinders with stainless steel valves that have been treated to minimize reactivity with the reactive gas. These mixtures have a shorter shelf life, typically 6 months to one year, because the concentration of the reactive gas is likely to dissipate over time.

“Non-reactive” is a broadly used terms for chemicals that are stable under most conditions and are not affected by moisture, oxygen or other chemical interactions. Non-reactive gas mixtures include alkane or alkene hydrocarbons (methane (CH4), propane (C3H8), hexane (C6H14), isobutylene (C4H8), etc.), nitrogen (N2), hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), etc. Non-reactive gas mixtures are normally filled in steel cylinders and typically have a shelf life of about 3 years.

2. Gas Concentration of Reactive Gases

In some cases, a higher concentration of a reactive gas can have a longer shelf life than a lower concentration. In low concentrations, a few reactions can have a much larger effect on the overall composition of the mixture than the same reactions in a highly concentrated mixture.

3. Gas Cylinder Quality and Size

A well-made gas cylinder will have, on a microscopic level, the smoothest interior walls as possible. If the walls are rough, it allows the gas to come in contact with a larger surface area which increases the likelihood of a reaction with contaminants or the cylinder material itself. The quality of the internal walls and the material of the valves are both factors that affect the shelf life of reactive gases. In addition to the quality of the materials, larger, high pressure cylinders allow for longer shelf life because the ratio of the internal wall surface to gas volume is substantially less and thus there is less potential for a reaction.

Regardless of the type of gas mixture, cylinders that do not bear a legible written, stamped or stenciled identification of the contents should not be used. It is also important to note the expiry date and not to use the gas past that date. If an inappropriate amount of calibration gas is used or if expired gas is used during calibration or bump testing, the result could be improper calibration and may result in a potentially dangerous situation.

For suggestions on gas detection systems, indoor air quality monitors and calibration, please visit www.critical-environment.com

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Gas Detectors

CETCI gas detectors are used to detect many different gases. Some of the most common are Carbon Monoxide, Carbon Dioxide, Nitrogen Dioxide, Nitric Oxide, Ammonia, Chlorine, Ozone, Combustible Gases like Methane and Propane, Oxygen, Refrigerants and more.

IAQ Monitors

The YES Series of IAQ Monitors are essential for those responsible for conducting Indoor Air Quality (IAQ) Investigations. These instruments are specifically designed to measure and record the quality of indoor air in offices, buildings, homes, schools, parking garages, ice rinks, etc.