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March 26, 2015

Gas Detection in Public Swimming Pool Facilities

Written by: Rebecca Erickson

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 will alarm and must trigger 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 transmitter 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.
 
Likewise, in a typical swimming pool application that uses Chlorine and Ozone to disinfect the pool water, in addition to the aforementioned gas detection system for Chlorine, we suggest a similar setup for the Ozone generator. 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.
 
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 working 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 determine if 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.

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