Fixed Gas Systems FAQs

Are there other considerations for locating sensors?


Sensors should not be placed near ventilation fans or openings to outside. They should be placed in areas where there is good air circulation, but not in the path of rapidly moving air. Pay particular attention to “dead air spots” where there is little or no ait movement.

Does gas detection equipment need maintenance and calibration?


Yes. Maintenance on a properly installed, quality system is minimal and need on consist of a visual inspection and verification of operation. Calibration frequency depends on sensor type and application. Typical frequency for commercial applications is 1 to 2 times per year. For areas where health hazards may exist, 3 to 4 times per year. Industrial applications 4 to 6 times per year or even monthly.

What does % LEL mean?


Combustible gases form flammable mixtures with air. For each gas there is an explosive range within which the fuel to air mixture will support combustion. LEL is an abbreviation for Lower Explosive Limit, which is the minimum concentration for each gas in air that must be present for combustion or explosion to occur.

% LEL refers to a method of measuring the concentration of a combustible gas where the range of the sensor is set to correspond with the concentration of gas that is below the explosive range. In this case the Lower Explosive Limit equals 100% LEL.


What is cross-sensitivity?


Cross-sensitivity refers to the response of a sensor to a gas other than the target gas (also called an interference gas).

What is the breathing zone?


The breathing zone refers to the area 4-6 feet from the floor, where most human breathing takes places. This is a good default location for sensors.

What should the mounting height of the sensors be?


This depends on the density of the gas relative to air. Heavier than air gases should be detected 6 inches from the floor, lighter than air gas sensors should be placed on or near the ceiling and gases which have a density close to that of air should have sensors installed in the “breathing zone” 4-6 feet from the floor. Consider accessibility for calibration when locating sensors.

Why do I need a fixed system when I can use portable personal monitors?


Fixed systems monitors 24/7 whether personal are in the risk area or not, personal monitors operate only whilst the person takes the monitor in to an area, and until the batteries need replacing/recharging.

Fixed monitors can provide audible and visual indication of an alarm at multiple entries to a room and over a wide area within a room using linked warning beacons, personal monitors can only indicate to people within close vicinity – especially in noisy areas.

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