Q. What should the mounting height of the sensors be?
This depends on the density of the gas relative to air. Heavier than air gases like LPG should be detected 6 inches from the floor, for lighter than air gases like Methane, 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 to 6 feet from the floor. Consider accessibility for calibration when locating sensors.
Q. What is the breathing zone?
The breathing zone refers to the area 4 to 6 feet from the floor, where most human breathing takes place. This is a good default location for sensors.
Q. Are some gases heavier or lighter than others?
All substances have a molecular weight determined by the number and type of atoms in the molecule. In a gaseous state, the larger and heavier the molecule, the heavier the gas.
Q. Are there many types of sensors used for gas detection?
There are many sensors used to detect gases. Types of popular sensors include Solid State ( Metal Oxide Semiconductor), Electrochemical, Catalytic, Infrared, Galvanic, Photoaccoustic, PID.
Q. Why are different kinds of sensors used?
Different sensors use different physical or chemical properties of different gases for detection and measurement. Toxic gases are generally detected using Electrochemical Sensorss. Flammable gases are generally detected using Catalytic Sensors. Most gases can only be detected by one or two sensor types. Sensor choice also depends upon required accuracy and specificity, sensor life expectancy and cost.
Q. What are the advantages and disadvantages of Semicoductor sensors?
Advantages : Low cost, long life, quite resistant to poisoning
Disadvantages : Broad spectrum, non-specific, not as accurate as other types
Q. What are the advantages and disadvantages of Electrochemical sensors?
Advantages : Accurate, repeatable, more gas specific, defined cross sensitivities
Disadvantages : Relatively short life, moderately expensive
Q. What are the advantages and disadvantages of Catalytic sensors?
Advantages : Range 0 — 100% LEL for many combustible gases, accurate, long life
Disadvantages : Moderately expensive, can be poisoned
Q. What are the advantages and disadvantages of Infrared sensors?
Advantages : Very gas specific, can measure upto 100% gas, best way to detect CO2, very accurate & stable, long life
Disadvantages : Expensive
Q. What are the advantages and disadvantages of Galvanic sensors?
Advantages : Range 0 to 100% volume Oxygen, long life
Disadvantages : Expensive, poor low-end accuracy
Q. Does gas detection equipment need maintenance and calibration?
Yes. Maintenance on a properly installed, quality system is minimal and need only 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 and for critical Industrial applications 4 to 6 times per year or even monthly.
Q. What is calibration?
This process verifies that the instrument is operating properly and adjusts for any sensor drift or loss of sensitivity.This involves exposing the sensor to a known concentration of the target gas, usually from a calibration gas cylinder, and resetting the instrument to adjust for sensor drift.
Q. Can gas detection equipment produce energy savings?
Yes. A properly installed, maintained and calibrated gas detection system can produce significant energy savings by running ventilation fans only when required, minimizing energy usage and expense.
Q. 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).
Q. What are combustible gases?
Combustible gases are those that are monitored because they present a risk of explosion or fire.
Q. Where does CO come from?
Usually occurs as a product of combustion of an organic compound. Most commonly found in vehicle exhaust
Q. I get confused between CO and CO2 — what’s the difference?
CO is the chemical symbol for Carbon Monoxide which usually comes from vehicle exhaust in commercial applications.
CO2 is the chemical symbol for Carbon Dioxide which usually comes from human respiration in commercial applications and is used as an indicator for Indoor Air Quality.
Q. Where do NO and NO2 come from?
Nitric Oxide (NO) and Nitrogen Dioxide (NO2) usually occur as a byproduct of combustion, often from vehicle engines. (see Nitrogen Oxides)
Q. What is Nox?
Nox is an abbreviation for Nitrogen Oxides. (see Nitrogen Oxides)
Q. What are Nitrogen Oxides?
A group of compounds most commonly found in vehicle exhaust, where Nitrogen Oxides are a byproduct of combustion formed from the Nitrogen and Oxygen in the air. In exhaust, the most common is Nitric Oxide (NO) followed by Nitrogen Dioxide (NO2). Other Nitrogen Oxides found in much smaller quantities are N2O, N2O3, N2O4, N2O5, N3O4 AND NO3.
Q. Where does CO2 come from?
Carbon Dioxide is a naturally occurring gas in air (less than 1 %) and since it is exhaled during respiration, it is often used as an indicator of Indoor Air Quality. CO2 is produced in the combustion of organic compounds and it is also formed during fermentation. CO2 is used in many industrial and food & beverage applications and may present a hazard if it leaks from cylinders.
Q. Where does H2S come from?
Hydrogen Sulphide is commonly produced from decay of organic matter and in industrial processes such as Pulp & Paper and Oil & Gas. It is often found in ‘Sewer Gas’.
Q. 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 of 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.
Q. What does PPM mean?
Parts Per Million. 100 % volume equals 1,000,000 ‘parts’ , 1 % volume equals 10,000 ‘parts’.
Q. What does % volume mean?
The percentage of a gas in the total volume of mixture.
Q. What are the most common commercial and institutional applications?
For more information on applications
vWhat gases are present in parking garages?
Vehicle exhaust gases : CO, Nitrogen Oxides Combustible gases from fuel leakage : Propane, Gasoline, Methane
Interference gases : Solvent fumes from paint or sealer
Q. What gases are present in chiller rooms?
Chiller room gases: Ammonia, Refrigerants
Q. What gases are present in swimming pools?
Water purification chemicals: Chlorine, Ozone
Q. What gases are present in warehouses?
Forklift or truck exhaust gases : CO, Nitrogen oxides
Interference gases : Solvent fumes from warehoused products
Q. What gases are present in repair garages?
Vehicle exhaust gases : CO, Nitrogen Oxides
Combustible gases from fuel leakage : Propane, Gasoline, Methane
Interference gases : Solvent fumes