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installed GD10P Detector

Selecting, Positioning and Locating Fixed Gas Detectors - General Information

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Unlike Fire detection systems, we are not aware of a definitive standard, regulations or a guidelines that determine the exact location or number of gas detectors to use. Each application presents its challenges and restrictions and each potential gas leak must be evaluated on its own to determine the risk to people and property.

First one must identify the most appropriate gas detector type for any application. A gas detector must be fast, reliable and its reading must not be effected by the presence of other gases in the area (cross interference can be a major limitation to detection technology).  The gas detector must also be suitable for use in the environment it is installed in. For example a catalytic type gas sensor must not be used in locations that contains lead, sulphur or other fumes which could damage the catalytic beads and reduce detection sensitivity.

A commonly asked question is about the area of coverage of a gas detector?? Once again there are no official standards that specify an exact area. A reasonable guide (rule of thumb) for Fixed Point Gas Detectors in open areas is approximately a 5m radius coverage for each detector or working with an area of coverage of 75 to 100m2 per detector.  Additional detectors must always be added nearest potential leak sources or where a gas cloud might accumulate. However one must ALWAYS evaluate the full gas risk in the surrounding environment and its consequences.

Locating the detector at the correct height is a very important factor. Knowing the gas composition of any target gas is very important. Gases tend not to separate out but are present as a homogeneous mixture. Therefore it is easier and safer to treat gases as either a light cloud likely to rise or a heavy one tending to sink when deciding on locating a gas detector. As a general rule, gas detectors detecting lighter than air gases should be located in higher locations while those meant for heavy gases should be placed closer to ground level. In general, assuming no forced ventilation exists, detectors for heavy gases are best located close to ground level (15 to 25cm).  Similarly lighter than air gas sensors should be placed on or near the ceiling (where the gas cloud is likely to accumulate). Otherwise they should be located above the leak source to detect and alarm when rising gas passes the detector.  Gases with density close to that of air, tend to flow with air due to draughts and / or ventilation, so it is better to locate detectors at a height as close as possible to the breathing areas of personnel working in that area (150 to 175cm) where most human breathing takes place. When working on gas detection systems one must always consider that sometimes the same gas may behave differently in different locations when subjected to different conditions.


 

General information on gases relative to Air

Ammonia

Lighter

Butane

Heavier

Carbon Dioxide

Heavier

Carbon Monoxide

Slightly Lighter

Methane

Lighter

Chlorine

Heavier

Ethane

Slightly Heavier

Ethylene

Slightly Lighter

Heptane

Heavier

Hydrogen

Lighter

Hydrogen Chloride

Heavier

Hydrogen Cyanide

Lighter

Hydrogen Sulphide

Heavier

Methyl Alcohol

Heavier

Nitric Oxide Slightly

Heavier

Nitrogen Dioxide

Heavier

Pentane

Heavier

Propane

Heavier

Sulphur Dioxide

Heavier

Toluene

Heavier

 

 


Mounting Heights for Common Gases...

On or Near the Ceiling:

  • Ammonia (NH3)
  • Hydrogen (H2)
  • Methane (CH4)
  • Methanol (CH4O)

 

Breathable Area:

  • Acetylene (C2H2)
  • Carbon Dioxide (CO2)
  • Carbon Monoxide (CO)
  • Ethylene (C2H4)
  • Formaldehyde (CH2O)
  • Hydrogen Sulphide (H2S)
  • Oxygen (O2)
  • Nitric Oxide (NO)
  • Nitrogen Dioxide (NO2)
  • Phosphine (PH3)
  • Silane (SiH4)

 

Closer to Floor Level:

  • Alcohol
  • Benzene (C6H6)
  • Chlorine (Cl2)
  • Diesel Fuel
  • Ethanol (C2H6O)
  • Fluorine (F2)
  • Gasoline
  • Hydrogen Chloride (HCl)
  • Hydrogen Cyanide (HCN)
  • Hydrogen Fluoride (HF)
  • Hexane (C6H14)
  • Isobutane (C4H10)
  • Isobutylene (C4H8)
  • Jet Fuel
  • Ozone (O3)
  • Propane (C3H8)
  • Pentane (C5H12)
  • Propylene / Propene (C3H6)
  • Refrigerants
  • Sulphur Dioxide (SO2)
  • Toluene (C7H8)
  • Xylene (C8H10)

 NOTE: Content is for general information only - You MUST NOT base your decision on where to locate a gas detector on this content. A full risk assessment must be conducted to determine the best location, number and type of any detector in any installation.


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