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Gas Safety

Exam revision materials for Plumbing Level 2&3 and ACS Gas Safety test

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Natural Gas

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Safety Devices and Controls

Air/Gas ratio valves

Appliances Controls

Flame Supervision Devices FSD

Gas Controls

Gas Meter Controls

Safety Cut-off Devices

Spare Part Identification


Open-vented System


Gas Appliances

Ventilation Sizing

Unsafe Situations

Dealing with Unsafe Situations

Emergency Notices and Warning Labels

Gas Leak




Tightness Test

Gas Performance

Gas Rate

Heat Input

Gas Supply

Gas Meters

Gas Pipework

Gas Fittings and Pipes

Gas Supply


New Installation

Pipe Protection

Pipework Sizing

Chimney and Flue


Flue Construction

Flue Inspection and Testing

Flue Terminals

Flue Types


Carbon Monoxide Poisoning

Combustion Process

Natural Gas

Portable Combustion Gas Flue Analysers


Components and Safety Devices

Constituents of Natural Gas

  • Methane CH4 - 90%
  • Ethane C2H6 - 5.3%
  • Propane C3H8 - 1%
  • Butane C4H10 - 0.4%
  • Nitrogen N2 - 2.7%
  • Carbon Dioxide CO2 - 0.6%

Natural Gas prior to combustion is not poisonous

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Calorific Value

  • Calorific Value - the amount of heat given when 1m3 of natural gas is completely burnt is 39MJ/m3
  • Gross Calorific Value - latent heat
  • Net Calorific Value - sensible heat
  • Specific Gravity of Natural Gas is 0.6 - lighter than air

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    Wobbe Number

    • Wobbe Number = CV/√SG
    • Heat output from the burner depends on:
      • Calorific Value
      • Specific Gravity
      • Injector size
      • Gas Pressure
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    Gas Families

    • Family 1 - manufactured gas
    • Family 2 - natural gas
    • Family 3 - liquid petroleum gas

    Flammability Limits - natural gas burns with 5 to 15% gas in air

    Flame Speed - natural gas burns speed is 0.36m/sec

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