ACS CCN1 Core Domestic Gas Cheat Sheet

Cheat sheet ACS CCN1 Core Domestic Gas Cheat Sheet Practice Questions Study Guide Print / Save PDF

Legislation & Duties Not published of exam GSIUR 1998 Gas Safe Landlord CP12 ECV RIDDOR

Tightness, Let-By & Purge Not published of exam Let-By & Tightness Purging & Pipework Permissible Drops Bonding

Gas Rate & Pressure Not published of exam Gas Rate & Heat Input Natural Gas Properties Calorific Value Working Pressure

Ventilation & Flueing Not published of exam Ventilation (BS 5440-2) Flue Types Flue Flow & Spillage Terminal Siting

Combustion & CO/CO2 Not published of exam Combustion Analysis CO Hazard & Alarms CO/CO2 Ratio Flame Picture

Unsafe Situations (GIUSP) Not published of exam GIUSP Classifications Emergency Actions ID vs AR 0800 111 999

Quick Facts Exam ACS CCN1 Credential Gas Safe core domestic Format Open book + practical Pass Each subject; ~80% theory Reassess Every 5 years Test pressure 20-21 mbar CO/CO2 limit ≤ 0.004 Standards GSIUR, IGEM, BS 5440

Legislation & Duties LE GSIUR 1998 Primary gas safety law Gas Safe Register Legal registration body CORGI ended Gas Safe from 2009 Regulation 3 Operative must be registered Regulation 36 Landlord annual check CP12 Landlord Gas Safety Record ECV Emergency control valve Operative duty Leave installation safe

Commissioning Order TE Check, Test, Purge, Light, Analyse Visual check Tightness test Purge Light + rate Flue / spillage

Let-By vs Tightness TE

Let-by Tests ECV seal 7-10 mbar No rise 1 min

Tightness Tests whole system 20-21 mbar 2-minute drop Valve vs system

Tightness Test Decision TE Before tightness test → Let-by test ( 7-10 mbar ) ECV lets by → Stop ( Do not test ) Existing, ≤28mm pipe → Allow 4 mbar ( U6/G4, appliances ) Existing, >28mm pipe → Allow 2.5 mbar ( With appliances ) New pipework only → No drop ( Any drop fails ) Pressure drop seen → Trace leak ( Rectify, retest ) Test satisfactory → Purge ( Then commission )

Let-By & Tightness Test TE Let-by test Check ECV seals First Let-by pressure 7-10 mbar applied Let-by pass No rise 1 minute Test pressure 20-21 mbar working Stabilisation 1 minute settle Timed test 2 minutes Drop ≤28mm 4 mbar max (U6/G4) Drop >28mm 2.5 mbar max New pipework only No drop permitted IGEM/UP/1B Tightness test standard

Purging & Pipework TE Purging Remove air from pipe Purge point Vent to safe place Max pipe drop 1 mbar meter to appliance Pipe sleeving Protect through walls Sleeve seal One end only Bonding Within 600mm meter outlet Bonding standard BS 7671 equipotential

Gas Rate Formula GA Volume × 3600 ÷ time = rate Then × CV CV ≈ 10.76 kWh/m³ Gives kW input

Standing vs Working GA

Standing Appliance off No flow Static pressure

Working Appliance firing Full rate Dynamic pressure Off vs running

Gas Rate & Heat Input GA Gas rate Volume × 3600 ÷ time Units m³ per hour Gross CV ≈ 39.5 MJ/m³ CV multiplier ≈ 10.76 kWh/m³ Heat input Gas rate × CV kW formula m³/h × CV ÷ 3.6 Compare with Appliance data plate Working pressure 21 mbar nominal

Natural Gas vs LPG GA

Natural gas Methane RD ≈ 0.6 Rises when leaking

LPG Propane/butane RD > 1 Sinks when leaking Lighter vs heavier

Natural Gas Properties GA Main constituent Methane (CH₄) Relative density ≈ 0.6, lighter than air Escape behaviour Rises, collects high Flammability limits 5% to 15% gas Standing pressure No flow, appliance off Meter outlet band 18.5-23 mbar (IGEM/G/13)

Flue Types A-B-C VE A=none, B=open, C=sealed A: flueless cooker B: open-flued C: room-sealed

Open-flued vs Room-sealed VE

Open-flued (B) Room combustion air Needs ventilation Spillage test

Room-sealed (C) Outside combustion air No room vent No spillage test Room air vs sealed

Flue & Spillage Check VE Open-flued appliance → Flue flow test ( Smoke first ) Flue proven clear → Spillage test ( At diverter ) Extract fan fitted → Run it ( Worst case ) Smoke spills ~5 min → Fail ( Classify unsafe ) Room-sealed appliance → No spillage test ( Sealed circuit ) Terminal near opening → Check clearances ( BS 5440-1 )

Ventilation (BS 5440-2) VE BS 5440-2 Ventilation standard ≤70kW Open-flue vent 5 cm²/kW above 7kW First 7kW Covered by adventitious air Net input basis Ventilation uses net kW Room-sealed No purpose vent needed Flueless vent Room volume + openable window Compartment High and low vents

Flue Types VE Type A Flueless (e.g. cooker) Type B Open-flued, room air Type C Room-sealed, balanced Draught diverter Open-flue spillage point Balanced flue Air in, products out Fanned flue Fan-assisted room-sealed

Flue Flow & Spillage VE Flue flow test Smoke confirms flue clear Test order Flow before spillage Spillage test Products not entering room Worst case Doors and windows closed Extract fans Run during test Spillage check Smoke match ~5 minutes Terminal siting BS 5440-1 clearances

Complete vs Incomplete CO

Complete CO₂ + water Blue flame Ratio ≤ 0.004

Incomplete Produces CO Yellow/sooty flame Ratio > 0.004 Safe vs dangerous burn

Combustion Analysis CO Complete combustion CO₂ + water vapour Incomplete combustion Produces carbon monoxide CO/CO₂ pass ≤ 0.004 ratio Investigate band 0.004 to 0.008 Sampling point Products at full rate High CO, low CO₂ Incomplete combustion sign Good flame Crisp blue picture Standard BS 7967 / BS 5440

CO Hazard & Alarms CO Carbon monoxide Colourless, odourless, toxic CO effect Binds haemoglobin, starves oxygen Common cause Blocked flue, poor air CO alarm BS EN 50291 audible ASD / ODS Shuts off on vitiation Symptoms Headache, dizziness, nausea

GIUSP Levels UN ID worst, AR next, NCS least ID: immediate danger AR: could become NCS: old standard

ID vs AR UN

Immediately Dangerous Immediate danger Turn off + label Disconnect (permission)

At Risk Could become dangerous Turn off + advise Rectify soon Now vs could-be

ID vs AR vs NCS UN Immediate danger to life → ID ( Turn off, label ) Fault could become dangerous → AR ( Turn off, advise ) Safe but old standard → NCS ( Advise, leave on ) ID permission refused → Warning notice ( Inform authority ) Live escape can't stop → ECV off ( Call 0800 111 999 ) CO spillage confirmed → ID ( Disconnect appliance ) After rectification → Retest ( Before returning use )

GIUSP Classifications UN GIUSP Unsafe situations procedure Standard IGEM/G/11 ID Immediately Dangerous AR At Risk NCS Not to Current Standards Action Turn off with permission Label Attach warning notice RIDDOR Report dangerous fittings

Emergency Actions UN Gas escape Turn off at ECV Emergency number 0800 111 999 Ventilate Open doors and windows No ignition No flames or switches ID + refusal Warning notice, inform authority Before relight Rectify then tightness test Re-establish Purge before ignition Confirm supply Working pressure at rate

Common Traps

Let-by vs tightness Let-by tests ECV ≠ Tightness tests system

ID vs AR ID immediate danger ≠ AR could become dangerous

Open-flued vs room-sealed Open-flued needs vent ≠ Room-sealed does not

Ratio pass vs fail ≤ 0.004 passes ≠ > 0.004 investigate

Natural gas vs LPG Natural gas rises ≠ LPG sinks low

Standing vs working pressure Standing is off ≠ Working is firing

Last Minute 1 . Test pressure 20-21 mbar, 2 min 2 . Let-by: 7-10 mbar, no rise 3 . Drop: 4 mbar ≤28mm / 2.5 >28mm 4 . New pipework = no drop 5 . Pipework drop max 1 mbar 6 . Bonding within 600mm of meter 7 . Gross CV ≈ 39.5 MJ/m³ 8 . Open-flue vent 5 cm²/kW >7kW 9 . CO/CO₂ ratio ≤ 0.004 passes 10 . GIUSP: ID, AR, NCS 11 . Gas escape → close ECV 12 . Emergency line 0800 111 999 13 . Flue flow test before spillage 14 . Room-sealed = no spillage test

ACS CCN1 Core Domestic Natural Gas Safety Assessment Practice Questions 118 questions Study Guide 34 topics Cheat Sheet 89 facts Flashcards 50 cards Course Playlist 49 videos Blogs 1 blog Podcast

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