Legislation & Duties
Not publishedof exam
GSIUR 1998Gas SafeLandlord CP12ECVRIDDOR
Tightness, Let-By & Purge
Not publishedof exam
Gas Rate & Pressure
Not publishedof exam
Ventilation & Flueing
Not publishedof exam
Combustion & CO/CO2
Not publishedof exam
Unsafe Situations (GIUSP)
Not publishedof exam
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
- 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
Check, Test, Purge, Light, Analyse
Visual checkTightness testPurgeLight + rateFlue / spillage
Let-By vs Tightness
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
- 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
- Let-by test
- Check ECV sealsFirst
- 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
- 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
Volume × 3600 ÷ time = rate
Then × CVCV ≈ 10.76 kWh/m³Gives kW input
Standing vs Working
Standing
- Appliance off
- No flow
- Static pressure
Working
- Appliance firing
- Full rate
- Dynamic pressure
Off vs running
Gas Rate & Heat Input
- 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
Natural gas
- Methane
- RD ≈ 0.6
- Rises when leaking
LPG
- Propane/butane
- RD > 1
- Sinks when leaking
Lighter vs heavier
Natural Gas Properties
- 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
A=none, B=open, C=sealed
A: flueless cookerB: open-fluedC: room-sealed
Open-flued vs Room-sealed
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
- 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)
- 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
- 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
- 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
Complete
- CO₂ + water
- Blue flame
- Ratio ≤ 0.004
Incomplete
- Produces CO
- Yellow/sooty flame
- Ratio > 0.004
Safe vs dangerous burn
Combustion Analysis
- 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
- 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
ID worst, AR next, NCS least
ID: immediate dangerAR: could becomeNCS: old standard
ID vs AR
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
- 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
- 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
- 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
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