Core Domestic Gas Safety revision notes
The core module everything else builds on — classifying unsafe situations, tightness testing, ventilation, flueing and emergency actions.
- 27notes, free to read
- 330questions on Premium
- 13topics
GSIUR Part A & B: General Provisions & Safety Precautions
GSIUR Part D: Installation Pipework & Jointing
GSIUR Reg 37: Gas Escape Procedures
GSIUR Regs 22 & 26: Tightness Testing, Purging & Safety Checks
Approved Document J Section 1: Air Supply & Combustion Ventilation
Gas Industry Unsafe Situations Procedure (GIUSP)
Acting on an unsafe situation: warn, label and report
The ordered actions that follow once a gas defect has been classified under the unsafe situations procedure.
GIUSP unsafe-situations decision flow (diagram)
How the Gas Industry Unsafe Situations Procedure sorts a defect into Immediately Dangerous, At Risk or Not to Current Standards, and the action each one needs.
GIUSP: defect classification and safety actions
How to classify gas defects as Immediately Dangerous, At Risk, or Not to Current Standards and the safety steps to take.
ID, AR or NCS: classifying an unsafe situation
The three GIUSP categories at a glance and how classification drives the action you take.
Calculations: ventilation free area
Sizing high and low vents for an appliance in a compartment
A worked free-area calculation for a boiler in a cupboard, showing both the high and the low vent, with rates to verify.
Sizing purpose-provided ventilation for an open-flued appliance
A worked free-area calculation for an open-flued appliance, framed so you verify the rate in the standard.
Calculations: gas rate & heat input
Imperial gas rate from a cubic-feet meter
A worked gas-rate calculation for an older imperial (cubic feet) meter, converted to heat input in kW.
Working out gas rate and gross heat input (metric meter)
A worked metric gas-rate calculation, converted to gross heat input and checked against the data plate.
Air Supply & Ventilation for Gas Appliances
Adventitious air versus purpose-provided ventilation
Why some appliances need a permanent air vent and where the rest of their combustion air comes from.
Inspecting a combustion-air vent: what makes it acceptable
A practical checklist for judging whether an existing combustion-air vent is doing its job.
Open-flued appliance air supply (diagram)
Why an open-flued appliance needs permanent purpose-provided ventilation, and how combustion air and products move.
Flueing & Spillage Principles
Flue flow test: proving a flue pulls before the spillage test
Why an open-flued appliance gets a flue flow (draught) check before the spillage test, and what it proves.
Flue types compared: room-sealed, open-flued, flueless (diagram)
A side-by-side comparison of room-sealed, open-flued and flueless appliances: where the air comes from and where the products go.
Open-flued spillage test: an ordered method
A step-by-step way to prove an open-flued appliance clears its combustion products to outside.
Telling flue types apart: open-flued, room-sealed and flueless
How to recognise the three flue arrangements on sight and what each one means for safety checks.
Combustion & Carbon Monoxide Awareness
Carbon monoxide alarms: the standard and where they go
What a carbon monoxide alarm is for, the standard it should meet, and the principles of where to site one.
Combustion and carbon monoxide glossary
Plain definitions of the combustion and carbon-monoxide terms that come up across the gas modules.
Reading a gas flame: complete versus incomplete combustion
How a healthy natural-gas flame looks and the visual warning signs of incomplete combustion.
Gas Safety Law: Duties & Competence
Appliance Isolation & Safe Reconnection
In-depth guides for this module
Longer walkthroughs that sit alongside the revision notes.
CCN1 revision plan: what to study first and how to practise
Revise CCN1 by safety decision, in order: legal boundary and emergency actions, tightness testing and controls, combustion air and flues, unsafe situations (ID/AR/NCS), then make the four calculations automatic — gas rate, heat input, ventilation free area and CO/CO2 ratio.
CCN1 exam questions and answers: how to practise the right way
Good CCN1 practice is not memorising letters; it is explaining the safe action, the test that proves it and the rule boundary.
CCN1 qualification explained: core domestic gas safety and ACS route
CCN1 is the domestic gas core: it proves core gas-safety competence, but appliance work still needs the relevant appliance categories.
More gas modules
Every module has its own revision notes and question bank.