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Core Domestic Gas Safety · Gas revision

CCN1 revision notes

The core module everything else builds on — classifying unsafe situations, tightness testing, ventilation, flueing and emergency actions.

Start reading Try 25 free CCN1 questions
  • 36notes, free to read
  • 341questions; 25 free to try
  • 20topics

GSIUR Part A & B: General Provisions & Safety Precautions

  1. Gas standards & abbreviations explainedPlain-English meanings of the gas qualifications, laws, procedures and standards you meet in ACS assessment and on site.Glossary
  2. General precautions: what GSIUR Parts A and B requireWho may do gas work, the materials allowed in buildings, the precautions while work is under way, and what must not be done to premises.

GSIUR Part E: Gas Appliances & Operating Pressures

  1. Carbon monoxide: warning signs and first actionsHow blocked vents, blocked flues and poor maintenance create carbon monoxide, how to prevent it, and what to do first if exposure is suspected.
  2. Gas appliances: what GSIUR Part E requiresConnections, flues and dampers, the rooms that need room-sealed appliances, and the checks required after installing or working on a gas appliance.

GSIUR Part C: Gas Meters & Regulators

  1. Meters, regulators and the emergency control valveWhere the ECV sits and what it needs, how meter regulators are sealed and protected, the notices meters need, and what happens when a meter is removed.

GSIUR Part D: Installation Pipework & Jointing

  1. Gas pipework sizing: maximum allowable pressure dropHow to size natural-gas pipework to the 1.0 mbar limit step by step, and the support, protection and clearance rules the finished run must meet.
  2. Installing gas pipework: supports, joints, sleeves and routesClip spacing, thread sealants, sleeves through walls, cavity and void rules, burial cover, clearance from electrics and where the main bond is made.

Approved Document J (J3): Carbon Monoxide Warning & Awareness

  1. Carbon monoxide warning and immediate actionRecognise carbon monoxide symptoms, act on them first, explain what an alarm can and cannot do, and know when Approved Document J calls for one.

GSIUR Reg 37: Gas Escape Procedures

  1. Gas escapes: immediate safety and reportingProtect people, use the emergency control valve only where safe, report from safety, and restore gas only after the fault is repaired and proved tight.

GSIUR Regs 22 & 26: Tightness Testing, Purging & Safety Checks

  1. Domestic gas tightness testing procedure under IGEM/UP/1BThe duty to test after gas work, the let-by, stabilisation and timed stages, and the purging, commissioning or make-safe steps that follow.

Approved Document J Section 1: Air Supply & Combustion Ventilation

  1. Flue flow and spillage testing procedures under BS 5440-1What Approved Document J covers, where flue products must discharge, and how flue-flow and spillage tests prove an open flue works.
  2. Open-flued ventilation: choosing the rule before calculatingWhich appliances need a room vent, the Approved Document J room-vent rate, and when the 7 kW allowance applies, with a worked 15 kW example.

Gas Industry Unsafe Situations Procedure (GIUSP)

  1. Acting on an unsafe situation: warn, label and reportStep-by-step actions for Immediately Dangerous and At Risk situations: disconnect or turn off, label, warning notice, refusals, owners and RIDDOR.Checklist
  2. GIUSP unsafe-situations decision flow (diagram)How to read the GIUSP diagram: the two unsafe categories, the separate safe-shortfall panel, and the question that decides the action.
  3. GIUSP: defect classification and safety actionsThe two unsafe categories, Immediately Dangerous and At Risk, typical examples of each, and the three action routes that follow.
  4. ID and AR: unsafe situations and safe standards shortfallsHow to tell Immediately Dangerous from At Risk, the details that move a fault from one to the other, and why a safe shortfall is neither.

Calculations: ventilation free area

  1. Sizing high and low vents for an appliance in a compartmentWorked high- and low-vent sizes for an open-flued boiler in a cupboard, vented into a room or direct to outside, and the checks before relying on them.Worked example
  2. Sizing purpose-provided ventilation for an open-flued applianceTwo worked room-vent sizes for an open-flued boiler, with and without the 7 kW allowance, and how to choose and keep the vent.Worked example

Calculations: gas rate & heat input

  1. Imperial gas rate from a cubic-feet meterA worked gas-rate calculation for an older imperial (cubic feet) meter, converted to heat input in kW and cross-checked with the metric method.Worked example
  2. Working out gas rate and gross heat input (metric meter)A worked metric gas-rate calculation, converted to gross heat input and compared with the data plate on the same gross or net basis.Worked example

Air Supply & Ventilation for Gas Appliances

  1. Adventitious air versus purpose-provided ventilationAdventitious air versus permanent purpose-provided ventilation, what sets the vent size, and what changes an air-supply assessment.
  2. Inspecting a combustion-air vent: what makes it acceptableAn ordered check of an open-flued appliance's combustion-air vent: type, permanence, free area, route to outside, obstructions and extract fans.Checklist
  3. Open-flued appliance air supply (diagram)How an open-flued appliance in a room or compartment gets its combustion air, where the products go, and why high and low vents matter.

Flueing & Spillage Principles

  1. Flue flow test: proving a flue pulls before the spillage testHow the flue-flow test proves the route before the spillage test, and what makes a natural-draught flue pull or fail.
  2. Flue types compared: room-sealed, open-flued, fluelessTell room-sealed, open-flued and flueless appliances apart by where air comes from and products go, and know what each type makes you check.
  3. Open-flued spillage test: an ordered methodThe ordered spillage test for an open-flued appliance: warning signs, adverse room conditions, the specified smoke position and action on a fail.Checklist

Combustion & Carbon Monoxide Awareness

  1. Carbon monoxide alarms: the standard and where they goWhy carbon monoxide needs an alarm, which alarm to fit, where Approved Document J places it, and how to keep it working.
  2. Combustion and carbon monoxide glossaryPlain definitions of the fuel-gas properties, combustion terms and carbon monoxide words used across the gas modules.
  3. Reading a gas flame: complete versus incomplete combustionWhat a healthy gas flame looks like, which flame and soot signs point to incomplete combustion, and what to do when you see them.

Gas Safety Law: Duties & Competence

  1. Gas safety law: who must do whatWho may do gas work, what landlords must do and by when, and the duties every engineer carries on site, from instructions to records.

Appliance Isolation & Safe Reconnection

  1. Isolating and safely reconnecting a gas applianceChoose the right valve, prove the gas is off, seal open ends, prove every disturbed joint tight, and take an unsafe appliance out of use correctly.Checklist
  2. Temporary continuity bonding before cutting into gas pipeWhy a temporary bond goes across a cut in metal gas pipe, the order of work, and how it differs from permanent main protective bonding.Checklist

Carbon Monoxide Alarms

  1. CO alarms: warning, placement and responseAct on a CO alarm before troubleshooting, site it to Approved Document J and the model's instructions, and know what its self-test cannot prove.

Tightness Testing: Principles of a Sound Result

  1. Judging a tightness test result: what the gauge is telling youHow to make a tightness reading valid, what counts as no perceptible movement, when an existing-appliance loss can pass, and what to do after.

Purging Principles for Gas Installations

  1. Purging: why it is done, where it goes, and what follows itWhat purging does, the Edition 4 purge volume of 1.5 × installation volume, where purged gas may go, and the commissioning that must follow.

Working & Operating Pressure Concepts

  1. Standing, working and burner pressure: three different readingsWhat standing, working and burner pressure each show, the 20 and 21 mbar figures, and how to find a pipework pressure loss.

Build a CCN1 revision session around one safety decision

Start with a topic you find difficult: interpreting a tightness-test result, distinguishing flue flow from spillage, or calculating gas rate. Read the matching note, then explain the decision without looking at the answer. A remembered pressure or formula is only useful when you know the conditions attached to it.

Use the free CCN1 practice questions to check that understanding, then try a CCN1 mock test with feedback at the end. For ACS reassessment revision, include topics you use less often at work. The gas-rate calculator helps check your arithmetic after you have written down the meter units and working.

In-depth guides for this module

Longer walkthroughs that sit alongside the revision notes.

Guide

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) and separate safe standards shortfalls, then make the four calculations automatic — gas rate, heat input, ventilation free area and CO/CO2 ratio.

Guide

CCN1 exam questions and answers: free practice and mock tests

Start with 25 free questions covering gas safety decisions, diagrams and calculations. Use the same set for a mock test, then review the reasoning behind each answer.

Guide

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.

CENWAT · Central Heating & Water HeatersCPA1 · Combustion Performance AnalysisCKR1 · Domestic Gas CookersHTR1 · Gas Fires & Wall HeatersMET1 · Domestic Gas MetersCONGLP1 · LPG ChangeoverWRAS · Water RegulationsG3 · Unvented Hot Water