Gas standards & abbreviations explained

These are the short names you will meet in ACS assessment and on site, and what each one means in practice.

Competence and registration

• ACS — Accredited Certification Scheme: the accredited route for assessing whether a gas operative is competent to work safely on gas. It is about a person's competence, not an instrument, a flue type or a pipework product.
• ACS assessment — a periodic competence assessment, renewed rather than held for life, that underpins Gas Safe registration. It is not a plumbing qualification and not a landlord's safety paperwork.
• ACS categories — assessment is category-based. You are competent and registered only for the appliance types and classes of work your categories cover, and a core certificate does not cover every appliance.
• Gas Safe Register — the official registration scheme a gas business must belong to in order to work on gas legally: the class of persons approved by HSE. ACS certificates on their own do not authorise a business to do gas work.
• CCN1 — core domestic gas safety: the foundation assessment that underpins the appliance-specific modules. It is broader than any single appliance or meter and regulator work, and it is not the non-domestic commercial and catering core.
• The appliance modules — CENWAT (central heating and water heaters), CKR1 (cookers), HTR1 (fires and wall or space heaters) and MET1 (meters). CPA1 (combustion performance analysis) has been part of the CCN1 core since 1 April 2012.
• ACS certificate expiry — every ACS certificate carries an expiry date no more than 5 years after the assessment. Gas Safe Register does not accept an out-of-date certificate as evidence of competence, so book reassessment before that date to keep the work on your registration.

Law and procedures

• GSIUR — the Gas Safety (Installation and Use) Regulations 1998: the law that governs gas work and the duties of the people doing it, with the aim of protecting people from the dangers of gas.
• GIUSP — the Gas Industry Unsafe Situations Procedure: how you classify and act on an unsafe situation.
• ID / AR / NCS — Immediately Dangerous / At Risk / Not to Current Standards. ID and AR are the two unsafe classifications; NCS describes a shortfall assessed as safe, recorded separately and outside the current GIUSP.
• RIDDOR — the statutory reporting requirements under which a registered gas engineer may have to report a dangerous gas fitting to HSE, so the regulator is informed and can investigate.
• Landlord gas safety record — often called a CP12: the record of the annual check of the gas appliances and flues a landlord provides. Each record is kept until two further checks have been made, or for 2 years from the last check if the appliance or flue has been removed.

Standards and guidance

• Approved Document J — the Building Regulations guidance on combustion appliances, air supply and flues. The legal requirement is "Part J"; the guidance is the "Approved Document". Requirement J3 covers warning of carbon monoxide release; J1 covers the air supply, J2 the discharge of products of combustion and J4 protection of the building from heat and fire.
• BS 7967 — the British Standard for carbon monoxide and combustion analysis in dwellings: the basis for CO/CO₂ ratio work.
• BS 5440 — flueing and ventilation for gas appliances up to 70 kW net input.
• BS 6798 — selection, installation and maintenance of gas-fired boilers.
• BS EN 50291-1 — the standard Approved Document J says a carbon monoxide alarm should meet.

On-site terms

• ECV — Emergency Control Valve: the hand-operated valve that shuts off the gas supply to the whole installation. Its handle lies across the pipe when it is shut.
• FGA — Flue Gas Analyser.
• CO/CO₂ ratio — carbon monoxide divided by carbon dioxide, both in the same units, from a flue gas analyser: the key indicator of combustion quality. In a valid sample, a lower ratio means more complete combustion at that test point.