Free ACS CCN1 Exam Flashcards

The Gas Safety (Installation and Use) Regulations 1998 - the principal law covering the safe installation, maintenance and use of gas fittings and appliances in Great Britain. It requires anyone doing gas work for hire or reward to be competent and Gas Safe registered.

The Gas Safe Register - the legal registration body since 1 April 2009, when it replaced CORGI. Registration is required under GSIUR for anyone carrying out gas work for reward.

Every 12 months (GSIUR Regulation 36). The engineer issues a Landlord Gas Safety Record (LGSR, often called a CP12); a copy must be given to the tenant, normally within 28 days of the check.

The Health and Safety Executive (HSE) enforces GSIUR 1998. The Gas Safe Register holds the register of competent businesses and operatives - enforcement and registration are separate roles.

Current, relevant ACS certificates under the Nationally Accredited Certification Scheme - CCN1 core plus the appropriate appliance modules (e.g. CENWAT, CKR1, HTR1). Competence is normally re-assessed every 5 years.

You cannot ignore it. Follow the GIUSP: make it safe where possible (with the gas user's permission), warn the responsible person in writing, and label the appliance. Discovering it during other work still triggers the duty to act.

No. It is an offence to leave a gas appliance or installation connected and in use when it is known to be dangerous. It must be made safe or disconnected following GIUSP, after seeking the gas user's permission.

20-21 mbar. The meter regulator holds the supply at this pressure; a reading well below this can indicate an undersized supply, a partially closed valve, or a regulator fault.

To confirm the emergency control valve (ECV) is holding and not letting gas pass. With the ECV closed, apply 7-10 mbar and observe for 1 minute - any rise in pressure means gas is passing the closed valve.

Any rise in gauge pressure over the 1-minute test period. A rising gauge shows gas is passing the closed ECV, so a valid tightness test cannot proceed until the valve is rectified or isolated.

At the working pressure of 20-21 mbar, after a 1-minute stabilisation period. Stabilisation lets the gas temperature settle so the timed reading is not affected by temperature change.

2 minutes. The permissible pressure drop over this period depends on the meter, the pipework size, and whether appliances are connected.

4 mbar (traditional meter-size method). For pipework over 28mm the allowance reduces to 2.5 mbar. IGEM/UP/1B Edition 4, mandatory from 1 October 2026, instead bases the permissible drop on calculated installation volume.

2.5 mbar over the 2-minute test (traditional method), versus 4 mbar for pipework up to 28mm. The larger internal volume of bigger pipework means a smaller allowable drop.

No drop at all - zero. A new installation must be completely sound before appliances and any let-by allowances are considered; any measurable drop means a leak that must be found and fixed.

About 38.76 MJ/m3 (roughly 10.76 kWh/m3) is the standard gas-rating figure. Actual National Grid supply CV varies (about 37.5-43 MJ/m3, typically near 39.5), but 10.76 kWh/m3 is the value used to convert a measured gas rate to kW.

kW = gas rate (m3/h) x gross CV (MJ/m3) / 3.6. Using a CV of about 38.76 MJ/m3 this simplifies to kW = gas rate x 10.76. Divide by 3.6 because 1 kWh = 3.6 MJ.

With only that appliance running, time one revolution or a known volume of the test dial: gas rate (m3/h) = volume x 3600 / time in seconds. Multiply by the CV to get heat input in kW, then compare with the data plate to check the appliance is burning correctly.

About 0.6 (air = 1.0), so natural gas is lighter than air and rises. This affects where a leak accumulates and where detectors are sited - the opposite of LPG, which is heavier than air and sinks to low level.

Roughly LEL 5% to UEL 15% by volume. Below 5% the mixture is too lean to ignite and above 15% it is too rich; between these limits a source of ignition can cause an explosion.

Standing pressure is measured with the appliance(s) turned off, so there is no gas flow; working pressure is measured with the appliance running. An excessive drop between the two can indicate an undersized supply or a regulator problem.

1 mbar. Pipework must be sized so that at full flow the pressure loss from meter to the furthest appliance does not exceed 1 mbar, ensuring appliances receive correct working pressure.

Within 600mm of the meter outlet, on the consumer's side of the meter and before any branch or tee. It clamps the gas pipe to earth to prevent dangerous potential differences.

Bonding is electrical work carried out to BS 7671, so it is the electrician's remit. However, the gas operative must check that bonding is present and correctly positioned within 600mm of the meter, and advise or report if it is missing or inadequate.

It must run in a continuous sleeve through the wall, with the sleeve sealed at one end so any gas leaking within the wall is vented to a safe place, and the pipe protected from contact damage and corrosion.

Purging displaces the air (or gas) in the pipework with the fuel gas so that no potentially explosive air/gas mixture remains inside the system. It ensures appliances light on gas rather than air and removes any residual air after installation.

To supply combustion air and prevent products of combustion, including carbon monoxide, from building up in the room. Insufficient air causes incomplete combustion and spillage, creating a CO hazard.

5 cm2 of free area for every kW of net input above the first 7 kW. Example: a 20 kW net open-flued appliance needs (20 - 7) x 5 = 65 cm2 of purpose-provided ventilation.

No. A room-sealed appliance draws its combustion air directly from outside and discharges outside through a sealed system, so it needs no combustion-air vent to the room - a key safety advantage over open-flued types.

Net (rated) input. BS 5440-2 covers gas appliances up to 70 kW net, and the (input - 7 kW) x 5 cm2 open-flue rule is applied using the net input figure.

Low-level vents supply combustion and cooling air, while high-level vents remove the heat that builds up in the enclosed space, preventing the appliance from overheating. These are additional to any room combustion-air requirement.

An open-flued appliance takes combustion air from the room and discharges products up a flue; a room-sealed appliance takes air from, and discharges products to, outside through a sealed system, isolating combustion from the room air.

An appliance with no flue that discharges products of combustion straight into the room, such as a cooker. Because of this it needs adequate room volume and ventilation and is limited in heat input relative to the room size.

That the flue is clear and drawing correctly. Smoke (from a smoke pellet or match) held at the draught diverter should be pulled up the flue with no significant spillage into the room, confirming an adequate updraught before appliance operation.

That combustion products are carried safely up the flue rather than spilling into the room. With the appliance running at full rate, spillage is checked (typically after about 5 minutes) using smoke held at the edge of the draught diverter.

To test the worst case. An extractor fan can depressurise the room and pull products of combustion back down an open flue (spillage). The test must still pass with fans running and doors and windows in their least favourable position.

BS 5440-1. Terminals must be sited with minimum clearances from windows, doors, corners and other openings so that combustion products disperse safely and cannot re-enter the building.

Carbon dioxide (CO2) and water vapour (H2O), plus heat. Complete combustion requires sufficient air/oxygen; a crisp blue flame is usually a sign of it.

Carbon monoxide (CO). Causes include insufficient air or ventilation, a blocked or restricted flue, and a dirty or misaligned burner. CO is toxic, colourless and odourless, which is why it is so dangerous.

0.004 (0.0040) or below is the accepted limit for a correctly operating appliance. A ratio above 0.004 indicates incomplete combustion, so the appliance must be investigated, serviced, or taken out of use.

BS 7967. The analyser measures CO and CO2 (and derives the CO/CO2 ratio, along with oxygen and flue temperature) to confirm whether an appliance is burning safely and efficiently.

A crisp blue flame indicates good, complete combustion. Lazy yellow flames, sooting or yellow tipping suggest incomplete combustion and possible carbon monoxide production, so the appliance needs investigating.

BS EN 50291. A CO alarm is an audible warning device only - a backup, not a replacement for correct installation, ventilation, flueing, servicing and combustion checks.

The Gas Industry Unsafe Situations Procedure (GIUSP), published as IGEM/G/11. It defines the classifications - Immediately Dangerous, At Risk and Not to Current Standards - and the actions an operative must take.

An installation or appliance that, if used or left connected, is an immediate danger to life or property. It must be made safe (with permission) or disconnected, labelled 'Danger - Do Not Use', and reported - never left in use.

A situation where one or more recognised faults exist that could become dangerous. With the user's permission the appliance should be turned off and labelled; the user is advised not to use it until it has been rectified.

The installation does not meet current standards but is not immediately dangerous or at risk, so it is safe to continue using. The gas user should be advised in writing so it can be upgraded over time.

A 'Danger - Do Not Use' warning notice/label. The operative must seek the gas user's permission before turning off or disconnecting; if permission is refused, the situation is still recorded and reported as appropriate.

0800 111 999 - the free, 24-hour national gas emergency line for reporting suspected gas escapes or emergencies in Great Britain.

A registered gas engineer must report to the Health and Safety Executive (HSE) any gas fitting they consider so dangerous - by design, construction, installation, modification or servicing - that someone could die, be hospitalised, or be rendered unconscious. In practice this covers Immediately Dangerous situations.