RGII Domestic Gas Safety cheat sheet

The Gas Safety (Installation and Use) Regulations 1998 apply to gas fittings and appliances used for domestic and commercial premises; they do not apply to premises used wholly as a factory or mine.

Regulation 3 places duties on installers: work must be carried out in a competent manner and gas fittings must be maintained in a safe condition so that gas is not allowed to escape.

Regulation 26 requires a landlord's gas safety check on every relevant appliance and flue in let domestic premises at intervals of no more than 12 months, with a record given to tenants within 28 days.

Regulation 36 prohibits the installation of any gas appliance in a room used or intended to be used as a bathroom or shower room unless it is a room-sealed appliance.

The Gas Safety (Management) Regulations 1996 govern gas network safety, while the Pipelines Safety Regulations 1996 cover larger transmission and distribution pipelines; neither is the domestic installation rulebook.

British Standard BS 6891 covers low-pressure installation pipework up to 35 mm nominal size; BS 5440 Parts 1 and 2 cover flues and ventilation; BS 6400 covers domestic meter installation.

Manufacturer's instructions are the primary benchmark for installation, commissioning and servicing under the Gas Safety (Installation and Use) Regulations; where instructions conflict with a standard, the more onerous requirement normally governs.

The Health and Safety at Work etc. Act 1974 imposes general duties on employers and the self-employed to ensure safety so far as is reasonably practicable, and gas work falls within it.

Natural gas is predominantly methane (typically around 90%) with a gross calorific value of about 39-41 MJ/m3; it is lighter than air, with a relative density of approximately 0.6 (air = 1).

Liquefied petroleum gas (propane) has a relative density of about 1.5-2.0, so it is heavier than air and accumulates at low level in basements, pits and drains.

Complete combustion of methane: CH4 + 2O2 -> CO2 + 2H2O. Each cubic metre of gas needs roughly 2 volumes of oxygen, which is about 10 volumes of air.

Incomplete combustion produces carbon monoxide; a CO/CO2 ratio above 0.004 (0.4%) on a flue gas analyser indicates a potentially unsafe appliance condition.

The upper and lower explosive limits for natural gas in air are approximately 5% and 15% by volume; for propane approximately 2% and 10%.

Ventilation for a room-sealed appliance is generally not required for combustion air, but ventilation openings must never be obstructed and air bricks must be checked for blockage.

For open-flued appliances, permanent ventilation is sized from the appliance input rating in kW; the manufacturer's instructions give the exact free area required, commonly 5 cm2 per kW above a threshold.

A spillage test confirms combustion products are clearing the appliance draught diverter; smoke or a flame is held at the draught hood and must be drawn into the flue, not escape into the room.

BS 6891 applies to low-pressure natural gas installation pipework up to 35 mm; pipework must be supported at intervals not exceeding those given in the standard, generally 1.5 m for 15 mm and 2 m for 22 mm copper.

Sleeving is required where pipework passes through a wall, floor or cavity: the sleeve must be sealed to the wall and the annular space between pipe and sleeve left open to allow gas to disperse.

Only joints of a type permitted by the standard may be used; compression fittings must be accessible unless the manufacturer permits otherwise, and soldered capillary joints must be made with lead-free solder.

A let-by test is performed before a tightness test: the test medium pressure is applied to the installation with the meter or test nipple closed, and any rise in pressure indicates gas passing an internal valve.

For a low-pressure installation, the tightness test uses air at 20-30 mbar (or as specified) and the permissible pressure drop depends on installation volume and test duration, per BS 6891 tables.

Purging displaces air from new or disturbed pipework with gas before an appliance is lit; purge volume is calculated from pipe internal volume and the number of volume changes required by the standard.

Pipework must not be installed in a lift shaft, in an unventilated void, or buried in concrete without protection; it must be accessible for inspection and testing.

A soundness (tightness) test must be carried out on any new or altered installation before it is commissioned and the result recorded.

A domestic natural gas meter is installed by the gas transporter; the installer must not break the meter seals or remove the meter unless authorised, and must check the meter regulator outlet pressure is within tolerance (typically 19-23 mbar for natural gas).

The meter inlet and outlet must be fitted with an emergency control valve (ECV) on the outlet side, accessible and clearly labelled; the ECV is the primary means of isolating gas to the installation.

The meter installation must be in a ventilated position, with specified clearances from electrical fittings and openings, and protected from corrosion and mechanical damage.

An emergency control valve must be fitted at the point where the service pipe enters the premises and be readily accessible; it must be capable of being operated without the use of a tool.

Where a meter is installed in a meter box, the box must be ventilated, the ECV must be accessible, and the installation must comply with the relevant standard for meter housings.

The meter outlet pipe must be sized for the total load of the installation; the meter size and pipework must accommodate the maximum gas rate with an acceptable pressure drop.

A meter must be earthed/bonded in accordance with the IET Wiring Regulations where metallic pipework enters the premises; main protective bonding must be within 600 mm of the meter outlet on the consumer side.

Gas escape procedures: if a leak is suspected at the meter or service, the ECV should be turned off, the area ventilated, and the gas transporter notified; no flames or electrical switches should be operated.

Every appliance must be installed in accordance with the manufacturer's instructions; the installer must check the appliance is suitable for the gas family and supply pressure at the premises.

Commissioning includes a gas rate check (meter reading over a timed period), operating pressure check at the appliance test point, and combustion analysis where the appliance has a flue.

A gas rate check is calculated from the meter dial reading over 2 minutes and converted to kW using the calorific value of the gas and the meter conversion factor.

Servicing must include inspection of the heat exchanger, burner, seals and flue, cleaning where necessary, checking safety devices, and confirming combustion performance with an analyser.

Room-sealed appliances draw combustion air directly from outside and discharge products outside; they must be installed with the correct terminal position and must not be modified without manufacturer approval.

Open-flued appliances require a draught diverter and a flue with sufficient pull; a spillage test must be performed on commissioning and after any service or installation change.

Appliances must be electrically safe and cross-bonded where required; the installer must check the appliance is suitable for the location, including bathroom restrictions under Regulation 36.

A warning notice or unsafe situation classification must be applied where an appliance fails a safety check, and the customer must be informed in writing.

Flue terminal positions are specified in BS 5440 Part 1: minimum distances from openings, windows, doors, vents and boundaries, e.g. 300 mm from an opening window or door, 600 mm from a boundary or neighbouring building (check current table).

A flue must be of the correct diameter and type for the appliance, adequately supported, and must not have more than the permitted number of bends specified by the manufacturer.

Flues must terminate in the open air and must not discharge into a covered area, lightwell, or internal space; terminal guards are required where accessible to the public.

A draught diverter is required on open-flued appliances to prevent down-draught affecting combustion and to allow spillage of products if the flue is blocked.

Flue flow and spillage tests confirm the flue is clear and drawing correctly; a smoke pellet is used to check flue flow, and a flame or smoke at the draught diverter checks for spillage.

Shared flues and chimneys must be checked for integrity and correct termination; a flue serving a gas appliance must not serve any other fuel appliance unless it is a suitably designed shared flue.

Chimneys must be swept and checked before a new appliance is connected; a flue liner may be required where the existing chimney is unsuitable.

Combustion products must not enter another dwelling; flue terminals must be positioned so products cannot re-enter the building through windows, vents or air bricks.

A tightness test must be carried out on new pipework and after any alteration; the test medium is air or inert gas, never gas, and the test pressure and permissible drop are taken from BS 6891.

Before a tightness test, a let-by test is performed to confirm the meter or test valve is not passing; a pressure rise during the let-by test indicates a passing valve.

For natural gas low-pressure installations, the test pressure is typically 20-30 mbar with a stabilisation period, and the permissible drop is calculated from the installation volume and test duration.

Purging is required before commissioning new pipework: the volume of gas needed is calculated from the pipe volume and the number of purge volumes required to displace air safely.

A gas rate check and operating pressure check are part of commissioning; the burner pressure must match the data plate value within tolerance, and the gas rate must match the rated input.

A combustion analysis records CO, CO2, O2 and CO/CO2 ratio; a ratio above 0.004 is a potential unsafe situation requiring investigation.

Safety devices such as flame supervision devices (FSD), overheat thermostats and pressure switches must be function-tested during servicing and commissioning.

Records of tightness tests, purge volumes and commissioning results must be kept and provided to the customer where required.

An Immediately Dangerous (ID) situation is one where there is an immediate risk to life or property; gas must be shut off, the appliance isolated, and a warning notice attached with the customer informed not to use the appliance.

An At Risk (AR) situation is one where a fault could become dangerous; the appliance should be isolated and a warning notice issued, with the customer advised of the defect and the action required.

Warning notices must record the defect, the date, the engineer's details and the action taken; the customer should sign to acknowledge receipt where possible.

If a gas escape is suspected, the ECV should be turned off, the area ventilated, no flames or electrical switches operated, and the gas transporter or emergency service contacted.

Carbon monoxide alarms should be fitted in rooms containing open-flued appliances and in sleeping areas where required by current guidance; an alarm is not a substitute for correct servicing.

Where an appliance is classified ID, the gas supply to that appliance must be disconnected and capped or the ECV turned off if the escape is upstream.

The engineer must inform the responsible person (landlord, homeowner or occupier) in writing of any unsafe situation and retain a copy of the warning notice.

Reconnection after an ID classification must only occur once the defect has been rectified and the appliance has been retested and found safe.