The ECV rules, why every gas meter position must be ventilated, where a meter must not go, and the checks after meter work.
The emergency control valve (ECV)
The ECV is the hand-operated valve at or near the meter inlet, upstream of the regulator and meter. It shuts off gas to the whole installation in an emergency. It must be:
- readily accessible wherever the meter is, including communal and internal positions
- operable by hand without tools, with the handle fitted and turning freely
- clearly identifiable, with its on and off positions shown
- accompanied by a notice telling the user what to do in a gas emergency
A lever is parallel to the pipe when open. If it moves in a vertical plane rather than only horizontally, fully downward must be the closed position.
The ECV is there for the user. When work at the meter is finished, the user must be able to shut the gas off unaided. Isolation cannot be left to a managing agent alone or to the valves on individual appliances.
Where a medium-pressure supply is reduced to low pressure at the meter, the installation also needs automatic protection against regulator failure. An over-pressure shut-off (OPSO), also called a slam-shut, trips closed when its sensed downstream pressure reaches the over-pressure setting.
Why meter positions are ventilated
No installation is assumed to stay perfectly leak-free, and a meter position puts several joints, a regulator and the ECV in one small space. Ventilation lets a small escape disperse to a safe place before it builds up into a mixture that will ignite. Natural gas becomes flammable at around 5% in air.
- An external meter box has permanent vents so escaped gas disperses to outside air. Keep them clear.
- Ventilate an indoor meter housing so a small escape at a meter joint, regulator or valve can disperse instead of collecting in the enclosure. Use the applicable BS 6400 provisions for the actual housing.
- Never put a meter in an unventilated cupboard or void: a leak could collect and cause an explosion or asphyxiation.
- In a cellar or basement, natural gas is lighter than air, so an escape tends to rise and collect at high level. High-level ventilation and gas detection need particular attention, but the gas also mixes and travels, so lower levels are not automatically safe.
Where a meter must not go
- In a sealed cupboard beside electrical switchgear: the least suitable position, with no ventilation and ignition sources next to the meter.
- Hard up against a consumer unit or other electrical equipment: keep separation, or suitable protection, so an escape is less likely to meet a spark and both services can be worked on safely.
- Where it is exposed to excessive heat or likely damage from vehicles, impact or weather.
- Where it would adversely affect the means of escape or let escaped gas into the building. A new meter in a building with two or more floors above the ground floor is not sited on or under a stairway, or anywhere else, that forms the sole escape route. Elsewhere, such a position needs fire protection, such as a fire-resistant meter or housing or a thermal cut-off, if it cannot reasonably be avoided.
External boxes, semi-concealed boxes and an integral garage position protected from vehicles are common positions, provided the installation requirements for that position are met. In a garage, protect the meter and pipework from vehicle impact and mechanical damage, keep them clear of ignition sources, and keep ventilation and access.
Support and meter exchange
Clip or bracket the pipework at suitable intervals so joints are not strained. Never let it carry other loads, such as a shelf: there is no safe weight. The installation should let the meter be isolated and removed without disturbing the rest of the pipework.
After a meter exchange, tightness test and purge before relighting appliances. A test pass does not replace purging, appliance checks or the rest of recommissioning.
A tightness test checks whether the section enclosed by its test boundary holds pressure under the specified conditions. It neither locates a leak nor certifies branches outside that boundary. Working-pressure and flue-spillage checks answer different questions, and a soundness result does not replace purging.
Exam cues
- Least suitable position: sealed, unventilated and next to electrics.
- Why ventilate a meter box? So escapes disperse instead of accumulating; the vents are not for combustion air or condensation.
- Communal or internal meter: the ECV must still be readily accessible.