Gas Safe ACS - Accredited Certification Scheme Meters and Regulators Questions and Answers

Question 1

An engineer is installing a new U6 diaphragm meter in a purpose-built surface-mounted meter box on the external wall of a domestic property. According to BS 6400-1, what is the minimum required horizontal clearance between the meter box regulator vent and an opening window?

Accepted Answer

300 mm

Answer

BS 6400-1:2016 specifies the installation standards for low-pressure gas meters. To prevent any vented gas from entering the property, a minimum horizontal clearance of 300 mm must be maintained between the regulator vent and any opening, such as a window or door.

Question 2

What is the primary function of an Over-Pressure Shut-Off (OPSO) device fitted within a domestic gas meter regulator assembly?

Accepted Answer

To shut off the gas supply if the downstream pressure rises to an unsafe level.

Answer

The Over-Pressure Shut-Off (OPSO) is a critical safety device. Its sole purpose is to detect if the regulator fails and allows excessive pressure into the installation pipework. If the downstream pressure rises above a pre-set safe limit, the OPSO will activate (trip) and completely stop the flow of gas, protecting appliances and occupants.

Question 3

An engineer is assessing an existing gas meter installation in a domestic property and finds the Emergency Control Valve (ECV) is located in a kitchen cupboard, behind a fixed shelf stacked with tins and jars. According to the Gas Safety (Installation and Use) Regulations 1998, why is this positioning non-compliant?

Accepted Answer

The ECV is not in a readily accessible position for operation.

Answer

Regulation 13 of GSIUR 1998 mandates that an emergency control must be provided and maintained in a readily accessible position. Placing it behind a fixed shelf and obstructing it with other items means it cannot be quickly and easily operated in an emergency, making the installation non-compliant.

Question 4

While checking the working pressure at a meter test point, you record a reading of 18.5 mbar with all appliances operating. The nominal working pressure for Natural Gas is 21 mbar. According to the Gas Industry Unsafe Situations Procedure (GIUSP), how should this situation be classified and managed?

Accepted Answer

At Risk (AR) - Turn off the supply at the ECV, apply a warning notice, and advise the customer to contact the Gas Transporter.

Answer

Under GIUSP, a working pressure between 18.0 mbar and 18.9 mbar (i.e., less than 19 mbar) is classified as 'At Risk' (AR). The engineer must not leave the installation operating. The correct procedure is to turn off the gas at the Emergency Control Valve (ECV), attach a 'Danger Do Not Use' warning notice, explain the situation to the responsible person, and advise them to immediately contact the gas supplier or Gas Transporter, as the fault lies on the network side.

Question 5

Before an engineer begins to physically remove an existing gas meter for replacement, what is the most critical safety check that must be performed immediately after closing the Emergency Control Valve (ECV)?

Accepted Answer

A check to ensure the ECV is not passing gas (let-by test).

Answer

Before breaking any gas seal downstream of a valve, it is a fundamental safety requirement to verify that the valve is holding tight and not allowing gas to pass. This is often called a 'let-by' test. If the ECV is passing gas, attempting to remove the meter would cause a significant and dangerous gas escape. This check must be completed before any union is loosened.

Gas Safe ACS Practice Test

Gas Safe ACS Practice Test

Gas Safe ACS - Accredited Certification Scheme Meters and Regulators Questions and Answers