Gas Safe ACS - Accredited Certification Scheme Tightness Testing and Purging Questions and Answers

Question 1

An engineer is performing a tightness test on an existing domestic Natural Gas installation with a U6/G4 meter and 22mm pipework. If there is no smell of gas, what is the maximum permissible pressure drop over the two-minute test period according to IGEM/UP/1B?

Accepted Answer

4 mbar.

Answer

According to the guidance in IGEM/UP/1B, for an existing domestic Natural Gas installation with a U6/G4 meter and pipework up to 28mm, a maximum pressure drop of 4 mbar is permissible over the two-minute tightness test, provided there is no smell of gas.

Question 2

What is the primary purpose of purging a new gas installation pipework before commissioning any appliances?

Accepted Answer

To displace air with fuel gas, ensuring a safe, non-explosive mixture is present at the appliance burners.

Answer

Purging is the process of replacing the air or inert gas inside a new or modified pipework installation with fuel gas. This is a critical safety step to ensure that a flammable mixture of gas and air is not present when an appliance is first ignited, preventing potential explosions.

Question 3

Which of the following describes the correct sequence of tests when recommissioning a domestic gas installation at the meter, according to IGEM/UP/1B?

Accepted Answer

Let-by test, Tightness test, Purge.

Answer

The correct procedure is to first conduct a let-by test on the Emergency Control Valve (ECV). If that passes, a full tightness test is performed on the installation. Only after the installation is confirmed to be tight is it then purged of air to introduce fuel gas.

Question 4

An engineer performs a tightness test on an existing installation and records a pressure drop of 7 mbar over 2 minutes, which is outside the permissible limit. The leak cannot be immediately located or repaired. What is the correct immediate action required under the Gas Industry Unsafe Situations Procedure (GIUSP)?

Accepted Answer

Turn off the gas supply at the Emergency Control Valve, attach an 'Immediately Dangerous' warning notice, and inform the responsible person that it must not be used.

Answer

A failed tightness test indicates a gas leak, which is classified as 'Immediately Dangerous' (ID) under GIUSP. The engineer has a duty to make the situation safe by isolating the gas supply at the ECV, clearly labelling the installation as unsafe with a 'Do Not Use' warning, and informing the responsible person.

Question 5

According to IGEM/UP/1B, when must the gas from a direct purge be ignited at an open burner rather than being vented to the atmosphere?

Accepted Answer

When the installation volume (IV) is 0.02m³ or greater.

Answer

The guidance in IGEM/UP/1B specifies that for Natural Gas installations with a volume of 0.02m³ or more, the purge gas must be ignited at an open burner. This is because venting such a volume of gas directly into a property would be dangerous and could create an explosive atmosphere.

Gas Safe ACS Practice Test

Gas Safe ACS Practice Test

Gas Safe ACS - Accredited Certification Scheme Tightness Testing and Purging Questions and Answers