Gas Safe ACS - Accredited Certification Scheme Tightness Testing and Purging Questions and Answers Flashcards
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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?
Answer: 4 mbar.
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.
What is the primary purpose of purging a new gas installation pipework before commissioning any appliances?
Answer: To displace air with fuel gas, ensuring a safe, non-explosive mixture is present at the appliance burners.
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.
Which of the following describes the correct sequence of tests when recommissioning a domestic gas installation at the meter, according to IGEM/UP/1B?
Answer: Let-by test, Tightness test, Purge.
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.
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)?
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.
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.
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?
Answer: When the installation volume (IV) is 0.02m³ or greater.
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.
During a tightness test on a domestic Natural Gas installation, what are the specified test pressure and duration for the main tightness test phase, following the initial 1-minute stabilisation?
Answer: 20 mbar for a duration of 2 minutes.
As per IGEM/UP/1B, after the initial let-by test and a 1-minute stabilisation period at the test pressure, the main tightness test for a domestic Natural Gas installation is conducted at approximately 20 mbar for a duration of 2 minutes.