ACS Tightness Testing & Purging 3

Question 1

What is the purpose of a let-by test on a gas installation?

Accepted Answer

To check for leakage past the closed Emergency Control Valve (ECV)

Answer

To measure the total gas consumption of all installed appliances

Answer

To verify the gas meter is recording consumption accurately

Answer

To test the pressure integrity of the meter installation pipework

Question 2

How is a let-by test correctly performed on a domestic gas installation?

Accepted Answer

Close the ECV and check for a pressure rise on the downstream side using a manometer

Answer

Open all appliance valves and monitor the gas meter for unexpected flow

Answer

Pressurise downstream of the ECV and check for a pressure drop over 2 minutes

Answer

Connect a manometer upstream of the ECV and monitor for pressure changes

Question 3

During a let-by test, what does a pressure rise on the downstream side of the closed ECV indicate?

Accepted Answer

The ECV is allowing gas to pass through when in the closed position

Answer

The installation has passed the let-by test and is safe to proceed

Answer

The downstream pipework has a significant blockage restricting normal flow

Answer

The test equipment has been incorrectly connected to the installation

Question 4

At what stage of checking a gas installation should the let-by test be performed?

Accepted Answer

As the first check, before the tightness test

Answer

After completing the full tightness test of the installation

Answer

Only when the ECV is visually suspected to be faulty

Answer

After purging, immediately before lighting the appliances

Question 5

If a let-by test reveals that the Emergency Control Valve (ECV) is faulty, what is the correct action?

Accepted Answer

Notify the gas transporter, as the ECV is their responsibility to repair

Answer

Bypass the ECV with a temporary valve and complete the installation work

Answer

Replace the ECV immediately using a standard compression fitting

Answer

Cap off the service pipe and advise the customer to contact their energy supplier

Question 6

Under the Gas Industry Unsafe Situations Procedure (GIUSP), what classification applies to an unlocated gas escape discovered during a tightness test?

Accepted Answer

Immediately Dangerous (ID)

Answer

Not to Current Standards (NCS)

Answer

At Risk (AR)

Answer

Potentially Dangerous (PD)

Question 7

What action must a gas engineer take when an Immediately Dangerous (ID) situation is identified during tightness testing?

Accepted Answer

Turn off the gas supply and prevent the consumer from using the installation

Answer

Issue a written warning to the customer and revisit within 28 days

Answer

Complete a RIDDOR report and notify HSE within 24 hours

Answer

Advise the consumer verbally and allow them to decide whether to shut off the gas