CCN1 Purging Procedures 2 — Questions and Answers
Question 1: What safety precaution is taken after purging gas into the atmosphere outside?
- Confirm the purge point is clear of ignition sources, the gas is fully dispersed before any ignition sources are introduced, and the area is ventilated (Correct answer)
- Light a match at the purge point to confirm gas is present
- Allow immediate reoccupation of the building
- Apply a pressure test immediately after purging
Correct answer: Confirm the purge point is clear of ignition sources, the gas is fully dispersed before any ignition sources are introduced, and the area is ventilated
After purging gas to atmosphere, the purge point and nearby area must be kept clear of ignition sources until the gas has fully dispersed. Good ventilation speeds dispersal. Only when gas is confirmed to have dispersed should ignition sources be reintroduced.
Question 2: What is an 'inert gas purge' and when is it used?
- Purging with nitrogen to displace gas before hot work — used when it is not safe to purge directly to atmosphere or when a flame-free environment must be maintained (Correct answer)
- Purging with CO2 as a fire protection measure
- Using compressed air as a purge gas instead of nitrogen
- Inert gas purges are only used in offshore gas installations
Correct answer: Purging with nitrogen to displace gas before hot work — used when it is not safe to purge directly to atmosphere or when a flame-free environment must be maintained
An inert gas purge uses nitrogen (or another inert gas) to displace gas from pipework before hot work. This creates a gas-free, non-flammable environment in the pipework, allowing cutting or welding safely.
Question 3: What does the term 'purge point' mean in a gas installation?
- A fitting or valve where gas can be vented to the outside atmosphere during purging operations (Correct answer)
- A location on the gas main where the network operator connects the supply
- A test point for checking operating pressure
- A valve used to control the flow rate during purging
Correct answer: A fitting or valve where gas can be vented to the outside atmosphere during purging operations
A purge point is a fitting — typically a valve or plug — that allows gas to be vented to the outside atmosphere during a commissioning purge. It must vent outside, not into any enclosed space.
Question 4: According to current gas industry guidance, how long should an engineer wait after purging before attempting to light an appliance?
- The time specified in the appliance manufacturer's instructions — typically enough time for any residual air-gas mixture near ignition components to clear (Correct answer)
- 10 minutes regardless of appliance type
- There is no waiting period — the appliance can be lit immediately after purging
- 30 seconds while operating the fan to clear the burner area
Correct answer: The time specified in the appliance manufacturer's instructions — typically enough time for any residual air-gas mixture near ignition components to clear
The manufacturer's instructions specify the required pre-ignition procedure, which includes any required purge period before attempting ignition. Following the manufacturer's instructions is mandatory under PUWER and the GSIUR 1998.
Question 5: What is the purpose of 'soundness testing' following re-commissioning of a gas installation after repair?
- To confirm that all repaired joints and connections are gas-tight before the installation is returned to service (Correct answer)
- Soundness testing is another term for a performance test of the appliance
- To confirm the gas pressure has returned to normal
- To confirm that all appliances have been successfully re-lit
Correct answer: To confirm that all repaired joints and connections are gas-tight before the installation is returned to service
Soundness testing (tightness testing) after re-commissioning confirms that all repair work has resulted in a gas-tight installation before it is returned to full service. It is a mandatory step before restoring the gas supply.
Question 6: What record must a Gas Safe engineer make following completion of a new installation, including purging?
- A commissioning record including tightness test results, operating pressure measurements, appliance performance data, and confirmation that purging was carried out correctly (Correct answer)
- Only a receipt for the work done
- Only a note of the date of commissioning
- Records are only required for commercial installations
Correct answer: A commissioning record including tightness test results, operating pressure measurements, appliance performance data, and confirmation that purging was carried out correctly
Commissioning records must document tightness test results, measured operating pressures, appliance performance and combustion analysis results, and confirmation that purging was completed correctly. These records are the engineer's legal protection and the customer's proof of compliance.
CCN1 Purging Procedures 2
What safety precaution is taken after purging gas into the atmosphere outside?