Petroleum and gas safety alert no. 81 | 11 April 2018 | Version 1

Unsafe gas purging practices

What happened?

A licensed gas installer sustained burns to his face, hands and legs from a 'flash over' fire caused by a build-up of LP gas in a plant room.

How did it happen?

A licensed gas installer conducted an unsafe purge practice during the commissioning of a LP gas system in a nursing home plant room. The concentration of air/gas mixture released into the room through the unsafe purge method exceeded safe levels. After completing the pipework purge, the installer attempted to ignite the hot water units. This ignited the gas build-up in the plant room resulting in a 'flash-over' fire and injuries to the installer.

Key issues

• The gas system was not purged in accordance with a safe 'purge procedure'.
• Large volume installations should only be purged directly to outside atmosphere.
• The unsafe purge process conducted allowed a build-up of gas within the plant room.
• The hot water unit was turned on before it was established any gas released during the purge had dispersed.
• The hot water unit ignited the build-up of gas resulting in a 'flash-over' fire.

Recommendations

• Gas Work license holders should ensure they are familiar with the principals of purging.
• Gas work license holders should undertake refresher training if they are not confident in purging methods.

Comments

Purging is carried out to avoid the possibility of an explosive air/gas mixture existing or forming in piping, appliances or confined spaces. Purging is required when commissioning or decommissioning a gas system, part of a gas system or a gas appliance. Purging is the displacement of—
(a) air, or an inert gas, by a fuel gas; or
(b) a fuel gas by air, or an inert gas.
Note: Nitrogen is the preferred inert gas.

• Smaller volume gas systems can be purged inline with the methods provided in AS/NZS5601.
• Where large volume gas systems (>30ltrs = 0.03m³) are to be purged a specific 'purge procedure' will be required.

References and further information

AS/NZS5601.1 Gas installations Part 1 General installations.

• Clauses 2.2.2, 2.2.9, 3.3.2, 3.3.3
• Appendix D