Australia’s Woodside Energy is investigating an incident at its Pluto liquefied natural gas plant, which unions have described as an explosion whereas the operator prefers the term “audible release” of gas from the flare tower.

All personnel were evacuated from the site, and no one was injured or killed in the incident that occurred at 23.30 local time on Friday when Woodside was performing planned maintenance at Pluto LNG in Karratha, Western Australia. The noise of the incident itself and resulting emergency siren were heard by residents in Dampier about five miles away.

“Personnel on site were mustered. All personnel have been accounted for and we are investigating the cause of the incident. Operations at Karratha Gas Plant (KGP) continue as normal,” Woodside posted in the following hours onthe Woodside North West Facebook page.

The flare line was in the process of being shut down in preparation for the tie-in of Pluto Train 2 at the time of the incident, according to one worker at the plant.

“Friday night’s explosion at Pluto was not simply an “audible release” as they’ve told employees and contractors. Woodside are lucky that no-one was killed or seriously injured as the explosion shook the ground and surrounding crib huts,” said the Offshore Alliance union on its Facebook page.

The OA claimed that Woodside knew on Friday morning that something was amiss and had delayed by two hours the start time of the day shift, due to an impending black start.

“It appears that the air assist flares weren’t functioning, with gas coming back through the line and igniting. There has been significant damage to the flare blowers and pipework to the bottom of the tower is completely destroyed and the outer skirt of the flare itself is split,” said the OA.

Upstream has approached Woodside for comment on the incident and its response to the union’s claims.

“If you’re in the city of Karratha today you may notice some unusual dark smoke and flaring from our Pluto LNG facility. While we aim to minimise flaring, it is essential for the safe operation of a gas plant and during some maintenance activities,” the operator on Sunday posted on the same Facebook page.

“We are continuing to investigate the cause of Friday night’s audible release incident.”

Woodside on Thursday had advised via the same social media that it would be undertaking planned maintenance at the Pluto LNG Plant for the next few weeks, which will likely result in increased flaring, with potential for dark smoke.

“Flaring is essential for safe operations of a gas plant and is required during some maintenance activities. Woodside closely monitors and aims to minimise its flaring as part of normal operations,” the company said.

“As operator of the Pluto LNG Plant, Woodside’s priority is safe and reliable operations.”

However, the following day “an audible release” occurred in the Pluto flare tower.

Australian Workers’ Union state secretary Brad Gandy told the Australian Financial review that workers at the LNG plant were fortunate to escape serious injury.

Despite Woodside “trying to downplay this by labelling it an audible release – this was an explosion,” Gandy was quoted by the AFR.

Union members at Pluto were reportedly stood down on part pay on Saturday and then asked to take Sunday as a day off.

“Woodside need to be transparent about what has occurred and the cause of the explosion, as their spin and bullshit doesn’t cut it,” added the OA, apparently angered that the contractor workforce had been stood down with pay.

“Woodside have nearly killed workers, lied about the incident and are now ripping off the same workers that they nearly killed or maimed.”

Pluto LNG exploits gas from Woodside’s Pluto and Xena gas fields offshore Western Australia. The gas is delivered via a 180-kilometre trunkline to an onshore processing train before being sent to the KGP.

Woodside and US contractor Bechtel last August started construction of the Pluto Train 2 expansion.

The OA is a partnership between the Australian Workers’ Union and the Maritime Union of Australia.