The Mining and Energy Union says a "catastrophic failure of safety systems" triggered the crash of a Rio Tinto train in Western Australia, with the group accusing the mining giant of putting workers lives at risk and potentially contaminating the region's drinking water.
The autonomous train hit a set of stationary wagons about 80 kilometres outside Karratha, in the state's Pilbara region, just after midnight on Monday, damaging 22 wagons and three locomotives.
The mining giant has confirmed it's now re-opened one of the two tracks damaged in the incident.
A Rio Tinto spokesperson said no people were in the vicinity and no one was injured, but the union later said five staff were further down the line working on stationary equipment, which had broken down.
In a statement released on Friday, the union said the crash impacted six workers, claiming the mining giant had downplayed the seriousness of the incident, which "could have easily led to serious harm or death".
"Rio Tinto have put out an incomplete version of events that underplays the risk to workers' lives," a spokesperson said.
"We want the facts to get out there. We want accountability and safety.
"We are at the forefront of automation, we have accepted and embraced it, we just want to ensure that we get home safely to our families at night."
The union said it believed there was a series of errors made by Rio Tinto's train controllers and, because the train was fully autonomous, no driver was on board to realise the transmission error and halt it.
Rio said after the incident that it had reported details to authorities, and the Office of the National Rail Safety Regulator had launched an investigation.
It was understood the rail line had since been cleared and operations would resume after repairs were conducted on the track.
Rio Tinto did not respond to all the union's claims but said worker safety was its top priority.
"We are confident that our signalling system, AutoHaul, and operating procedures are safe for our railway's operation," a spokesperson said.
The union also raised concerns about spilled diesel from the trains contaminating the Harding River catchment, which was the main source of drinking water for the towns of Dampier, Karratha, Roebourne, Wickham and Point Samson.
"The attending workers are concerned that the environmental impact of this incident has not been adequately reported by Rio Tinto," the spokesperson said.
"The three derailed locomotives spilled thousands of litres of diesel fuel into the Harding River water catchment … further, the incident occurred squarely in the Millstream-Chichester National Park, not far from the iconic Red Dog Gorge."
Water Corporation said there was no sign the water had been impacted.
"We're still confident there is no immediate risk to the reservoir due to the dry weather conditions and the distance between the derailment and the reservoir," a spokesperson said.
"We’re working with Rio Tinto and will continue to monitor the situation."
Monday's incident was the second Rio Tinto derailment in the Pilbara this year and the third in the past 12 months.
An empty autonomous train left the tracks about 120 kilometres from Dampier in February.
In June 2023, a Rio Tinto driverless train derailed near Karratha, damaging 30 wagons and 700 metres of track.