Drainage systems are under the microscope after the ATSB found the December 2015 derailment of a sulphuric acid train in North West Queensland was likely the result of a ballast washout.
Aurizon train 9T92 was travelling east to west along the Mt Isa railway on the morning of December 27, 2015, when it encountered a washout site, where floodwater had scoured the ballast and formation.
The train was travelling at 51km/h, 9km/h below the maximum track speed, when it ran over the washout, according to the Australian Transport Safety Bureau’s preliminary report, released late last week.
The narrow gauge (1,067mm) track at the derailment location was constructed of 41kg/m rail fastened to sleepers by resilient clips, the preliminary report states.
The track formation was comprised of black vertosol soil overlaid with ballast with a nominal design depth of 200mm.
Around seven hours before the incident, heavy rain was reported to Queensland Rail’s far-west control board, by another train roughly 50km east of the derailment site. Around the same time, the Rail Management System signalled – to the same control board – high water at Holy Joe Creek, roughly 60km west of the derailment site.
Excessive rainfall was caused by an active monsoon trough extending across the tropical north of Australia, the ATSB said.
To assess the track during the weather incident, Queensland Rail had a track inspector working along the line from west to east, and had directed another track inspector to work from east to west.
Neither inspector had reached the derailment site before the derailment occurred, however.
A member of the train crew saw the washout with the train roughly 45m away.
The driver moved the throttle to idle and moved the brake handle to the emergency position, but the train entered the washout shortly afterwards, according to the Bureau.
“The crew felt the locomotive bounce and saw water splash on the windscreen before it derailed and began to tip over,” the preliminary report states.
“The pitching of the locomotive while traversing the washout and tipping, ejected the train crew from their seats.”
Fortunately all crewmembers survived the incident without any major injuries.
More than 60,000 litres of sulphuric acid, owned by mining and chemicals firm Incitec Pivot, were spilled in the derailment.
The ATSB has outlined a number of exploratory paths it intends to take as it completes its investigation.
One path is an examination of the arrangement of drainage systems on the section of railway where the washout took place.
There was a grouping of three 1050mm diameter corrugated steel pipes installed under the track formation at the derailment site.
Immediately west of the site, three additional 600mm diameter corrugated steel pipes were installed at about 10m intervals.
In addition to this arrangement, a series of concrete culverts pass under the Flinders Highway, a little to the north of the railway.
The setup is designed to allow water to flow from a catchment north of the highway, to the watercourse south of the railway.
As well as a further investigation into the drainage system, the ATSB will look into whether organisational systems and procedures are adequate to identify, monitor and respond to a weather event.
The Bureau also plans to investigate the training programs for train crew with regards to responding to weather events, as well as the ease with which train crews can get out of a locomotive cabin in the case of a derailment.
According to the Bureau, the crew was unable to break the train’s front windshield with the safety hammer provided, and had to use a passer-by’s mobile phone to contact Aurizon after the train’s communications equipment was rendered useless by the floodwaters.
The ATSB also wants to investigate the adequacy of tanker crashworthiness, after at least one of the train’s acid tankers burst during the derailment.
Train 9T92 was a freight service operated by Aurizon between Townsville and Phosphate Hill. It consisted of one locomotive (2814), hauling 26 GATX freight tanker wagons, giving it 354.3m of total length, and a trailing mass of 2,028 tonnes.
The 60,800 litres of sulphuric acid was a small portion of the 819,000 litres being moved by the train.