Investigation to focus on two likely causes

First steps: Worksafe and Energy Safety inspectors at the scene in Morley. Picture: Mogens Johansen/The West Australian

An investigation by electrical safety experts into how events at the Morley Galleria went catastrophically wrong yesterday will focus on two likely explanations.

After revelations the electrical contractors killed and injured were working to fix problems that had caused blackouts at the complex in recent days, investigators believed two possibilities could be behind the incident.

The first involved whether a defect with a high-voltage circuit breaker that was filled with oil caused it to explode.

The second line of inquiry, which is understood to be the more likely explanation, revolved around whether human error might have led to a massive arc - a kind of electrical flash fire.

Either way, the four contractors working inside the switch room that houses the circuit breakers at the complex were exposed to a terrible fate.

Industry insiders said regardless of whether the failure caused an explosion or an arc, the workers would have been sprayed with globules of molten, gaseous metal.

They would have also been hit by a shock wave of "enormous" force when the switchgear ignited.

Accounts from the scene of yesterday's accident suggest that much of the equipment inside the switch room was left melted by the ignition.

It took emergency services hours to secure the site in order to allow investigators inside because of the damage and the heat.

It is understood EnergySafety will look at the two likely explanations before compiling a report or provide advice to whichever agency leads the investigation.

The watchdog will also look at the procedures followed by the workers.

The contractors had been working on circuit breakers and transformers after a series of blackouts at the centre in the preceding days, including on Monday.

It is believed the equipment, which was owned by the centre, may have been more than 40 years old. The equipment helps convert high voltage power from the network into lower voltages so it can be used by commercial customers.