A telecommunications expert has warned the nation’s IT infrastructure is not “up to top scratch” as federal regulators investigate Optus' Singapore parent company Singtel after a disastrous triple zero outage left three people dead across two states.

Under-pressure Optus CEO Stephen Rue fronted the media last week to announce the nation’s second-largest telecommunications company had experienced a 13-hour outage on Thursday, which impacted hundreds of triple zero calls in South Australia, Western Australia and the Northern Territory.

Mr Rue, who has faced intense scrutiny for waiting more than 40 hours to reveal the disruption, said the substantial “technical failure” took place during a routine firewall upgrade, and three people had died due to their triple zero calls failing to registe

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