After the first serious disruptions to the emergency lines since 1961, the Department of Communications has made 11 recommendations, including seven directly to Telstra, with action to improve back-ups on the network and introduce live reporting.

The Department of Communications announced a formal investigation into the outage the day it occurred on May 4, with assistance from the Australian Communications and Media Authority (ACMA).

The ACMA investigation found a total of 3912 emergency calls were made that did not connect during the disruption. Of those, 1433 weren't connected due to the disruption while the remainder weren't connected because the caller voluntarily ended the call when it reached a voice announcement or terminated the call while waiting for an operator.

"Triple Zero is the lifeline for Australians in life-threatening or emergency situations. Community confidence in the emergency call service must be maintained," ACMA chair Nerida O’Loughlin said on Monday.

A Telstra spokesman said the telco undertook an "extensive investigation into what occurred".

"We take our responsibilities as the service provider for 000 extremely seriously. One failed call to Triple Zero is one too many and we apologise again for what occurred," he said.

The outage was first noticed at 2am by emergency services and went on for several hours. The cause  was later found to be the result of a fire at a cable pit near Orange in NSW. While the fire was initially suspected to be the result of a lightning strike, this was ruled out as a possibility by the NSW Rural Fire Service. Questions were raised by industry experts about why back-ups, known as "redundancies", were not working as planned.

In the days after the incident, chief executive Andy Penn publicly apologised, however, the telco repeatedly refused to confirm how many emergency calls were missed on the morning of the outage. Typically, 25,000 calls a day are made to the Triple Zero line across the country (25 per cent are not emergencies).

All telecommunications companies were hit by the network problem on the Friday morning in May, as Telstra is contracted to provide the 000 connections for all calls, with providers frustrated by the length of time it took Telstra to alert them about the issue. Some telcos called back customers whose attempts to contact emergency services had failed.

It's understood rival providers raised their concerns about the response time as part of the investigation.

A second outage for Triple Zero, which Fairfax Media revealed on May 31, was the result of offshore hackers swamping the phone line, and also formed part of the investigation. It is understood that Telstra has made changes to its Triple Zero service since the incidents.

Issues with failed emergency services connections in the past have resulted in large penalties, including a $400,000 fine paid by TPG Telecom in 2014 after an ACMA investigation into a complaint made by a customer who tried to call 000 in 2011 when their partner had a heart attack.

Consumer advocacy group Australian Communications Consumer Action Network (ACCAN) chief executive Teresa Corbin said in a statement the Triple Zero service should be modernised to include other channels than calls. The ACMA will be reviewing the rules around emergency services in the future.

The Department of Communications is discussing additional technology with Telstra to provide coordinates to emergency services using mobile location.

"It is not acceptable that Australians in their time of need were unable to reach emergency assistance,” Ms Corbin said.

The Sydney Morning Herald