The ACT government failed to properly test for two toxic substances in the aftermath of the 2011 Mitchell chemical fire disaster, an independent report has found.
The scathing report was withheld by the government for more than a year before its publication on Thursday going into the Christmas shutdown.
The report recommends continuing testing of the site for toxins and any effects on the surrounding environment and livestock.
The explosion at the Energy Services Invironmental (ESI) site in September 2011 hurled fireballs 200 metres into the air and shut down Mitchell for four days. The site was used to treat and store polychlorinated biphenyls (PCBs) and concern lingered after the disaster that the fire had exposed the Canberra community to harmful toxins.
The University of Queensland report, completed in April 2012, found the government did not conduct enough testing and analysis "to cover two of the major potential contaminant types of concern to the Canberra community".
The report says the government performed "insufficient sampling and analysis" for residues of PCBs as well as polychlorinated dioxins and dibenzofurans (referred to as dioxins and furans).
"Substantial media comment was made in respect of the perceived risks of community exposure to dioxins and furans, which are persistent and toxic organochlorine compounds that can be generated in combustion processes," the report says. "Yet none of the environmental samples taken in relation to the Mitchell fire were analysed for these chemicals."
The review found the government had not clearly mapped where it conducted testing after the fire. The government also failed to take duplicate samples from the site - a process that would ensure results from laboratory testing could be checked.
The review criticises the government's communication to the broader community during the fire.
The government has been urged to publish an "up-to-date environmental sampling manual similar to those used by Australian states such as WA, Victoria, NSW and Queensland" to give clear protocols in any future disaster.
The report also suggests the government develop contingency arrangements for emergency response agencies that serve industries such as the ESI plant that store toxic materials.
"We recommend sampling and analysis of material still on site to assess evidence of dioxins/furans generation," it says. "Since dioxin-like chemicals comprise several hundred individual chemicals, an appropriate chemical analysis can provide a mixture of 'fingerprint' for the fire site that can be used for comparison with environmental samples collected in future long-term monitoring."
Environment and Sustainable Development Minister Simon Corbell defended the delay in publishing the report.
''The government has been seeking further advice and preparing its response,'' he said.
Mr Corbell said it had been important for the government to review its response to the fire and continue to make improvements to its processes and procedures.
"Expert advice from ACT Health is that the risk to human health was very low, emphasising that the precautionary approach taken by the emergency authorities served to minimise any public health risk,'' he said.
Opposition environment spokeswoman Nicole Lawder said she was disturbed by the timing of the publication of the report. ''I do find it quite disturbing that a report available from the 3rd of April, 2012, was released to the public late on a Thursday afternoon before Christmas,'' she said.
Ms Lawder said the government should address the failure by authorities to test for dioxins.
''They didn't test for dioxins and some other contaminants which obviously have other long-term exposure risks,'' she said.