Melbourne's famous rectangular stadium AAMI Park, where flares were set off by football fans last weekend, is covered in material that is classified as combustible, inspections carried out as part of a safety audit have revealed.

Key points: AAMI Park is covered in geodesic domes made of steel-clad polyurethane "sandwich panels"

AAMI Park is covered in geodesic domes made of steel-clad polyurethane "sandwich panels" Material used at the stadium was not approved in the building permit

Material used at the stadium was not approved in the building permit The building authority says it is safe due to other design features

The geodesic domes are made of steel-clad polyurethane "sandwich panels", which were not the materials approved in the original building permit and were substituted in after the building permit was issued.

Stephen Kip, fire safety engineer and lecturer in building regulations at the University of Melbourne confirmed "polyurethane foam is combustible" according to tests applied in the Building Code of Australia.

However, both the Victorian Building Authority and Metropolitan Fire Brigade have assessed the building and deemed it to be a low fire risk.

Because of other design and safety features of the stadium, the VBA said AAMI Park can be classified as complying with the Australian Building Code, despite the use of the polyurethane sandwich panels for the outside walls.

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The management of AAMI Park declined to answer specific questions about the permit process and any possible risk from flares set off by soccer fans last weekend.

Exterior of burning apartment building in Docklands on November 24, 2014. ( Audience submitted: Wade Savage )

Communications manager for Melbourne and Olympics Parks Enna Giampiccolo said the building was compliant with the building code and "safe to occupy".

"We have received independent advice from fire engineers and building surveyors and can confirm the facade material meets the performance requirements of the Building Code of Australia," she said.

The widespread use of combustible material was uncovered during the VBA's audit of cladding on high-rise apartment buildings in Melbourne, which began in response to the Lacrosse Building fire in November 2014.

On Wednesday, the VBA revealed 51 per cent of the 170 buildings examined contained cladding that did not comply with Australian standards.

But the authority reassured the public that the buildings were all safe to occupy.

VBA audit 'identified inconsistencies'

A spokesman for the VBA said substitution of products was identified as a major issue in the VBA's audit.

In relation to AAMI Park, a VBA spokesman confirmed that "the VBA audit identified inconsistencies between the material used in construction and the material specified in the relevant building permit [for AAMI Park]'.

The material originally approved for use in AAMI Park's building permit was a sandwich panel with a polyisocyanurate core.

Several fire safety engineers have told 7.30 this material would also generally be classified as combustible, though less combustible than the polyurethane material that was eventually used.

Melbourne Victory fans light a flare during the Melbourne City and Melbourne Victory A League match at AAMI Park on Sunday. ( AAP Image: Tracey Nearmy )

One said, in his opinion, even the polyisocyanurate material should not have been approved for use.

It is understood neither were tested to Australian standards.

However, the VBA said it was "satisfied that the Melbourne and Olympic Parks have adopted the appropriate approach, engaging a fire safety engineer, to establish that the building's construction continues to meet the performance requirements of the code".

CEO of the Fire Protection Association of Australia Scott Williams said the substitution of products at AAMI Park was a good example of how common the practice had become.

"Substitution of products from the original is a major issue in the industry and something we call on the regulator to address urgently," he said.

"Any building component which is required to protect occupants from the risk of fire should not be left to chance.

"Luckily, in this case, the owners of the facility have taken immediate, proactive steps to ensure compliance and safety of patrons, however they should not need to do this as compliance should be guaranteed."