Orica is carrying out safety tests at its Kooragang Island plant.
It comes as local residents and Newcastle councilors voice their concern over the possible re-opening of the plant, the Newcastle Herald reports.
A statement from the company and the NSW EPA stated that safety testing is being carried out "prior to its consideration of lifting the prevention notices currently in place".
"The safety tests involve turning on the steam system to test its integrity.
"The steam will then be used to check a range of systems and to prove that the vent stack is clean of any contamination from the 8 August incident."
The explosives manufacturer closed its ammonium nitrate plant facilities on 9 November in response to an ammonia vapour leak from the site.
Its ammonia plant has been shut since an initial chemical leak in August.
Local confidence in the plant’s safety record is currently low, with Newcastle Greens councilor Michael Osborne telling the ABC "Orica has a long way to go to regain any trust in this community and so has the EPA.
"Even if the EPA considers that pressure testing has been a success we still have the same plant that there in August that leaked the hexavalent chromium.
He went on to say that "the community of Stockton and in the greater Newcastle area is in no better situation now" as community consultation on the plant’s future begins this week.
"I spoke to the start-up committee and the [NSW environment] minister [Robyn Parker] insisted that there would be no start-up until the community had been involved in the process," Newcastle MP Tim Owen explained to the Newcastle Herald.
"I’m expecting there will be engagement this week with the consultative committee as well as people from the Stockton Action Group to be briefed by the start-up committee and the Environmental Protection Authority."
In better news for the company, Orica advised that a separate leak earlier this month had been smaller than first thought.