The company has been granted approval by the Environmental Protection Agency to use the older stack despite it not being used since 2004.

The stack will take the place of the fibreglass chute that collapsed at the waste gas cleaning plant on Monday night.

BlueScope general manager of manufacturing John Nowlan said the stack had been upgraded since it was last used, but admitted sinter operations would be scaled back to ensure the company's emissions did not breach environmental guidelines.

"The electrostatic precipitators were upgraded in 2009. It is in a much better situation, and more capable, than when we originally commissioned it," he said.

An electrostatic precipitator is a filtration device that removes fine particles, including dust and smoke, from a gas stream.

A BlueScope spokesperson said the precipitators, along with the now-offline waste gas cleaning plant, were responsible for filtering and controlling emissions from the sinter plant.

"The precipitators are significantly better than when we last used them in 2003," Mr Nowlan said.

"We have the capabilities to run two fans in the plant, but will only run one in this configuration. The sinter plant is designed to process 800 tonnes per hour, but we will now run at a significantly reduced production."

Mr Nowlan claimed the reduced production and upgraded precipitators would mean emissions from the older stack "will be the same" as those from the fibreglass chute.

Before issuing formal restart approval, the EPA consulted with Professor Alison Jones, a toxicologist and the Executive Dean of Wollongong University's Faculty of Science, Medicine and Health.

The EPA will monitor stack emissions daily for a two-week period, with readings to be publicly available on the BlueScope website. Giselle Howard, director (metropolitan) for the EPA, said the agency could impose a number of measures on the company if emissions exceeded allowable limits.

Mr Nowlan said any increased risk to workers exposed to the older stack would be "minimal".

A community meeting will be held next week for residents to voice concerns and hear from BlueScope and the EPA.