A faulty valve has been identified as the source of leak of 20 metric tonnes of tar pitch at the Koppers Mayfield plant late last month.
Koppers site manger Nick Moretti described the valve failure as ‘very rare’.
“The valve is being cleaned and tested to determine the mechanism of the failure. This investigation is still underway,” he said.
Emergency services were called to the plant in the early hours of Sunday October 21 after residents reported plumes of smoke coming from the area.
The NSW Environment Protection Authority confirmed it is reviewing an incident report before deciding on future actions.
The business processes coal tar, a by-product of the steel industry, to produce coal tar pitch and other products, used to produce aluminium, rubber and steel.
All of the pitch that escaped was contained on site.
Mr Moretti said the valve that failed was supplied by MRC Global and was used in industries with similar processes to Koppers.
“We have testimonials from three large petroleum companies that have all added this style of valve to their approved valve manufacturer list and all have this valve in use on site,” he said.
“We will have to complete the investigation into the failure mechanism of the valve before we formulate and implement actions to eliminate the same incident happening again.”
The EPA put additional conditions on the plant in June following an investigation of air emissions over a six month period.
The new requirements included prohibiting the storage of odorous solvents in the tar tank farm and the use of the large ship loading pump for carbon black feedstock transfers, along with limiting the transfer of material between tanks within the tar tank farm.
It also required the company to undertake daily benzene monitoring while benzene emitting activities are occurring.
However, in July Koppers announced that concerns over its benzene emissions had been allayed after the company found it had “overstated its own emissions” and had sent new figures to correct the National Pollutant Inventory as a result.
According to the inventory, Koppers was putting an average of 47 tonnes a year of the potentially carcinogenic hydrocarbon into the atmosphere from its Woodstock Street, Mayfield, address.
But Mr Moretti said an external review had found a major error in the way the company had been “indirectly measuring” the amount of benzene and other pollutants leaving the plant during its processes.
Mr Moretti said that as a result, it had recalculated the amounts to be “about 10 per cent of what we had previously said”.