Safety at Marsden Pt a complex issue

Press, 1 July 1983, Page 4

Safety at Marsden Pt a complex issue

PA Whangarei “Bring some cigars out here and I’ll go anywhere on that site with you and light them and as from the last two days, that includes the control room.”

This challenge has been thrown down by Mr Jack Hardie, the project manager for the Marsden Point oil refinery extensions. The day before, 1000 people at a public meeting in Whangarei had been told by a union spokesman, Mr Ray Hikuroa, that the local superintendent of the Labour Department had said the site was as safe to work on as a petrol station. Since four men were badly burned on June 14 in an explosion in the control room being built for the expanded refinery, controversy has raged about the safety of the entire site. With four men burned, two of them very seriously, is has become an issue unlikely to be resolved without emotion.

Initial reports on the

cause of the blast, which sent a wall of flame racing through the bunker-like basement of the building, said it could not have been caused by hydrocarbons from the existing refinery.

But within a week chemical anaylsis, showed that hydrocarbons identical to those produced in the refinery were the likely cause. Somehow these had seeped into the basement and continued to do so.

The implications were serious as the building was designed as a virtual bombproof, waterproof structure, to house the largely automated controls of the new refinery.

With the concrete floor nearly one metre thick and 300 mm walls, the seeping into the building should not have occurred.

It is a relatively complicated matter to understand how the hydrocarbon highly volatile and “light tops” could have got into the building.

The New Zealand Refining Company was forced to

admit that its storage tanks had to some extent failed. Over a period, probably of years, there had been a gradual build-up of hydrocarbons into the underground water-table. This is apparently not unusual at oil refineries, a visiting Australian safety expert, Mr Mark Tweeddale, confirmed the day after the explosion.

He said small amounts of hydrocarbon that leaked into the soil could build up in the groundwater.

Mr Tweeddale declined to comment further as he did not know the particular circumstances of the Marsden Point installation.

The acting general manager of the refinery, Mr Eric Dodd, admitted there had been losses of naphtha and “light tops,” which are light petroleum vapours. Four out of five storage tanks normally containing “light tops” had been extensively rebuilt over the last two or three years, he said. The fifth tank was built new in 1976.

Mr Dodds said that steps had been taken to minimise the amount of hydrocarbon getting into the drainage system from the floating roofs of these tanks. All of the more volatile substances held in tanks at the refinery have floating roofs as a safety measure. Without them huge amounts of explosive vapours could build up in the tanks when they were empty or nearly empty. The company now manually opens the roof drains on all of its tanks every time it rains, so minimising the time any refined products can run out through this system. However, this may not be the only source of groundwater contamination.

Serious corrosion problems are believed to have occurred in the bottom plates of some bitumen and fuel oil tanks.

These products are stored hot and it is suspected that the heat draws moisture from the soil towards the bottom of the tanks, accel-

erating the corrosive problem. Mr Dodds said that to assist in determining when there were any leakage problems the refinery had about 30 bores drilled in the tank farm areas. Under normal circumstances samples were drawn off these bores about every two months for testing. Any hydrocarbons lost from the tanks showed up these bores.

Mr Dodds confirmed that the levels of hydrocarbon contamination in the bore water had varied from about 50mm to 910 mm. However, he emphasised that recent tests, which were now taken every fortnight, had indicated much lower levels of hydrocarbon contamination than previously.

Part of this could be explained by the tank maintenance procedures and the revised roof drain use.

However, the dewatering process necessary before major excavations can be

made on the expansion site adjacent to the operating refinery could also be responsible.

Because the natural groundwater table is relatively close to the surface it has to be lowered. Under normal circumstances, Mr Dodds said the hydrocarbons trapped in the groundwater moved little more than two metres each year.

But by sucking all of the water out of the ground at the nearby construction site, the hydrocarbons were being induced to move at a much faster rate.

This action may be responsible for the naphtha and “light tops” being drawn to the control room excavation in sufficient quantities to have been responsible for the explosion.

Mr Dodds said that once the hydrocarbons had been absorbed into the soil in sufficient quantities there was very little deterioration in their quality.

He said the hydrocarbons found in the basement were just as volatile as when they had entered the ground an indefinite period before.

In some ways it was a “catch 22” situation, he said. De-watering had to continue during construction, but this was accelerating the travel of the more volatile hydrocarbons towards the excavation sites.

One side benefit, however, had been that the over-all level of hydrocarbon contamination in the ground water appeared to have been significantly reduced. He said the company had been criticised for not taking enough preventive action, but apart from its tank maintenance programme it had done everything possible to minimise the problem, including digging up and checking a number of drains.

The refinery, he said, was also installing a recovery system to get the hydrocarbons back out of the ground, for later re-use.

Mr Hardie, the project manager, said it was still not possible to say how the control building could be fixed.

Two extra dewateUng pumps had been installed tn the area and the watertable was now well below the bottom of the basement;.

It would soon be possible to make a careful investigation of the building and identify the problem.

Mr Hardie said that since the water-table had been lowered, there had been no explosive gases or vapours detected in the control building.

JV2 had now drilled 19 bores throughout its construction site and only three of these had shown traces of hydrocarbons. All of these had been adjacent to the control building, Mr Hardie said.

At no time had the construction crews actually dug into the water-table, although they would have if the site had not been dewatered, he said.