Safety concerns about the gas storage tank and piping at the ICL Plastics factory in Maryhill, Glasgow, were raised by experts 15 years before the explosion which destroyed the plant and killed nine people.

The second day of the ICL public inquiry heard evidence from engineers from Calor Gas, who supplied the liquid petroleum gas (LPG) storage tank outside the factory.

Witnesses spoke of the tank being in an unsafe position and of warnings that LPG pipes should not be routed into a basement.

Letters from the Health and Safety Executive (HSE) to ICL and Calor Gas show the company was told to excavate and inspect the underground pipe work leading from the tank to the building.

ICL Plastics was also told to reduce the volume of LPG they stored for use at the factory and make major structural changes to their property surrounding the storage tank.

However, the inquiry was told no records proving work was carried out have been found so far.

In a letter dated January, 1989, John Ives, Her Majesty's Inspector of Factories told of concerns that were raised by drivers. This prompted a visit to the factory by safety inspectors.

The letter contained a series of recommendations which had to be complied with. It said the quantity of LPG should be reduced, the size of the tank should be reduced, a wall close to the tank should be removed and the tank should be located further from the factory wall.

It also instructed: "The part of the underground pipe work carrying LPG vapour into the building should be excavated. The pipework and any corrosion and protective coating should be examined by a competent person and any recommendation made as a result should be carried out."

Maurice Coville was Calor Gas group safety inspector for Scotland from 1978 until 1993.

He said he had records showing he visited the site but had no accurate recollection from memory. A letter from Mr Coville to Mr Ives showed plans he drew up to alter the layout of the tank area, to comply with Mr Ives requirements. The HSE said that, for the work to be carried out, ICL would need to take ownership and control of land outside their factory wall to provide enough space.

Calor Gas representatives said that, despite an extensive search for documents for the inquiry, they had no record of such work being carried out.

Henry Betts, the current central operations manager with Calor Gas, was shown a sales document for the replacement of the large two-tonne storage tank to be removed and two smaller ones to be delivered in its place.

However, he said a separate document would be required for the actual delivery and installation procedure.

He was told no such document was found and asked if Calor Gas had tried to find documents for the inquiry. He replied "Yes."

A total of 56 people were caught up in the blast which happened on May 11, 2004, with nine killed and more than 30 seriously injured.

The public inquiry chaired by Lord Gill continues.