The operators of a plastics factory were fined a total of £400,000 today over a gas explosion which killed nine people.

ICL Plastics and ICL Tech were handed the financial penalties at the High Court in Glasgow.

The firms admitted four charges under the Health and Safety at Work Act over the blast which killed nine people and injured 33 in Glasgow on May 11, 2004.

Imposing the fines, trial judge Lord Brodie said the sums involved were not meant to equate to the lives lost or injuries and suffering caused.

"These are not things that are capable of being expressed in terms of sums of money," said the judge.

More than 30 relatives sat silently in court as the judge passed sentence.

Five men and four women died in the explosion.

The charges, which the two companies admitted, alleged that between 1993 and May 2004 they failed to ensure there was no risk to employees from pipework at the factory.

Passing sentence, the judge said he accepted financial details of ICL, which had been provided by the defence.

And he noted that the company intended to continue to trade and continue to employ its workforce.

The judge told relatives gathered in court: "That it was a tragedy is beyond question.

"Nine people were killed, 33 people were injured, many of those people were very seriously injured indeed.

"Seventeen, while not physically injured, were placed at risk of death.

"That summary takes no account of the psychological impact of the event, both on the survivors and the families of those killed and families of those that were injured."

The firms said they would welcome any inquiry into the accident.

A statement from the directors of the two firms read outside court said: "The information brought to light by the complex technical investigation and subsequent court proceedings will, we hope, have provided meaningful answers to many of the questions surrounding this terrible tragedy.

"Since May 2004, all concerned have made enormous efforts to sustain the companies and to maintain the employment of our workforce.

"The heroic input from so many who were injured in the blast, and the loyalty and support of many others, is the reason for the companies' survival to this day."

The statement went on: "We remember colleagues lost and their families, and our sentiments and feelings are expressed in the creation of a memorial garden.

"The companies welcome any form of inquiry that will properly establish all the facts and circumstances relating to the disaster.

"It is hoped that an inquiry will result in a full understanding of the circumstances and bring about necessary changes that will prevent any similar accidents occurring across business and industry in Scotland and beyond.

"For our part in this, we have and will continue to assist by being transparent in all aspects of our business both prior to the accident and since."

The judge said the nature of any response the court was able to make to the tragedy was limited to imposing fines.

"That response is by its nature an inadequate response. When the firm first pleaded guilty on August 17, relatives of the victims had said no court case or penalty could bring back their loved ones or provide an explanation as to why they died," said the judge.

But the two-day hearing, which ended today, provided an explanation of the mechanics of the fatal explosion and what had caused it, said the judge.

The court heard yesterday that a propane LPG tank and pipework were installed at the factory in or around 1969.

Part of the pipework came vertically out of the ground before entering the building, but five years later, around 1974, the yard outside the building was raised, burying this exposed section of pipework.

Around 1980, a steel floor was installed, creating an underground basement.

The court heard that the buried pipework deteriorated and corroded, as did a bend joining two sections of the pipework.

This led to an escape of LPG, which accumulated in the basement area then exploded, causing the building to collapse.

Emergency services arrived at the scene shortly after the blast, while people who were trapped and had been able to shout for help were being freed by local people who ran to help.

Eventually, 200 firefighters searched through the rubble in a bid to find survivors and rescue teams, who normally search for earthquake survivors around the world, were brought in.

Seven people were eventually rescued alive from the rubble but nine workers lost their lives. The last body was recovered on May 14, 2004.

Passing sentence today, Lord Brodie said there had been no risk assessment or system of inspection of the pipework between the LPG tank and the point at which it entered the factory.

But the Crown had not suggested this was a wilful failure, said the judge.

The Crown had argued that the failure to assess the risk was negligent, but the defence had argued it was "inadvertent", said Lord Brodie.

"I find it difficult to accept the word 'inadvertent'," he continued.

"With the benefit of hindsight, it seems remarkable that, through the whole period covered by the indictment, nothing was done by the accused companies to satisfy themselves that the pipe was sound and likely to remain so."