Families of workers who died in Scotland's worst industrial accident in a generation yesterday called for new corporate killing laws and condemned the financial penalty imposed on the operators of the factory involved.

ICL Plastics and ICL Tech were yesterday handed fines totalling £400,000 over the gas explosion which killed nine people and injured 33 in Glasgow in May 2004. The firms had previously admitted four charges under the Health and Safety at Work Act.

Imposing the fines at the High Court in Glasgow in front of more than 30 relatives of those killed, trial judge Lord Brodie said the sums involved were not meant to equate to the lives lost or injuries and suffering caused, adding that "these are not things that are capable of being expressed in terms of sums of money".

Immediately after the court's decision, a statement on behalf of seven of the families who lost relatives described the fine as inadequate.

It said: "No financial penalty can justify our losses nor ease the pain of the last three years, pain that we have to continue to live with.

"Unfortunately the justice process that we have now completed probably raises more questions than it has answered. And we redouble our calls for a comprehensible full public inquiry. The current legal system is too restrictive and until company directors face personal prosecution for their negligence, families will never receive justice."

Margaret Brownlie, Annette Doyle, Peter Ferguson, Thomas McAulay, Stewart McColl, Tracey McErlane, Kenneth Murray, Tim Smith and Ann Trench lost their lives in the explosion.

Relatives of some of the victims spoke of their anger at the fine imposed on the company.

Angela Rowlinson, 38, who lost her sister Tracey McErlane, 27, in the blast, said: "We are devastated, absolutely devastated. I just feel as if they got off lightly."

She added: "We need a public inquiry for closure.We need it for the sake of Ryan, Tracey's wee boy, because we need to have answers to give him."

The Scottish Trades Union Congress, speaking on behalf of the victims and their families, said many were "very upset" at the size of the fine.

Grahame Smith, general secretary of the Scottish TUC, told a press conference in Glasgow: "If you are a doctor and you are negligent, you are struck off, if you are a lawyer and you are negligent, you are struck off. "If you are a company director and you are negligent in relation to health and safety, you can continue being a company director and that is not acceptable.What has happened here is just not good enough."

The charges alleged that between 1993 and May 2004 the companies failed to ensure there was no risk to employees from the pipework.

On Monday the court heard how just £405 for the inspection and replacement of a corroded and leaking LPG pipeline would have prevented the explosion.

Passing sentence, the judge 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.

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

Lord Brodie said that the nature of any response the court was able to make to the tragedy was limited to imposing fines, adding that in setting the fine he was taking account of the ability of the two firms to stay in business and jobs.

He said: "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.

"I find it difficult to accept the word inadvertent'. With the benefit of hindsight, it seems remarkable that, through the whole period, nothing was done by the accused companies to satisfy themselves that the pipe was sound and likely to remain so."

The two-day hearing was told that a propane gas 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 exposed pipe was buried in a building project.

The court heard that the buried pipework corroded, as did a bend joining two sections of the pipework, leading to an escape of gas, which accumulated in the basement area then exploded.

Stewart Campbell, director of the Health and Safety Executive in Scotland, said lessons needed to be learned to ensure "problems which are out of sight are not out of mind".

A statement issued on behalf of the company's directors 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."