Gillian Beckingham, who is being retried on manslaughter charges after appealing her conviction on the same charges at Preston Crown Court last year, failed in her duty to look after the air-conditioning unit at Forum 28 Art Centre in Barrow, prosecutors said.
In the summer of 2002 the system sprayed deadly bacteria into the air and led to an outbreak of Legionnaires' disease. Six women and one man died, while 172 others were infected.
Alistair Webster QC, prosecuting, told the jury of eight men and four women that both the deaths and illnesses were 'avoidable and unnecessary'.
He said: 'It was an outbreak which could have been avoided by the exercise of no more than a moderate amount of care and common sense.
'These were deaths, with all the consequence, trauma and sadness for the families and victims infected, which we say were avoidable and unnecessary.
'These were serious illnesses, with all of their continuing effect upon the lives of their victims, which similarly were avoidable and unnecessary.'
'The Crown says the person who was principally responsible for this human disaster, both in human terms and in criminal terms, was Gillian Beckingham, a qualified architect who was employed by Barrow Council as head of the Design Services Group.'
The court heard that air-conditioning systems were normally covered by a code of practice, published by the Health & Safety Executive.
Unless preventive measures were taken, systems could provide an 'almost perfect breeding ground' for legionella bacteria, Webster told the court.
'The steps that have to be taken are not complicated, they are far from being rocket science. They could and should have been applied in Barrow.
'The central ones - monitoring the condition of the water in the air-conditioning system, putting in chemicals to ensure bacteria cannot thrive and ensuring that those chemicals are put into the water in appropriate doses - had been applied in Barrow in Forum 28 for years before this outbreak took place.
'However, they had been cancelled. Nothing was put in their place.
'It had been months since any control system had been applied to the air-conditioning system.'
The court heard that Beckingham cancelled a contract which ensured that necessary tests were carried out on the system.
After a few months, during which the system was not covered by any maintenance agreement, she signed a new contract, the court was told.
But Webster said this new contract 'did not provide for any effective water-treatment system, no regime for the cooling towers.'
He said: 'You will hear evidence that she was warned by a service engineer as to the serious dangers brewing in the air-conditioning system at Forum 28, before the outbreak occurred.
'Such a warning made it imperative for her to take swift and effective action to eliminate the danger.
'She failed to take any effective action at all and the tragedy unfolded,' he added.