ARB-registered Gillian Beckingham was in charge of the air-conditioning unit at the Forum 28 Arts Centre in Barrow, Cumbria, when it sprayed deadly bacteria into the air in August 2002.
She is being prosecuted as part of her responsibility as the council's head of design services.
The incident was the worst ever outbreak of legionnaires' disease in Britain, killing six women and one man and infecting nearly 200 other people, Preston Crown Court heard.
Alistair Webster QC, prosecuting, told the jury the deaths were 'avoidable and unnecessary'.
'It was an outbreak that could have been avoided by the exercise of a moderate amount of care,' he said. 'The person who was properly responsible for this human disaster was Gillian Beckingham.
Mr Webster said Beckingham, 45, 'failed to take any effective action' to prevent the tragedy. '[The] outbreak was caused by negligence so gross it was criminal,' he said.
Beckingham denies unlawful killing of Richard Macauley, 88, Wendy Milburn, 56, Georgina Somerville, 54, Harriet Low, 74, Elizabeth Dixon, 80, June Miles, 56, and Christine Merewood, 55, all from Barrow. Barrow Borough Council faces the same charges. The case continues.