Liverpool Magistrates Court heard how Retro Future 2000 ignored orders by the Health and Safety Executive to improve standards on the waterfront site.
The inspection in April of the six-story apartment blocks, on Keel Road, found several areas of the site had no barriers to stop workers falling and being seriously injured or even killed.
They included an open lift shaft, a staircase landing between the fourth and fifth floors with no walls or rails, and an empty floor-to-ceiling window frame on the sixth floor with a rubbish chute attached.
The HSE investigation concluded that a worker could easily have fallen out of the window frame while emptying rubbish into the chute, if they had tripped on a plank of wood next to it.
The HSE also issued four enforcement notices following a previous visit to the site on 22 October 2009. They included a prohibition notice relating to falls from height, stopping work taking place until improvements had been made.
Retro Future 2000 Ltd was fined £7,000 and ordered to pay costs of £1,981.
Kevin Jones, the investigating inspector at HSE, said: “This is one of the worst cases I have ever dealt with and Retro Future is extremely lucky that no one was seriously injured.
“The company was managing a major construction project in Liverpool city centre, but the conditions on the site were appalling.
“There were several instances where Retro Future had failed to do anything to prevent falls, and put lives in danger as a result. We issued four enforcement notices, and offered written advice on managing the risks from falls, following a previous visit.
“Sadly, despite initially making improvements, the company appears to have fallen back into old habits within a few weeks.”