The creator of an inflatable artwork that broke free and carried dozens of people into the air, killing two women when they fell from it, stopped an evacuation that could have saved lives, a court was told yesterday.

The women fell to their deaths and more than two dozen others were injured when the giant PVC sculpture, hit by a gust of wind, became airborne in July 2006 at a park in Chester-le-Street, Co Durham.

Maurice Agis, the 77-year-old artist who designed and supervised the Dreamspace installation, is accused of manslaughter by gross negligence over an alleged litany of safety failings It was not the first time one of his artworks had broken free and caused injury.

A jury at Newcastle upon Tyne Crown Court watched CCTV footage of the moment when one side of the inflatable suddenly lifted 150ft from the ground and became vertical. It twisted over and was blown towards a river before snagging on a high pole and collapsing to the ground.

Paul Sloan, QC, for the prosecution, said that those trapped inside gave graphic accounts of standing on firm ground one moment and then, as the structure took off and turned on its side, of facing a sheer drop before tumbling down and bouncing off the internal columns as they fell.

The court was told that the inflatable was not properly anchored and its risk assessment had been inadequate. Not enough ropes were used, they were unevenly distributed and neither the ropes nor the metal ground pegs were strong enough to withstand strong winds.

Mr Sloan said that one employee noticed that wind was getting underneath the structure — a group of interconnected ovoid pods the size of half a football pitch. It was lifting the floor several feet into the air.

The employee followed procedure and started to evacuate those inside.

The visitors had paid to remove their shoes, put on a coloured cape and walk though the pods, “experiencing changes of space, light and colour” to an accompanying soundtrack. Mr Sloan said that Mr Agis, “having taken a look, said that it was safe for members of the public to re-enter”. But he instructed two members of staff to attach more ropes.

Before they had completed their work, they were, “interrupted by Maurice Agis, who told them to resume their duties at the entrance so that he and his partner, Paloma Brotons, could enjoy a refreshment break”. This meant that no extra ropes were attached to the rear of the structure, on its west side.

The two women who died, Elizabeth Collings, 68, and Claire Furmedge, 38, suffered severe injuries when they fell and hit the ground after the inflatable took to the air.

Mr Sloan said that Mr Agis, who denies two counts of manslaughter and a charge brought under health and safety regulations, owed a duty of care to those inside, which he breached by failing to ensure that the inflatable was properly designed and anchored. The artist, he said, was only too aware of the need to ensure that his creations could cope with sudden changes in weather conditions, because this was not the first time that one of his inflatable structures had broken free from its moorings.

In 1986, an Agis installation called Colourspace, anchored to the ground by stakes, was exhibited at Travermünde, a small town on the north German coast. When a pleasant sunny day changed dramatically with the arrival of a summer storm and strong gusts of winds, the structure broke loose and several of those inside fell and sustained injuries.

In the light of that incident, Mr Agis’s conduct could only be described as gross negligence amounting to a crime, the crime of manslaughter, Mr Sloan said.

The court heard that Riverside Park, where the tragedy happened, was owned by Chester-le-Street District Council, which has admitted a breach of health and safety requirements, as has Brouhaha International, a company assisting in the installation’s UK tour. The tour was part-funded by the Arts Council of England.

Mr Sloan said that Brouhaha, whose managing director was Giles Agis, the defendant’s son, assembled the artwork at a warehouse in Liverpool, where it went on display for a month before being taken to Chester-le-Street. After the incident, Maurice Agis, of Bethnal Green, East London, was said to be visibly shaken.

Interviewed later by police, he declined to answer any questions but offered prepared statements. In these, he emphasised that he would not open Dreamspace to the public in windy conditions and that he had not been aware of any wind on the day of the incident.

The trial continues.

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