According to Russian media reports the high speed lift holding the four victims of the blaze initially became jammed when its safety locks came on, indicating that the lift cables had already melted through or snapped.
However, as the blaze spread further downwards, the lift suddenly plummeted into the basement, followed by its counterweight.
Roger Howkins, Ove Arup & Partners associate, said a possible cause of the fall was that the lift roller guide tyres that follow the shaft guide rails - a feature of all high speed lifts - may have melted in the heat from fire below.
'This would allow the lift to move around inside the guide rail and eventually break free of the safety locks, ' he said.
Alternatively he suggested that the guide rails themselves may have buckled or distorted in the heat.