However, the HSE launched an investigation prompted by concerns that the "lift slab" technique used to build Pipers Row could lead to structural failures at other car parks.
The report found that the collapse was caused by a problem with the concrete, rather than a fault inherent in the lift slab design.
It said: "Deterioration of the concrete over and around the column–slab zone led to failure of the concrete slab. The mechanical column–slab connection unique to the 'lift slab' method of construction did not fail."
The concrete deterioration at Pipers Row resulted from localised damage to the overlying waterproof membrane. This allowed water access to areas of poor quality concrete in the upper part of the slab, leading to frost damage and loss of strength.
The HSE cautioned that the structural integrity of the lift slab design required careful engineering judgement, as current design codes could result in the underestimation of the load acting on the car park structure.
It also warned that for some types of reinforced concrete structures, including flat slabs without adequate provision of bottom reinforcement over the columns, there may be a risk of progressive collapse.