B4/2003Y Dropped ceiling of indoor spa resort collapsing in Kuopio, on September 4, 2003
On Thursday morning September 4, 2003, the dropped ceiling above the main pool in the new pool compartment of Rauhalahti spa-resort hotel in Kuopio, Finland, collapsed in its entity. At the time of the incident, there were three persons swimming in the pool. At 8.52.48 hours the swimmers perceived that the ceiling was falling down. In two seconds the dropped ceiling had collapsed in the water slide end of the pool, and in three seconds the entire dropped ceiling had fallen down. The swimmers failed to escape from the blow of the collapsed ceiling, but they were located in a way that they managed to avoid losing consciousness by the blow. In fact they managed themselves move over towards the edge of the pool, and two of them were able to get out of the water themselves while after over eight minutes in the pool under the collapsed ceiling, the third person was helped out by the spa staff.
The swimmers were lucky only to suffer some minor injuries. The entire area of the dropped ceiling measuring 256 m² and covering the main pool, as well as its lighting fixtures, fire detector facilities and wiring system had to be rebuilt. When collapsing the ceiling broke a surveillance camera, pool equipment and fittings. The direct costs of the incident amounted to about €75,000 and the sales return losses suffered by the spa-resort hotel were estimated to about €111,000. The new pool compartment had to be closed over a period of almost six weeks.
The collapse of the dropped ceiling was caused by a breaking of the suspension wires made of stainless steel, as a result of stress corrosion. Some wires close to one another having broken, the stress in the adjacent wires grew to the extent that other wires that had weakened by the stress corrosion, broke and spring suspensions came loose from the supporting long beams. As wire material, AISI 304 stainless steel had been selected, as at the time of the realization of the project, the designers, planners, constructors and building supervision authorities had no knowledge of the SFS-ENV 1993-1-4 Eurocode preliminary standard with its national implementation instructions, and they were hence unable to use it in the selection of an appropriate steel quality for indoor swimming-pool and spa conditions. According to an investigation conducted by the Technical Research Centre of Finland (VTT), the AISI 316 acid resistant steel specified in the original plans would not have been a significantly better solution as regards stress corrosion. Stress corrosion is not only conditioned by stresses caused by load, but a more important conditioning factor is to be seen in the residual stresses generated by wire treatment. In practice residual stresses can hardly be avoided as they are generated even in the installation phase.
The complete collapse of the dropped ceiling was a result of the ceiling having been built as entirely integral without any expansion joints or special joints that would have prevented a progression of the collapse. Moreover the ceiling was relatively heavy as one suspension wire was stressed by an about 33 kg load. The bearing rate of the spring suspension was 25 kg with the maximum admissible load being defined as 328 N (33.4 kg). A dropped ceiling is not considered as a support construction, and consequently, a progressive collapse had not been considered in the relevant plans.
The ceiling having been built, the condition of its suspension and supporting structures had not been inspected, as the dropped ceiling featured no inspection hatches and its height from the upper level of the pool was over five meters.
To prevent corresponding collapses of dropped ceilings, the Accident Investigation Board of Finland recommends that the regulations and instructions pertaining to planning and design should include detailed specifications for such important load support construction materials that are appropriate for indoor swimming-pool and spa conditions, in terms of safety. Moreover the instructions concerning dropped ceiling structures of indoor spa resorts and swimming pools ought to be updated so as to consider dropped ceilings as support constructions and to realize the air-conditioning of the space above the dropped ceiling in a way rendering impossible any chlorine penetration or accumulation on the surfaces of non-corrosion-resistant structures.
The summary, introduction and the legends for the figures and tables in the report are also in English.