Y2015-01 Collapse of a bridge being demolished in Mikkeli on 15 June 2015

In Mikkeli, the light traffic bridge on Selännekatu over highway 5 collapsed uncontrollably on 15 June 2015 at 12:58 pm.

The concrete bridge collapsed while being demolished. When the demolition work had advanced to the deck element beams, the traffic flowing under the bridge was stopped. The traffic along Rinnekatu that also passes under the bridge was also supposed to be stopped, but there were no separate traffic controllers for this part of the bridge. Hammering of the deck element beams caused the deck plate to break in half. The plate fell, first at the end resting on the land abutment, and then knocking down the pillar that had been supporting the bridge. This made one end of the middle deck plate fall down as well. Three cars were able to pass along Rinnekatu under the deck plate that had just collapsed, and several cars were allowed to pass later, after the site crew had estimated that it was safe to go under the bridge.

The first call to the emergency response centre came at 12:43, before the bridge collapsed. A person who had passed the site called, because he had doubts that the demolition work was not being conducted safely. The emergency duty officer assigned the mission to a patrol from the South Savo Police Department, who arrived on site after the bridge had already collapsed.

The next call to the emergency response centre came at 13:12 from the demolition site, reporting that there was no need for rescue units or emergency medical care, because no personal injuries had occurred. The police controlled traffic and conducted a forensic investigation. The police did not intervene in the traffic steered along Rinnekatu under the partly collapsed bridge. The collapse stopped the traffic on the highway for several hours.

In accordance with the demolition plan, the bridge was supposed to be demolished at night to minimise the impact of stopping the traffic. At the request of the main contractor, the demolition work was begun at daytime from an opening in the bridge, located outside the driveway.

The bridge being demolished was in good condition and met the regulations valid at the time of construction. The uncontrollable collapse clearly resulted from an insufficient demolition plan that was not even followed. The demolition plan was written in such general terms that it did not steer the work towards safe execution of the demolition work. The parties who had seen the demolition plan did not observe any shortcomings in the plan. It was trusted that the demotion work contractor and, ultimately, a single excavator driver, would guarantee safe execution. The multi-stage risk management system failed. None of the parties who processed the demolition plan were experts in the structural technology of bridges, and such qualifications were not even required.

Demolition of the bridge proceeded in an uncontrollable manner, causing a hazardous situation to road users and the site crew. No preparations had been made for a situation like this, and there were not enough traffic controllers on site. The flow of traffic was not properly controlled either when the incident happened or after the collapse.

The Safety Investigation Authority repeats the recommendation that it first made during the investigation of the collapsed Torna Bridge in 1998, according to which

• the Ministry of Transport and Communications is to ensure that instructions and minimum requirements be drawn up for demolition plans of state-owned and municipal bridges. The demolition plan must be sufficiently detailed as to cover all the essential stages for successful implementation of the work and to allow supervisors to ensure that the plan is applicable. The same level of quality should be required in planning demolition work as in new construction.

Y2015-01 report, in finnish (pdf, 1.86 Mt) Annex 1. Accimap, in finnish (pdf, 0.01 Mt)