Y2024-03, Ex­plo­sion ac­ci­dent at a con­struc­tion site in Helsinki on 9 Au­gust 2024

18.12.2025

An unintentional explosion occurred at a construction site in Helsinki, on 9 August 2024. The explosion propelled stones of different sizes into the construction area and outside it, up to a distance of approximately 300 metres. There were several people in the area affected by the explosion. Two workers were seriously injured after being struck by stones. The accident caused material damage and danger at the site and its surroundings.

The construction project involved a lot of excavation work and thus several hundred explosions. One of the areas scheduled for blasting was charged with explosives two months before the accident. When explosives were transferred to the blast area in connection with the charging, some dynamite cartridges ended up in the wrong place, in the so-called wide-spaced relief drilling line. The blasters were able to remove some of the cartridges. No report of the incident was made, in accordance with the construction project’s procedures, nor was any information added to the blasting plan regarding explosives that may have remained in the wrong location. Information regarding the incident was communicated orally, but it remained known only to a limited group of individuals. Verification of explosives lost during the charging was not completed.

The dynamite cartridges left in the wrong location did not explode when the adjacent blast area was exploded a few days later. Two further minor levelling blasts were conducted in the area, after which the blasted field was cleared of rock and crushed stone, during the summer. During the clearing of the blast area, no explosives or parts thereof were detected in the blasted rock.

Upon removal of the blasted rock, it was observed that the bedrock had not fully separated along the wide-spaced relief drilling line. The sections that were still connected were decided to be separated using hydraulic rock hammer attached to an excavator. This work started on the day before the accident. The accident occurred when hammering the point where the hidden dynamite cartridges were.

The large construction project was implemented using an alliance model. This is a collaborative contract form in which the parties to the project are responsible for the planning and construction of the project and share the risks and benefits. The underground and surface excavation and blasting works were performed as a sub-alliance project and allocated to two different operators. Due to a number of incidents, surface excavators were replaced, eventually ending up in a situation where the company responsible for the excavations acquired the work from external excavation companies. The team carrying out the blasting work as a subcontract consisted of several small limited liability companies. The reconciliation of the safety cultures of several large operators and the integration of the alliance did not fully succeed. The processing of previous incidents had weakened the interaction between the parties to the construction site. The incident during the blast area charging, where explosives ended up in an incorrect location, was not communicated in accordance with the project’s reporting procedures.

Large construction projects are scheduled and time-critical. Financial factors guide operations, and subcontracting is layered. There are many operators at the construction sites, and various work is carried out simultaneously. Occupational safety activities focusing on accidents, exposures and physical strain, as well as the separate planning of hazardous tasks, such as blasting, are not always sufficient for identifying and managing accident risks during construction work.

Blasting work is hazardous work and mainly strictly regulated. However, not all work phases are regulated in detail. Blasting workers are responsible for deciding on the methods for transferring explosives at the site, as well as the procedures for searching for potential unexploded explosives. Both work phases involve risks. Explosives may end up in the wrong place, and unexploded explosives may not be found. There may be explosives in the blasted field or among the blasted rock to be extracted. There is a risk of unplanned explosion in drilling operations and hydraulic hammering in excavated areas, as well as in crushing of blasted rock. There have been serious accidents in Finland related to these work phases, including two occupational fatalities. The risks of accidents increase when excavation is carried out in the middle of an urban area.

The Safety Investigation Authority recommends that

1. the Building InformationFoundation draws up guidelines on good practices in the safety management ofcollaborative contract forms.
2. The Confederation of FinnishConstruction Industries RT (CFCI) and the partnership network of rescuedepartments prepare guidelines for the systematic identification and managementof accident risks at construction sites.
3. The excavation division ofInfra ry and the Centre for Occupational Safety ensure that good practices havebeen compiled into instructions and included in different templates, so thatall work phases related to the use of explosives are planned considering theassociated risk.

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