An explosion at a Helsinki hospital construction site that injured two people last summer could have been avoided, according to the Regional Administrative Agency of Southern Finland (Avi).
The explosion was caused by a leftover charge that was inadvertently detonated during excavation work. The accident occurred at a construction site at the Laakso Hospital area in Helsinki's Meilahti district in August.
The blast scattered rocks and debris hundreds of metres away, damaging a number of parked cars and injuring two people.
Controlled blasting and excavation work at the site had taken place between 6 and 22 May. The set of explosives involved in the accidental blast were placed on 20 May and detonated two days later.
The charge that later detonated in August had been in place for more than two months, Avi explained in a report.
The agency said that the accident could have been avoided if workers had ensured that all of the placed charges had actually detonated and if the undetonated charge had been removed.
A week after the accidental explosion, the construction company Destia said that explosives dogs had found two more undetonated charges at the site.
Missing document
The manager in charge of blasting work at the site submitted a report to Avi about the accident. According to that report there were two possible reasons for the charge not detonating as it should have.
It was either due to another explosion causing it to malfunction or there was a fault in the charge itself, according to the manager's report.
According to Avi, if an adjacent explosion prevented the blast, there would be reason to suspect the ignition sequence was incorrect.
According to the manager, the explosives team said that the equipment in question was functioning correctly at the time of the controlled blast.
However, Avi said this information could not be confirmed, as the agency has not been able to reliably check the explosive equipment because the report it received was lacking a log file document about the ignition device.
The agency's report did not comment on how the log file could have been missing.
Triggered by excavator
Avi said that the accidental explosion was triggered by an excavator machine hammer, as it was removing rock at the site.
The operator of the excavator was injured by rocks flying through the machine's window. According to Avi, the driver's injuries could have been mitigated or prevented with the use of a metal grill on the excavator's windscreen. However, the agency noted that the driver said additional protection offered by a grille would have been mostly theoretical.
Another worker at the site was also injured in the blast, who was between 40 and 50 metres away from the explosion.
The explosion threw debris and chunks of rock as far as 300 metres away from the blast site.