The Lapua Cartridge Factory explosion (Finnish: Lapuan patruunatehtaan räjähdys) was an industrial disaster in an ammunition factory in Lapua, Finland on 13 April 1976. Forty workers^[1] were killed and 60 people injured. This was Finland's worst industrial disaster.^[2]

The explosion occurred at 07:43, completely destroying the building.^[3] The blast was heard up to 20 kilometres (12 mi) away.^[4] Most of the injured had been in the factory at the time, but some outside were injured by shrapnel.^[5] Of the dead, thirty-five were women. Fifty-two children under the age of 16 lost at least one parent in the accident.^[5]

A strike by telephone engineers meant that there was reduced communication in Lapua at this time,^[3] as many of the circuits had not been fully repaired after the winter and the telephone exchange was quickly overwhelmed as relatives phoned searching for information.^[4] Rescue efforts were hampered by fires, causing several of the remaining cartridges to explode at sporadic intervals.^[6] Beginning at 08:05, the injured began to be transferred to the district hospital in Seinäjoki.^[3] Staff at this hospital had already received training in preparation for a major incident, as the town was located at a railway junction.^[4] Medical staff were concerned that the clothing worn by victims of the incident could include live ammunition which could be accidentally set off.^[5] Military helicopters brought blood supplies from Helsinki for transfusions.^[5]

The day of the disaster, the Minister of Defence, Ingvar S. Melin, visited the health centre in the town and the Parliament of Finland observed a minute's silence.^[5] The funeral service of all 40 victims took place in the southern park of Lapua Cathedral and was broadcast live on Finnish television.^[1][5] The accident resulted in an enhanced level of crisis support from the Finnish authorities and donations from private individuals came in from across the nation to help.^[1]

Debris from the scene was taken to the laboratory of the Finnish Defence Forces for analysis.^[7] In November 1976 investigators found that the explosion had begun with a machine which dispensed gunpowder and had spread from there, causing a chain reaction.^[8] Investigators tested numerous possible scenarios, among them the theory that rust had caused the machine to malfunction or that a foreign object had lodged in it. However, a definitive cause of the explosion was never discovered.^[8] Investigators speculated that poor ventilation in the factory had caused a buildup of gunpowder dust, which was then ignited by a spark.^[4] The accident resulted in new legislation in the armaments industry which brought in stricter safety measures.^[7]

In 1978 legal action against the factory's owners began; this ended in 1982 with all defendants being acquitted.^[8] A few weeks after the explosion, the decision was taken to rebuild the factory. It was rebuilt 6 kilometres (3.7 mi) from the town centre.^[8]