"There are no other injured people," she said.
Bulgarian prosecutors have opened an investigation into the incident, which is normal procedure in an incident when someone is killed or seriously hurt.
Last month, two workers were killed in an explosion at Arsenal, triggering a fire.
There have been several other accidents in the arms industry in the country. In 2014, a series of powerful blasts at a Bulgarian explosives plant killed 15 employees in the village of Gorni Lom, some 145 km (90 miles) northwest of Sofia.
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