An explosion killed at least three people and injured another on May 6 in the Uralchem Azot ammonia plant at Berezniki, in central Russia, according to the Interfax news agency.
The explosion occurred during welding work being carried out to repair facilities within the plant, which is owned by the Uralchem combine.
The company produces ammonia, ammonium nitrate, urea, sodium and potassium nitrate and crystalline sodium nitrite.
Production was not affected by the incident and the Federal Service for Ecological, Technological and Nuclear Supervision have apparently dispatched experts to assess the environment at the plant, while the Russian Investigative Committee has initiated a case into violation of safety requirements at a hazardous industrial facility.
Berezniki has been the site of large scale potash mining for 70 years.