Three people were killed and four others critically injured from an explosion at a box company in Soulard this morning. St. Louis Fire Chief Dennis Jenkerson told reporters the blast occurred at the Loy-Lange Box Company on South Russell Boulevard, killing one person and critically injuring four others. The blast propelled a cast-iron boiler from the Loy-Lange Box Company almost 500 feet in the air before it landed on the Faultless Healthcare Linen Company, killing two persons inside. Four other people were critically injured.  Emergency crews remain on the scene of the blast.