A criminal investigation is underway in Russia into possible negligence that may have led to an explosion at an arms depot yesterday.At least two firefighters died as they tried to tackle the flames caused by the blast in the town of Ulyanovsk, around 900 kilometres south east of Moscow. The explosions occurred as navy personnel were disposing of ammunition, which included artillery shells and torpedoes. Investigators want to know if all the correct procedures were followed. Around 3,000 local residents were evacuated. Some described how they returned to their homes in the early hours of the morning to find windows shattered. With the fire now out, the attention turns to finding up to 11 people still reported missing and treating several people in critical condition in hospital.