Residents living in Llangennech, near Llanelli of Carmarthenshire, Wales, the UK, were evacuated from their homes after three carriages of a freight train carrying diesel caught fire and exploded on 26 August.
Natural Resources Wales (NRW) is now evaluating the impact of the diesel spill.
About 100 residents living within 800m of the blaze were evacuated.
According to the British Transport Police, the two workers on board the freight train were not injured.
The Rail Accident Investigation Branch (RAIB) is conducting a preliminary probe into the accident, which was reported at about 23:20 BST on Wednesday.
According to the police, this is considered to be a ‘major incident’ given the ‘initial risk of harm’ to the residents living nearby, some of whom had to leave their homes in the middle of the night.
Flames from the fire were seen from several miles away.
The three train carriages carrying a significant amount of diesel derailed before catching fire.
The accident site is close to the Loughor Estuary, which is part of the Carmarthen Bay and Estuaries Special Area of Conservation.
NRW was quoted by BBC as saying: “Our officers have attended the diesel train fire and are providing advice to help manage the environmental impact of the diesel spill.”
The BTP stated that it was ‘securing key witness statements and CCTV’ and would work with the Office of Rail and Road and the RAIB to understand the exact circumstances behind the fire.