The Nuclear Regulation Authority has started analyzing local television footage to determine what caused the hydrogen explosion at the No. 3 reactor building at the Fukushima No. 1 nuclear power plant run by Tokyo Electric Power Company Holdings Inc. after the 2011 earthquake and tsunami.

The NRA hopes the colors of the flames and timing of the explosion can provide insight into how much hydrogen was involved, the size of the explosion and other matters.

The authority reopened an investigation into the cause of the disaster last year, and NRA officials visited the reactor building in December. Officials hope to find out what caused the explosion by analyzing new findings obtained during the site visit along with the footage.

The footage used in the analysis is from Fukushima Central Television Co., which is based in Koriyama, Fukushima Prefecture, and shows orange flames and black smoke coming from the building after the explosion.

The Great East Japan Earthquake on March 11, 2011, caused meltdowns at Nos 1, 2 and 3 reactors at the plant. The hydrogen explosion at No. 3 reactor occurred in the morning of March 14, three days after the earthquake.

The areas most severely damaged by the explosion were mostly on the building’s southeast side and part of the third floor ceiling.