At 4:52am on Sep. 26, fire following the earthquake burned down a crude oil tank (32,778 kl) in the Hokkaido Refinery in Tomakomai (Idemitsu Kosan Co. Ltd.). Simultaneously, oil leaked from the piping in the refinery, and resulted in a fire, which was brought under control at 12:09pm on September 26. The roof type of the tank caused fire is called a "floating roof," whose steel roof is floating on the stored oil in the tank and moves up and down depending on the quantity of the oil. According to the Fire Department, a fire may have initiated due to "sloshing" actions of the floating roof. The roof swung together with the oil in the tank that was shaken by the earthquake ("sloshing"), and then the oil spilled out onto the roof. The fire ignited the oil due to the friction between the roof and sidewall of the tank. A Naphtha tank (26,000 kl) in the same refinery initiated a fire at 10:36 on September 28. The floating roof had been tilted due to sloshing and the oil had spilled on the roof. It is thought that the spilled oil on the roof had caught a fire for some reason. It is reported that, in the refinery, there were about 90 oil tanks out of which oil spilled onto the floating roof due to "sloshing."