A government-affiliated organization that checks the safety of storage tanks has found that more than half of the 395 large outdoor oil tanks in and near Tomakomai, Hokkaido, were damaged in the late September quakes that sparked a fire at an oil refinery in the city.

The Hazardous Materials Safety Techniques Association said it found 205 of the tanks that hold at least 500 kiloliters had been damaged.

Most of the damage was minor, but the association observed that more than 80 percent of the problems occurred around tank covers, including loose covers falling in or oil leaking from the upper area.

The Fire and Disaster Management Agency is mulling new regulations on the strength and structure of covers for withstanding earthquakes, agency officials said.

A 1977 amendment to the fire protection law calls for strengthening the structure and walls of existing oil tanks by 2020, but not the tops.

Two major quakes that hit southern Hokkaido on Sept. 26 damaged oil storage facilities at Tokyo-based Idemitsu Kosan Co.'s oil refinery in Tomakomai and sparked a fire in a crude oil tank. A naphtha tank ignited Sept. 28, causing a 44-hour raging inferno.

The association said damage was found in 168 tanks in Tomakomai and the adjacent eastern Iburi district, and 37 tanks in Kushiro and the northern Ishikari district.