The plant was shut down. A private fire brigade participated in the response along with the local fire department.

At 4:50 on September 26, the earthquake and the first fire (at the crude oil tank) occurred almost simultaneously. About 7 hours later, the fire was extinguished.

After the sinking of the roof of the naphtha tank, the substance was exposed to the air. Sealing with foam was prepared to prevent evaporation. However, at 10:49 on September 28, two days after the earthquake, the naphtha caught fire. At 11:07 transfer of naphtha to another tank started and was conducted intermittently. In the meantime, foam and cooling water were applied by four fire engines and a fixed foaming system to bring the fire under control. At 6:55 on 30 September, the fire was extinguished.

In Tomakomai City a smell of oil, soot, and fire extinguishing agent was detected, and high numbers of inhabitants and school children complained of physical discomfort.

The environmental concentration of formaldehyde, xylene, toluene, and benzene was measured at three locations about 3 km away from the plant for two hours from 22:30 on September 29th. As a result, the value of benzene temporarily reached the maximum of 8.2 micrograms per 1 m3, which surpassed the environmental threshold of 3 microgram.

Several thousands tons of products were burned, and recovery costs were high: 7 tanks suffered major damage, many other tanks suffered lesser damage and experienced minor spills. The site restoration rose to about 10 billion JPY.

Since Tomakomai west harbour shut for 43 hours due to the naphtha tank fire, 4 ferry companies asked for financial compensation of a total of about 100-200 million JPY.

Infrastructure (e.g. roads, railways, air transport)

Tomakomai west harbour shut for 43 hours due to the fire in the naphtha tank. This caused about 20 ferry trips to be canclled.

In the restoration of the plant the latest standard requirements for floating roof tanks were met (e.g. lowering of the storage volume to lower levels; retrofitting of the tanks to comply with the latest requirements). Moreover, the procedures to avoid tank fires after roof sinking were revised.

It was found that the roof type and earthquake shaking period influenced the magnitude of the sloshing and thus the damage intensity. In fact, analytical studies showed that sloshing damage can occur if the maximum height of the sloshed liquid exceeds 3 m in floating roof tanks of 30,000-40,000 m3 volume. Also, it was found that in addition to the fundamental sloshing mode, higher modes can also trigger damage. For this reason, the code for the construction of storage tanks was revised.

For tanks built according to more updated standards, only leaks were observed while the two tanks that suffered major damage were built in compliance with older regulations. This highlights the effectiveness of following updated design codes.

The full-surface fire of the naphtha tank due to a sloshing-triggered sinking roof was the first of its kind in Japan and was not expected to occur. Preparedness for this type of event was therefore low. This included the lack of sufficient fire-fighting foam.

Since the available foam for fire fighting was insufficient, it had to be collected from all over the country, indicating a lack of preparedness.

Also, it turned out to be difficult to cover the whole tank's top with foam due to wind and flames.