Global menu

  • NGK News
  • Products
  • About NGK
  • Investor Relations
  • Research and Development
  • CSR
  1. Home>
  2. NAS Battery Fire Incident and Response>
  3. Q&A Concerning the NAS Battery Fire

Main contents.

Q&A Concerning the NAS Battery Fire(Updated June 15, 2012)

  • Contact
Please provide details of the fire.

NGK-manufactured NAS (sodium-sulfur) batteries used for storing electricity caught on fire on September 21, 2011. The batteries are owned by The Tokyo Electric Power Company, Incorporated and installed at the Tsukuba Plant (Joso City, Ibaraki Prefecture) of Mitsubishi Materials Corporation (Head office: Chiyoda-ku, Tokyo). This fire caused the NAS batteries which had been installed in a special package outside to burn. The fire did not spread to the customer's buildings or facilities, and nobody was injured.

What was the cause of the fire? (Updated June 15, 2012)

A third-party investigation committee, with Japan's Hazardous Materials Safety Techniques Association serving as secretariat, reviewed the cause of the fire and judged that the details regarding that were reasonable and appropriate. (Refer to Diagram 1)

  1. The NAS battery system is made up of 40 battery modules. In one of these modular batteries, which are made up of 384 battery cells, 1 battery cell was faulty. That battery cell had a breach and leaked hot molten material.
  2. This molten material flowed over the sand filler portion between blocks inside the battery module, causing a short between battery cells in an adjoining block.
  3. Because there was no fuse installed between the battery cells that shorted, the short circuit current flowed continuously and emitted heat, which destroyed a number of other battery cells, which in turn caught on fire. This fire spread to the whole battery module in question.
  4. The combustion of the particular battery module released flames and hot molten material that melted battery cell casings inside battery modules installed above and below, causing the fire to spread further.

Diagram 1 Cause of the Fire

Were you able to pinpoint the cause of the manufacturing fault of the battery cell? (Added June 15, 2012)

We were not able to specify the cause of the manufacturing fault because the battery module that caught on fire completely burned. After carrying out an inspection of battery modules that escaped fire damage and the same production lot of battery cells, we didn't find any manufacturing or design faults.

Based on data analysis at the time of the incident and our knowledge from the results of numerous experiments, we have presumed there is possibility that some multiple irregularities deviating from safety mechanism of the battery happened during the manufacturing process.

What safety enhancement measures are you implementing? (Added June 15, 2012)

Based on the results of the investigation by the third-party investigation committee, NGK decided to voluntarily implement the following safety enhancement measures under the guidance of the Fire and Disaster Management Agency.

1) Measures to prevent the spread of fire in modular batteries (Refer to Diagram 2.)
  1. Fuses will be added between battery cells in modular batteries to prevent a short circuit current from causing a fire.
  2. Insulation boards will be placed between blocks in battery modules to prevent leaking molten materials from causing a short circuit.
  3. Anti-fire boards will be placed between battery modules above and below to prevent fire from spreading to other battery modules.

Diagram 2 Fire Containment

2) Other safety enhancement measures
  1. The monitoring system will be strengthened to enable quick fire detection.
  2. Fire extinguishers and fire-prevention equipment will be installed and a fire-fighting structure put in place in preparedness for a fire.
  3. A fire evacuation route will be developed and a guidance system put in place in preparedness for a fire.
Have there been similar fires in the past?

On February 15, 2010, there was a fire at the Oyama Plant (Oyama City, Tochigi Prefecture) of Takaoka Electric Mfg. Co., Ltd. (Headquarters: Chuo-ku, Tokyo). These NAS batteries were the first line of high-output batteries, with all the batteries cells in the module connected in series in order to produce high output. The NAS batteries that caught on fire recently were a standard type and therefore different. However, NGK takes it very seriously that there have been two incidences of fires involving NAS batteries installed at customers' premises. In February 2005, there was also a fire at NGK's NAS battery plant in Komaki City, Aichi Prefecture. This fire broke out when a modular battery was undergoing high-voltage testing—a high voltage that would not be applied during normal operation.

How does NGK take actions on installed NAS batteries? (Updated June 15, 2012)

Since the fire incident, NGK has asked almost all customers to suspend using NAS batteries or to restrict their usage. NGK is working so that these batteries can be re-used after quickly implementing safety enhancement measures according to installation conditions, while following the guidance of the fire authorities having jurisdiction in the installation locations.

NGK is giving priority to these measures so that as many customers as possible can use NAS batteries as a means of ensuring sufficient energy during the summer months in Japan. NGK aims to complete these measures during the year ending March 31, 2013.

How many NAS batteries are in use in the market?

As of March 31, 2011, NAS batteries storing 305,000 kilowatts of electricity were in use in 174 locations in Japan and 5 overseas countries (the U.S., the United Arab Emirates, France, Germany and the U.K.).

When will NGK resume NAS battery production? (Updated June 15, 2012)

Since the fire incident, NGK has suspended operations at its NAS battery factory in Komaki City, Aichi Prefecture, Japan. However, operations will resume at this facility from June 2012 now that the cause of the fire has been investigated and safety enhancement measures devised.

For the time being, the plant will put priority on reforming NAS batteries that continue to be used by customers. However, NGK plans to commence production of new batteries in the second half of the current fiscal year, which starts on October 1, 2012.

When will you resume NAS battery sales activities? (Updated June 15, 2012)

For the time being, the plant will put priority on reforming NAS batteries that continue to be used by customers. For that reason, full-fledged sales activities will be conducted based on when production of new batteries commences.

What is the outlook for the NAS battery business? (Added June 15, 2012)

NGK is projecting sales of ¥8.0 billion for the NAS battery business for the year ending March 31, 2013, with production of new batteries scheduled to commence from the second half of the fiscal year. In terms of earnings, while NGK expects an improvement from the large loss posted in the fiscal year ended March 31, 2012, it expects to continue having difficulty generating earnings in this business as it puts priority on implementing safety enhancement measures for NAS batteries already installed at customers' facilities.

Global demand for large-capacity electricity storage batteries has continued to increase, driven mainly by the utilization of renewable energy, smart grids, and government energy policy reviews. NGK will work hard to turn around its performance in the NAS batteries business by meeting market expectations.


Page top

Copyright(C) 1997-2014 NGK INSULATORS, LTD. All rights reserved.
NGK INSULATORS, LTD.