On September 21st, 2011, sodium-sulfur (NAS) batteries installed at Mitsubishi Materials Corp’s Tsukuba Plant, Japan, caught on fire. It took firefighters more than 8 hours to control the blaze, and two weeks to extinguish the fire. NGK Insulators Ltd., the company that manufactured the energy storage system, said the fire authorities are still investigating the cause of the fire. NGK has suspended production of its NAS cells, and advised customers around the world refrain from using their batteries until it tracks down the cause of the fire and finds a solution.