SHANGHAI - An initial investigation showed that the liquid ammonia leak that killed 15 in Shanghai on Saturday was caused by a detached pipe cap, local authorities said Sunday.

A cap on a pipe carrying liquid ammonia fell off, releasing the chemical at around 10:50 a.m. Saturday, which resulted in the death of 15 and left 25 others injured, sources with the Shanghai Municipality Information Office said.

All 25 injured are receiving hospital treatment and in stable condition, according to the Shanghai Health and Family Planning Commission.

Baoshan District environmental authorities have sent environmental monitoring vehicles to test the impact of the leak.

Initial test results show that odors reported early in the morning by nearby residents were unrelated to the leak, and no pollution was detected as of Sunday, according to an official statement from the Shanghai Environmental Protection Bureau.

The liquid ammonia was used in food refrigeration units at Shanghai Weng's Cold Storage Industrial Co., Ltd., which is engaged in the import,export, storage, processing and sale of seafood.

Liquid ammonia is a colorless liquid frequently used in industrial  sterilization and refrigeration processes. The corrosive and volatile chemical may cause suffocation after heavy inhalation.

Further investigation into the accident is under way.