According to initial investigation, a gas valve malfunction is believed to have caused the leak. The leak was from one of two chemical tanks that had been left unattended since March 2020 due to the COVID-19 lockdown.[25] The malfunctioning of the tank's refrigerating unit led to an increase in temperature, causing the liquid chemical to evaporate.[26] The leaked gas is suspected to be evaporated styrene. However, experts have claimed that other chemicals may have also leaked, as styrene is unlikely to spread to 4 or 5 kilometres (2.5 or 3.1 mi) due to its chemical properties.[27][4][28][6][29]