The environmental pressure effect on thermal runaway and fire behaviors in the 18650 lithium-ion battery (LIB) with various cathodes and states of charge (SOC) are experimentally investigated in this work. The fire hazards were characterized by the combustion process, total mass loss (TML) and total heat release (THR). The TML and THR increase with the ascending of the SOC at two pressures. The amount of materials ejected by both LiFePO4 and LiCoO2 batteries during the combustion is slightly affected by the environmental pressure. Meanwhile, the environmental pressure has a significant influence on the combustion heat that the THR value at high pressure is relatively bigger than that at low pressure. The unit growth rate in combustion heat between the two pressures also increases with the SOC. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.