When insurers are reviewing a BESS project, their primary concern is thermal runaway. Thermal runaway is an uncontrolled exothermic reaction that raises cell temperature and can propagate between cells, occurring when a cell achieves elevated temperatures. Thermal runaway can occur due to mechanical and. Probable Maximum Loss (PML) is an insurer's risk analysis of a project's 'worst case' loss scenario. For BESS projects, the PML is likely to be a thermal runaway event that causes the total. Insurers will always ask for proof that the manufacturers batteries have undergone successful UL9540a testing - the UL9540a is a test method for. Gases being given off by battery cells are an early indicator that a thermal runaway event is occurring, so early detection of gases is critical before a build-up can become volatile. In. Insurers will review the Battery Management System's ability to identify, control, and eliminate potential risk scenarios. Battery.