This class will begin with UL FSRI's findings and recommendations following a reconstruction of the energy storage system (ESS) explosion that occurred in April 2019 in Surprise, AZ, that seriously injured four firefighters. It will cover research conducted in 2020 to enable a better understanding of the development of fire and explosion hazards in containerized commercial ESS, the effectiveness of common extinguishing designs, the efficacy of size-up tools, and initial insights into manual ventilation. It will provide an overview of two recent residential ESS projects conducted in a partnership with the IAFF, UL Solution, and UL FSRI under an agreement with the U.S. Department of Energy. The first project investigated ESS involvement in residential fires and found substantial changes in fire behavior with lithium-ion batteries involved. The second project evaluated the development and severity of explosion hazards under conditions when an ESS undergoes thermal runaway but does not catch fire immediately. The class will review the lessons learned and revied the Fire Service Tactical Considerations developed by the project panel.