Hydrofluoroolefin 1234ze (1,3,3,3-Tetrafluoropropene) is a fluorinated hydrocarbon introduced as a low global warming potential alternative for HFC-134a (1,1,1,2-tetrafluoroethane) and is classified as mildly flammable (A2L). Definition of appropriate engineering controls and electrical area classification requires accurate knowledge of the flammable properties of a material. Gaps and conflicts in published flammability data for HFO-1234ze are a concern for defining safe handling practices and appropriate layers of protection. The data available in literature has been compiled and analyzed to understand the sources of the data variability and the conditions under which HFO-1234ze will pose a flammability hazard. New data on the minimum ignition energy at 25C, flammable limits at 25C, and maximum experimental safe gap at 40C is also reported here and discussed in context with the large body of data from literature. It is proposed that much of the data measured at ambient conditions in the absence of water vapor does not effectively measure the true limits of flame propagation. Additionally, it appears that ignition limitations, and potentially other design factors, in the current standard test methods may result in the inaccurate measurement of flammable limits for HFO-1234ze under some conditions. It is concluded that HFO-1234ze can be safely handled when appropriate engineering controls are implemented based on a thorough process safety risk assessment. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.