Spray explosions can bring serious hazards to the personnel and equipment, and hence the related safety issues deserve more detailed investigations. In this study, a series of spray deflagration experiments were performed in a 3 m x 3 m x 3.4 m enclosed compartment. Two modes of spray deflagrations were observed: strong and weak deflagrations. It was found that strong spray deflagration induces a large flame ball and causes the flame to quench within a second, while weak spray deflagration induces a spray flame with a period of tens of seconds. The overpressures in the strong spray deflagration are significantly larger than those in the weak spray deflagration. Because of the pulsations of the spray flame, the induced overpressure has more high-frequency fluctuations in the case of weak spray deflagration. However, no high-frequency overpressure fluctuations were observed in the case of strong spray deflagration. The deflagration strength is significantly determined by flow rate and ignition distance. (C) 2017 Elsevier Ltd. All rights reserved.