Influence of Curing Time on the Burning Characteristics of a Spray Polyurethane Foam

The effects of curing time on the burning characteristics of spray polyurethane foam (SPF) are investigated, with a particular emphasis on the emission behavior of volatile organic compounds (VOCs ). The concentration of VOCs increases rapidly immediately after the application of SPF, reaching a maximum at approximately 2.5 min regardless of the SPF thickness, and subsequently decreases to essentially 0 ppm after approximately 35 min. In the early curing stage, the extensive release of volatile components shortens the ignition time and increases the heat release rate, effective heat of combustion, and yields of incomplete combustion products such as CO and soot. As curing progresses, the combustion behavior is dominated by stable surface pyrolysis mechanisms owing to the depletion of VOCs and structural stabilization, with most combustion parameters converging to consistent levels after approximately 20 min. These results provide fundamental data that enable the systematic assessment of fire hazards associated with SPF applications and are expected to facilitate the development of fire safety management guidelines for on-site construction processes.