For the case where a dust or gas explosion can occur in a connected process vessel, it would be useful, for the purpose of designing protection measures and also for assessing the existing protection measures such as the correct placement, to have a tool to estimate the time for flame front propagation along the connecting pipe. Measurements of data from large-scale explosion tests in industrially relevant process vessels are reported. To determine the flame front propagation time, either a 1 m(3) or a 4.25 m(3) primary process vessel was connected via a pipe to a mechanically or pneumatically fed 9.4 m(3) secondary silo. The explosion propagation started after ignition of a maize starch/air mixture in the primary vessel. No additional dust was present along the connecting pipe. Systematic investigations of the explosion data have shown a relationship between the flame front propagating time and the reduced explosion over-pressure of the primary explosion vessel for both vessel volumes. Furthermore, it was possible to validate this theory by using explosion data from previous investigations. Using the data, a flame front propagation time prediction model was developed which is applicable for: -gas and dust explosions up to a K value of 100 and 200 bar m s(-1), respectively, and a maximum reduced explosion over-pressure of up to 7 bar; -explosion vessel volumes of 0.5, 1, 4.25 and 9.4 m(3), independent of whether they are closed or vented; -connecting pipes of pneumatic systems with diameters of 100-200 mm and an air velocity up to 30 m s(-1); -open ended pipes and pipes of interconnected vessels with a diameter equal to or greater than 100 mm; -lengths of connecting pipe of at least 2.5-7 m.