To prevent the combustion of an exhaust gas outflowing from a lance insertion hole that is provided at a dust collection hood arranged above a furnace inlet and wherein an immersion lance penetrates, when the immersion lance is immersed in a molten iron in a torpedo car and the molten iron is mixed and dephosphorized while an oxygen gas or an inactive gas is supplied from the immersion lance.

In the method of preventing flaming in dephosphorization of molten iron, an immersion lance 4 is immersed in molten iron 10 in a torpedo car, and the molten iron is mixed and dephosphorized while an oxygen gas or an inactive gas is supplied from the immersion lance. In such an operation, a nitrogen gas is sprayed to a lance insertion hole 7 and/or its periphery that is provided at a dust collection hood 5 arranged above the furnace inlet 3 of a torpedo car 1 and wherein the immersion lance penetrates, so that the concentration of the oxygen gas in an atmospheric gas in the lance insertion hole and its periphery is reduced to prevent the combustion of an exhaust gas outflowing from the lance insertion hole.