Flame-retardant sealing material

A flame-retardant sealing material comprising a polyurethane foam formed from a polyurethane raw material containing a polyol component, an isocyanate, a foaming agent, a catalyst, a water repellent and a flame retardant,

• wherein the polyol component contains 80 to 100 parts by mass of a hydroxyl-terminated prepolymer obtained by the reaction of a polyether polyol and an isocyanate per 100 parts by mass of the polyol component,
• the water repellent contains at least one selected from the group consisting of a polybutadiene polyol, a hydrogenated polyol of a polybutadiene, a polyisoprene polyol and a hydrogenated polyol of a polyisoprene,
• the hydroxyl-terminated prepolymer has a viscosity at 30° C. of 2000 to 30000 mPa·s,
• the polyether polyol has a molecular weight of 300 to 10000,
• the amount of the water repellent is 3 to 25 parts by mass per 100 parts by mass of the polyol component,
• the flame retardant is a halogen-containing non-condensed phosphate ester that is liquid at room temperature which is tris(1,3-dichloro-2-propyl)phosphate,
• the amount of the flame retardant is 3 to 12 parts by mass per 100 parts by mass of the polyol component, and
• the isocyanate index is 100 to 150.