Abstract: A fire stop assembly for bordering a conduit access through a building separation, includes a rigid body portion with an access opening with the access opening being adjustably closed to define a conduit fitting opening within the access opening. The remainder of the access opening is adjustably closed by a fire block arrangement comprising a lining of intumescent material on opposite sides of a conduit fitting opening and a series of non intumescent flame retardant members cooperating with the lining of intumescent material to close the remainder of said access opening. Preferably the non-intumescent flame retardant members are a series of plastic sleeves filled with mineral wool or other suitable insulation material. The sleeves and fill material are removable to adjust the opening size. The sleeves serve to protect the insulation material during the normal life of the fire stop assembly until a fire condition occurs.