Described herein is a kitchen ventilation system, comprising: a kitchen hood communicative with a kitchen exhaust duct; a fan communicative with the hood to create an air flow through the hood and to the exhaust duct; a fire barrier air filter mounted to the hood to receive and filter the air flow, the fire barrier air filter comprising a plurality of elongate extruded bodies in parallel alignment; each extruded body bound by first and second opposing concave surfaces and first and second baffle surfaces, the first and second baffle surfaces oriented transverse to the air flow; and at least one of the of the first and second concave surfaces oriented in facing opposition to a neighboring concave surface provided by a neighboring extruded body to form a cooperating pair of facing concave surfaces, the pair of facing concave surfaces defining a narrow longitudinal inlet gap, a narrow longitudinal outlet gap, and a longitudinal tubular chamber communicating therebetween. A kit providing at least a fire barrier air filter of the system and instructions for its installation is also described. A method of fire prevention using components of the system or kit is also described.