The use of flexible foam material to provide ignition mitigation in fuel tanks is described. In one example, a system for ignition mitigation includes a number of foam blocks, wherein each foam block is pre-cut from a flexible foam material. Each foam block can have a unique profile corresponding to inner surfaces of a fuel tank at a particular sector within a compartment of the fuel tank. In other aspects, one or more of the foam blocks can include one or more upper cutouts to provide clearance for upper stiffeners in the fuel tank, one or more lower cutouts to provide clearance for lower stiffeners in the fuel tank, and one or more arcuate cutouts to provide clearance for a tank fuel pump. The foam blocks can be arranged in a stack corresponding to a sequential installation at respective sectors within the compartment of the fuel tank.

A process method utilizing customized, specifically-shaped pieces of reticulated polyurethane foam (RPF) to fill an aircraft fuel tank or tank compartment to provide ignition mitigation and prevent explosion in the tank. The process involves inserting the shaped pieces of RPF through existing access ports into a fuel tank in order to fill the tank, excepting minimal planned void spaces. This process effects ignition mitigation by acting as an ignition blocker, mechanically interfering with the compression wave that precedes the flame front in an explosion, and changing the vaporous mixture above the fuel level (ullage) in the tank. The foam pieces are assembled and fitted together throughout the tank in a pattern that replicates the shape of the tank. After the foam insertion is complete, the fuel tank is filled with purging fluid, drained through a filter until no debris is found, and the new maximum fuel quantity is recalibrated.