FIA FT3/3.5/5 Fuel Cells
Racing fuel cells are designed for the storage of fuel in competition vehicles. In general, a racing fuel cell has a rigid outer shell and flexible inner lining to minimize the potential for punctures in the event of a collision or other mishap resulting in serious damage to the vehicle. It is filled with an open-cell foam core to prevent explosion of vapor in the empty portion of the tank and to minimize sloshing of fuel during competition that may unbalance the vehicle or cause inadequate fuel delivery to the motor.
They are approved by FIA with their FT3, FT3.5, and FT5 ratings. The design meets the minimum requirements of the FT3 standard whose objective is to have fuel safe cell that resist explosion in case of impact or rollover of the vehicle. All three standards lay out the same requirements for materials, construction, and testing. The only difference between them is in the strength of the bladder material. The tests are the same, but the certification is based on the results.
FT3 is the lowest level, requiring a minimum of 450 pounds of tensile and puncture strength. FT3.5 is the middle, requiring at least 1000 pounds. The highest level, FT5, requires that the material withstand a full 2000 pounds of tearing and puncturing force. FT5 is required in F1 for obvious reasons. SCCA requires at least FT3 (FT3.5 and FT5 are also acceptable).