Secondly, the relative recovery quote R(%) is given by (Eq. 3) and describes the percentage of injected particles regained after the AFFF run. The relative recovery is determined by comparing the peak area m in the respective fractogram to the peak area m 0 of a calibration run under standard conditions without crossflow. We strive for a recovery > 70% when optimising AFFF methods. R(%) = m m 0 • 100%