In this report, we present the initial version of the method MASK. This is a combined mathematical model and pedagogical concept used to estimate the number of casualties resulting from mass casualties events involving long-range weapon systems. We present how statistical data and simulations lies at the foundation of MASK and furthermore how the method can be employed in practice. We finally supply the material that constitutes the method as appendices to the report or - in cases where this is not possible - supply references to where to find the material.