A $20$ m bench is required to be blasted for a large face shovel. The hole diameter is $250$ mm and the stemming is set to $20$ times the hole diameter. The burden has been set to $6\mathrm{.}0$ m and the spacing set to $7\mathrm{.}0$ m to provide the best fragmentation. The charging plan is to use a toe charge of $3$ m of $1\mathrm{.}3$ density heavy ammonium nitrate fuel oil $($ANFO$)$ and a cap of $1$ m of $1\mathrm{.}2$ density heavy ANFO. The remainder of the column is ANFO $($density$=0\mathrm{.}83).$ Calculate the powder factor for this blast. State any assumptions made