We implemented this functionality as when we played the real board game: chits are drawn for each single damage burst.

I.e. if you get shooted by two different enemies in the same turn, you draw the first set of chits (say BRR) then you return it in the box and then draw the second series of chits (say RR).

We played this way because the two shots are totally independent one from another, so there is no reason to link them togheter. E.g. If you get B + B damage and are lucky enough, you can draw SMOKE twice and suffer no damage at all from the second chit.

Actually we created a virtual deck of chits that we mix every time someone have to pick some chits. Then the computer 'draw' the correct amount of chit and then it uses the Blue or Red part of it according to the combat chart result.

This way you cannot get both sides of a chit in a single draw.

Just for clarification, chits are defined this way:
"N-W1-W5" is the 1 WING / 5 WING damage chit,
"S-SMK-FIR" is the SMOKE / FIRE chit,
"S-OBW-OBK4" is the observer wounded / observer killed + 4 fuselage.
(The first letter indentify the Normal or Special damage chit, that are used in different versions of the game).

Hope this clarify the situation,
Nick.