Could you not just copy/paste the explosion event and sound triggering event triggered once, twice with a 2 second wait between?
If its a random 2-4 times you could nest them under a primary variable testing event that got a number and then filtered any remaining times with else condition...
ie. something like:
times=choose(0,1,2,3)
play explosion event
play sound event
if choose = 0
play explosion event
play sound event
else if choose = 1
play explosion event
play sound event
wait 2
play explosion event
play sound event
else if choose = 2
play explosion event
play sound event
wait 2
play explosion event
play sound event
wait 2
play explosion event
play sound event
else if choose =3
play explosion event
play sound event
wait 2
play explosion event
play sound event
wait 2
play explosion event
play sound event
wait 2
play explosion event
play sound event
I am sure it could be written much more efficiently.