Hallo warhammer73,
this sounds strange, just some things you could test:
a) Fire and explosions are cloudlets (in the normal OFP Video settings) have you turned them on ?
(or if you throw a hangrenade can you see, the explosion smoke ?)
b) Burning people run from destroyed Vehicles (please test the mission bomberman, there you can easy detroy some vehicles.
Is the situation improved ?