Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Strength
EXPLOSIONOBJECT_STRENGTH
Parameter: Speed
EXPLOSIONOBJECT_PSPEED
Parameter: Angle Speed
EXPLOSIONOBJECT_ASPEED
Parameter: End Size
EXPLOSIONOBJECT_ENDSIZE
Parameter: Randomness
EXPLOSIONOBJECT_RANDOM