It's Moderate or higher damage. Roll 2d6. If this number is higher than or equal to the Object Resistance rating of the objects in the area of effect (on the target, for example) than the target is affected. Moderate damage spells must add 4 to the OR rating, Serious damage must add 2 to the OR rating. Deadly damage spells have no modifier.
Alternately, as a house rule, you can use the Barrier rating of the object instead for those who don't feel that how natural the object is should affect its fortitude and instead its actual physical nature.
For example, a ganger is hit with a moderate damage Acid Stream spell. 2d6 is rolled, and 7 is the total result. The ganger's baseball bat (OR 3+4= 7) is damaged but his leather jacket (OR 5+4=9) is not. If the spell were deadly damage it would have affected natural objects like trees, water, rocks and simple materials like leather, bricks, and simple plastics and simple metals and alloys. If the roll had been 8 and Deadly, the spell would have also wasted high-tech electronics, advanced plastics (Like credsticks, body armor, etc) and advanced alloys. If 10 or higher had been rolled the Deadly spell would have affected everything.
I recommend that you roll this way for every object to simulate randomness and splash effects but is not really required and you can make a blanket roll to save time.