Passive voice is not always bad.
That being said, you should use it sparingly.
Imagine that you're are chemist, and you're witnessing an accidental chemical reaction. You don't really know what is happening, except that you've accidentally mixed two compounds together, and now there is a lot of color, bubbles and heat overflowing from your beaker.
You're not sure what is causing these results, but you can observe that heat was given off, bubbles were created, and colors were emitted
Then again, you can also state more directly that the reaction (actively) precipitated all of these things. You're not sure about the details, but you can say for certain that the reaction did it.
So, in this case, you could use passive or active voice and get away with it. However, in my opinion (as usual) the active voice would make a report describing this event much compelling for the reader.
Suppose you work for a secret government agency, and you have been ordered to wait at a certain place for a certain extraterrestrial event.
Your boss told you that "something" should happen eventually. Your job is to record this event as it happens and offer no explain. Simply record events as they unfold.
In this case, you might observe that the sky "was filled with a bright light" and the ground "was shaken" as something that looked suspiciously like an alien spacecraft landed nearby. You're not supposed make any conclusions, so the best you can say is the environment nearby "was affected."
A case such as this practically requires passive voice.