We've covered fake glass before, and all sorts of ways to use it, but even though sugar glass is generally safe, it can still be pretty sharp, and for applications where you need your actors to be able to step on or touch it, it can still be too hard and sharp for that, so I thought I would come up with a way to have fake shards of glass that you can handle without having to worry about getting cut! 

First, get a flat non-porous surface (I chose a metal lid from a can of tea), and a cool glass of water. 

After getting it hot, squeeze some shots of glue into the water, where it will solidify more or less immediately.

Pull it out of the water, and pull the pieces apart, and taking some scissors, cut off any stringy parts sticking off of it, so you're left with irregular clumps rather than long or stringy pieces.

For the piece of tin, squeeze some globs out, wait for them to cool, and peel them up. I like having flat sections because you can take your scissor and cut it at angles, and it can look like a flat shard. Having inconsistency with the pieces is what's important, so I like having more than just the clumps from the water.

Keep doing this, and within about 10 minutes and a stick of hot glue later, I had a full fistful of crumbled glass. You could easily sprinkle this on the ground and have your actors roll around and fight in it, squeeze it in your hands, or throw it at your actors during a cut-away shot of a window being shot out or blown in from an explosion. 

I like this a lot since it's cheap, squishy, and looks a heck of a lot like glass, without having to worry about cutting yourself.

Good luck!