Initially I voted thumbs down on your comment, then I read it again... Never mind it's still a thumbs down.

You know that's not how it works right? You choose between ydi and fyl not yes and no.

They meant when moderating

That's one intense explosion.

This. The worst risk is setting it on fire, which, since you should be in tame of your microwave when using it (especially with non-food items) you should be able to notice and turn it off before it finishes catching fire. They do start to smell after a while, though.

My mom makes these warmable rice bags for us. They last forever and never explode or anything. You can also put a little lavender oil or cinnamon or something inside if you don't like the smell of the warm rice. She also made me a bag this winter of one with a bunch of hard mixed beans. It actually holds the warmth a lot longer than the rice. Warm them for 2 minutes and you're good to go.

I'm using coarse salt. It can be heated to any temperature safely, cheap, and takes any shape.