Cleaning Inner Fenders

Does anyone know how to easily remove the dirt and grime from the inner fender area. I need to be able to do this in my garage, and I can't use any kind of hazardous materials or toxic materials. I have considered making my own small sandblaster but am unsure of what type of sand to use, as I have heard some of it can be hazardous and a pain on clean up. I was just curious if there was a spray or something I can pick up that would do this job easily.

Presently I am using a wire-brush and sandpaper and that is just not cutting it. Some areas I have to almost chisel the dirt off. I am wondering if these inner fenders have ever been cleaned.
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Here's my work:


I have removed all the dirt and grime from the inner fender area with a wire brush :)

You can see all the pictures on my website:
I wouldn't use sand. It can distort panels very easily unless you really know what you're doing. A knotted wire cup on a small grinder works well but you have to be very careful. If it grabs something it can throw it up in your face or other body parts. Another option is a disc made by 3M that fits on a drill. It's very porous. You can buy them at Walmart. Whatever you do make sure you don't get the body parts hot because heat can distort.