Detecting Overflow in Accumulation Buffer

I was wondering if anyone had code/references on detecting when the R G B channels are about to overflow (bitwise) when doing accumulations? Right now I am rendering many >>100 textures on a single polygon Each texture is projected at a different angle onto the polygon. My interest is in the accumulation of all my projections together. However, I am seeing banding occur in my final image due to overflow of the color buffers.

  1. Is there a way to know how many bits I have per channel? Can this be set explicitly?
    If so how?

  2. Is there a way to know when the channel may overflow ?