Last semester I wrote a small paper on the iec6880 standard for safety software in power nuclear stations..  It is more a homework than a real paper, so it shouldn't be taken so seriously... However, it may be helpful if what you want is to know a little bit more about the standard.

In this paper I also made some comparisons with other safety software related standards, but forgot to mention them in the bibliography...

Anyway, you are free to download the paper (it's in the downloads section). Nevertheless, I wouldn't use it as a reference --as it is not published in the IEEE or something.