SIL ratings

[centaur21]

Does anyone know of a really good site or article that explains SIL (safety integrity level) ratings in detail (i.e., how safety instruments are classified as SIL 1, 2, etc...). Thanks!

 

[Fieldbus]

Triconex (part of Invensys) have a series of white papers on SIL levels available on their website.
They are also featured in this e-magazine:

http://www.controlglobal.com/wp_downloads/triconex_truth_4and5.html