HFACS | Wiegmann and Shappell Publications
This is pretty much the industry standard technique at the moment, and marries really well with Swiss Cheese / Accident Chain explanations. Used properly it should help identify all of the causal factors, not just put it in a convenient box (which as alf rightly says, does sometimes happen, and is inappropriate).
I have a colleague slightly at a loose end before he starts a new job as a university lecturer, who used the Wiefmann and Shappell model extensively on his PhD thesis into air accident causality. I imagine he'd be delighted to sell you a couple of days of his time and run a training course for you in-house. Drop me a PM if you wish and I'll give you his contact details.
G