Deepwater Horizon - Transocean Oil Rig Fire

First of all – my condolences to the families of those killed and injured in this incident.

I’ve read most of this thread – but may have missed some parts of it. Does anyone know how much straight riser is above the BOP and whether or not a set of shear rams could just be clamped on and activated to pinch this thing off.

Pardon me if this is just a stupid question – but this would seem be the obvious thing to try – if it’s possible and if the section of riser would hold the pressure.