LHC magnet failure

John Conway at Cosmic Variance has a post which I thought corrected my misunderstanding of 'quench'.

This was apparently due to a “quench” in which the magnet goes rapidly from the superconducting to the normal conducting state, which then means that the tremendous electric current in the magnet suddenly starts heating it up, causing huge internal mechanical stresses.

But on reading further I find my initial guess may be on the right lines after all:

While a beam of particles by itself creates very little heat, beam particles straying from the core of the beam will heat up surrounding material. It takes just a small number of beam particles hitting a magnet in one spot to raise the magnet’s temperature above a critical point, causing it to suddenly change from superconducting to “normal” conducting. This change, called a quench, releases the stored energy of the magnet and its neighbors; it can heat a small part of the magnet from -271 to 700°C (-456 to 1300°F) in less than one second.

But yesterday's press release from CERN definitely says there was no beam circulating.

Geneva, 20 September 2008. During commissioning (without beam) of the final LHC sector (sector 34) at high current for operation at 5 TeV, an incident occurred at mid-day on Friday 19 September resulting in a large helium leak into the tunnel. (emphasis mine)

I'm still confused!