Hard drive spontaneous combustion?

Many people have heard of the term spontaneous human combustion (SHC) this belief of some is that the body ignites and burns without any external influence whatsoever, of course this is not a qualified or exact science and is consigned typically to the anecdotes of history, however our labs received a hard drive which did spontaneously ignite and smoke while in the users hands.

The story began back in 2005 when a lady on an extended sabotecial from the USA contacted our labs for help here data and that of here partner which was a three year thesis and some 100,000 words was stored on said hard drive.
Following the computer system at here home failing she inlisted the help of here IT department, sensible move especially as the IT department was a division of the MOD with high end equipment and well trained professionals.

Technicians at the clients workplace connected up and switched on the power to the 3.5″ Maxtor hard drive, instantly the drive began to smoke a few seconds later the drive popped with a flash clearly seen and heard within the department.

After they had cleared the smoke filled room they realised that this possible recovery was beyond their capability and enlisted our services.
What has caused such a seemingly catastrophic failure?
Upon diagnosis at our labs it was imediately apparent that there was a major issue with the PCB or printed circuit board as one the chips was completely charred and burnt.
What chip had blown?

Hard drives are comprised of spinning magnetic media commonly known as platter(s) these platters are span via a spindle motor and bearing system, the spindle motor is controlled via a smooth chip, this smooth chip which had died can suffer from several conditions that may cause premature failure such as thermal changes within the computer system and if the actual hard drive has no adequate cooling it can cause thermal runaway of the component which will cause it to fail as in the particular case.
Further examination of the hard drive revealed more damage to the media and the head stack assembly (HSA) was diagnosed as faulty this issue was compounded as the Maxtor drive was not a widely used model and the head preamplifier was difficult to trace.

Logistics and hard drive tracing department sourced a drive from the USA following clean room work on the disk enclosure which involved head stack replacement and surface mount electronic repairs access to the user data area was established.

Imaging was then initiated from the begining to the end of the user data area from this image our engineers were able to extract all the required information including the 3 year thesis.