Thanks for telling me what everyone already knows. That was not my question.
Both can withstand 3400G's/6.5ms Impact ( Hint, much higher than when you fall off the barstool), and have fire resistance of 1100c/ 30minutes.
Yeah, yeah, yeah. They also have to survive a pressure test of 5000 lbs and submersion for 30 days in salt water. So what? None of the required tests, good as they are, apply in the case of the Pentagn and the WTC.
That is 100c higher than what the estimated temperatures in the towers were. Added to that, inside each is a CSMU, ( crash survivable memory unit) that is coustructed out of stainless steel , titanium alloys. It can withstand temperatures of 2000c for one hour.
But they've never tested to see how long-term exposure to intense heat LOWER than 2000c would affect the contents have they? You don't have that information because it doesn't exist. The tests attempt to duplicate conditions reasonably expected in a normal crash situation on land and in water. The Pentagon and WTC could not be described as normal.
You're also not making any distinction between the newer solid-state recorders and the older ones, which use magnetic recording tape. Many planes still use the older recorders. But I imagine either could melt under the right circumstances (the tape would simply melt faster). Insulation isn't a "forever" thing.
These have been used when the 'black box ' has been damaged and are referred to as virtually indestructible.
Except when they're destroyed by heat:
" Lopatkiewicz said there have been cases where recorders were rendered useless by fire after a crash, but he knew of no case where a recorder was destroyed by impact."
They'll be found eventually, but they may not have anything left inside them to read. There is no substance on earth than cannot be destroyed under the right circumstances.