UPS = Uninterruptible Power Supply (lead acid batteries on 81st floor corner) AND United Parcel Service, according to NIST.
See this article: "UPS on the 81st floor of WTC2?" by Enrico Manieri - Henry62
Plus, here's a related article quoted at length:
Paolo Attivissimo, based on research by Enrico Manieri
'UPS vs UPS?'
NIST speculates, in the chapter cited above and in its 2006 FAQ, that the fountain "could have been molten aluminum" from the Boeing 757 [sic] aircraft, which is largely made of alloys of this metal whose melting points are well below steel's.
The molten metal might have pooled within the building and then, as the floor trusses of the 81st and 80th floors failed and tilted, found a path to flow outward.
However, some rather unusual clues found by Enrico Manieri suggested in 2006 an alternative explanation.
NIST's NCSTAR1-1 report, which discusses structural alterations to the Twin Towers made by their tenants, shows that the part of the building where the glowing fountain occurred had been altered: specifically, the so-called "two-way trusses" (the trusses that span the corner area of each floor of the building) had been reinforced on the 81st floor in 1991 "in area occupied by United Parcel Service" (NCSTAR1-1, page 136).
The same alteration is mentioned in the NCSTAR1-1C report, on page xlviii, but with a slightly different wording which will turn out to be very significant: instead of referencing "United Parcel Service", it uses only the acronym ("UPS").
The same acronym turns up in the NIST report (NCSTAR1-1C) again in relation to alterations made by tenants to reinforce structural members: remarkably, it appears in the only two reported reinforcement alterations made to WTC2, as shown below.
Curiously, the floor is the same (the 81st), the trusses are the same "two-way" ones, but the year is given as 1999, not 1991, and the tenant is Fuji Bank.
Note that as mentioned, these are the only reinforcement alterations to WTC2 reported by NIST.
There is no mention of United Parcel Service being a tenant who made reinforcement alterations to the 81st floor. Moreover, the "UPS" referenced here does not stand for United Parcel Service, but for Uninterruptible Power Supply.
This is the name given to battery-based systems which must ensure the continuous supply of electric power for computer rooms and electrical medical devices which cannot tolerate the slightest power outage.
A bank, such as Fuji Bank, would certainly have an uninterruptible power supply for its computer systems.
These power supplies are extremely heavy: basically, they are massive racks of lead batteries, which would undoubtedly warrant truss reinforcement.
It is instead quite unlikely that Fuji Bank would perform very expensive truss reinforcement work to accommodate a United Parcel Service workspace. There's more.
In the NIST reports there is no mention of United Parcel Service ever being a tenant on the 81st floor of WTC2 at all, regardless of any alteration work.
And NCSTAR1-1H provides a list of all tenant alterations (including non-reinforcement work, such as installing an escalator) to WTC2.
In this list, shown below, Fuji Bank is given as a tenant of the 80th and 81st floors in 1990. Its locations are the northeast and southwest parts of the floor (the northeast part is where the plane exited). There is no mention of United Parcel Service.
- NIST confirms 'UPS' on 81st floor of WTC2 was power supply; may explain glowing 'fountain'" by Paolo Attivissimo, based on research by Enrico Manieri (Henry62)
Just to clarify, I know that exceedingly high temperatures were witnessed at Ground Zero.
In response to the above article, it seems important to completely explore the possibility of its accuracy.