The section of the Equitable Building specifications that contains information on tile arch floors is “Hollow Tile Fireproofing.” Most of the information in that section, unlike the floor arch paragraphs, lives up to the name: it concerns non-structural elements that are related to fire protection. The terra cotta partitions used to create interior rooms were fireproof compartmentalization, the column enclosures were fireproofing for the steel frame, and so on.
It’s important to look at the specs in terms of their immediate context. The reason that the building was being constructed was that its predecessor was badly damaged by fire. The year before that fire, the Triangle fire had killed over 140 people in roughly 15 minutes, and had professionals questioning whether structural fireproofing was enough to guaranty safety. (It was not, as they figured out then and we are tragically reminded every so often.) In 1906, the fire following the San Francisco earthquake caused more damage than the quake itself had. And in 1904, the center of Baltimore’s business district was devastated by fire. Fireproofing technology was developing rapidly, and had been since the 1870s. but people were still looking for tests that would accurately predict how materials and systems would perform in fire. In short, everything was tested one way or another – most often by the Underwriters’ Laboratories or by private labs following specs from the American Society for Testing and Materials – but buildings still did not necessarily perform as expected. There were forensic examinations after every major fire, as people in the AEC professions tried to get a handle on fire safety.
The page above is from the report by the National Fire Protection Association on performance of buildings in the Baltimore Fire. It shows the rear facade of the Continental Insurance Building, where thermal movement of cast-iron window mullions damaged the masonry curtain wall and, by disrupting the masonry fireproofing, damaged the adjacent steel spandrel girders. How does that relate to Equitable?
Spandrel Girder Protection:
All spandrel girders throughout shall be most thoroughly enclosed and fireproofed with hollow tile materials, unless otherwise specified or indicated on drawings.
Especial attention is directed to the fireproofing of the girders, beams, etc., over the exterior windows on the various stories, for which special tile forms must be made fitting the flanges to which they must be securely anchored, as indicated by the sectional drawings.
It is to be clearly understood that a strict compliance with these requirements will be demanded, the fireproofing in all cases to be self-supporting or securely anchored to steel, completely fireproofing the beams and girders and so set as to be entirely free from any support from the window frames below.
Spandrel girders other than those indicated in exterior walls shall be fireproofed as indicated in a careful and secure manner.
Wherever girders or beams are indicated as fireproofed with concrete or brick, the work will be executed as herein specified under Masonry.
If you didn’t know that people were specifically reacting to the failure of metal window frames – at Continental Insurance and elsewhere – as a cause of structural damage, the second and third paragraphs would seem odd. I suspect that everyone at Equitable knew exactly why that language was there, as the horrific fires that led to those clauses were still fresh in memory.
Similarly, it was well known by 1913 that elevator shafts were potential routes for fires to spread. The text regarding the terra-cotta-block shaft enclosures includes “The framing around elevator shaft in all stories, also all other openings in floors, shall be fireproofed clear around, it being clearly understood that in no case shall any structural iron or steel be left exposed, except small steel beams crossing elevator shaft between cars, used only for attaching of elevator guides.” Since all of the structural steel was meant to be fireproofed, this language might seem redundant, but experience in various fires showed that gaps in the fireproofing within the shafts were more dangerous than gaps elsewhere.
It is a cliché to say that engineers learn by experience, and so past disasters help prevent future ones, but it’s also largely true. The language in this section of the spec shows the direct link between disasters and the planning of the new building.