Editing Brooklyn Bridge (section)

====Caissons====
The towers rest on underwater [[Caisson (engineering)|caissons]] made of [[southern yellow pine]] and filled with cement.<ref name="Barnes p. 28" /> Inside both caissons were spaces for construction workers. The Manhattan side's caisson is slightly larger, measuring {{Convert|172|by|102|ft|m|abbr=}} and located {{Convert|78.5|ft|m|abbr=}} below high water, while the Brooklyn side's caisson measures {{Convert|168|by|102|ft|m|abbr=}} and is located {{Convert|44.5|ft|m|abbr=}} below high water. The caissons were designed to hold at least the weight of the towers which would exert a pressure of {{Convert|5|ST/ft2||abbr=}} when fully built, but the caissons were over-engineered for safety. During an accident on the Brooklyn side, when air pressure was lost and the partially-built towers dropped full-force down, the caisson sustained an estimated pressure of {{Convert|23|ST/ft2||abbr=}} with only minor damage.<ref name="Barnes p. 28" /><ref>{{harvnb|ps=.|National Park Service|1966|pp=2, 5}}</ref> Most of the timber used in the bridge's construction, including in the caissons, came from mills at [[Gascoigne Bluff]] on [[St. Simons, Georgia|St. Simons Island, Georgia]].<ref>{{cite book | last1=Davis | first1=J. | last2=Galland | first2=B. | title=Island Time: An Illustrated History of St. Simons Island, Georgia | publisher=University of Georgia Press | year=2013 | isbn=978-0-8203-4245-0 | url=https://books.google.com/books?id=6QJ5AAAAQBAJ&pg=PA144 | access-date=February 16, 2020 | page=144}}</ref>

The Brooklyn side's caisson, which was built first, originally had a height of {{Convert|9.5|ft|m|abbr=}} and a ceiling composed of five layers of timber, each layer {{Convert|1|ft|m|abbr=}} tall. Ten more layers of timber were later added atop the ceiling, and the entire caisson was wrapped in tin and wood for further protection against flooding. The thickness of the caisson's sides was {{Convert|8|ft|m|abbr=}} at both the bottom and the top. The caisson had six chambers: two each for [[dredging]], supply shafts, and [[airlock]]s.<ref name="structure mag">{{cite web|url=https://www.structuremag.org/?p=10604|title=Brooklyn Bridge, Part 2|date=November 5, 2012|website=Structure magazine|access-date=June 18, 2019|archive-date=March 8, 2021|archive-url=https://web.archive.org/web/20210308125625/https://www.structuremag.org/?p=10604|url-status=live}}</ref><ref name="NRHI Nomination Form p. 2" />

The caisson on the Manhattan side was slightly different because it had to be installed at a greater depth. To protect against the increased air pressure at that depth, the Manhattan caisson had 22 layers of timber on its roof, seven more than its Brooklyn counterpart had. The Manhattan caisson also had fifty {{Convert|4|in|cm|abbr=|adj=mid|-diameter}} pipes for sand removal, a fireproof iron-boilerplate interior, and different airlocks and communication systems.<ref name="NRHI Nomination Form p. 5" /><ref name="structure mag" /><ref>{{harvnb|ps=.|McCullough|1972|pp=269–271}}</ref><ref name="nydh18710418">{{cite news|url=https://www.newspapers.com/clip/33000026/|title=Brooklyn's Bridge; The Mammoth Caisson for the New York Tower|date=April 18, 1871|work=[[New York Daily Herald]]|access-date=June 18, 2019|page=13|via=newspapers.com}}</ref>