To achieve a solid foundation for the bridge, workers excavated the riverbed in massive wooden boxes called caissons. These airtight chambers were pinned to the river’s floor by enormous granite blocks; pressurized air was pumped in to keep water and debris out.
Workers known as “sandhogs”—many of them immigrants earning about $2 a day—used shovels and dynamite to clear away the mud and boulders at the bottom of the river. Each week, the caissons inched closer to the bedrock. When they reached a sufficient depth—44 feet on the Brooklyn side and 78 feet on the Manhattan side—they began laying granite, working their way back up to the surface.
Underwater, the workers in the caisson were uncomfortable—the hot, dense air gave them blinding headaches, itchy skin, bloody noses and slowed heartbeats—but relatively safe. The journey to and from the depths of the East River, however, could be deadly. To get down into the caissons, the sandhogs rode in small iron containers called airlocks. As the airlock descended into the river, it filled with compressed air. This air made it possible to breathe in the caisson and kept the water from seeping in, but it also dissolved a dangerous amount of gas into the workers’ bloodstreams. When the workers resurfaced, the dissolved gases in their blood were quickly released.
This often caused a constellation of painful symptoms known as “caisson disease” or “the bends”: excruciating joint pain, paralysis, convulsions, numbness, speech impediments and, in some cases, death. More than 100 workers suffered from the disease, including Washington Roebling himself, who remained partially paralyzed for the rest of his life. He was forced to watch with a telescope while his wife Emily took charge of the bridge’s construction. Over the years, the bends claimed the lives of several sandhogs, while others died as a result of more conventional construction accidents, such as collapses, fires and explosions.
By the early 20th century, scientists had figured out that if the airlocks traveled to the river’s surface more gradually, slowing the workers’ decompression, the bends could be prevented altogether. In 1909, New York’s legislature passed the nation’s first caisson-safety laws to protect sandhogs digging railway tunnels under the Hudson and East rivers.