Posted on April 15, 2024
“The response to the Francis Scott Key Bridge collapse is an unusual mission with an uber-extreme work environment of dark, cold water. Beneath those waters, divers are moving as if playing an underwater game of Twister and Jenga with hundreds of tons of shattered concrete and twisted steel in complete darkness,” said Rick Benoit, Emergency Management specialist at the U.S. Army Corps of Engineers (USACE) North Atlantic Division (NAD). “If divers fail, the price of failure could be severe injury or death; safety must be the top priority at all times.”
Under an interservice agency agreement, USACE is working in a joint effort with the U.S. Navy’s Supervisor of Salvage and Diving (SUPSALV) to oversee the commercial dive companies performing the work underwater. As the lead dive subject matter expert at NAD, Benoit provides guidance for the USACE’s role in the underwater response.
This team of experts works with the U.S. Navy SUPSALV and dive teams to ensure that the dangerous work in Baltimore Harbor is being handled with caution at each step.
“The USACE dive community of practice is making themselves available to give guidance or advice as needed or as requested,” said Benoit. “It may sound dramatic but given the wreckage field created by the collapsed bridge the environment divers are working in and the dangers posed to them is like cleaning the site of 9/11 with blinders on.”
If the divers don’t proceed with caution, they may be impaled by rebar, cut by jagged steel or be hit by falling, broken pieces of heavy concrete and asphalt, causing them to be trapped or drowned.
“I guarantee every diver down there has that on their mind, but they can’t be afraid—they can’t stop going into work—because the work has to be done,” said Benoit.
The threat of the wreckage is multiplied by the conditions in the water. The divers’ visibility is confined to only one to two feet in front of them. With such low visibility, they must rely on survey data from Light Detection and Radar (LiDAR) and advanced sonar imaging tools to help them map out underwater routes. Even with these tools, some elements of the wreckage might not be completely detected. Rebar, for example, can’t be located by sonar.
Divers also must be wary of stepping on the bottom of the Patapsco River, as the riverbed is muddy, silty and imbedded with wreckage. If divers tried to stand on it, they could sink in and potentially injure themselves on fragments of metal or concrete.
Dive supervisors above the water play a crucial role in directing divers away from these hazards. In addition to using detection tools, supervisors use live feeds from cameras attached to divers’ helmets to provide detailed verbal directions.
Although the current only moves at about a knot, or a little more than one mile per hour, it poses another challenge if wreckage were to shift. Dive teams must be mindful of not only the diver but the hose the dive tender holds.
The dive tender, who is responsible for ensuring divers are properly outfitted for the dive, also ensures that the surface supplied air system is reaching the diver and maintained throughout the dive. Although divers are equipped with an emergency air tank on their backs, having the air hose to the surface cut or entangled by wreckage would be life-threatening.
To ensure their safety, divers are restricted by how long they can be in the water. This restriction is due to two main reasons: water temperature and water pressure.
“There is nothing worse than being so cold you have a hard time moving,” said Benoit.
Since the beginning of the mission, water temperatures have hovered around 48 degrees, which is cold enough to cause a diver to experience hypothermia after an hour in the water, depending on the type of diving suit used.
According to Benoit, the timeline also varies greatly depending on depth. At 60 feet, a diver can stay in the water approximately an hour. The divers in Baltimore Harbor are diving as far down as 50 feet. In a typical dive at that depth, a person would have approximately 92 minutes in dive time. As a safety measure, divers in the Harbor are restricted to 45 minutes underwater.
Staying longer than the advised times also increases the risk of decompression sickness, or “the bends.” The farther down a person swims, the smaller amount of air one’s body processes. When a person comes up too fast, the body is not able to process the larger quantities of air that come with the change in water pressure. This can cause the bends or worse—an arterial embolism.
“It’s like your body, specifically the lungs, are a balloon; if you ascend to the surface too fast, alveoli, or air sacks in the lungs, will rupture, spilling air bubbles into the circulatory blood system which can cause a diver to embolize,” said Benoit.
As an emergency precaution, recompression chambers sit on barges onsite. These recompression chambers artificially re-create the pressure a diver experiences in the water. This allows their bodies to adjust to the air pressure back on the surface.
When emergencies such as these occur, dive supervisors are responsible for coordinating procedures. They are responsible for determining when the standby diver needs to go in, briefing them on the situation and directing them on where to reach the distressed diver.
“Dive supervisors have total control over the dive site. He or she determines who is going to dive and who is going to tend,” said Benoit.
The supervisors also take notes and document all the work that takes place by the team. With a complicated map of wreckage beneath the surface and multiple hazards to consider, supervisors need as much information as they can get to act quickly in emergencies.
Despite the risks, these dives are critical to the overall mission. Before the wreckage can be moved with cranes, divers need to survey and investigate the safest methods to remove it from the water.
Large steel beams reaching from the surface to the bottom of the river are currently too large and heavy to be picked up by cranes and must be cut first, but where and how they are cut poses its own problems.
“If you take a rubber band, twist it enough times and then cut it, what happens? It’ll snap back on you,” said Benoit. “The steel has been twisted in an opposite way than it was intended to exist, so it’s trying to get back to its original dimension. When you start cutting into it, it is like cutting a branch off a tree. You get to a certain point where inertia takes over and it snaps.”
There is a risk the entire structure could move due to the release of force on that section of the beam. Because that force will resonate down the entire structure, experts must carefully determine the best place to cut the steel.
Divers also must pay careful consideration to the possibility of discovering human remains.
“We would do all we could to support authorities and to make sure that everything is done right,” said Benoit.
If remains were discovered, the state police and public safety divers would take charge over recovering them with the assistance of local assets more equipped to ensure proper recovery.
“The enormity of this disaster is hard to imagine without seeing in person,” said Benoit. “Divers will probably need to be on the scene for the entirety of the mission. What takes a person on the surface to do in one hour can take up to 10 hours to do underwater.”
This underwater mission is one of the most challenging aspects of the response to the Francis Scott Key Bridge, but Benoit and his colleagues at USACE and elsewhere in the Unified Command are dedicated to supporting the mission with safety and precision as a top priority.
“One of the things about USACE is that it allows you to serve your country and to do good for the people of the United States. This will go down as one of those missions, when I look back on my career, I will be proud to have been part of,” said Benoit.
