Published on 11-Aug-2023

Safety Challenges and Design Considerations in OceanGate's Titan Submersible

Safety Challenges and Design Considerations in OceanGate's Titan Submersible

"OceanGate promoted the Titan's construction, which consisted of carbon fiber with titanium endcaps, as a lighter and more efficient option compared to other deep-diving submersibles on their website. According to court documents, they claimed that the vessel was designed to safely dive to a depth of four kilometers (2.4 miles) with a comfortable safety margin. However, Graham-Jones explained that carbon composites have a limited lifespan when subjected to excessive loads or poor design, leading to stress concentrations. While composites are durable and long-lasting, they can fail in different ways than other materials.

Pressure Resistance

Submersibles and submarines are designed with the shapes of spheres and cylinders because these geometric forms offer greater resistance to crushing pressures. Unlike operating in a breathable atmosphere at 1 bar, the Titan would need to endure 370 bars of pressure in seawater at the depth where the Titanic sank. Any flaw in the hull could lead to instantaneous implosion. The question arises: What is the critical point at which a departure from a perfectly circular geometry becomes a defect? Industries that utilize underwater vessels at depths of a few hundred meters often employ steel hulls, which typically have a threshold for out-of-circularity below 0.5% of the vessel's diameter. However, would this criterion be sufficient for ensuring the safety of the Titan's pressure hull at a depth of 4,000 meters? The Titan's hull is constructed from a composite material consisting of carbon fiber and titanium. Designing and assessing the structural integrity of such materials is considerably more complex compared to conventional metallic materials. This likely explains why OceanGate equipped the Titan with a ""real-time hull health monitoring system."

It remains uncertain whether this system measures stress using strain gauges on the hull or if it relies on acoustic analysis, as cautioned by Lochridge. If the latter is the case, it would only provide a warning of imminent issues "" often milliseconds before an implosion."" Ensuring the safety of the pressure hull's integrity involves analyzing various failure modes and determining a safety coefficient for each mode, based on the intended deep diving depth. Once the design is verified through calculations, real-world validation should proceed in two steps. First, non-destructive testing should be conducted on the manufactured pressure hull to assess the precision of its geometry and identify any out-of-circularity issues. Following that, actual dives (preferably unmanned) should be carried out at progressively increasing depths, employing stress gauges to measure actual values against predictions. It is unclear whether the Titan underwent such tests.

Safety Systems

For the Titan, utilizing a tether connected to a mothership would have provided instant two-way communication and a faster data exchange rate. However, the presence of potential hazards at a shipwreck site increases the risk of entanglement with these cables. As a result, tethers are primarily used for unmanned vehicles, while manned submersibles prefer to rely on the expertise of the pilot. Furthermore, underwater use of tools like GPS, portable satellite phones, and automatic identification systems is not possible. These devices rely on electromagnetic waves that do not propagate effectively in deep underwater environments, although they can be used on the surface.

Some submarines are equipped with distress beacons similar to emergency position-indicating radio beacons (EPIRBs). These beacons can be activated either by the captain's order or through a "dead-man" switch. If the pilot fails to respond to regular interval tests, the system assumes that the crew is incapacitated. It is hoped that the reported "banging" sounds are the result of the Titan's crew and passengers intentionally striking the pressure hull every 30 minutes. Military submarine crews are trained in this technique when grounding on the sea floor. To enhance efficiency, a high-frequency acoustic pinger would provide directional accuracy for locating a distressed submersible. There are also potential challenges that may arise on the surface of the Titan manages to float up. Even if it does ascend, the crew and passengers would likely be unable to open the vessel's bolted hatch, leaving them to contend with potentially contaminated air inside. Additionally, the white color of the Titan complicates matters by making it harder to spot in the turbulent sea. Floating assets typically use orange or yellow shades, which offer higher visibility when detected from above.

Analysis By Industry Experts, Renowned Organizations, and Professors

Operated by OceanGate Expeditions, the Titan had been transporting individuals to the Titanic since 2021. It garnered attention for its distinctive cylindrical cabin, constructed from carbon fiber, a departure from the commonly used titanium sphere-shaped cabins found in most submersibles. "The perfect shape," according to Chris Roman, a professor at the University of Rhode Island's Graduate School of Oceanography, is the sphere. This is because water pressure is distributed evenly across all areas of the shape. While Roman had not personally been on the Titan submersible, he has extensive experience in deep dives using Alvin, a submersible operated by the Woods Hole Oceanographic Institute in Massachusetts.

Graham-Jones compared fatigue to bending a wire repeatedly until it breaks, while delamination is akin to splitting wood along the grain, which is easier than chopping across it. Additionally, Graham-Jones noted that the Titan's hull, which was 5 inches (12.7 centimeters) thick, had experienced repeated stress during approximately two dozen previous dives. With each trip, the structure would develop minuscule cracks that might initially go unnoticed but would eventually become critical, leading to rapid and uncontrollable growth. OceanGate was warned about the potential catastrophic safety issues that could arise from a lack of third-party scrutiny during the development of the vessel. In a 2018 lawsuit, David Lochridge, OceanGate's then-director of marine operations, expressed concerns about the insufficient testing and certification, stating that it could expose passengers to extreme danger in an experimental submersible. He advocated for nondestructive testing, such as ultrasonic scans, but the company refused. Ultrasonic testing, according to Neal Couture, the executive director of the American Society for Nondestructive Testing, can help identify areas within the structure where the composites may be deteriorating. Couture emphasized the importance, role of NDT and safety protocols to assess the viability and susceptibility of the structures under stress.

The Marine Technology Society, an organization comprising ocean engineers, technologists, policymakers, and educators, also voiced concerns to OceanGate about the size of the Titan, the construction material, and the lack of third-party examination of the prototype. They warned that without proper certification, critical factors might be overlooked, leading to negative outcomes with serious consequences for the industry. Graham-Jones noted that seeking outside expertise to ensure vessels conform to the highest industry standards is standard procedure in engineering. In a 2019 blog post, OceanGate criticized the third-party certification process, claiming it to be time-consuming and stifling innovation. They argued that involving external entities in every innovation before real-world testing hindered rapid progress.

Renowned undersea explorer Robert Ballard, who first located the Titanic wreckage in 1985, referred to the lack of outside certification and classification as a "smoking gun" in the submersible's failure. He mentioned that numerous dives to similar depths had been conducted without incident. Director James Cameron, known for his exploration of the Titanic wreck, suggested that the failure of the composite hull was the most likely cause of the submersible's destruction. While other factors could also be responsible, Cameron placed his focus on the composite material, stating that composites are not typically used in vessels subjected to external pressure."

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