What Caused the Titan Submersible Accident?

On June 18^th, 2023 a submersible vessel named Titan imploded on its way to visit the site of the Titanic shipwreck, instantly killing all five people on board. In the days since the accident, experts have started scrutinizing the design of the submersible to put together what happened deep below the ocean’s surface.

What is the Titan submersible?

A submersible is a small vessel capable of staying underwater for long periods of time. Some submersibles are designed to dive deep into the ocean, which requires an ability to withstand extremely high pressures applied to the outside of the vessel.

The Titan submersible was developed and built by the company OceanGate, which sold trips to the Titanic shipwreck about 500 miles off the coast of Newfoundland, Canada, for a quarter of a million dollars per person.

Why did the accident happen?

Experts are working on determining the exact causes of the accident, and it will likely be a while before the cause can be proven beyond a shadow of a doubt. That being said, there are some red flags that have risen to the surface in the weeks after the disaster that are likely to have had an impact on the vessel’s implosion.

The Titan submersible’s design

According to their website (which has since been taken down and is only accessible via archive), OceanGate claimed to be able to dive to 13,000 feet with Titan, although it only made it to more than 1250 ft 13 out of 90 times. The vessel’s dimensions were 22 ft by 9.2 ft by 8.3 ft, it could carry 1,500 lbs, and the vessel itself weighed about 21,000 lbs.

The hull was made from titanium hemispheres attached to an 8ft long carbon fiber cylinder. Titan also had a “real-time hull health monitoring system” made of strain gauges and acoustic sensors placed around the hull. The monitoring system was supposed to allow the pilot to see if the hull was failing and return to the surface.

Submersibles can be considered a specific type of pressure vessel, since in order to dive into the ocean they have to be able to withstand high pressures or collapse and implode. Many of the design principles are similar, although most pressure vessels used commercially or in research are meant to hold pressure applied from within the vessel, not applied from the outside, and are designed to meet rigorous industry standards.

How do people know designs are safe?

Pressure vessels and boilers available in industry are often ASME certified, which means their design and manufacture meets standards set out by a panel of industry experts.

There are certifications available for submersible design, although they are generally covered under marine equipment instead of pressure vessel standards.

How was the submersible design tested for safety?

Novel designs like those of the Titan submersible usually undergo a wide range of testing to ensure the product is working as intended and is safe. This testing can involve non-destructive evaluation of parts, pressurizing the hull to see if it will be damaged, and cyclic testing to see if the hull will sustain damage over time from repeated applications of high pressure.

OceanGate skipped “critical non-destructive evaluation”, according to a lawsuit filed by an ex-employee fired immediately after raising safety concerns with the vessel.

The submersible had “not been approved or certified by any regulatory body and is constructed of materials that have not been widely used for manned submersibles”, according to the waiver would-be passengers were required to sign, stating they understood the risks of the expedition.

The problem with Titan’s hull

For some materials, the direction the force is applied doesn’t have much of an impact on the material, or it has been thoroughly tested and studied. However, other materials like the carbon fiber used in Titan’s hull are highly dependent on the direction the force is applied. This is because they do not have a uniform structure in every direction.

What is carbon fiber?

Carbon fiber used in aerospace is lightweight and versatile – but most of the studies done on its material properties and performance over time have been for applications that don’t match the conditions the Titan submersible was designed for.

When used in aerospace, when people talk about carbon fiber they’re actually referring to a composite material made from the fibers mixed with plastic resin. A lot of the time, this composite is made from layers of carbon fiber and resin sandwiched on top of each other, with the fiber direction varied with each layer to increase the strength of the material.

Composite materials are notorious for having complex material properties that depend on the angle a force is applied. Their material properties, especially for laminate composites, have to be calculated for each layer. Most importantly, their properties depend on the angle the force is applied at, so studies done under one set of conditions can be inaccurate if your conditions don’t match or you don’t have the same amount of layers arranged in the same pattern.

What is cyclic loading?

Cyclic loading refers to loads applied to a system that repeat and can be expected to continue repeating. In the case of the Titan submersible, the process of descending 13,000 ft and returning to the surface for each dive would be a cyclic load.

You can learn more about cyclic loading with a quick overview, or our more in-depth guide geared towards pressure vessel design.

Why is it important to test materials under cyclic loads?

Cyclic loading can lead to fatigue over time as the materials are deformed. Cracks form, delaminations can occur in composite materials, and other flaws grow as the material weakens with the repeated applied forces.

This means the pressure vessel that was able to withstand a certain pressure right after it was manufactured might not be able to withstand that pressure after it has undergone enough cycles. The material is weaker. Continuing to operate the vessel under the same conditions might not be safe if you don’t know how the materials will react under repeated cyclic loads.

What happens next?

An accident review board has been put together by the US Coast Guard to investigate the causes of the submersible’s implosion. The Royal Canadian Mounted Police is looking into the disaster as well. The US Coast Guard is working to recover pieces of the imploded submersible, map the debris field, and collect recordings from the submersible’s mother ship, the Polar Prince.

Once the investigations are complete, the board will recommend what actions should be taken next, which could include consequences for anyone liable for the disaster.