Lahey tells the committee about two submersibles OceanGate purchased which he was involved in building, before he later established his company.

He says were both reviewed by independent bodies in a process known as "classing" but adds that he does not know if OceanGate continued to certify them.

"I don't know the condition of those subs any longer, and nor do I know if they're still classed," he says.

He adds that during a sailing vacation to the Bahamas in 2019, he coincidentally happened to get a tour of the Titan sub that later imploded.

Wearing a T-shirt for his company at the bar, someone saw it and approached him and offered to show the sub being tested.

"I wasn't particularly impressed by what I saw," he says.

"It looked to me like a lot of the stuff was not quite ready for the prime time," he says, adding that he told the OceanGate team about his concerns.

Image source, US Coast Guard

Lahey talks about the one and only time he saw the Titan submersible in person, in the Bahamas.

He says he saw "a few concerning things" about the structure of the vessel.

Lahey adds that the submersible was not necessarily "innovating or cutting edge" in its construction, saying that vessels before it had been constructed with filament-wound cylinders.

Lahey says he didn't have extensive conversations with OceanGate's CEO, Stockton Rush, who died aboard the Titan last year.

Rush says he knew Lahey wasn't a "big fan" of his work when they would bump into each other at conferences.

Lahey repeats again that he believes vessels must be certified by independent parties.

Lahey is telling the panel about the importance of safeguards when trying to innovate in the deep sea.

"We're constantly building new sub designs. We're always challenging conventional thinking, trying to innovate," he tells the panel about his industry.

Lahey he says he's a "firm believer in innovation".

"But innovation has to be done within the crucible of a set of rules that give you guardrails. You can't just go freestyle," he says.

Rebecca Morelle
Science editor

Patrick Lahey just told the hearing about his views of the importance of certification for deep sea subs.

Submersibles can undergo a process called certification – which is also sometimes referred to as classing.

It’s an extensive safety assessment carried out by independent, specialist, marine organisations. These include the American Bureau of Shipping (ABS), the DNV (a global accreditation organisation based in Norway) and Lloyds Register.

This essentially means that the vehicle must meet certain standards on aspects including stability, strength, safety and performance.

During the process the sub is monitored all the way from its design through to construction, testing and operations. And once the sub is in service it needs to be checked periodically to ensure it still meets these criteria.

The process costs money and takes time, but almost all deep-sea submersibles are certified.

But it is not mandatory.

And while OceanGate did talk to certification organisations earlier in the Titan’s development, they opted not to get it certified.

Image source, US Coast Guard

Lahey is telling the Coast Guard panel about the importance of certifying submersible vessels. The Titan submersible was not certified, which was not required for the vessel.

"Certification matters because it's about building something that's robust, durable, reliable" and something people can "dive in with confidence", Lahey says.

"Any machine that's going to be carrying human beings into the deep sea has to meet the high bar of certification" by a third-party group, Lahey tells the panel.

"I don't believe that we should be operating experimental vehicles in the deep sea," he says.

Lahey is being quizzed on the difference between a submarine and a submersible.

He says the difference is a submersible is not capable of regenerating its own power - a submarine has to have the capacity to do so.

A submersible is usually powered by batteries and is "limited in its endurance", he says.

We're back from the break and now hearing from a key witness, Patrick Lahey, the co-founder of Triton submersibles.

He begins by discussing how he got involved working with submersibles.

Lahey says he started his company in 2006, amid "tremendous scepticism" about the vessels.

He says he's at the hearing to try to address this scepticism.

Rebecca Morelle
Science editor

Patrick Lahey is the co-founder and chief executive of Triton submersibles - a leading manufacturer of deep sea crafts, and the next witness appearing at the Titan inquiry from 13:00 EST (18:00 BST).

His company built a sub called the Limiting Factor that descended to the deepest places in the ocean, many times.

There’s no other sub like this - it’s about as experimental as a sub can get.

However, it still went through a process called certification - where the craft is given an extensive safety assessment by an independent, specialist marine organisation.

Most subs do go through this process - but it is not mandatory. And OceanGate’s chief executive Stockton Rush opted not to get Titan certified.

The assessment would have confirmed whether the vessel - from its design through to construction, testing and operations - met certain standards.

Stockton Rush said that certification “slowed down innovation” and that his own safety protocols were enough.

But Lahey was highly critical of this decision. He spoke to the BBC before the public hearings.

“You want to leave no stone unturned, you want to absolutely go through whatever testing and validation process is necessary to substantiate that the machine that you're in and that you're getting people to climb in is safe.”

There's another short break in the hearing. So let's take a moment to look into some background on the submersible.

This week we've been listening to testimony about the hull on the Titan.

For context, the sub’s hull was made of carbon fibre, an unconventional material for a deep-sea vessel.

Metals such as titanium are most commonly used as they are reliable under immense pressures.

You can see from the graphic below the key weaknesses on Titan.

Rebecca Morelle
Science editor

Image source, US Coast Guard inquiry

Dave Dyer from the University of Washington’s Applied Physics Lab has been giving evidence.

In 2013, Oceangate entered a contract with the university to develop, construct and test a sub made of carbon fibre - a prototype for Titan.

Dyer told the US Coast Guard inquiry that he originally thought the sub could be viable.

“With the initial concept we felt like there was a very good chance it could be successful - the design looked like it was heading down the right path," he said.

The entire structure was originally supposed to be made of carbon fibre - including its end domes.

But when a smaller model of the sub was placed in a special chamber that recreates the pressure of the deep it failed several times.

So instead the carbon fibre end domes were swapped for titanium ones.

But the relationship between the university and OceanGate began to break down with disagreements about OceanGate’s approach to engineering and testing.

The university stopped working with Oceangate in 2017.

Dave Dyer, an engineer from the University of Washington's Applied Physics Lab, is now sharing his testimony at the public hearing.

We'll bring you the highlights on what he has to say once he wraps up his evidence, but until then, you can watch live at the top of the page.

Rebecca Morelle
Science editor

Fred Hagen was a paying passenger who made several dives on Titan.

When asked by the US Coast Guard about specific problems with the sub during the dives, he described a number of incidents.

These included the front dome of the sub falling off when it was dropped while being lifted onto the deck from the water.

“The force of the platform hitting the deck…. it basically sheared off several bolts and they shot off like bullets. And the titanium dome fell off,” he said.

On another dive, because the sub was incorrectly weighted, it was off balance and spiralled thousands of metres to the sea floor. Then when it got there the thrusters failed to work.

“The starboard thruster failed and we realized that all we could do was spin around in circles,” he told the hearing.

On that same dive some of the weights that were supposed to drop so the sub could ascend were stuck - but the Titan did eventually make its way back to the surface.

He also described how the sub briefly became caught in the wreckage of the Titanic and spoke about a loud bang that was heard on another ascent.

When outlining these incidents, he didn’t seem particularly worried about any of them. He told the hearing he knew the sub was experimental and risky.

Fred Hagen, from Pennsylvania, was on Titan in 2022 and had several friends aboard the sub when it imploded in June last year.

"It's this iconic moment, and you've dreamt about it, and you've read about it, and suddenly it's there, and you've achieved this dream," Hagen told local media about his experience.

He's now giving evidence to the hearing - and while we won't be bringing you regular text updates on his testimony, you can watch it live at the top of the page.

Image source, US Coast Guard inquiry

Marita Moloney
Reporting from Washington DC

Welcome back to our live coverage of the public inquiry into the implosion of the Titan submersible.

Today we'll hear from Fred Hagan, a mission specialist with OceanGate, the company behind the Titan sub. A mission specialist refers to a paying passenger who was taken on an expedition to see the Titanic.

Dave Dyer, an engineer from the University of Washington's Applied Physics Lab, is up next, before Patrick Lahey appears at the afternoon session.

Lahey is the co-founder and CEO of Triton submersibles - a leading manufacturer of deep sea crafts.

The US Coast Guard inquiry is hearing two weeks of evidence into the deadly implosion of the experimental submersible in which all five people on board died.

We'll be bringing you updates from the hearing, which you can also follow along on our stream above.

Marita Moloney
Reporting from Washington DC

We're pausing our live coverage of the inquiry into the Titan sub implosion, after the former OceanGate scientific advisor concluded his evidence today.

Dr Steven Ross's 90-minute testimony followed earlier evidence from Renata Rojas, a mission specialist who was on the support vessel on the surface when the submersible vanished.

In an at times emotional testimony, she likened the Titan to the famous Apollo space programme and in a final closing statement said she hoped "innovation continues".

Before the hearing started, we saw new footage released by the US Coast Guard showing the wreckage of the submersible, which imploded killing all five inside in June 2023, on the sea floor.

The public hearings began on Monday as part of a two-week inquiry by the Coast Guard into the disaster. The investigation has been going on for 15 months.

We'll be back tomorrow to bring you more from the inquiry, and until then there's plenty more to read across the BBC on the disaster:

• What we heard on the third day of the inquiry
• 'All good here': Titan sub's last messages before implosion
• Five key questions that remain

Thanks for joining us.

The hearing has finished for the day after testimony from Dr Steven Ross, the former scientific director of OceanGate.

We'll bring you a recap of events in a moment.

We're now hearing the testimony of Dr Steven Ross, the former scientific director of OceanGate, at the US Coast Guard inquiry into the company's deadly Titan voyage.

It follows evidence from mission specialist Renata Rojas, who told the hearing she "knew the Titanic dive was risky", but "never felt unsafe".

You can follow Ross's evidence on our stream above by clicking the watch live button - and we won't be bringing you regular text updates on the page.

Stephen Dowling
Deputy editor, BBC Future

Underwater explorer Victor Vescovo – who has travelled to the deepest part of the ocean, Challenger Deep, 15 times – says the Titan disaster could affect ocean exploration in the short term.

He says it could make people "more fearful of diving into the depths of the extraordinary ocean, the lifeblood of our world". But that would be the wrong response, he argues, akin to refusing to fly on an aircraft because of a plane crash.

"Those of us in the submersible community – the builders, pilots and researchers – have not hesitated in continuing to extensively dive in these vehicles, which should give everyone else confidence in their safety," he wrote in an article for BBC Future on the first anniversary of the disaster.

• Read more on what he had to say here