Caitlin Wilson
Live editor

The second day of hearings about what went wrong in the Titan submersible disaster last year focused on testimony from former OceanGate employee David Lochridge.

He had raised concerns about the sub since 2018, including over the materials it was made out of, but was fired from the company.

It was "inevitable" something would eventually go wrong, Lochridge told investigators on Tuesday.

The hearings are set to resume on Wednesday, but we are closing our live coverage for now.

In the meantime, you can read more about the story below:

Whistleblower testifies Titan sub tragedy was 'inevitable'

'All good here': Titan sub's last messages before implosion

Titan sub disaster: Five key questions that remain

The writers on this page were Lana Lam, Tinshui Yeung, Imogen James, Sophie Abdulla, Jessica Murphy and Jacqueline Howard.

It was edited by Jamie Whitehead, Nathan Williams, Aoife Walsh and me.

Thank you for joining us.

Five people perished when the Titan submersible imploded last year.

The men on board the sub included Stockton Rush, the 61-year-old CEO of OceanGate, British-Pakistani businessman Shahzada Dawood, 48, and his son Suleman, 19, and British businessman Hamish Harding, 58.

The fifth man on board, Paul-Henri Nargeolet, was a 77-year-old former French navy diver and renowned explorer who had been to the Titanic dozens of times.

Dive expert David Mearns said he lost two friends, Harding and Nargeolet, in a "most horrific way".

And Azmeh Dawood that nephew Suleman was “terrified” to go on the trip but wanted to please his father. His family thanked rescue crews for their efforts.

OceanGate called the group of men “true explorers”.

Image source, Dawood family/Lotus Eye Photography/Reuters

Rebecca Morelle and Alison Francis

Many were concerned about the Titan sub - including its former director of marine operations David Lochridge.

US Court documents from 2018 show, external that David Lochridge had identified numerous “serious safety concerns” and the lack of testing could “subject passengers to potential extreme danger in an experimental submersible”.

Engineers from the Marine Technology Society also said that OceanGate’s experimental approach could result in “negative outcomes (from minor to catastrophic)” in a letter shared with Stockton Rush.

In an email exchange, shown to BBC News last year, deep-sea specialist Rob McCallum told Rush that the sub should not be used for commercial deep dive operations.

In response, Rush said he had “grown tired of industry players who try to use a safety argument to stop innovation” and dismissed warnings that he would kill someone as “baseless”.

With the death of OceanGate’s CEO, we will never be able to ask why he chose not to listen to these concerns.

But the remaining days of public hearings could reveal more about who else at the company knew about them - and why no action was taken.

Image source, US Coast Guard

The second day of US Coast Guard hearings on the Titan sub disaster focused on testimony from David Lochridge, a former OceanGate employee. Here's some key takeaways:

• Lochridge said he was most worried about the material the Titan was made out of - carbon fibre - as it got weaker with each successive dive
• He also worried that the sub was not fully tested for the depths it was to dive to, saying he had "no confidence whatsoever" in the way the vessel was built. "Hands down, I would never go in that thing," he told the hearing

• He criticised OceanGate for being only interested in making money, with "very little" in the way of science behind the operation
• He also blasted what he called "arrogance" within the company, along with the "control freak" tendencies of CEO Stockton Rush, who died in the Titan implosion along with four others
• After he was fired, Lochridge took his concerns to Osha, the US employment safety agency, describing how he began to receive "threats" from OceanGate
• But Lochridge said he was not protected by Osha, which left him feeling "deeply let down and disappointed"

The hearing is set to resume again on Wednesday.

Prior to the hearing, forensic experts examined the Titan's wreckage to look for the root of failure.

The viewport window was only rated to a depth of 1,300m (4,300ft) by its manufacturer, but Titan was diving almost three times deeper.

Titan's hull was also an unusual shape - cylindrical, rather than spherical. Most deep-sea subs have a spherical hull, so the effect of the crushing pressure of the deep is distributed equally.

The sub's hull was also made out of carbon fibre, an unconventional material for a deep-sea vessel. And David Lochridge has told this hearing about his worries about the quality of the material, which he said became weaker with every descent.

Read more: Key questions over the Titan sub disaster

How the Titan sub accident affected other deep-sea explorerspublished at 21:13 British Summer Time 17 September

21:13 BST 17 September

Stephen Dowling
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.

After a short break, the hearing wraps up with a closing statement from Lochridge.

He says the situation has been "troubling" for him as Osha did not protect him or his family from facing "retaliation" from OceanGate.

"I believe that if Osha had attempted to investigate the seriousness of the concerns I raised on multiple occasions, this tragedy may have been prevented," Lochridge adds.

Lochridge says he feels "deeply let down and disappointed" by a system that was meant to protect him as a seafarer and the general public.

And with that, the hearing ends for the day. We'll bring you the key lines here shortly - stay with us.

Lochridge says Stockton Rush, OceanGate's CEO, refused to have any emergency life support in the sub as it was a "complete waste of money".

Lochridge says it was "in my eyes, [Rush was] showing off", as Rush was with some board members.

"He was a control freak," Lochridge says of Rush, referring to instances of bullying other staff.

"It was his way or not at all," he finishes.

Just before the hearing went to a short 10-minute break, we heard about the medical certifications for submersible pilots at OceanGate.

Lochridge says it could be “quite expensive”, around $700 (£531), “so the company wasn’t willing to pay for the trainee pilots to get that certification".

He's then asked if there was any written policy on the use of over-the-counter medicines or substances for pilots.

Lochridge says there may have been something in an employee handbook but he's not sure.

He's also asked if there was a policy on reducing the effects of fatigue, which can impair human performance to the same level of being intoxicated.

“There may have been, there may not," he replies.

Lochridge says he's not clear on the type of formal training that Stockton Rush went through to operate the Titan submersible.

He is asked whether he maintained formal training records for submersible pilots that were qualified to operate the company's equipment in his time with the firm.

"I did when I was there," he says.

Lochridge is now asked about how the Titan was towed on the water's surface on a platform for 300 miles. Is this normal?

"No, I wouldn't say that's normal at all," Lochridge replies.

He says if there is bad weather and the water is choppy, a sub "runs the risk" of damage as it hits the platform along the surface.

Lochridge called the Titan an experimental manned submersible - one that "they had already taken deposits (on) to go to the Titanic".

He was asked about whether he had concerned about carrying passengers on such a vehicle.

"I was very concerned, and I didn't agree with it," he said.

Lochridge says training is "absolutely" necessary to using these types of underwater vehicle, and an "imperative".

"Stockton's vision was give somebody this PlayStation controller and within an hour they're going to be a pilot - it's not the way it works," he says of the OceanGate boss.

He compares it to somebody being shown how to fly a helicopter and then expecting them to take passengers up on a flight.

We're now hearing more details about the Cyclops One sub - which as we reported earlier, is the same as the Titan - which dived to the Andrea Doria shipwreck.

Lochridge says the Cyclops sub was never "fully classed", or tested.

He's asked whether it bothered him to carry out operations on an unclassed sub.

Lochridge says he "had confidence" as things like the life support system had been "thoroughly inspected" and certain components like the scrubber were approved.

Lochridge says OceanGate was "bypassing all the standardised rules and regulations set in place" by experts such as the US military and the Coast Guard.

"They bypassed it all," he tells the hearing, including classification agencies and manufacturers.

"It was inevitable something was going to happen, and it was just when," he says.

Rebecca Morelle
Science editor

After facing delays with his case with Osha and increasing pressure from OceanGate’s lawyers, David Lochridge decided to settle the lawsuit with his former employer.

But this meant signing a non-disclosure agreement, or NDA, preventing him for speaking out about the company and its sub again.

He hasn’t spoken publicly until now.

At the hearing today, Lochridge says he was happy he has been subpoenaed so he could finally air his concerns to the world.

As the US Coast Guard holds hearings this week on the demise of the Titan submersible, they have released a picture showing the craft on the ocean floor after its voyage ended in disaster last year.

Image source, Pelagic Research Services/US Coast Guard

David Lochridge tells investigators that OceanGate served him with their lawsuit "the day my wife and I were going home for my father-in-law's funeral".

He answered the door and was served papers in a lawsuit against them both by the firm's lawyers.

He said, on his lawyer's advice, he immediately notified Osha, which he had been in touch with about his disputes with the company, about "further retaliation" by the firm.

Lochridge says with his new attorney, they decided to countersue OceanGate as "Osha were dragging their heels".

But instead of OceanGate's legal action in the civil courts, where the proceedings are behind closed doors, Lochridge says they decided to sue in the federal courts so that "it would become public knowledge".

The hearing restarts with David Lochridge, OceanGate's former operations director, explaining the settlement and release agreement that he mentioned just before the break.

He goes through a number of emails that were sent between him and his caseworker at the US Occupational Safety and Health Administration (Osha) agency in March and April 2018.

OceanGate wanted me to pay US$10,000, Lochridge says, and "we declined".

He told OSHA about the request and they responded by saying OceanGate lawyers wanted to know if he was interested in "alternate dispute resolution" (ADR).

I had "no interest" in an ADR or on the settlement agreement.

Lochridge says he was "wrongfully under the assumption" that he was going "to be protected" by Osha.

The Coast Guard hearing on the Titan disaster has resumed after a lunch break.

Stick with us as we bring you all the updates from the testimony.

And as a reminder, you can watch the proceedings live at the top of this page.

You can also watch by pressing the Watch Live button above.