The submersible known as Titan, which is intended to explore the wreckage of the sunken ship Titanic, has been missing with five people on board in the Atlantic Ocean since Sunday (18 June).
“I know the logistics of it and I know how vast the ocean is and how very tiny this craft is,” he told BBC Breakfast on Monday (19 June).
“If it’s down at the bottom I don’t know how anyone is going to be able to access it, much less bring it back up,” he added.
Reiss explained that he had gone on three different dives with the company OceanGate Expeditions, which owns Titan, and that “you almost always lost communication”.
“I got on the sub and at the back of my mind was ‘well, I may never get off this thing,’ that’s always with you,’ he said.
Reiss said that Titan is “a beautifully designed craft”; however, the nature of the expedition makes problems possible.
“This is not to say this is a shoddy ship or anything, it’s just that this is all new technology and they’re learning it as they go along,” he said.
“You have to just remember the early days of the space programme or the early days of aviation, where you just make a lot of mistakes on the way to figuring out what you’re doing.”
The five people onboard the Titan are British billionaire explorer Hamish Harding, renowned French diver Paul-Henri Nargeolet and Pakistani businessman Shahzada Dawood and his 19-year-old son Sulaiman Dawood, and Stockton Rush, the founder of OceanGate Expeditions.
The Titan is equipped with a four-day emergency oxygen supply, which will run out around 10.30am GMT on Thursday.
On Tuesday’s edition (20 June) of ITV chat show Loose Women, Janet Street-Porter questioned the “morality” of submarine tourism.
“I don’t want to appear heartless, but I do think that the people who are on board will have understood the risks,” she said.
“Because this kind of trip is a new kind of tourism which we’ve seen in space trips and now underwater trips and people scaling the highest mountains in the world. Only the richest people in the world can afford this kind of tourism.
“… Let’s hope that people don’t put their lives in danger trying to rescue them too, because they’re people doing a job that they’re paid a lot less money for doing,” she said.