While a number of news outlets are reporting the Titanic tourist submarine that went missing over the weekend has 40 hours of oxygen left, at least one expert is saying that’s a very generous estimate. Bobby Chacon, a former team diver with the FBI, says odds are the five people inside the sub don’t have anywhere near that long before their oxygen runs out. “Those calculations are estimates based on normal working conditions,” Chacon says.

“If a person is injured, or they’re stressed, or they’re panicking, their air consumption increases. So those numbers of available hours go down. So if people are injured on that vessel, if they’re panicked on that vessel, they’re going to use more oxygen or more air more quickly.”

The OceanGates sub, which takes tourists underwater to catch a glimpse of the world’s most famous shipwreck, went missing about one hour, 45 minutes after it launched on Sunday morning, authorities say. It had enough oxygen to last 96 hours when it left, officials say.