What Is Nitrogen Narcosis? Explaining the ‘Martini Effect’

Two divers died in a dangerous underwater cave in Florida on Sunday, prompting questions about how the men—who were described as very experienced divers—could have failed to resurface at the rendezvous point with a third friend.

The medical examiner’s office will determine the cause of death, but people in the diving community have put forth many possible explanations. The site, Eagle’s Nest Sinkhole, was described by one expert as a “Venus fly trap,” with its complicated layout and vast range of things to see. It’s possible that the men lost their lines, struggled with visibility, or had issues with their equipment. But some have speculated that nitrogen narcosis, or the “martini effect,” may have played a role in the tragedy. Here’s how that condition affects divers.

What is nitrogen narcosis?

Nitrogen is a major part of the air we regularly breathe. But when divers breathe from their air supply underwater, it is much more dense, increasing the quantity of nitrogen in the body. This has an outsized effect on the nervous system, so divers’ functioning can become impaired at a depth of about 100 ft. (depending on the person). The sensation has been dubbed “the martini effect” because divers liken it to drinking one martini on an empty stomach for every additional 50 ft.

What does it feel like?

Some divers can experience euphoria, earning nitrogen narcosis another nickname, “Raptures of the Deep.” Others can become anxious, numb or dizzy. The loss of reason can lead some to fail to take the necessary care in navigating, checking the oxygen tank and rising to the surface slowly enough to avoid the bends. Errors like these can result in death.

How can it be avoided?

For deep dives, some people use mixes of oxygen, helium, and nitrogen (a trimix) or of just oxygen and helium (a heliomix) to reduce or eliminate the chance of nitrogen narcosis. Scuba enthusiasts also emphasize the importance of looking out for your dive buddy for signs of impairment, and ascending in the event of these symptoms.