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Seat belts, oxygen masks, the 3.4-ounce rule: What keeps you safe on a plane?

Rules are designed to keep us safe, along with many other airplane features. Now is a good time to revisit the safety details of a plane in light of Tuesday's breathtaking and tragic emergency landing of Southwest Flight 1380 in Philadelphia. (AP Photo/Pablo Martinez Monsivais, file)

Zoning out during the pre-flight safety instructions is, to many of us, as routine as the pretzels and cookies that come mid-trip.

But, of course, the rules are designed to keep us safe, along with many other airplane features. Perhaps now is a good time to revisit the safety details of a plane in light of Tuesday’s breathtaking and tragic emergency landing of Southwest Flight 1380 in Philadelphia. The Dallas-bound plane’s engine failed shortly after takeoff from New York’s LaGuardia Airport, forcing passengers to jump into survival mode.

Here’s what keeps us safe on a flight:

Those tiny windows

Air pressures in and outside the plane cabin differ so much that if a hole opens up in the plane, whatever is inside the high-pressure cabin will be sucked out.

Such is what happened with Jennifer Riordan, the mother of two killed on the Southwest flight. When the window next to her busted open, half her body was sucked outside until two passengers pulled her to safety.

Had the window been bigger, her entire seat, with her buckled in, could have been sucked out, said Richard Anderson, the director of the Eagle Flight Research Center at Embry-Riddle Aeronautical University.

Seat belts

You should wear them.

While planes are designed to withstand turbulence, passengers aren’t so much. It’s why all passengers should wear their seat belts to stay safe during the jostling brought by turbulence, notes retired airline captain John Cox.

“Pilots do all we can to avoid turbulence,” he said. “Occasionally, we must fly through it. I recommend keeping your seat belt fastened when you are in your seat (I do) to avoid the risk of injury from unexpected turbulence.”

Oxygen masks

Passengers aboard Flight 1380 didn’t quite get it right. When the oxygen masks fell during their emergency landing, several passengers placed the masks over their mouths — not both their noses and mouths, which is the correct way.

The masks are designed to make sure passengers get adequate oxygen. If a cabin “decompresses,” air is sucked out quickly, creating a lack of oxygen.

They are, “the first line of defense against the potentially lethal effects of hypoxia and carbon monoxide poisoning,” notes the Federal Aviation Administration. Hypoxia occurs when a person isn’t getting enough oxygen, which can cause dizziness, reduced vision, impaired judgment, unconsciousness and death.

Seats upright and locked during landing

If the plane makes a hard landing, having your seat back and unlocked increases the distance your head would travel on impact and the force at which it would spring forward, reports Smithsonian’s Air & Space. There’s also the wisdom of creating as much room as possible for a “quick exit,” Air & Space says.

Tray tables up

This is actually a federal regulation.

Ex-flight attendant Kelly Kincaid told Travel + Leisure it’s in place so the trays “won’t block you from evacuating in the event of an emergency.”

No cellphone use

The Federal Aviation Administration maintains cellphone signals “could interfere with critical aircraft instruments,” which is why we’re told to shut off our phones, or place them in airplane mode, during a trip.

3.4 ounces

The trash can at an airport security checkpoint is filled with bottles and containers, those items which failed to meet the Transportation Security Administration’s 3.4-ounce limit on liquid, aerosols, creams and gels.

The limit used to be an even 3 ounces and was implemented after terrorists tried to sneak liquid explosives onto a plane in England, reports the New York Times.

It appears there is a rhyme and reason to the rule:

“Tests showed that a container of a certain size is needed for an effective explosion,” the Times wrote. Quoting former TSA administrator Kip Hawley, the newspaper explained, “Separate three-ounce containers limited in number to what will fit inside a single one-quart bag do not have ‘enough critical diameter’ to blow up an aircraft.”

The 3-ounce rule was later changed to 3.4 ounces to become in sync with the European Union, which adopted a 100-milliliter limit. Since 100 ml equals 3.4 ounces, not 3 ounces, 3.4 ounces become the new standard.