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There are plenty of nervous flyers. We get it, airplanes can be a bit scary if you aren’t familiar with what’s going on.

So if plumes of smoke, for example, appear in the cabin while you’re on board, we get why that might freak you out. This happened on two flights in the past week alone. One was on a Delta flight as it waited to depart Jacksonville (JAX). Cellphone footage shows thick fog inside the New York-bound plane as alarmed passengers look on.

On a different flight, a passenger — who happens to be the sister of The Points Guy himself, Kristin — filmed a similar scene.

Fire and smoke in aviation are extremely serious. Onboard fires, for example from cigarettes, can bring down planes. It’s why “tampering with, disabling or destroying a lavatory smoke detector” is a serious federal offense in the US. Smoke in the cabin is a pretty automatic trigger for an immediate diversion in flight and, once on the ground, often an evacuation.

But as it turns out, while scenes of smoke in the cabin may appear serious, it’s normal, totally safe, and in some climates it happens all the time.

That’s because you’re not looking at smoke in the video above. What you’re seeing is mist — hot and humid outside air rapidly condensing upon contact with the aircraft’s onboard air conditioning unit that creates billows of water vapor. In this specific instance, there’s so much water vapor because the air conditioning is blasting, the doors are open and we’d bet the flight crew cranked up the AC just a few minutes prior, and water vapor is the result of all that hot and humid air mixing with air that’s much cooler. Not unusual in Florida in the summer.

Dave Powell, a retired Boeing 777 captain and now Dean of the College of Aviation at Western Michigan University, helped us understand.

He explained, “it is really nothing more than the very cold air coming out of the air conditioning forcing the air to release it’s moisture.” He reiterated that it happens “all the time” when flying and out of hot and humid locations and crews are looking to cool off the aircraft.

Consequently, you’ll experience this phenomenon most frequently when departing from hot and humid climates, as the blasting air conditioning units cause the hot, heavy air to condense and turn to mist. And unlike arriving flights, which have been climate-controlled for hours already during the flight, they’ve been sitting on the ground, doors open and humidity settling inside. This isn’t unique to aircraft either: A support page for GE air conditioners outlines this same effect — the worse the humidity, the more intense the mist, and it closes with a comforting conclusion: “The fog or smoke should disappear rapidly, usually in less than a minute or two, as the air conditioner removes the humidity from the air and the room air becomes cooler.”

Most planes are even equipped with something called a water separator to prevent this from happening often, but even that can’t keep up with conditions in especially hot and humid climates. A simple rule of thumb: if you board an airplane filled with what appears to be smoke, and the cabin crew and pilots are conducting business as usual, it’s a pretty safe bet it’s not toxic fumes that are filling the cabin.

Jordan Allen contributed to this story.

Featured image courtesy of Air Transat. 

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