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What happens when your plane windows crack?

Updated: Jan 29, 2021

Have you ever sat on a window seat in an aircraft and wondered, "what if my window cracked?"


Join us to learn more about pressure, the human body in flight what happens when your plane windows crack.



What is cabin pressure?


Cabin pressurisation is a mandatory process where conditioned air is pumped into the cabin of an aircraft or spacecraft to create a safe and comfortable environment for passengers and crew flying at high altitudes.


How air pressure gets pumped into the aircraft cabin

Aircraft pressurise their cabins by pumping air into them. As jet-engines suck in air, a percentage of the excess air is diverted into the aircraft cabin. The air is both cooled and humidified, meaning moisture is added to the air that circulates in the cabin. Once the cabin achieves an ideal pressure level, the aircraft will maintain the pressure throughout the flight till the stage of flight where the aircraft begins descending.


Most aircraft control their cabin pressure via an outflow valve. If an aircraft’s cabin exceeds the pressure for which is specified, the outflow valve will open. In the open outflow valve position, excess air will bleed out which will allow the cabin pressure to drop to an appropriate level, resulting in the outflow valve closing. Sone aircraft use other methods to regulate cabin pressure, but the outflow valve method exists in most modern-day commercial airplane systems.


Why does the aircraft cabin need to be pressurised?

Pressurising the cabin mimics the 14.7 pounds per square (PSI) of pressure that humans are the most accustomed to.


Most commercial aircraft today fly at 30,000 – 40,000 feet, and due to the high altitude, the air is much thinner and oxygen levels are much lower than at sea level. At that altitude and above, the atmospheric pressure drops to less than 4.0 PSI, which would cause significant breathing difficulties for the aircrew, passengers and even live cargo such as racehorses on board.


Therefore, cabin pressurisation is crucial to ensure a safe and comfortable environment for aircrew, passengers and even cargo.


Risk of cabin pressurisation


Despite being crucial to flight operations, cabin pressurisation has its own risks too. The main risk of cabin pressurisation is that the pressure in the cabin could cause structural damage to the aircraft in the long-run which could risk causing a blowout.


What is depressurisation?

Depressurisation, also called decompression, is the reduction of atmospheric pressure inside a contained space such as the cabin of a pressurised aircraft. Pressurised commercial aircraft can suffer from 2 types of decompression, the first being rapid depressurisation, a form of depressurisation that occurs at a rate greater than 7000ft/min and is normally associated with a loud “bang” and a sudden fogging of the cabin air.


In rapid depressurisation, hypoxia kicks in quickly and flight crew will need to descend the plane to a certain altitude for aircrew and passengers to breath normally.


The second type of decompression that can be faced by commercial aircraft will be gradual decompression. It is harder to recognise a subtle decompression as the symptoms will appear slowly.


What causes depressurisation

Failure of pressure control system


The most common cause of pressurisation system failures is the malfunction of the relevant control system. This can be a result of the failure of the outflow valves that maintain cabin altitude at the desirable level.

Reduced cabin air inflow


Depressurisation events can be attributed to air inflow failure. Typical inhibitors of fresh cabin air inflow include unserviceable components in the air-conditioning system or the malfunction of an engine or compressor.

Structural failure


Aircraft structural failures that can lead to depressurisation includes the impaired sealing of a door or window, cracked windows etc.


What will the flight crew do?


When the flight crew notices that the aircraft is experiencing a pressurisation problem or a depressurisation, they will conduct a series of emergency procedures like a rapid descent to 10,000 feet, an altitude where aircrew and passengers can breathe normally, or the lowest safe altitude that the terrain around permits.


As the aircraft oxygen supply is finite, it is important to carry out a rapid descent to reduce the risk of injury to all persons on board. A rapid descent also minimises the time passengers and crew are exposed to cold temperatures and minimises the risk of decompression sickness.


After descending to a safe altitude, the crew will then decide whether it is in the best interest of the aircraft and persons on board to continue the flight or a diversion is required and will advise when it is safe for all persons on board to remove their oxygen masks.


If depressurisation takes place during the flight such as a window breaking or emergency door opening, everything inside the aircraft could be sucked out as the pressure attempts to equalise. As depressurisation occurs, the air molecules move further from each other quickly, resulting in a rapid decrease in oxygen levels, causing breathing difficulties for aircrew and passengers.


As the level of oxygen received by the brain drops, hypoxia, a medical condition where the brain doesn’t receive enough oxygen, will kick in. Hypoxia can affect a human’s decision making and functioning during rapid depressurisation in as fast as 8 seconds. Within 30 seconds, passengers would be too impaired to complete even a simple task such as putting on the oxygen mask.


Also, since a person can be sucked out of the aircraft, the blunt trauma the body experiences at such a high altitude and speed can seriously injure the person and can be fatal too.



What could happen to the persons on board a depressurised aircraft?


Loss of cabin pressure in a pressurised aircraft exposes passengers and crew to a high-altitude environment with an extremely low temperature and lower atmospheric pressure with less oxygen. The most common problems associated with being directly exposed to the atmosphere at high altitudes are hypoxia, hypothermia and barotrauma.



What does the human body need to survive?


Oxygen


Atmospheric air only contains around 21 percent oxygen; however, it is a key component of the chemical reactions that keeps the body alive, including the reactions that produce Adenosine triphosphate (ATP). Adenosine triphosphate is the energy-carrying molecule found in the cells of all living things and human brain cells are especially sensitive to lack of oxygen because of its requirement for a high and steady production of ATP. Brain damage is likely within five minutes without oxygen and death will most likely occur within 10 minutes.


Temperature


News has shown athletes who died of heart stroke, or hikers who died of prolonged exposures to low- temperature environments. Such deaths occur due to as temperature sensitive chemical reactions cannot take place as one’s body isn’t within the range of temperatures. This is because when one’s temperature rises well above or drops alarmingly low, certain proteins (enzymes) that facilitate chemical reactions lose their normal structure and their ability to function and metabolism’s chemical reactions hence cannot proceed.

With that being said, one’s body can still react effectively to short-term exposure to heat or cold. One of the body’s first responses to heat is through the process of perspiration. As one’s sweat evaporates from the skin, it removes some thermal energy from the body resulting in a drop in body temperature. Not surprisingly, the process of perspiration is less effective in a humid environment as the air is already saturated with water therefore, the perspiration on the skin’s surface is not able to evaporate, and internal body temperature can get dangerously high.

The body reacts to short-term exposure to the cold through shivering, which is random muscle movement that helps the body to generate heat. Another response is increased breakdown of stored energy to generate heat. When that energy reserve is depleted, however, as the body’s core temperature begins to drop significantly, red blood cells will lose their ability to give up oxygen, denying the brain of the critical component of ATP production.


This lack of oxygen can result in confusion, lethargy, and eventual loss of consciousness and death. The body responds to low-temperature environments by reducing blood circulation to the extremities, the hands and feet, in order to prevent blood from cooling there so that the body’s core can stay warm. Even when core body temperature remains stable, tissues exposed to severe cold can develop frostbite when blood flow to the extremities has been reduced by a significant amount. This form of tissue damage can be permanent and lead to gangrene which requires amputation of the affected region.


Atmospheric pressure


Atmospheric pressure is pressure exerted by the mixture of gases such as nitrogen and oxygen in the Earth’s atmosphere. Although one may not perceive it, atmospheric pressure is constantly pressing down on one’s body. Atmospheric pressure keeps gases within one’s body, such as the gaseous nitrogen in body fluids, dissolved.


If rapid depressurisation occurs, one will go from a situation of normal pressure to one of very low pressure, resulting in an increase in pressure of the nitrogen gas in one’s blood. Therefore, the nitrogen gas in one’s blood will expand and form bubbles that could block blood vessels and even cause cells to break apart.


Atmospheric pressure does not only keep blood gases dissolved, but also affects one’s ability to breathe. The ability to take in oxygen and release carbon dioxide also depends on a precise atmospheric pressure. Altitude sickness occurs as high-altitude atmosphere exerts less pressure, reducing the exchange of these gases, resulting in shortness of breath, confusion, headache etc.


A loss of atmospheric pressure due to high altitudes or a loss of cabin pressure can lead to hypoxia and barotrauma that can severely affect an individual in flight.



What will happen to the human body during depressurisation?


Hypoxia


Blood is the body’s hyper-efficient transportation system and is dealt in two primary commodities: nutrients and oxygen. Organs and muscles require both to operate and hence a deficiency of either nutrients or oxygen can lead to health issues.


Hypoxia and Hypoxemia both concern the body’s oxygen levels. Hypoxemia refers to low oxygen content in the blood, whereas hypoxia means low oxygen supply in body tissues. Hypoxemia is closely related to Hypoxia since low oxygen concentration in the blood tend to affect oxygen delivery to the tissues.


When an aircraft depressurises, air escapes the cabin, resulting in a drop in oxygen levels in the cabin. As the oxygen levels decrease, individuals in the cabin will receive an insufficient supply of oxygen, which will lead to hypoxia.


Symptoms of Hypoxia


The common symptoms of hypoxia include the following:

  • Shortness of breath

  • Coughing

  • Wheezing

  • Increase in heart rate

  • Headache

  • Skin discoloration

  • Confusion

  • Difficulty speaking

  • Fainting

  • Temporary memory loss

  • Difficulty in moving


Complications

Hypoxia can lead to a condition called hypercapnia and it occurs when the lungs retain too much carbon dioxide due to breathing difficulties.


When one isn’t able to breathe in, it’s likely one cant be able to breathe out as he should and will elevate one’s carbon dioxide levels which can be deadly. Also, as one can’t receive sufficient oxygen, there will be damage to vital organs such as the heart and the brain which can potentially be fatal.




Hypothermia

Hypothermia is a medical condition that occurs when one’s body loses heat faster than it can produce heat, resulting in a dangerously low body temperature. Normal body temperature is around 37 degrees Celsius (98.6 F) and hypothermia reduces one’s body temperature to lower than 35 degrees Celsius (95 F).

When one’s body temperature drops, the heart, nervous system and other organs would not be able to function normally. If untreated, hypothermia can lead to a complete failure of one’s heart and respiratory system which results in death.

Hypothermia is often caused by exposure to cold weather or immersion in cold water. Primary treatments for the condition is to warm the body back to a normal temperature.

When depressurisation occurs due to a hole in the aircraft, temperatures will begin to drop to dangerously low levels due to the rapid amount of cold wind gushing into the aircraft cabin. As temperatures dip to lower levels, the human body will not be able to produce sufficient heat to react to the environment and hence hypothermia will kick in.


Symptoms of Hypothermia


There are many symptoms of hypothermia and the most common symptom is shivering as it is the body’s automatic defence against cold temperature – an attempt to warm itself.

Signs and symptoms of hypothermia include:

  • Shivering

  • Slurred speech or mumbling

  • Slow, shallow breathing

  • Weak pulse

  • Clumsiness/ lack of coordination

  • Drowsiness or very low energy

  • Confusion or memory loss

  • Loss of consciousness

  • Bright red, cold skin for infants

One with hypothermia isn’t usually aware of his or her condition as the symptoms typically begin gradually. Also, the confused thinking associated with hypothermia prevents self-awareness which can lead to risk-taking behaviour.


Complications

People who develop hypothermia because of exposure to cold weather or cold water are also vulnerable to other cold-related injuries, including:

  • Freezing of body tissues (frostbite)

  • Decay and death of tissue resulting from an interruption in blood flow (gangrene)



Barotrauma


Barotrauma is a tissue injury caused by pressure changes, which compresses or expands gas contained in various body structures like the lung.

As the increase in pressure outside the body is transmitted equally throughout the blood and body tissues, which do not compress as they are made of liquid. Thus, the legs for example, do not fell as squeezed as water pressure increases. However, gases such as the air inside the lungs or sinuses continues to compress or expand as outside pressure increases or decreases. This compression and expansion can result in pain and body tissues damage.

Barotrauma most often affects one’s ears but barotrauma affecting one’s lungs is the most serious. Risk of barotrauma is increased by conditions that can keep air from freely flowing between spaces such as blocking of an Eustachian tube.


In a pressurised aircraft, the cabin pressure matches the pressure in one’s body and hence no expansion or compression of body tissues take place. However, when depressurisation of the aircraft occurs, the cabin pressure will be lower than the body’s internal pressure, which will cause the body tissues to expand in an attempt to match the cabin pressure. If the pressure difference is too high, the body will be damaged by the expansion of tissues.

Types of Barotrauma

The different types of barotrauma include:

  • Pulmonary barotrauma

  • Mask barotrauma

  • Ear barotrauma

  • Sinus barotrauma

  • Dental barotrauma

  • Eye barotrauma

  • Gastrointestinal tract barotrauma

What are the symptoms of Barotrauma?

Ear barotrauma is the most common barotrauma experienced by travellers and it has the following symptoms:

  • Ear pain

  • Sensation that the ears are stuffed

  • A need to “pop” the ears by swallowing, yawning or chewing gum.

More severe signs can include:

  • Extreme pain in the ear

  • Dizziness (Vertigo)

  • Bleeding or fluid coming from the ear, which indicates a possible ruptured eardrum.

  • Hearing loss

Complications


Ear barotrauma typically isn’t serious and responds to self-care. Long-term complications may occur when the condition is serious or prolonged or if there is damage to the middle or inner ear structures. Rare complications include:

  • Permanent hearing loss

  • Ongoing tinnitus

Prevention

Some tips to prevent ear barotrauma are as follows:

Yawn and swallow during ascent and descent

These activate the muscles that open your Eustachian tubes. One can suck on candy or chew gum to help you swallow.


Use the Valsalva manoeuvre during ascent and descent

Gently blow, as if blowing your nose, while pinching your nostrils and keeping your mouth closed. Repeat several times, especially during descent, to equalise the pressure between your ears and the aircraft cabin.


Don't sleep during takeoffs and landings

If you're awake during ascents and descents, you can do the necessary self-care techniques when you feel pressure in your ears.


Reconsider travel plans

If possible, don't fly when you have a cold, a sinus infection, nasal congestion or an ear infection. If you've recently had ear surgery, talk to your doctor about when it's safe to travel.


Use an over-the-counter nasal spray

If you have nasal congestion, use a nasal spray about 30 minutes to an hour before takeoff and landing. Avoid overuse, however, because nasal sprays taken over three to four days can increase congestion.


Use decongestant pills cautiously

Decongestants taken by mouth might help if taken 30 minutes to an hour before an aircraft flight. However, if you have heart disease, a heart rhythm disorder or high blood pressure or you're pregnant, avoid taking an oral decongestant.


Take allergy medication

If you have allergies, take your medication about an hour before your flight.


Try filtered earplugs

These earplugs slowly equalise the pressure against your eardrum during ascents and descents. You can purchase these at drugstores, airport gift shops or a hearing clinic. However, you'll still need to yawn and swallow to relieve pressure.


If one is prone to severe ear barotrauma and must fly often or if he is having hyperbaric oxygen therapy to heal wounds, the doctor might surgically place tubes in one’s eardrums to aid fluid drainage, ventilate one’s middle ear, and equalise the pressure between one’s outer and middle ear.



Incidents


Aircraft windows has cracked and resulted in multiple blowouts before.


An example would be Southwest airlines flight 1380, where a window broke because of cowl fragments damaging the fuselage. In that incident, a lady was sucked out of the window and took 4 people to pull her back in while the pilots initiated a rapid descent to match a pressure that is comfortable for humans. The medical examiner in Philadelphia concluded that the lady died because of blunt trauma to her head, neck and torso.

Although these occurrences do happen, it is still an extremely rare incident which affects less than 1% of all flights worldwide. So the next time you decide to choose a window seat, you can rest assure and enjoy the scenery of the outside.



To recap, the aircraft are pressurised to mimic the breathing environment that humans are accustomed to so as to ensure the safety and comfort of the pilots, crew members and passengers. In the event of depressurisation, conditions such as hypoxia, hypothermia and barotrauma will quickly set in. Therefore, the flight crew will need to be quick in conducting a series of emergency procedures such as rapid descent before these adverse conditions have the potential to cause permanent damage.



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