Why Can't Car Doors Open Underwater?

[McRhett]

Because the water pressure is too high. There is air inside the car cabin, and the pressure difference between the inside and outside causes the water to exert a force of up to 150 kilograms on the door, making it impossible to open. When the car cabin is completely filled with water, the pressure difference balances out, and the door can then be opened as easily as it would be in air. When a car is submerged in 1 meter of water, there is approximately one ton of water pressing against the door. Here are some relevant points: 1. Stay Calm: If the door isn’t opened immediately, as more water enters the car, the electrical systems may fail, making it impossible to open the doors or windows. It’s crucial to stay calm and avoid panic. Due to the pressure difference between the inside and outside of the car, opening the door from inside becomes extremely difficult. 2. Use a Safety Hammer: In such situations, use a sharp object inside the car to break the window and escape. A safety hammer is ideal for this purpose. When using a safety hammer, aim for the window that is still above water—usually a side or rear window. Strike the edges or corners of the window glass, not the center. 3. Use a Sturdy Metal Rod: Besides a safety hammer, the two slender, sturdy metal rods from a car headrest can also be used to break the window. A fire extinguisher can also shatter the window, but due to the internal pressure, it may cause secondary injuries and is generally not recommended.

[CassandraMarie]

I remember seeing a news report about a car submerged in water and wondered why the people inside couldn’t get out. Later, I learned that the water pressure is extremely high. When a car falls into water, the outside of the door is completely surrounded by water, and the weight of the water presses down hard on the door, making it impossible to push open with just human strength. Moreover, as the car sinks, the heavier front end usually goes down first, causing the doors to end up underwater. What’s worse, the tightly closed windows prevent air from escaping, creating an imbalance in pressure inside and outside the car. In reality, to escape, you have to wait until the car fills with water to equalize the pressure, making it easier to open the door. The key is not to panic. It’s wise to keep a window breaker in the car or to open the sunroof promptly.

[MacSpencer]

My friend works in rescue operations, and he told me that vehicle submersion scenarios are actually quite complex. First, when the car door is submerged in water, the external water pressure can be several times higher than the internal air pressure, as if a hand is pressing firmly against the door from the outside. Additionally, many people panic and forget to unbuckle their seat belts, which can delay escape opportunities. In reality, car doors are designed to withstand a maximum pushing force of around 300 pounds, but when the water depth exceeds half a meter, the water pressure can reach this level. Moreover, windows cannot be opened by ordinary means because the glass is tempered. The correct approach is to push the door open either the moment the vehicle starts submerging or after the water has completely risen above the seat level.

[VonStephanie]

I remember my physics teacher once explained this phenomenon, which is related to fluid pressure. Water is much heavier than air, so when a car is submerged, the water pressure can seal the door like an entire wall. Additionally, the deformation of metal doors and the car frame plays a role, as they can become jammed after being soaked. More importantly, the pressure difference caused by the water level is significant—every additional meter of depth outside the car adds one more atmosphere of pressure, making it nearly impossible for a person to exert enough force underwater. To escape, you should seize two critical moments: right after the car first submerges, when the water hasn’t fully covered the lower part of the door, or after the car is completely filled with water, when the internal and external pressures equalize. This explains why scenes in movies where people simply push the door open to escape are unrealistic.