Breaking car windows underwater

If crossing a river in a car in anything but ideal conditions, or worse if you get caught in a flood, you would be insane not to open a window as the situation can quickly become life threatening with the car being swept into deep water after which it is usually impossible to open doors and windows.

To put it simply, if you get into deep water and have not opened a window, you will most likely drown, and whilst there are a number of manufacturers pushing tools they claim will break windows, I’ve seen no report that doesn’t appear to have been placed by the manufacturers to substantiate that they are any help whatsoever.

But whilst the key to escaping a vehicle in deep water is opening a window ASAP, what would be the best strategy to escape if you were caught in a sinking car?

First the scam

Like the global warming scam, I think money had distorted to information available on cars in water. And like the global warming scam, the promotion of car window tool/ seat belt cutter tool works by a similar slight of hand. Like CO2 warming, it is a fact that several hundred people die each other by drowning in cars in the US. It is also a fact that some window break tools can break windows when operated by an experienced person promoting the tool on a video.

However, just as the climate cult fail to mention that CO2 can’t cause all their warming and that most climate change is clearly natural, so the rescue tool companies also fail to mention the key information that in almost all instances where a car is so severely damaged that a seat belt needs cutting, the victim is so seriously injured that they could not operate any seat belt cutting tool. And likewise, most people who end up in water, do so as a result of a serious road accident,  usually at night and more often than not when they are drunk. So, it is likely that they are too seriously injured and/or so stunned and/or won’t be able to find any rescue tool or even remember they had one.

The way to save lives, is not to buy another gadget designed to use scare-tactics to con gullible motorists, but to avoid accidents and particularly drink driving accidents near water.

So, this is not an article about “how to escape a sinking car”. This is instead an article about the properties of car class

Breaking car class

Let us suppose, that you had locked your car keys in the car, and for some reason you desperately had to get in. What would be the most obvious way in? A hammer? This video shows how easy that approach is (bearing in mind smaller windows are generally easier to break).

But … I hear you saying … a woman and kids were bound to fail. So here is a video of an adult man (ok a reporter) again using a hammer (in almost ideal conditions).

Or what about a thief with a brick:

How about kicking it:

Cops? Surely a cop will know how to break a car window?

The reality is that even in ideal conditions, most people using everyday objects fail to break car windows in good conditions on camera.

However, car thieves have long known that centre punches do usually work. Why? The reason centre punches work and not bricks or hammers appears to be that the key to breaking glass is the speed of the impact and not the weight of the hammer. So a small “nail” like structure in the centre punch moving at a very high speed breaks glass whereas a slowly moving heavy object fails. So, yes, tools designed on this “centre” punch technology can break glass, but not all glass!!

Rescue tools do not work on laminated glass!

In the car industry there are two main categories of glass: tempered glass which is heat treated so that when it breaks, it shatters into thousands of small pieces, these are still sharp, but their small size makes them much less likely to injure someone, and laminated glass, which is glass with a plastic sheet at the core. These do crack, but the crack does not break the plastic, so the glass stays in one piece. This glass is used where the vehicle designers want to stop occupants from being flung out. That used to be the front windscreen, but laminated glass is increasingly being used in side windows.

The result is that rescue tools do not fully break the glass and the occupants are still trapped even after their use!

And as bad, some rescue tools might look up to the job, but they are made of soft material like aluminium which doesn’t break glass:

Breaking a window when the car is under water

Unfortunately, the position gets much worse if the car is under water and you are trying to escape for a number of reasons.

First the situational issues:

  1. The time is strictly limited. Some cars will sink within a couple of minutes, but even at best cars remain afloat for perhaps 15minutes.
  2. Most people do not carry hammers or bricks in their cars,
  3. The space within a vehicle is cramped so that, for example, it is difficult for a kick to be effective.
  4. It is likely dark, and darker still if in water, so even in daytime, it will be difficult to see what you are doing (and difficult to find any handy object thrown around the car in the crash)
  5. The car is likely filled with water – so that the water puts a huge drag on any fast movement making hitting less effective (if it wasn’t already ineffective)

Now the physics:

As the car sinks, the water rises up the windows and begins pressing INWARD on the glass. The result of the water is to:

  1. Increase the effective mass of the window, because the water is a large mass at the back which effectively increases the weight or width of the glass
  2. The water acts to cushion and deaden vibration in the glass, therefore making it far harder for the fast impulse “shock waves” to propagate through across the glass
  3. The water is pressing in on the glass such that any outward blow tends to LESSEN the stress on the glass not increase it as we want

This all fits with what I have found from talking & reading accounts from the few people that have tried to use the “rescue” tools when the car is under water. They are designed to break glass and can do so in the dry, but it appears they lose much of their effectiveness when the car window is submerged – which is precisely the situation they are being sold to deal with!

How to get out of a car underwater

The reason I started writing this article, was because I was trying to find any videos showing car window glass breaking when it was underwater (at least on the outside). That I have been unable to find, so I cannot rule out the possibility that car windows can be broken in this situation. Instead the best evidence I have is accounts such as this forum which appears to be from people with first hand experience and which I think is likely impartial. I quote:

ADSNWFLD: Now as for breaking the glass. A spring loaded center punch works, however, if not cleaned and maintained well the punch begins to wear out and become less dependable. By placing your dive knife between the bottom of the window and the weather strip you can get the knife under the glass. When you pull outward the glass will break.

footrat: Shouldn’t a standard spring-loaded punch be the most consistent and safe way, even in the water?

Biofish: You would think so. But with that said, how often does a spring loaded punch fail above water? i know I’ve had that happen more than once. As for the knife drawing psi against the window i like that idea.

fire49: (link to video below)

ADSNWFLD: Sorry haven’t checked in for a while.
I have broken windows twice on incidents using the knife like the woman used the headrest in the video. I have never had it not work.


It appears centre punches can work but they are unreliable (especially if used under water). There is no mention at all of hitting the window by these rescuers. There is an absence of evidence it doesn’t work, but as hitting the window from the inside is reducing the stress on a window with water pressing in, if it is difficult to break normally, I think it will be next to impossible when under water.

So, the only reliable way to escape a car – is one where you are working with the pressure of the water on the outside, which is by using some form of lever at the edge of the window. This works, because the water in the centre is pressing in, and therefore the car window frame is already exerting an outward force. What the lever then does, is to work with the forces that already exist and increase the stress by increasing the outward force in one localised area.

Obviously headrests will not totally break laminated glass, and I have not seen any account of their use with such glass. However, once the glass is broken by using the headrest as a lever, the headrests could be used like a hammer to batter your way through the plastic. Or indeed, brute force such as bracing on the other side and pushing the window out may also work because the plastic will deform and if all else fails – it will eventually fold down.

Why does no one mention headrests when they appear so effective?

A while back, I wrote an article suggesting that many conspiracy theories were intentionally created in order to hide the (boring) truth. So, what do I find when I start looking at whether head rests can be used to escape cars under water? A whole series of articles “debunking” the idea that manufacturers intentionally designed headrests to be used to escape vehicles!!

I find that very odd, because it never occurred to me that manufacturers intended car seat rests to be used this way and indeed, what does it matter if they were designed to be used to escape vehicles? The important question is whether they work!

The simple truth, is that if you can remove the headrest, then they are the only readily “hammer” like object that is present in almost all cars. Furthermore, if they can used as a lever they are the only mechanism that has a potential to work reliably to break windows whether tempered or laminated.

The other obvious truth, is that there is (was?) an enormous market selling these “rescue” tools and I think that has been what has driven much of the interest and “information” on the internet. Some of these tools do work (at least when new) but they are only proven to work in the dry. Others however are just worthless gimmicks for the gullible


If there is even the slightest chance of ending in deep water – open your window as that is the ONLY reliable way to escape

Given that the main time a person is going to use a rescue tool is when they have been in a serious car accident and will be in no fit state to use them, the question of how to escape is realistically a pretty minor one in most instances. And in most instances where people will be able to use any tool, they are far far more likely survive if they open a window than if they get to the stage of having to break a window.

From what I have heard, the centre punch version that was effective (in the dry) is no longer as effective when the car is under water. This I think is because of the cushioning effect of the water at the back. And, the hammer like versions (which most people struggle to make work in the dry) are in my view, far less likely to work when the car is under water because the water is pressing in and hitting them outward just reduces the stress.

To add to the problem, new cars seem to be coming in with laminated side windows. The centre punch versions, might break the glass, but they will not get through the plastic, and whilst the hammer version may be able to break through the plastic, I do not think they will work at all reliably underwater.

So, unless you have a very high risk of going into water such as living in an area with many roads going alongside open water without safety barriers, these rescue tools are in my view about as useful as carrying rescue flares, a portable jetpack or indeed a tin hat in case of meteorite strikes.

In contrast, if you can remove your headrest and push it down between the glass and frame, I’ve no reason to believe it will not break the glass. And if laminated, the headrest can then be used like a hammer to break through the plastic layer.

But there’s a big “if” you can remove the headrest, because it appears to be very difficult if not impossible on some cars. So, that is why I say:

If there is even the slightest chance of ending in deep water – open your window as that is the ONLY reliable way to escape

…. Alternatively …. there is the old approach …

the theory goes, that you sit and wait till the pressure equalises on both side of the door so that you casually open the door and escape. But in reality, you sit and wait till the water reaches above your head and then try to open the door … it will not as it will be several more minutes before the pressure equalises … so you try to open the window. That will again be stuck due to the pressure. So you try to smash it. That will not work because force doesn’t work and the water dampens high speed movement which is needed to break glass. But keep trying! Because it will at least reduce the time it takes for you to drown.

Here is Top gear proving the point.

PART 1 (intro – no action)


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