How Does a Glass Breaker Work?

Recently we’ve been going deep on Rescue Knives. Usually these feature a glass breaker and a strap cutter.

These are great features to have in addition to the blade. But often people ask, do I really need a glass breaker?

They’re surprised to find out that you can’t just use a knife handle to break glass. These tools use specific design and materials that enable them to break glass.

But most people don’t appreciate the value of a glass breaker, because they don’t know how it really works. 

Of course you could just try breaking glass with and without the tool to see the difference. But for those who really want to understand why the glass breaker works, this article is for you.

Rescue Knives, OTFs, Car Escape Tools, and More!

We’ll start with a quick note - glass breakers aren’t just on Rescue Knives. You can find them in lots of places - most often on tools meant for emergency escape from a car.

Several different types of glass breakers exist:

• Emergency Hammers - These are the type features on many vehicle escape tools. They basically serve as a blunt object and require manual force to be effective.
• Spring Loaded Glass Breakers - These less common glass breakers use a spring system to apply more force without requiring manual effort. 
• Tungsten Carbide Glass Breaker Bits - This is the variant most often used on the handle of pocket knives - including OTFs and rescue knives.
• Rare Variants - There are no doubt countless other mechanisms that have been designed to break glass effectively. We’ve even read of gun-powder-driven glass breakers! But you are most likely to run into the first three variants we listed. 

Since it is the type used for pocket knives, we’re going to focus on Tungsten Carbide Glass Breakers. Luckily, of the commonly available glass breakers, these are also the most effective!

Tungsten Carbide Glass Breakers

These are the tiny glass breaker tips on the back of most rescue knives. And if you don’t understand how they work, you probably wouldn’t believe they can really break glass. But the reality is, they can do so quite effectively. 

Breaking glass with one of these is WAY more effective than trying to smash a window with a blunt object - like the handle of a knife that doesn’t have a glass breaker tip.

So how does this work? Two main elements put the physics in favor of these tips when it comes to smashing glass:

• Tungsten carbide is a tough material - much stiffer and much denser than steel. This firmness forces the glass to give way upon contact. 
• The tip is tiny. While you might think at first that a broader surface would break glass easier, the opposite is in fact true. The small surface area of the glass breaker tip means that the glass absorbs all the force in one spot, so it can’t disperse. This concentration of the force means less overall manual effort is required to break the glass.

It’s really as simple as that. Tungsten carbide tips manipulate physics to break glass with relative ease.

While we don’t recommend doing so, if you tested with different objects, you’d find breaking glass with one of these to be much easier than breaking glass with a blunt object.

Other Materials

There are also glass breaker tips that are similar in form to the tungsten carbide tips, but use different materials. This is often due to budgetary reasons. While they may be more or less effective, the physics of these glass breakers is fundamentally the same.

Glass Breakers on Rescue Knives

Because of their simplicity and effectiveness, carbide glass breaker tips are featured often on rescue knives. They are relatively cheap, and take up almost no space.

Glass breakers have the potential to be life saving in an emergency situation. For that reason, we recommend having a pocket knife with a glass breaker - it’s a no brainer.

You’ll find many pocket knives with glass breakers, but the most common are rescue knives and OTF (out the front) automatic knives.