Why Spark Plugs Are So Good At Breaking Windows

If you frequented your cul-de-sac's wiffle ball league as a kid, you were probably grateful for the strength of the neighborhood cars' windows that your friends occasionally whacked with foul balls. But being that sturdy, those windows would be quite a formidable obstacle if you ever found yourself trapped in a locked vehicle.

Having window-breaking tools available could save your life in an emergency, but breaking car windows is harder than you think, and only getting more difficult as glass techniques evolve. Historically, they've usually been made of tempered glass, which has a granular shatter pattern, but automakers have recently been replacing them with laminated glass panels that are stronger if there's a crash. For breaking through tempered glass, spring-loaded and hammer-style escape tools are commonly recommended (though hammers are difficult to use in an underwater emergency) as opposed to other objects you might find in a car, like the metal rods in your headrest.

Here's where the spark plug is an unlikely hero. Because they're manufactured to endure extreme heat and pressure, spark plugs are hardy, particularly the iridium and platinum varieties. The aluminum oxide ceramic and other materials used to make spark plugs pack energy and density, letting the plugs uniquely concentrate force at a single point. When thrown with enough "oomph," this concentration of force is enough to shatter a car window.

Everything from designated tools to extreme temperatures can cause car windows to shatter, but the ease with which they break depends on the type. Tempered glass is generally breakable with force, and most emergency tools (and spark plugs!) are sufficient for breaking it. Laminated glass is nearly impossible to break with human-applied force.

So does this mean you're just out of luck if you get trapped? Well, not exactly. Most cars still have tempered glass in at least one spot, and knowing your vehicle's glass type can prepare you to respond by rolling a window down as soon as possible should you encounter a water emergency with no breakable glass. But if you find yourself or someone else trapped in a car with tempered glass windows, now you know you can break them with spark plugs to provide escape. 

If you're outside the car, locate a spark plug in the top of the engine's cylinder heads, then remove the AC/DC converter from the plug and break off pieces of the spark plug insulation into smaller pieces. Then simply throw the pieces at the glass with as much force as you can. If you're inside the car, accessing the engine is obviously not an option, but now that you're informed about this trick you know: Keeping a spare spark plug inside your vehicle as an auxiliary emergency tool could save your life!