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#Hothchester strikes back: the “terrorist” windshield threat on Rochester’s highways

The answer to the present controversy over cracked windshields in Rochester may not be nearly so exotic or dangerous as we think.

We’ve been getting bombarded by reports over the last few months, at an ever-increasing rate: another reported incident of suddenly cracking windshields on 390, then 490 then even as far out as 104 in Ontario. Is there some lunatic waiting in the bushes, some wondered, waiting for their moment to do malevolence upon an unsuspecting car? Maybe someone with a near-silent air gun that might elude detection?

To test this particular hypothesis – that a pellet or BB gun might be able to shatter tempered glass – I started looking into the ultimate test case. That turns out to be a British-made pellet gun called the Daystate Air Ranger, a .22 calibre pellet rifle capable of firing at 1020 feet per second. Using the heaviest and therefore most destructive pellet I could find in that calibre, 32 grain, and an online impact force calculator, I came up with the following:

(2mv)/t or (2*0.00208kg*310mps)/1sec = ~1.29N

The tensile strength required by Federal Specification DD-G-1403B, which governs the definition of tempered glass, is 120 to 200N per square millimeter. In other words, while crazier things have happened, it is extremely unlikely that even the most powerful pellet gun will crack a windshield. And weighing in at $2000 for a single gun, it’s safe to say Daysiders are probably not that common in Rochester. Your kid’s Daisy plinker is woefully inadequate to the task, and not likely to be a suspect in this case, at all.

So, when all else fails, the best thing to do is look for the most obvious answer. And that answer is: weather.

Our winter was epic, as we all well know. Those of you who are on Twitter (and why aren’t the rest of you?) will be familiar with the great fun we all had with the #Hothchester hashtag:

Temperatures never seemed to go above zero for a month. Then, after an extraordinarily long, cold early spring, we suddenly shot up into the 80’s and 90’s, with barely a moment’s transition. This kind of weather plays havoc with all kinds of materials, but your car has probably borne the brunt of the abuse, spending all of it’s time out doors in the deep freeze.

And the thing is: tempered glass is very strong, but only because it is inherently unstable. The tempering process involves laying thin layer after thin layer of glass in an ever-thickening mat, in such a way that the tension lines in each layer oppose one another at odd angles. The result is that, since one layer wants to split in a direction directly opposite of another, the faults cancel each other out. In the event that something large enough hits the glass and shatters it, those tension lines will cause the glass to shatter into small, smooth-edged pellets that will only cause minor skin lacerations at best.

However, those tension lines get stressed by the shrinking that happens in extreme cold. Follow that up with the beating sun of an unexpectedly intense summer, and you’ve got a recipe for a whole lot of shattered windshields. Any small stone or nut from an overhanging tree could be enough to cause a crack. In fact, the window may spontaneously crack all on its own, as has been frequently reported in the past. Rest assured that when the crack happens, however it happens, it will be loud

Considering the fact that no one has observed a man by the side of the road; a bullet-shaped hole in a windshield; anything more major than a small crack in the windshield. Considering the fact that we can safely rule out pellet guns as a non-lethal, whisper-quiet means to shatter glass. Considering the fact that cracked windshields rarely make headlines in any other circumstance; that a whole industry is built around repairing minor cracks (Safelite, anyone?). Considering all these facts, it really begins to look like a jumpy police force and an overeager media community are making a very obvious problem into a self-propelled mystery.

By Tommy Belknap

Owner, developer, editor of DragonFlyEye.Net, Tom Belknap is also a freelance journalist for The 585 lifestyle magazine. He lives in the Rochester area with his wife and son.

2 replies on “#Hothchester strikes back: the “terrorist” windshield threat on Rochester’s highways”

Your research is horribly off. You can buy High Powered Air Rifles in NY, for much cheaper than 1000 dollars.

Gammo Rifles around 1000FPS sell for 150-200 Dollars.

On top of that, you can get an air rifle shooting at 1400FPS for under 300. Very easy to obtain and pretty popular brand of air rifles.

So you are looking at a sub 300 Dollar Air rifle capable of shooting a 32 grain pellet at 1400 FPS.

Now what about the speed of the car traveling towards the “shooter?”

Where have you taken that into account?

I don’t believe every car had a windshield broken, most were side or back windows, but just so you are aware, a Pellet Rifle will most definitely break out a side window, and is more than capable of cracking a windshield. How fast do you think a little stone is traveling when it chips and cracks a windshield.

By the way, I agree with you, I don’t believe there is a mad gunman out there shooting people on the highway, but this was a horribly researched article.

I agree with everything here. I came down here (to the comments) specifically to state that the speed of the car was not factored into these “calculations”.

Some of these cracked windshields could be because of flying stones, especially considering the terrible winter left us with destroyed roads. However, I don’t see how a flying stone would hit a rear window, or even a side window. I’ve had loose stones hit my windshield many times, and left small cracks in the glass. A stone flying from the road into a side window is a lot less likely, or even less likely a rear window. especially at 55-65 mph.

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