I work in an office with 30 people. In the past two days three of my co-workers windshields have cracked without being struck by anything and someone who works just a couple buildings down had hers crack today. That’s a lot of cracked windshields in 48 hours. The weather is pretty typical for November in NH: a lot of rain in the past week but not today and temps pinballing between the 30s and low 50s.
Two of the four windshields cracked across the bottom making those two owners wonder if the heat vents blowing on them was a contributing factor, but the other two cracked from an upper corner out.
I can’t speak to what the 4th person did, but the three I work with didn’t do anything abusive like pouring hot water onto them to melt frost or pound on them…
Any idea if there’s a likely common cause or if it’s just four rapidly occurring coincidences? I don’t want to be #5!
This makes me think that it’s simple mechanical stress caused by thermal expansion and contraction. It’s the same basic concept as your abusive situation of dumping hot water on a cold windshield, only not as dramatic. But all you need is a small crack to start forming, maybe from a small chip or crack that was already present, and if you get enough of a temperature differential, the thermal expansion stresses will do the rest.
Does your building have any large reflective surfaces that might be focusing sunlight onto car windows and exacerbating the problem?
ETA: The heat vents blowing warm air onto cold windows could very well have contributed to some of the cracks.
Don’t discount the possibility that it’s just a random thing, perhaps coupled with people suddenly noticing cracks, or talking more about them, primed by already hearing such talk. Something like this happened with the famous ‘windshield pitting’ epidemic in Seattle: Seattle windshield pitting epidemic - Wikipedia
Confirmation bias. I’ll bet if you asked enough questions you’d find other pockets off odd coincidental events in those same 48 hours. Maybe curling irons breaking, people spilling soup on themselves, previously good dogs peeing on the carpet. Look at background noise closely enough and you’ll find patterns.
I’m with kayaker that coincidence and confirmation bias are all we need to explain this. But let me ask another question: is there a lot of new road construction nearby? This can mean lots of pebbles in the road to chip glass and lots of potholes and rough transitions to twist cars.
Sidenote: I was going to say that the windshields in modern cars are an important structural element and are subject to twisting and bending forces from construction bumps. However, I can’t find any reputable sources to support that windshields contribute to structural rigidity. Everything I see on the importance of unbroken windshield glass comes from windshield installers. Anyone know if it’s true?
I used to live in northern Canada, and when the outside temp got to the -30 range (Take your pick, F or C) it was not uncommon a few decades ago for the heat stress to crack the windshield within a few inches of the bottom. You turn up the heat to stay warm and prevent windshield condensation as the snow on your boots melt. The windshields would have extremely heat blowing on one side and a 60mph blast of -30 air on the other side. Half the vehicles would have horizontal cracks across the bottom of the windshield. The problem had been happening a lot less in the last 20 years or so. I guess the question is - did your area have a batch of badly annealed windshields (unlikely unless it’s all the same make of car)? Are there different, less stringent glass fabrication standards for the USA? Did you have a bout of extreme cold? Are these older cars? Or perhaps it’s jus coincidence.
This is common in the Mid-South (for lack of a better geographical term). A small crack on the glass gets stressed by temperature changes then suddenly has a massive fracture. Said small crack probably came from road debris which was unnoticed because it was at the peripheral of the glass. Possibly ignored unintentionally as “what was the scary noise I don’t see anything” during even a short drive.
This happens regardless of manufacturing issues, automotive brands, cheese preferences, local squirrel populations, etc.
Small chips or star-type dings in windshields often become the starting points of long cracks in cold weather when the defroster heat kicks in. I’ve actually watched it happen.
I had a windshield crack while washing my pickup truck in summer. It was in the upper 90’s and I started squirting the vehicle with water and I heard a pop! Suddenly there was a horizontal crack on the drivers side about half way up. Truck was parked in the direct sun so I guess windshield was pretty hot and might have already had a small fissure and when the cold water hit it it cracked.