Bottle Rocket Cold Weather Explosion

I was wondering if anyone has noticed bottle rockets exploding more frequently in cold weather. I have launched more than 100 different rockets (80 in a single two-hour period) with a home built CO2-based pneumatic tiggered launching system. Most of the rockets I have launched have been built by kids ranging in age from 9 to 13. Most were launched between 100psi and 120psi and until now none have ever exploded. This past week, after a successful afternoon of launches, the last two rockets exploded on the launch pad -- each with a great big boom -- at 125psi and 120psi respectively. It was by far the coldest day I have ever launched with the temperature dropping below 40 by the time we left the field. The two succesive explosions and the cold weather seemed like too much of a coincidence. I was just wondering if anyone else has had similar experiences.
On a related note, the noise of the explosions were not as bad as I had been led to believe, and I am fairly sensitive to loud noises. My launch and fill hoses are 25' so we were a reasonable distance from the rockets.
Sam

On 3 Dec 2005 18:52:24 -0800, " snipped-for-privacy@machinescience.org"
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Hmmm. What, exactly, would "cold" be? Just wondering. I would suspect that the bottles would become more brittle, and less tolerant to expansion as the temperature drops.
Really, you should leave those dangerous, exploding water rockets alone, and use APCP reloadable motors. I have launched rockets with APCP motors in temperatures as low as 10 degrees F with results no different than if they were launched at 80 degrees F.[1]
<vbg>
No problems with BP motors at low temps either...
tah
[1] I could've flown at temps even lower than that, but hey, I'm getting old, and it's difficult to get an ignitor threaded through a motor nozzle when you can't feel your hands... ;)

Bottle rocket bursting temperature seems to be somewhere in the mid to lower forties F.
The APCP motors sound interesting, but what is the point of launching a rocket if there is not at least some chance that it will explode on the launch pad!
Sam
snipped-for-privacy@weinerboy.org wrote:
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On 8 Dec 2005 07:23:34 -0800, " snipped-for-privacy@machinescience.org"
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Hmmm.. Well, if it's a large scale model that took many months to build that would be a bad thing. Also, if you've got several hundred dollars worth of electronics onboard, that'd be a bad thing too.
So, was it in the mid to lower 40's when you had your, um, "anomoly"?
<g>
tah

" snipped-for-privacy@machinescience.org" wrote:
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I get your point, but that is in fact the case for AP motors, BP motors, hybrid motors and everything else we do. The thought that if everything doesn't go right - that an improperly inserted ignitor, incorrectly assembled motor, poorly packed chute, unarmed ejection charge, clay covered nozzle, or incorrectly configured altimeter - will cause your rocket to fail, perhaps spectacularly right on the pad - is what compels us to keep coming back again and again tempting fate with our $500 paint jobs and expensive electronics.
If all it ever does is go woosh, without fear of it going bang, zip or thud, then there ain't much thrill in it :)
Doug

Plastic does get more brittle at lower temperatures. PET bottles don't expand well in the cold, so they tend to burst instead of deforming.
Mark Simpson