i think beyond a certain temp it goes to liquid i dont hink it ever goes to a solid i believe water is one of the only ones that can change from gas to liquid to solid. but co2 is shipped around and stored in its liquid phase.
when you get it into your tank it is partly in liquid phase and gas phase (thats why you need a anti siphon tank so you donnt get liquid co2 in your tank also why it is almost nessesary to have a exp. x chamber if you want the most efficiany) now when it heats up outside the liquid in the tank goes to gas which in turm increases your presure which is why you have those pressure spikes and chrono spikes also why you may have to cut your main spring so your valve doesn't stay open for as long.
yet? ok so safe temp you shouldn't have to worry about that unless your worrying about buying burst disks. but you shoud be safe the tank you use has a safety feature on it known as a burst disk. when outsude temps rise and your co2 in your tank turns into gas the pressure rises increasing the chances of your tank exploding. well the predsesores of co2 tank design bult something called a burst disk. it is a little copper disk that is design to relieve the pressure of the tank once it gets to a certain preassure. a pressure in which it becomes unsafe to use that tank. what will happen is a co2 cloud will come out of the crease between the valve and the tank after that it will get a whole crap load of frost (DONT TOUCH IT YOU COULD GET FROSTBITE) it is extremely cold pick it up with towel and bring it to your local shop and have them replace the burst disk. but you will not be able to use the tank until the burst disk gets replaced.
to prevent this dont leave your tank and gun out in direct sunlight. keep it under a towel or shirt. also try not to keep it un your gun (pressurized) because the micro or macro line you use has a lower opperating ppressure than the tank so it will blow sending you tank and gun to the ground. other than that i think thats about it reply back if you have any questions.
but i just read what you asked and i just wrote this for nothing
i guess i just informed you on tank safety lucky you huh?
uGh back to my little hole