Low-temperature hobby rocketry I work with a lot of Boy Scouts who want to complete the Space Exploration merit badge.  It's a great program, and one of the coolest requirements is building, launching, and recovering a model rocket.  Unfortunately, my Scouts are in the city and finding a location to launch rockets is ... well ... tricky.
In the past, we'd drive out to the countryside and use either a park or a friendly farm to launch the rockets off.  It never used to be a big deal ... but someone got it into their head recently that these rockets pose a significant fire hazard (despite over a decade of fun without a single problem).
The biggest argument I've heard against the rockets is the nature of the engine.  Basically, model rocket engines are black powder-based.  A small electric igniter lights the engine and it produces a lot of heat and smoke to propel the rocket.
The parks and farms that have since banned us from launching rockets finally conceded that, if I could find a way to launch rockets without burning anything, they'd let me bring the Scouts back.
Every reference I can find to "cold rocket engines" seems to refer to older 1970s freon-based engines.  I don't want to go that route, but I'm looking for some ideas for cold or low-temperature rocket engines.  Even if it's something I'd have to build myself ...
Any ideas or suggestions?
 A: I found this water rocket video, which appears to attain sufficient altitude. The group that makes them has a nice website and tutorial.
Perhaps launching black powder based rockets from a boat might be an alternative solution. 
A: EAMann,
I know this is a physics site, and you are looking for a physics answer; but I noticed that you are in Portland, Oregon.  It seems amazing to me that you can not find a site reasonably close.
If nothing is closer, it seems to me that one of your beautiful beaches would make a nice launch site.  That is (IIRC) more than an hour away, but you could combine it with a camping trip.
My high school biology professor used to take us out to the Gingko petrified forest in eastern WA.  Along the way we would stop and jump down the sand dunes on the WA side of the Columbia River, not too far (a few hours) from where you are. 
There is a lot of desert in eastern WA and eastern OR.  Can't imagine not being able to find a launch site out there.  The other thing I would do is network through your own organization, BSA, to find out where other nearby scout troops are going.
I hope this helps.
A: You really need to look into Water Rockets as the ideal solution to your problem. In addition to being cold and the opposite of flame/fire, they are dirt cheap and very easy to make. The coolest thing about them is that they can be a lot more powerful than the little pyro rockets you have been using, so you can put some really impressive payloads onboard and conduct real science you would otherwise be unable to do (unless you have deep pockets and special high power certifications for pyro rockets).
I found this cool website where these guys show how to make different water rockets, and different launchers for them. Some of their experiments are interesting. They load multiple cameras on their rockets and they even have free instructions for making some kind of servo motorized parachute ejection system they invented. These guys seem to be like the NASA of Water Rockets, and hold the world record for altitude (over 2000 feet!)
Water rockets have come a long way since those silly plastic pump toys!
A: This doesn't answer the question, but it does solve the problem. Do it on the 4th of July along side your neighbors who (I assume) will also be launching bottle rockets etc. Here in South Carolina it sounds like a war zone on the 4th from about 8-12pm. It that doesn't work, maybe ask to do it before/after a fireworks display?
A: You can also take a look at the line of model rockets called the Micro Maxx series and similar. They are made by the Model Aerospace Company, and have a max launch height of 80 feet. These could be launched in just about any large, empty parking lot or baseball field (Barring local ordinances of course).
