What are some of the options on securing a casement window in the partial open position [maybe 2-4"]to allow ventilation? Thanks!
Is this for windows you already have (after market devices) or windows you are looking to purchase?
If new windows, consider tilt and turn windows.
They make what are called "sash limiters" which do just what your looking for. They use them all the time commercially i schools and apartment buildings.
This would be for windows that we already have.
They can still be gotten and retrofitted onto your window. It would make it easier if you knew the brand of window but most casement operators are made by a company called Truth Hardware so a good window hardware supplier should be able to get you what you need.
Check with the manufacturer of your windows. I am sure they have something like millworkman mentioned called a sash limiter. It is code in some states to prevent small children from falling out windows.
You can also search for "anti-fall device".