Well, it depends upon how big your batch is, how large your ale pail is, what yeast strain being used and the worts original gravity.
Size: 5.0 - 5.5 gallon batches in my 7.5 gallon bucket have worked just fine for me.
Yeast: Some strains are known for hardcore fermentation with huge krausens and others hardly make krausen. Manufacturer's websites will have descriptions of each strain.
Gravity: A strong beer (especially with a hard-fermenting yeast strain) will typically have a higher krausen.
Oxygen: I don't know so much if it will make fermentation appear more active but I believe it will speed up the first stage of their life-cycle (reproduction, an aerobic process.)
If you're worried (or paranoid
) you can attach a blow-off tube with a 3-piece airlock and a 3/8" ID racking hose. Example:
(not my pic)
I hope that helped