I'm just curious but how wet does film need to be before the emulsion swells ?

I spent a day photographing the base of waterfalls in the pouring rain.

Continuous heavy rain, very heavy spray shooting out from the base of the waterfall and a soaking mist off the falling column of water

Despite my best efforts, everything in the camera bag (camera, lenses, darkslides,,,,) all got very very wet as the day went on.

I started wondering, how wet (and for how long) does film need to be before it causes the emulsion to swell and affect the sharpness of the image.

The negatives (HP5) are fine, so swelling takes obviously longer than the 10hrs in damp/saturated conditions that I gave them

Thanks

Martin