Post History

When I deep-fried food fairly routinely, I had to keep to three "rules" on top of whatever common sense told me to do.

First, always place items into the oil so that they fall *away from you*.  If you let it go too quickly, if an air pocket forms, or anything else, you want that splatter pushed someplace where you won't be.

Second, you already know this, but make sure everything is dry on the outside.  If the surface is damp, you're going to get steam, which will pop and splatter the oil.  Part of this, though, is getting the oil hot enough to cook the exterior quickly, not overcrowding, and letting the temperature come back up between batches, because if you don't, the lower-temperature oil will give the *interior* time to cook, releasing steam through the not-yet-fried surface.

(In the case of donuts, maybe letting the dough rest for a while, so that the flour absorbs the water, would help.)

Third, let things come up to room temperature before frying.  Dropping something cold into hot oil will almost certainly splatter, though I admittedly never looked up whether this is a thermodynamics problem (some oil rapidly changing volume next to unchanged oil) or a moisture problem (condescension from the cold item).

You also probably want some air-space between the oil and the rim of the pot to contain some inevitable splatter.  In my experience, that's the real value of the cheap frying appliances:  They have a marking that tells you not to fill past it.  And worst-case, I've heard (never tried, never seen) that some people will lay the uncooked donuts out on scraps of parchment paper, and slide those in as a unit, making it a little easier to get into the oil safely.  It sounds like the paper pulls away like it typically does in baking.