I find it highly doubtful that the designers of artillery through history, were giving a great deal of thought to the dangers posed to gunners by solids being blown out the vents of their creations. This may not be due to any lack of insight (or worse yet cruelty) on their part, because it's very possible that they simply assumed that gun crews would figure out where to position themselves when operating their pieces, so as to almost completely avoid those perils.
Ok, I'm having a little fun, but even as late as the time frame of our Civil War; if someone could show me any evidence of Dahlgren, Parrott, Griffen, Brooke, Rodman etc., concerning themselves with this hazardous phenomena, then I'd be grateful to hear about it (also very surprised). The first instance that I know of any gun designer including a feature to protect against this occurence, is the screw on shield that Joseph Whitworth used on some of his breech loading cannon; and that shield was meant to protect against friction primers being blown straight back out of inline vents.