Several years ago I had propellant gas blowby get to my right eye. I was shooting Turkish surplus in 8 mm, many of the production lots of this stuff were famous for split necks and punctured primers, but some lots were better than others. I was shooting a Yugo Model 48 (Mauser 98K). The Yugo Mausers have an unusually strong and longer firing pin than other Mauser variants, I think it is to deal with the stubborn primers on the 1950's vintage Yugo ammo in 8mm.
The Mauser 98 is overbuilt for safety, 2 gas vents in the bolt, a gas shield at the end of the bolt, and triple lugged. When I fired my bad round, the primer got punctured and the gas came back at me, it all took fractions of a second, but I do remember the grayish green gas coming back like a storm wall and curling around my shooting glasses and hitting me in the right eye. At first I thought I had been blinded, nope, then I thought the gun blew up, no, the primer was only lightly punctured, I had seen worse cases of this before without problems.
Some puncturing of the Turkish ammo cases were so bad that I had to field strip the bolt at the range several times to clean it out from the corrosive primer gas getting into it, I stopped using that ammo. Still it was an experience to get hit in the right eye from the propellant, and lucky to have not been injured. I don't know how much my glasses helped, but I always use eye protection. My old girlfriend got hit in the eye from a brass fragment of a .22 RF shell ejecting from a Ruger Mk-2 pistol, she did not have glasses, it made me a believer to use protection on everything that goes bang.