For complicated reasons our hero's blimp in the Venus atmosphere at an altitude of 50 km gets a tear in it and sunlight floods inside (there is no gondola, the blimp is a semi-ellipsoid of breathable air), and he is in an area of direct sunlight for half an hour. He doesn't have to worry about air for a while as the blimp is huge and there is little pressure difference between the exterior and interior at that altitude. Does venus's atmosphere above 50km have a similar UV blocking effect to the ozone layer? Will he get badly sunburnt?
No sunburn risk.
It's very dark at 50km.
this article tells us the opaque clouds extend up to 60km.
The atmosphere of Venus absorbs UVs.
In addition, if it's important for your character to get a sunburn you'll need to raise your blimp up quite a bit.
Figure 4 in this paper would lead one to believe that the SO2 in the upper Venusian atmosphere does a poorer job of blocking the higher energy UV rays than Ozone on a per molecule basis. It's hard to say exactly how much SO2 there is compared to earth's Ozone layer though. But there is a thin ozone layer at Venus, and at 50 km, you're below the upper cloud deck so the would block most of the sunlight anyway. You would also need protection from the sulfuric acid droplets in any clouds you encounter, which is probably a bigger hazard than sun burn. So if you need a Tyvek suit anyway, it'll block the UV if you intended to be outside. Otherwise, your larger hazard may be hoping you don't drift into a cloud.