Steve, factor 50 is the norm here here - just found the following quotes, looks like 30 & 50 aren't all that different.

“Australia has one of the highest rates of skin cancer in the world, so the Australian government has the strictest requirements for sunscreen ... The highest SPF for sunscreen available in Australia is SPF50+. The SPF number is only a guide to a sunscreen's protection. In laboratory conditions, when used as directed, SPF30 sunscreen filters 96.7% of UV radiation and SPF50 filters 98%. Both provide excellent protection if they are applied properly" ...

I've been "lucky" enough to get almost migraine-level headaches from sun & glare for most of my life, so in avoiding the sun, I've also avoided the skin cancers my sun-loving friend & our generation & previous generations have. She is only 3 years older than me, but her skin is badly sun damaged, like many older men & women who grew up in the days before strong sun protection. My father loved fishing & skin cancer eventually killed him.