If the slide is no more than 4 feet high, the exit area should be no more than 11 inches above the protective surfacing, and when the slide is more than 4 feet high, the exit area should be between 7 and 15 inches above the protective surfacing.
As for the world's tallest waterslide, it sits a continent away in Barra Do Pirai, Brazil, near Rio de Janeiro at the Aldeia das Aguas Park Resort. Named Kilimanjaro, after the world's largest free-standing mountain, the waterslide is 164 feet tall, according to the Water Slide Database.
All riders must ride feet first while lying on their backs with arms crossed across their chest. Do not go down the slide head first. Do not sit up while riding the slide. Riders must enter the slide in a sitting position and wait for instruction from the lifeguard stationed at the slide starter tub.
35 degrees is more normal, 40 is a little steep. A drop slide can be as steep as 60 degrees at the top, but will need a much longer run out at the bottom to make the overall average angle stay within the 40 degree guideline.