30 storeys is a little high for a cat to survive, but in fact a cat is likelier to break something if it falls from the first floor window, or even the second storey, than it is from somewhat higher up. Cats require time to twist themselves into the proper aerodynamic shape -- back arched and upward with feet straight down. You don't have to prove this to yourselves, please. It has been thoroughly researched. But every so often National Geographic shows an extraordinary series of pictures of cats being dropped feet up, twisting as they fall, and landing literally on their feet, which sort of accordion up and straighten, the cats then walking away without even a sprain. I am sure Guiness's Book of Records has the height that is optimum between the most dangerous (low down) to again the most dangerous (too high).
A perfectly disgusting story one of my fathers-in-law used to tell on himself was about becoming bored one evening when he was staying in a hotel. His room was on the 5th floor as they count in Europe, which means the 6th floor in American figuring. He decided to see if he could hit people entering the stairwell from the lobby with milk containers (with the milk in them). This story only makes sense if you understand that by 3 in the afternoon he was always in an alcoholic haze, having started with a liter of wine for breakfast.
At one point, this game palled. The various guests of the hotel complained and a manager phone him to stop, but otherwise there was no real excitement. So he snatched up one of the hotel cats and tossed it down the stairwell. The cat miraculously landed on its feet and stalked away from the stairwell with its nose in the air, totally unhurt.
The hotel then asked my ex-father-in-law to leave. Not before time. My ex-husband remembers being both distraught over the cat (but, as I said, it happily was damaged only in its dignity), and being humiliated by the entire sight of his father behaving in such a fashion. The family had to shift their suitcases to go to another hotel, escourted by a very grim set of bellboys, and they had to pass the bottom of the stairwell, where the maids were trying to clean up all the mess of the milk and containers. And there, at one side, was the cat, happily lapping up the milk as quickly as it could before the maids got it all mopped up.
This is a true story. I repeat -- this is not a trick to try at home! And it does not minimize the danger of any fall. If the cat cannot right itself in the air, its body is actually very fragile and it can be horribly crushed. If it falls backwards, and doesn't have time to twist properly into position, it can snap its spine. I have had a cat fall from a misjudged jump from the floor to the top of a 5 drawer bureau and end up with a badly stained back. Better safe than sorry.