I'm working through the archives and one of the guest brewers said HSA may or may not affect the beer and that major breweries are looking to cut it out because it was one of the last things process wise that large breweries had left to worry about. Everything else in the process had already been taken care of. I agree that sanitation is way more important. Getting the beer chilled quickly and sanitarily is the biggest thing.

I believe that Charlie Bamforth spoke on it during one of his appearances.

If you don't mind some thermodynamic math here goes.

It takes 80 grams to melt a gram of water so melting the two gallons of ice will remove 80 x 2 x 3780 grams = 604,800 calories. In the 2.5 gallons of hot wort you have 2.5 x 3780 = 9450 grams. I am making some assumptions like the wort sg is 1.0 and it isn't but it is close enuf. The removal of 604,800 calories would drop the wort to a temperature to 210 - 604,500/9450 = 146 degrees but that does not take into account of the icewater that is at 32 degrees. The calories above 32 degrees = (146-32) X 9450 = 1,077,330 and those calories will be shared now with 4.5 gallons of liquid so the final temperature would be = 32 + 1077330/(4.5x3780) = 95 degrees.