As many of the replies have ...
Published by Terry Scheurman, President at Applied Specialties, Inc.
As many of the replies have already mentioned, it is best to have the acid diluted and added into the cooling tower basin. I have preferred to do this by having a 2" water line run to the rear of the basin. This line then becomes a source of water for a corrosion coupon rack and then it powers an eductor (hastalloy or kynar). The pH control signal then opens and closes the water supply to the eductor. This does several things all of which provide safety features.
1) acid will only be fed when the circulator header is pressurized (water running)
2) The acid is never under pressure to spray onto anyone or anything
3) acid is diluted in the eductor and you do not have a pump that will fail.
4) the acid is well diluted as it moves across the tower basin this avoids large spikes in pH