Rests for horns
Any general rules for writing rests for horns?
In writing a score that includes saxophones and trumpets, I notice that I may not have allowed enough time for the players to catch their breaths. Given an average tempo (say quarter note = 120), how many measures can each go before their air is exhausted? And how much of a rest is enough? Is an eight or quarter rest enough to replenish? What if you write whole notes for a large number of measures - will the players squeeze in inspirations periodically on their own or are notated rests necessary there as well?
I know that this is not specifically a notation issue but would appreciate help if anyone knows the answers. Thanks.