mba - High fan speed safe for long durations?

Heya everyone, just got a new 13 inch macbook air (been out of the apple world for a very long time) and so far I'm loving the machine.

I do notice that, as others have reported as being normal, under pressure the fan cranks up a fair bit. That's okay by me, under load this thing is still more silent than my old Dell was passively. However I am wondering if it's safe to run the machine like this for long periods, I gather things will just shut down if it gets into a critical temperature range but will this sort of use significantly reduce the lifespan of the machine?

If things are running smoothly, and the MBA isn't shutting down, there is nothing to worry about.
There is very little room for heat dissipation and ventilation in the MBA, so fans running fairly high when putting any sort of load on it would be expected.