The fires of the prânas are, as it were, awake in that town (the body). The Apâna is the Gârhapatya fire, the Vyâna the Anvâhâryapakana fire; and because it is taken out of the Gârhapatya fire, which is fire for taking out, therefore the Prâna is the Âhavanlya fire.

In plain words: Even while a person sleeps, the breaths in the body stay awake like sacred fires kept burning in a house. The teacher Pippalada compares the different breaths (prana, the life-breaths) to the three fires used in Vedic worship.