The breath bar was first introduced in the original Tomb Raider, where Lara had a blue breath bar. As long as Lara is underwater, the bar will continue to run down. Once it's depleted, Lara will start taking damage to the Health Bar.
Swimming on the surface will gradually restore the bar. Leaving the water will fully replenish the bar at once.
The Breath Bar also appears when Lara is situated in a place with toxic fumes. This happens for example in the VCI Section of Tomb Raider Chronicles and the levels Derelict Apartment Block and Galleries Under Siege in The Angel of Darkness.
In Tomb Raider Underworld the bar doesn't look like the same as in the previous games, but the player is still able to recognise it.
light blue Breath Bar (TRU)
- Tomb Raider (PlayStation Platinum, UK PAL, Page 5)