This blood gas barrier is extremely thin (approximately 2μm) (600–800 nm; in some places merely 200 nm) to allow sufficient oxygen diffusion, yet it is extremely strong. This strength comes from the type IV collagen in between the endothelial and epithelial cells. Damage can occur to this barrier at a pressure difference of around 40 millimetres of mercury (0.053 bar).
Failure of the barrier is often seen in racehorses and other domesticated horses due to exercise induced blood pressure rising above normal.
Failure of the barrier may occur in a pulmonary barotrauma. This can be a result of several possible causes, including blast injury, and breathing gas entrapment or retention in the lung during depressurization, which can occur during ascent from underwater diving or loss of pressure from a pressurized vehicle, habitat or pressure suit.