Hydrogen continued diffusion

Molecular hydrogen cannot diffuse into steel and, therefore, it accumulates on the grain boundary. Due to enormous pressures exerted by hydrogen, discontinuous microcracks are formed in the grain boundaries. The metal strength continues to decrease by the pressure by methane or hydrogen until damage occurs. A steel tube in a boiler would burst under the pressure. 

Whilst discussion continues on the details of hydrogen generation, adsorption and diffusion, and the relative contributions of these to the overall... 

Hydrogen does not appear free in the atmosphere except at levels below 1 ppm, since rapid diffusivity enables molecules to escape the earth s gravitational field and it is continuously lost from the atmosphere. It is present in the earth s crust at about 0.87% in combination with oxygen in water and with carbon and other elements in organic substances. It is prepared commercially on a small scale by action of sulphuric acid on zinc ... 

The carbon dioxide produced during cellular metabolism diffuses out of the cells and into the plasma. It then continues to diffuse down its concentration gradient into the red blood cells. Within these cells, the enzyme carbonic anhydrase (CA) facilitates combination of carbon dioxide and water to form carbonic acid (H2C03). The carbonic acid then dissociates into hydrogen ion (H+) and bicarbonate ion (HC03). 

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