Question

Coal Miners use gas mask while they are working in the mines . These gas masks consist of activated charcoal which adsorb harmful gases like methane . Since Physisorption is not specific in nature , The charcoal should adsorb oxygen gas also r?? Then how will the coal miners breathe ?? 

Answer 1

Gas masks  are also known as "air-purifying respirators" because they filter or clean chemical gases and possibly particles out of the air as you breathe. ... The cartridge may have a filter to remove particles (such as a biological weapon), charcoal (to remove certain chemicals), both, or other parts...
so they do not absorb oxygen they just purify the air and allow them to breathe

Answer 2

The activated charcoal containing gas masks are used by coal miners to protect them from the suffocating gases and particulate matter or ashes present in the coal mines. The activated carbon binds the materials by Vander Waal force or London dispersion force. Thus chemical compounds with large molecules , large molecular weight and insolubility are easily adsorbed. Activated carbon does not bind well to oxygen and oxygen containing molecules like alcohols, ammonia, glycols. Thus the oxygen gas does not get adsorbed on the charcoal.