To filter toxins from the Pandoran air
|Behind the scenes|
Pandora's toxic atmosphere is unbreathable by humans due to the presence of high concentrations of carbon dioxide (>18%) and hydrogen sulfide (>1%). Pandora's other main atmospheric constituents; nitrogen, oxygen, and xenon, are also present in Earth's atmosphere. Fortunately, Pandora's atmospheric oxygen content and its partial pressure (pO2) are suitable to support human life. So in order for a human to breathe it is only necessary to filter or "scrub" out the toxic components, which is the exopack's purpose.
Without the exopack, the potent mix of high concentrations of carbon dioxide and especially hydrogen sulfide will cause a variety of unpleasant or deadly reactions; including choking and burning of mucous membranes, followed by unconsciousness within twenty seconds and death within minutes due to cellular oxygen deprivation.
Carbon dioxide binds to human red blood cells as part of normal human metabolism in Earth's atmosphere (.036% carbon dioxide). However, high concentrations of atmospheric carbon dioxide (exceeding 4%) will decrease the amount of oxygen that is bound onto red blood cells, which leads to oxygen deprivation and asphyxiation. 
Hydrogen sulfide is considered a broad-spectrum poison, meaning that it can poison several different systems in the body but affecting the nervous system most severely. The toxicity of hydrogen sulfide is comparable with hydrogen cyanide in that it is a strong hemotoxin and will destroy red blood cells by irreversibly forming a complex bond with the iron in the red blood cells. This permanently destroys the blood cells ability to bind to and transport oxygen throughout the body which leads to cellular oxygen deprivation and ultimately death. 
The exopack utitilizes a full-face, transparent, perspex faceplate with a polymer static seal, which is connected by a hose to a small pack containing the filters and a power supply. There is a high-flow valve at the bottom of the mask, allowing the user taking deep breaths rapidly if necessary, especially if he was exposed to Pandora's atmosphere for period of time.
The filters function for two weeks before accumulated soot clogs the filter pores. The filter pads can be regenerated by gentle washing with running water and last indefinitely with proper care.