看片不仔細……

According to: http://james-camerons-avatar.wikia.com/wiki/Exopack

"The Exopack is a lightweight atmosphere filtration system developed from civilian rebreather technology that allows humans to survive on Pandora with a minimum of equipment. Pandora's atmosphere would be easily breathable if it wasn't contaminated by a pungent mixture of hydrogen sulfide and chlorine. The additional gases cause a variety of unpleasant reactions, including choking and burning of mucous membranes, followed by unconsciousness within twenty seconds and death within four minutes. Nevertheless, the partial presence of oxygen in the Pandoran atmosphere is similar to that of Earth's atmosphere. In order to breathe, it is only necessary to filter out toxic components. The filters will function for two weeks before accumulated soot clogs the filter pores. The filter pads can be regenerated by gentle washing with running water and will last indefinitely with proper care."