Decontamination

[i]"And you let it in ..." - Ripley to Ash[/i] The decontamination scene in [i]Alien[/i], is a brilliant and subtly executed plot device that operates on several levels. It serves to suspend our disbelief by appealing to the logical and rational thinking of human beings. It stands to reason that any human exploration of an extra-solar world would require protocols and procedures that would enhance the safety of the explorers. Thus, Ridley Scott grounds the future in understandable, and accepted contemporary thought. The scene is so subtle that we never question the need for decontamination procedures, nor that there is a chain of command. It further serves as a red herring. Initially, though perhaps suspicious, Ash's actions humanize him. It appeals to us to believe that his actions are motivated by concern for his crew mates. This, of course, sets the viewer up for the shocking realization that not only is he an android, but that his motivations were entirely nefarious. Suspension of disbelief is absolutely critical in any serious science fiction, and Ridley succeeded brilliantly with this one scene. And that brings me to the question of decontamination in [i]Prometheus[/i]. Characters are observed interacting with - presumably - alien substances. We witness them in spacesuits, and yet there are scenes where they lack their helmet. In Alien, Kane clearly felt protected from danger when he touched the facehugger egg. Yet, the characters in [i]Prometheus[/i] seem far less concerned in this regard. Is there some dramatic device that Ridley uses to allay any infection concerns the crew might have? Is it the deliberate and contrary action of a character, similar to Ash's actions? Is it something Ridley has purposefully or accidentally overlooked? Or - in my opinion this is the least likely alternative - are the decontamination procedures employed by the crew of the Nostromo, a result of the irresponsible actions of the crew of the Nostromo?