To enable their prescience, Guild Navigators not only consume large quantities of the spice, but are also continuously immersed in highly concentrated amounts of orange spice gas [REF].
In an unused passage by Frank Herbert from Dune Messiah published in The Road to Dune (2005), Edric is described as surviving without spice gas once a hole is opened in his tank, though his prescient abilities are practically useless in this state [REF].