In another question, I asked how airships could be made more viable. The first (and so far only) promising solution I came up with is to increase the density of air.
In the real world, air (on Earth) is composed mainly of nitrogen (~80%) and oxygen (~20%). I'd like to reduce the nitrogen content in favor of a heavier gas.
Unfortunately, most heavy gases seem to be toxic in one way or another, although both Krypton or Xenon seem to be ok(-ish); Radon would be the next step in the noble gas category, but it's radioactive. Changing the air composition from a (simplified) 80% nitrogen, 20% oxygen to 50% nitrogen, 30% xenon, 20% oxygen would raise the density from about 1.25kg/m³ to about 2.68kg/m³, roughly doubling the buoyancy.
Hence my question: what would the effects of reducing the Nitrogen percentage in air in favor of a heavier gas such as Krypton or Xenon be?
Addendum: I since read this question, which has an answer that states "xenon makes an excellent general anesthetic, so let's not adopt an atmosphere which renders us unconscious". I'm open to simply ruling that this property does not exist in my world (perhaps humans and other creatures developed an immunity) if Xenon turns out to be the otherwise best option.