What are the application requirements in case of a high altitude site, e.g. above 1,000m A.M.S.L.?

1.) <1000m A.M.S.L., no restrictions
     1000-2500m A.M.S.L. with power derating 1,5% / 100m
2.) According to Paschen the isolating capability of air is reduced. That reduces the max. allowed mains voltage to 400V.