Dell Vostro 270 Owner's Manual page 50

Environmental
Relative humidity
Altitude:
Operating
Storage
Airborne contaminant level
50
20 % to 80 % (noncondensing)
–16 m to 3048 m (–50 to 10,000 ft)
NOTE: For altitudes above 2950 feet, the maximum
operating temperature is derated 1ºF/550 ft.
–15.20 m to 10,668 m (–50 ft to 35,000 ft)
G1 as defined by ISA-S71.04–1985