Which condition prohibits the use of the EMER DEPRESS switch?

The use of the EMER DEPRESS switch is prohibited above 15,000 feet due to the need for maintaining cabin pressure and ensuring passenger safety. This switch, when activated, allows for a rapid depressurization of the aircraft cabin, which can be crucial during emergencies where immediate cabin altitude reduction is necessary. However, at altitudes above 15,000 feet, the risks associated with rapid decompression increase significantly, potentially leading to hypoxia for both crew and passengers who may not have supplemental oxygen available. Therefore, to maintain safety protocols and passenger health, the operation of this switch is restricted at altitudes above 15,000 feet.