According to the definition, what pressure must be exceeded for gases to be considered compressed?

The correct understanding of pressure in this context revolves around the definition of 'compressed gas.' Compressed gases are typically defined by their pressure relative to atmospheric pressure. At sea level, atmospheric pressure is approximately 14.7 psia. For gases to be considered compressed, they must be under pressure that exceeds this atmospheric baseline.

When discussing the pressure at which gases are classified as compressed, a threshold of 14.7 psia is significant because it delineates the boundary between a gas at atmospheric pressure and a gas that is considered to be compressed. This differentiation is crucial for regulatory purposes and safety protocols in medical gas applications, as pressures exceeding this level can lead to the unique behaviors of gases under compression, which require specific handling, storage, and safety measures. Hence, any pressure above 14.7 psia signifies a state of compression.

While 30 psia or 41 psia may represent higher levels of compression, they do not serve as the fundamental boundary for classification. The key aspect here is recognizing that the definition of compressed gas hinges upon surpassing the standard atmospheric pressure of approximately 14.7 psia.