Is ‘zero leakage’ as a requirement realistic?

No. ‘Zero’ is not demonstrable with the measurement methods we know; you can only show that the leakage current is lower than the detection limit under recorded conditions. That is why standards work with a maximum allowable leakage value (≤ X in Pa·m³/s, mbar·l/s or std cm³/s), including method, pressure, temperature, tracer, and measurement duration.

Why ‘zero’ is not verifiable – briefly explained:

• Detection limit: every instrument has a lower limit.
• Measurement uncertainty: results always have variation.
• Background/noise: environmental gas, residual tracer, and electrical noise influence the signal.
• Permeation and desorption: gases pass through materials or come from cavities (virtual leaks).
• Conditions: small variations in pressure/temperature change the measured leakage current.