Smoke release during the first commissioning test, resulted in the appropriate and expected, immediate drop of all the curtains, in a time span of less than one second, from the smoke detectors activation. The smoke curtains as viewed from the smoke invaded inside, of the atrium illustrate the curtain to curtain overlap when dropped on activation. The exitways on the clean air side of the curtains are thereby appropriately protected from smoke invasion, and at the same time "specified" access can be maintained through the curtain if required, from the smoke invaded stairs.