In the One-permanent-opening method, how far from the top of the enclosure must the permanent opening be?

The One-permanent-opening method is commonly used in mechanical ventilation and refers to the positioning of an opening for effective airflow and pressure balance. The correct answer indicates that the permanent opening must be located at a height of 12 inches (305 mm) from the top of the enclosure.

This height is pivotal because it ensures that the opening is placed above the expected level of contaminants or gases that may settle lower in the enclosure, facilitating better airflow dynamics and efficiency in ventilation. By positioning the permanent opening at this specific height, it helps promote the desired air exchange rates while reducing the risk of stagnant air pockets, leading to a more effective ventilation system overall.

Furthermore, standardized practices and regulations often dictate this height to maintain consistency across different installations, contributing to safety and operational effectiveness.