**3.7 Finding 7: relationship between pressure drop and airflow**

The study investigated two ventilation stages of a fully developed panel cave: with and without undercut ventilation using discrete and continuum CFD models [19]. With active undercut ventilation, we found that—(1) the cave act as a unique form of porous media, which influences flow through the production drifts such that the pressure drop model (in the production drifts) does not agree with either the existing models, hence, a unique model is required for the ventilation design, which provides opportunities for further research; and (2) increase in cave porosity decreases the drift's resistance to airflow. Without the undercut ventilation, the cave has less effect on the production drift ventilation as the pressure drop model agrees with the turbulent model; and an increase in cave porosity decreases the drift's resistance to airflow as shown in **Figures 16** and **17** (**Tables 3** and **4**).
