The level of protection from wildland fires that tree cavities provide to sheltered fauna is not well understood. Further, few experiments have been performed to investigate the transfer of combustion products into, and ventilation of, tree cavity shelters in wildland fires. This paucity of data is unlikely to change in the near future. However, increasingly realistic fluid and fire dynamics simulation software has made the execution of “virtual experiments” tenable. In such experiments, data from simulations are used to form empirical relationships between the investigated phenomena and simulated conditions. As an example of this approach, the National Institute of Standards and Technology’s (NIST) Fire Dynamics Simulator (FDS) was used to create formulas for estimating maximum combustion product concentrations, doses (concentration integrated over time) and maximum gas temperatures within a single-entrance cylindrical shelter at heights above 3 m.
A three-step approach was taken: First, FDS was validated for single-entrance ventilation by comparison of simulation results to data from large- and small-scale ventilation experiments. Second, data from 45 simulations of a single-entrance, cylindrical shelter subjected to frontal winds at various speeds, angles of incidence and temperatures, were used to create empirical formulas relating these variables to entrance flux and rates of temperature change. Third, these formulas were applied to data from 26 separate simulations of different surface fire scenarios. As a result, a single empirical formula was found relating gas concentrations, doses and maximum temperatures inside a shelter to fire intensity, flame depth and wind speed. The findings suggest that virtual experiments can help provide tools for forest and land managers to estimate the impact and minimize the hazards of prescribed burning, as well as evaluate the consequences of naturally occurring wildland fires.