A Wildfire-Smoke Refuge Room for a Classroom or Clinic Ward: An Integrated Sizing Law and a Priced Comparison of Box-Fan Filter Arrays and HEPA Purifiers

SIMULATED, NOT MEASURED. A first-principles sizing law and priced design for a 180 m3, 30-occupant wildfire-smoke refuge room: required clean-air delivery rate to hold indoor PM2.5 at or below 35 ug/m3 (and a strict 12 ug/m3 target) under outdoor smoke of 250-600 ug/m3, comparing box-fan MERV-13 arrays and HEPA purifiers with filter-loading decay over a five-day event, noise, power, and cost per protected occupant per smoke day, including the regimes where only the HEPA class, and where neither class, can hold the target.