When planning vertical ventilation, which factor must be considered to prevent blowing smoke and fire back into the structure?

• A. Wind direction has no effect on exhaust sizing.
• B. Exhaust opening size should be fixed regardless of wind.
• C. Wind direction and the exhaust opening size should be chosen to promote proper airflow and prevent blowback.
• D. Ventilation should be delayed until there is no wind.

Answer: (C)

Wind direction and exhaust opening size must be coordinated to create a dominant outflow and prevent blowback. When you ventilate vertically, you’re relying on a buoyant plume to rise and exit the structure. But wind can push air back toward the openings, forcing smoke and fire back inside if the exhaust isn’t sized and positioned to overcome that pressure difference. By assessing the wind direction and adjusting the exhaust opening size accordingly, you promote a steady, sufficient outflow that carries heat, smoke, and gases away from the building rather than pushing them back in. Delaying ventilation for wind-free conditions isn’t practical in most real fires, and assuming wind has no effect ignores a major factor that determines whether ventilation will help or worsen the situation.