He personally went to the Twin Towers to oversee evacuations by his department following the arrival of the first units there with 1st Battalion Chief Joseph W. Pfeifer and the companies with him, who were investigating a report of a smell of gas only a few blocks away when American Airlines Flight 11, piloted by Mohamed Atta, crashed into the North Tower, followed 17 minutes later by United Airlines Flight 175, piloted by Marwan al-Shehhi, slamming into the South Tower. Von Essen and his men evacuated as many people as they could until the South Tower collapsed 56 minutes after it was hit, at which point Chief Pfeifer ordered all personnel to evacuate the North Tower before it collapsed.
Von Essen personally went to the Twin Towers to oversee evacuations by his department following the arrival of the first units there with 1st Battalion Chief Joseph W. Pfeifer and the companies accompanying him, who were investigating a report of a gas smell only a few blocks away when American Airlines Flight 11, piloted by Mohamed Atta, crashed into the North Tower, followed 17 minutes later by United Airlines Flight 175, piloted by Marwan al-Shehhi, slamming into the South Tower. Von Essen and his men evacuated as many people as they could until the South Tower collapsed 56 minutes after it was hit, at which point Chief Pfeifer ordered all personnel to evacuate the North Tower before it collapsed.