Shelter-in-place, HOLD, SECURE is a short-term solution to a short-term problem. If an accident or attack that created contaminated air occurred in the nearby area, everyone would be brought indoors, including those in trailers. Building personnel would close all windows and doors and shut down the heating, ventilation, and air conditioning system (HVAC). This would create a neutral pressure in the building, meaning the contaminated air would not be drawn into the building.
Shelter-in-place or SECURE is a short-term measure (measured in minutes or hours, not days) designed to use a facility and its indoor atmosphere to temporarily separate people from a hazardous outdoor environment. The alternative would be to evacuate into a hazardous situation, thereby causing harm to all involved.
Shelter-in-place OR HOLD can also be used during medical emergencies or any time when the movement of staff and students should be limited.