During use of the shelter-in-place technique, the ventilation system should be __________.

During a shelter-in-place situation, the ventilation system should be turned off to prevent outside air, which may be contaminated, from entering the building. This is a critical step to protect occupants from exposure to hazardous materials or toxic environments outside. By shutting down the ventilation system, you minimize the risk of inhaling harmful substances that could compromise the health and safety of those inside.

Maintaining the ventilation system or performing upgrades would not address the immediate concerns of contamination. Checking the system regularly might be relevant in some contexts, but during a shelter-in-place, the priority is to create a seal against the outside environment, which requires deactivating ventilation. This understanding is essential for ensuring effective safety measures are in place during hazardous situations.