During shelter in place protection, which protective action must be taken?

• A. Close all windows
• B. Establish a water curtain
• C. Use positive pressure to protect the structure
• D. Ensure heating, ventilation, and air conditioning system remains operating

Answer: (A)

During shelter in place, the essential protective step is to limit outside air from entering the building. Closing all exterior openings, especially windows, reduces the inflow of hazardous fumes and lowers the risk of inhalation exposure. The other actions don’t support this goal: a water curtain isn’t a standard shelter-in-place measure, using positive pressure would push outside air into the building, and keeping the heating, ventilation, and air conditioning system running can pull contaminated air indoors. If advised, you may also seal gaps and turn off HVAC to minimize air exchange, but the foundational action is to keep windows closed.