In the event of a propane release from a tanker truck, which level's fresh air intake must be IMMEDIATELY shut down?

Shutting down the fresh air intake at street level is critical during a propane release from a tanker truck due to the nature of propane gas. Propane is heavier than air and tends to accumulate in low-lying areas. If the street-level intake is left open, it can allow propane vapors to be drawn into buildings, creating a risk of explosion or fire.

Immediate action to secure the street-level intake helps mitigate the risk of a hazardous buildup within structures and safeguards the safety of occupants and emergency responders. It is essential for containing the situation and preventing a more significant emergency.

The other levels, while they may also require attention, do not present the same immediate risk of drawing propane vapors into the building as the street-level intake does in this scenario.