What must occur at an AQI level over 500?

At an Air Quality Index (AQI) level exceeding 500, the primary concern is the severe pollution levels that pose serious health risks to individuals, particularly first responders and vulnerable populations. Under these conditions, the use of N95 masks becomes crucial because these masks can filter out harmful particles in the air, thereby protecting the respiratory health of personnel who may be exposed to hazardous environments.

While the other options might seem relevant in various scenarios, the immediate action required to ensure the safety of personnel in the context of extreme air pollution is to mandate the use of N95 masks. This proactive measure helps reduce inhalation of harmful substances, safeguarding health and well-being amidst unsafe air quality conditions.