The principal announces that the school will go into shelter in place mode to protect students and staff from a potential chemical release. During shelter in place, all doors, windows and outside air vents are sealed to prevent toxic fumes from entering the building. Shelter in place means staying indoors when an alert is given for a chemical release. Signs are posted near pipelines containing hazardous chemicals like anhydrous ammonia to identify their locations. If accidentally released, ammonia can burn skin and respiratory tissues. Radio, TV and phone calls will provide information on shelter in place orders and the all-clear.