If there is no shelter nearby, lie flat in the nearest ditch, ravine or culvert with your hands shielding your head. In the event of imminent or actual hostile enemy attack. Tornadic activity or sustained straight line winds in excess of 75 m.p.h. Whenever mass evacuation is necessary for an area whose outer boundaries extend at least 2500 feet from the point of incident, such as a hazardous material spill. Sirens are sounded only for a tornado warning or potential for a tornado warning, and are meant as an outdoor warning.
Local media advise the public when dangerous conditions no longer exist.
Sirens also are used in the event of hazardous material conditions and in that event, evacuation may be better than sheltering. In buildings without basements, go to interior hallways on the lowest floor, and get under something sturdy. In high-rise buildings, go to small interior rooms or hallways away from windows on the lowest possible floor. Do not stay in vehicles or mobile homes. If you are outdoors and there is no shelter nearby, lie flat in the nearest ditch or ravine with your arms over your head.