Tornadoes – a Destructive Force of Nature
Tornadoes and hurricanes are among the most destructive forces of nature. Unfortunately, these types of wind storms continue to cause injury and death to people who are unable to safely evacuate or find shelter from these events.
The National Weather Service did not start keeping organized records of tornadoes in the United States until 1950. Since then, the deadliest year for tornadoes was 2011, which claimed 553 lives. The single deadliest tornado to date was in Joplin, MO, on May 22, 2011, with 161 fatalities.
Compared with hurricanes and earthquakes, single tornado events typically affect smaller geographical areas but occur more often and cause more deaths. From 1950 through 2011, tornadoes caused about 5,600 fatalities in the United States, more than hurricanes and earthquakes combined over the same time period (NIST 2014).
Tornado Resistant Building Codes
FEMA has long supported the development of hazard-resistant codes and standards by assessing how structures respond in a disaster. Assessment conclusions and recommendations are applied through active participation in the process of creating and developing building codes and standards, including the Standard for the Design and Construction of Storm Shelters, known as ICC 500.
The most cost-effective way to design and construct a safe room is to include it in a new building. The cost of retrofitting an existing building (or portion thereof) is higher due to the additional design and construction constraints.
In new construction, the safe room is often built in the basement. The likelihood of wind-borne debris entering the basement is lower than for above-ground spaces; however, a basement safe room should still be designed to resist the extreme wind pressures that an above-ground safe room would need to resist. If you plan to add a basement safe room as a retrofitting project, keep the following in mind:
- You must be able to clear out an area of the basement large enough for the safe room.
- Unless the exterior basement walls contain adequate reinforcement as shown on the design drawings provided with this publication, these walls cannot be used as safe room walls because they are not reinforced to resist damage from wind-borne debris and extreme winds uplifting the home’s floor structure above.
- Exterior basement walls that are used as safe room walls must not contain windows, doors, or other openings in the area providing protection unless they are protected with an appropriate protective device or are designed to resist the debris impact and pressure associated with safe room design.
- The roof of the safe room must be designed to resist the wind pressures and debris impact forces.
- Just as the walls and roof of a safe room are designed and built to protect against extreme winds and wind-borne debris, so must the safe room door and assembly. Only door assemblies designed and tested to resist debris impacts and wind pressures can provide near-absolute life-safety protection.
- Some manufacturers produce and install prefabricated safe rooms.