Topic: Tornado Shelter Design


This month's meeting featured Brian Walker with Wallace Engineering.  Wallace is an IFMA Tulsa member company. Brian’s presentation focused on tornado shelter design.  One of IFMA’s core competencies is emergency preparedness and business continuity. 

With Oklahoma being situated in Tornado Alley, a discussion on having a safe place to retreat to in case of a tornado seemed like an important topic to present to the IFMA Tulsa membership.  As Oklahomans, we all know about the power of a tornado.

We generally hear about the power of a tornado being shared in terms of being as low as an F0 or as high as an F5. Did you know that the “F” comes from the Fujita Scale?  There is also an EF Scale with the “E” standing for Enhanced or an Enhanced Fujita Scale.  The EF Scale actually took the place of the F Scale back in 2007.  Breaking it down, an EF0 tornado is considered light damage, an EF1 being moderate, an EF2 being considerable, an EF3 being severe, an EF4 being devastating and an EF5 being incredible.

The hazards of a tornado are the wind pressure, the small, medium and large debris that gets tossed by the powerful wind speeds and the laydown and rollover from those speeds.  As tornado speeds tend to vary around the United States, safe rooms are designed for different wind speeds in different parts of the country.  Since some of the highest wind speeds are found in Oklahoma, hence, tornado safe rooms for Oklahoma are built to withstand wind speeds of up to 250 miles per hour.

In the design process of construction of a shelter that will withstand speeds of 250 mph, consideration is given to wind pressure on an enclosed building, partially enclosed building and  building components.  Also considered is the ability to withstand debris and missiles (debris impact).  Laydown and rollover is also a consideration.

A place where people gather during a tornado may be a shelter or a safe room.  There is a difference between the two.  A storm shelter is a shelter that meets ICC 500 standards and provides “life-safety protection” from wind events.  A safe room is a shelter that meets FEMA criteria and provides “near-absolute protection” from wind events.  Each provides a different level of protection and structural design criteria.

Costs for a safe room (per 2008 statistics) average $180.00 to $290.00 per sq. ft.  The cost to harden a safe toom for 250 mph winds is 15-20%.  For missile impact, the cost can increase anywhere from 5-25%.

In 2011, tornadoes were responsible for 400 deaths.  Safe rooms and shelters have been a proven way to save lives during a tornado.  It is important that your company have a place where your employees can go to should a tornado strike.