45 Be Prepared to Weather the Storm New Scoping in the 2015 IBC for Storm Shelters Using the ICC 500 ICC/NSSA Standard for the Design and Construction of Storm Shelters By Kimberly Paarlberg, RA, Senior Staff Architect and Dave Bowman, Manager of Codes, ICC The Storm Shelter standard, ICC 500, provides design and construction requirements for safe rooms offering refuge from high winds and debris generated by hurricanes or tornadoes. Two significant code changes, G94-12 and G95-12, will result in storm shelters being required in some buildings located in areas where tornado design wind speeds are 250 mph, per ICC 500, Figure 304.2(1) (shown below). This is basically the Midwest area of the United States, otherwise known as tornado alley. This includes all of Illinois, Indiana, Iowa, Missouri, Arkansas and Ohio, and part of 14 bordering states. FOR LARGER VERSION OF THIS MAP, CLICK HERE.
46 In tornado alley, storm shelters will be required in: 1. Group E with 50 or more occupants, including all grade schools and high schools, but excluding day care facilities and Sunday schools. 2. 911 call stations, emergency operation centers, fire stations, emergency rescue stations, ambulance stations and police stations; basically, the buildings for emergency responders. Providing storm shelters in these same facilities in other parts of the country, or in other types of facilities, will remain optional. However, where storm shelters are provided, they must comply with ICC 500. The ICC 500 addressed requirements for both hurricane and tornado shelters. While the scoping criteria in G94-12 and G95-12 states storm shelters, given the referenced figure, this is requiring tornado shelters, not hurricane shelters. This distinction will be explained later in this article. This article will be focused on tornado shelter requirements. What s the Hazard? Tornadoes can move with phenomenal speeds, sometimes exceeding 300 mph. Tornadoes last from a few minutes to a few hours. Most tornado deaths are from flying debris. The National Weather Service documents about 1,000 tornado touchdowns per year. A key point to remember is that the size of the tornado is not necessarily an indication if its intensity. The Fujita scale (F-Scale), is a scale for rating tornado intensity, based on the damage tornadoes inflict on human-built structures and vegetation. Scale Estimated wind Speed (mph) The Fujita Scale Average Damage Path Width (meters) Potential damage F0 40 72 10 50 Minor damage. F1 73 112 30 150 Moderate damage. F2 113 157 110 250 Considerable damage. F3 158 206 200 500 Critical damage. F4 207 260 400 900 Severe damage. F5 261 318 1,100 ~ Total Destruction. F6 319+ Theoretical category. Immeasurable damage. Approximately 74 percent of the tornadoes in the United States are category F0 or F1. Twenty five percent are strong tornadoes of category F2 and F3. Only 1 percent are the violent tornadoes of categories F4 and F5. Types of Shelters in ICC 500 Hurricane or Tornado Shelters The standard makes a distinction between shelters used for hurricanes or tornadoes. Wind is wind, so why make the distinction? The primary difference is the duration of the storm. Tornadoes are very short-lived storms; hurricanes can maintain their strength in one area for many hours. The base durations for shelters designed in accordance with this standard are 2 hours for tornadoes and 24 hours for hurricanes. Hurricane and tornado shelter requirements differ for: Occupant density Sanitation Water supply Ventilation Emergency power Size and speed of flying debris Community or Residential Shelters This standard makes a distinction between shelters used in the community and shelters used with a residence or small group of residences. The definition for Residential Shelters limits the occupant load to a maximum of 16. Shelters used for larger residential complexes such as hotels, larger apartment buildings or
47 dormitories would be considered community shelters. Essential Features for Commercial Tornado Shelters Occupant Density The occupant load used for sizing the shelter is based on the needs of the shelter. When calculating the usable floor area, reductions must be made for furniture or equipment that will remain in the shelter when occupied. For example, if a classroom is used for a storm shelter, the usable floor area is reduced by the area occupied by permanent counters, as well as desks in the room. If an alcove or baffle entry system is used, this area must also be subtracted (804.9.7). The occupant density for community tornado shelters is 5 square feet. per person (Table 501.1.1). Larger areas are required for shelters that will contain persons in wheelchairs or persons who are bedridden. At least one wheelchair space is required for every 200 occupants the shelter is designed for. Number of Doorways Community shelters are usually safe rooms designed for other uses during day-to-day operations. For example, a school safe room could be a classroom, the bathrooms, the library, etc. These rooms are hardened to resist the wind loads and flying debris at the levels required. For these types of shelters, the number of exits is based upon the number of exits required for the primary occupancy during normal use, not the occupant load of the shelter. Egress doors must be capable of being opened from the inside without special keys or knowledge. Example: A classroom in a school has a maximum occupant load of 40. The number of exit access doorways required from that classroom would be one. Therefore, regardless of the amount of occupants using the classroom as a shelter, the required number of exit access doorways remains at one. Emergency Escape When a community shelter is permitted to have a single doorway, a second emergency escape route is required via a stairway or ladder (501.4.1). The minimum dimensions of the emergency escape opening are the same as those for emergency escape windows given in the IBC. The purpose is to prevent the occupants from being trapped by debris that may pile up in front of a single door. Ventilation Ventilation can be via natural or mechanical means. The size of the natural ventilation openings depends on the number of anticipated occupants. If mechanical ventilation is provided, it must be connected to an emergency power system. Potable Water and Sanitation Facilities The requirements for sanitation are minimal (Table 702.2). Toilets and lavatories in the shelters can be part of the required sanitation if they can be converted for emergency mode. Other sanitation facilities can be temporary facilities or chemical toilets. Emergency Features Tornado shelters must include fire extinguishers and first-aid kits. Community tornado shelters must have emergency lighting. Location and Accessibility Community shelters are required to have an accessible route in accordance with ICC A117.1 (501.6). The assumption is that building systems are operational before the storm hits. Therefore, that route can be via an elevator. Standby power for the elevator is not required by this standard, but may be required for other reasons. At least one entrance to the storm shelter shall be an accessible entrance. The entrance to the shelter must have signs. A layout of the shelter should be provided within the shelter.
*ADVERTISEMENT 48 When storm shelters are located within areas subject to floods, coastal wave effects or storm surge, the floor of the shelter may be required to be raised to ensure the occupants will not be dealing with rising water, as well as high winds and debris (401). If storm shelters are located within precautionary zones for facilities containing Verify Metal Buildings are Built to Code Ask Manufacturers for their IAS AC472 Accreditation IAS provides the most comprehensive and trusted accreditation program (AC472) to assist building departments with approving metal building fabricators as defined in International Building Code (IBC ) Chapter 17. IAS audits the manufacturer s process for engineering, design/detailing, order documents, raw material usage, fabrication processes, quality assurance system, and technical qualifications of staff. The IAS program also provides for periodic, unannounced inspections. Building Departments can verify the accreditation status of manufacturers online 24/7 or by contacting IAS. hazardous materials, the designer must work with the Local Emergency Planning Committee to also shelter occupants from possible exposure (402). STRUCTURAL ISSUES The issues the storm shelter addresses include: the wind loads that should be used; 1-866-427-4422 www.iasonline.org and the size and velocity of flying debris. Wind Loads Wind loads for storm shelters will be based upon wind speed contour maps developed specially for this standard. For tornado wind forces, the best available data is the design wind speed map contained in FEMA 361, Design and Construction Guidance for Community Shelters. The wind speeds for tornado shelters [Figure 304.2(1)] is an adaptation of this map. The wind pressure will be determined based upon Method 2, Analytical Procedure, of Chapter 6 of ASCE 7, with several modifications to the factors used in the formulas (304). Debris The typical missile used for simulating possible flying objects that could breach the shelter envelope is a 2 x 4 of nominal sawn lumber. The speed of these missiles is dependent upon the wind zone in the tornado map. For the tornado alley, with tornado wind speeds of 250 mph, the horizontal speed of a 15 pound (7 kg) 2 x 4 is to be set at 100 mph (44 m/s) and the vertical speed at an astounding 67 mph (29 m/s). Chapter 8 of the stan- Helping Building Departments Meet IBC Chapter 17 Requirements dard provides the test methodology for testing walls, doors, shutters and windows for 13-08490
resistance to impact from flying debris. Other Structural Issues Chapter 3, Structural Design Criteria, addresses weather protection; enclosure within a host building; connection of the shelter to foundations or slabs; and penetration of the shelter envelope by systems and utilities. Evacuation to a storm shelter should be part of a building s safety and evacuation plan. Because fires could break out during or after a storm, the shelter must be protected by fire barriers and horizontal assemblies with a fire-resistance-rating of at least two hours (601). Conclusion Schools in tornado alley should include movement to tornado shelters in their safety plans and practice drills. Having tornado shelters in the buildings with emergency responders and services will increase the chance these facilities will remain up and running after the tornado has passed. Home or building owners should assess their risk and determine the best type of 49 *ADVERTISEMENT People Helping People Build a Safer World Learn the Residential Inspection Process Residential Inspection Institute (Based on the 2012 Codes) Phoenix, AZ November 18-22 3.0 CEUs Prepare to perform residential inspections with training from ICC, the source of the codes. In this Institute, you will learn the step-by-step processes to complete residential building, mechanical, plumbing and electrical inspections. Get answers to your code questions from nationally recognized code enforcement educators, discuss emerging code enforcement issues and challenges and share experiences with your peers. Only a few seats remain! Register now for the last remaining Residential Inspection Institute in 2013! Review the latest inspection tools and receive practical information from instructors who know the codes best. You will receive comprehensive and up-to-date resource manuals, developed exclusively by ICC, which you will reference long after this course is completed. Location Logistics: Event Location Details Dessert Willow Conference Center 4340 East Cotton Center Boulevard Phoenix, AZ 85040 (Conference Center is next to the Homewood Suites hotel) Hotel: Homewood Suites Phoenix Airport South 4750 East Cotton Center Boulevard Phoenix, AZ 85040 (Hotel is next door to the Conference Center) Room Rate: $119 per night plus tax Succeed in the building safety industry, register today. For additional questions, we can be reached by email at icctraining@iccsafe.org or by phone at 888-ICC-SAFE (422-7233) ext. 33818. shelter for their needs. A safe room is the preferred method of wind protection in highrisk areas. Having a shelter can greatly reduce injury or death caused by the extreme winds and storms associated with tornadoes and hurricanes. If the decision is to build a shelter, make sure evacuation plans are made known and are practiced. The current edition of the standard, ICC 500-2008, is undergoing a development cycle. The work plan is for the 2014 edition to be completed in time to be referenced in the 2015 IBC. The proposed revisions will not significantly affect the technical requirements discussed in this article. Additional information can be found on the ICC website under Standards Development. 13-08548