Seeking the Best Available Shelter Against Tornadoes& High Winds
Special thanks to James J. Abernathy, Architect and Oakland County, Michigan, Emergency Management
Tornado Shelter Survey Tips
The following "tips" are intended to help you avoid making serious errors of omission or commission while trying to assess the "best available" tornado shelter spaces in your facility.
Never "survey" a building from drawings alone! Why?:
- Buildings are frequently modified. Sometimes modification improve the shelter capability, although sometimes the changes reduce potential for shelter quality.
- A floor plan cannot show everything that is in the space. Even the architect's "blueprint" floor plan is an incomplete document. It "cuts" the building (usually on a plane that is 4' above the floor) and cannot show everything above that plane.
- Detailed information about door (swing directions, hardware, window size and material, etc.) will be incomplete.
Never attempt to "guarantee" that the "best available" tornado shelter spaces are good enough to prevent serious injury or death. There are a number of reasons for this statement, including:
- It is impossible to know the direction or intensity of the storm.
- It is impossible to know the relationship of the path of the storm to the building.
- It is impossible to predict how much warning the building occupants will have before the storm arrives.
- It is impossible to know whether procedural directives (such as closing doors, etc.) will be followed.
Tornado Shelter Survey
- Identify tornado spotting locations. Even with the technological communication advances there is no guarantee that the storm will be spotted, a warning issued, and heard by those in a building.
- Remember that many facilities are intensely used after 5 pm. Don't limit planning to 8 am to 5 pm.
- Some of the very best shelter spaces are rejected due to "unpleasant odors", "possibility of fire" or "limited access. Remember:
- The time of occupancy may be very short
- Fires during tornadoes are almost non-existent
- Many rescuers will appear very shortly after a storm hits.
- Don't get involved with operational decisions (unless you are the building manager or administrator).
- However, the "route to shelter" is an important topic.
- Encourage clear positing of shelter locations.
- Some organizations may wish to consider a "staged" shelter procedure. For this, some people are moved from dangerous locations to somewhat comfortable "staging areas". When the condition deteriorates or a storm is spotted, they move into the nearby shelter locations. This procedure might be considered when all of the following conditions are present:
- Building spotter has a clear, unobstructed view to the storm.
- An extremely quick, reliable, relay of information to occupants is possible.
- The final destination shelter is easily and quickly accessible.
- Identify obviously dangerous spaces.
- Make a note of spaces that look good but are really dangerous. These include locations where a high heavy wall or chimney might collapse into an interior space, or there is overhead heavy mechanical equipment that might fail.
Don't pretend to be a structural engineer or architect. Don't try to guess about the building's structural system or whether windows will resist tornado blown debris. However, it should be possible for you to clearly identify those locations that are likely to be very dangerous and to also identify many of the safer locations.
Best Available Shelter Against High Winds
This checklist procedure is designed to assist in a systematic review of a building to find the locations of the "best available shelter space against high winds". It is not intended to infer that these spaces guarantee safety during a severe storm, but they are the safest available in the building.
- Obtain the following equipment:
- Tape measure
- Soft tipped rod (pool cue)
- Know tornado history for the geographic area (consult nearest national Weather Service Office.)
- Obtain plans of the building for each floor. Ideal plans are small, to scale with sufficient detail. If the drawings aren't available, have someone prepare a simple, yet accurate drawing of each floor. Check the drawings against the actual building. Do not assume accuracy.
Established "true" (magnetic) north. Use a compass or compare the building to an accurate map of the locality. Place a north arrow on the floor plans of the building. Do not confuse "true" north with "building" north, a direction used by architects to simplify the drawings.
Observe completely around the building looking for and recording the location of:
- Potential missiles (site equipment, nearby buildings, debris, etc.) especially on the south and west sides of the building.
- Ground embankment against the building.
- Mechanical equipment on roof.
- Electric service entrance.
- High building elements (chimneys, higher portions of the building.)
- Changes in roof level.
Take a look from the south and west, noting building entrances and construction.
Interior Survey (Portion of the Building to Avoid)
Using the understanding of tornado behavior and its effects on buildings to predict what the tornado would do to a building. Carefully identify the following spaces as the most hazardous locations/spaces to avoid! Predict which portions of the roofs are most likely to be removed.
- Windward sides (usually south and west)
- Long spans
- Non-framed construction (roofs on load bearing walls)
- Roof with overhangs
Avoid locations where roofs are likely to be removed. The roof may fall on the occupants. Missiles also have direct access to interior spaces.
Avoid exterior walls that are most likely to be partially or completely destroyed. Examination of damaged buildings shows that any side of a building can be destroyed but that the most likely damage occurs in the following order:
- South Wall
- West Wall
- East Wall
- North Wall
Avoid corridors (if any) that may become "wind tunnels". Examination of corridors after tornadoes has revealed much debris and evidence of high speed winds. This evidence was found in corridors whose exterior doors exited directly (no turns) to the following directions (in order of severity):
- To the South
- To the West
- To the East
- To the North
Avoid those locations with glass facing the likely storm direction. Assume that the glass will blow in on the south, west, and occasionally on the east sides of the building. Some buildings are building using various types of construction. Avoid (when possible) parts that contain load-bearing walls. If the wall collapses, the roof or floor above will fall.
Interior Survey (Portions of the Building to Consider - but Not Necessarily Select)
Examination of building failures after high winds reveal a pattern of spaces still remaining after the storm. These are the spaces to consider for occupancy.
- Consider the lowest floor. If the building has a basement, or a partial basement, it is probably the safest space in the structure.
- Consider interior spaces. These are spaces that have no walls on the outside of the building. Do NOT select interior spaces that have large spans.
- Consider spaces having short spans. It is difficult to find one space that will offer a high degree of protection to all of the building occupants (exception is the basement). Therefore, seek out a number of smaller spaces.
- Consider portions of buildings that have structural frames (steel, concrete, wood) rather than those portions that have load bearing walls.
- The space per person depends on the age of people and their degree of mobility. Small children require only 4 sq. ft/person. 6 sq. ft/person is adequate for adults. However, nursing home or hospital patients will require much more.
Interior Survey (Poor Spots in Generally Good Locations)
It is essential that the spaces selected be refined to the very best possible. Often poor (relatively hazardous) spaces exist within generally safe areas. These poor spaces must be avoided or occupied as a last resort.
- Avoid spaces that are opposite doorways or openings into rooms that have south or west facing exterior walls. This is particularly critical if these exterior walls contain glass.
- Avoid interior locations that contain glass (example: display cases, transom glass, door sidelights, etc.)
- Avoid interior locations under or near skylights or clerestories.
- Avoid locations where interior doors swing. When the storm hits, the doors are likely to swing violently.
- Avoid spaces within the falling radius of higher building elements (such as chimneys, wall enclosing higher roof areas, etc.) Assume that the falling radius is equal to the height of the high element above the roof.
Questions to Be Answered Before Final Selection
Often the "best available" spaces in the building cannot be occupied during emergencies due to various legitimate reasons. These questions should help identify these potential conflicts before an emergency occurs.
- What portion of the space is usable? Permanent equipment, furniture, etc., reduce the usable space.
- Which good spaces are often inaccessible? Many excellent spaces are locked with few people having keys.
- Which good spaces are unsuitable for occupancy due to operational reasons? Many security areas offer excellent protection but are operationally not good due to the need to retain security over records, equipment, or money.
- Where is the building first-aid kit or medical supplies? These items should be in one of the "best available" spaces.
- Would protection levels increase significantly (and time to shelter decrease significantly) if people were "jammed" in at a lower square foot per person ratios? This is a valid alternative to lower quality protection with more adequate space per person. A plan is almost worthless if it is not tested and understood by the people it is intended to protect. A good plan has the following features:
Recorded & published
- Identifies one or more "spotters" who are responsible for prompt, accurate visual identification of an approaching storm. (National Weather Service will provide training).
- Prompt, clear warning alarm that is readily understood by all.