OFFICE PRACTICE AIDS


Storm Power Scale Designed By Miamians
By Jeanne Bellamy


The Richter Scale is to earthquakes as the Saffir-Simpson Scale
 is to hurricanes.
 People have been understanding the magnitude of earthquakes
 for nearly half a century since Prof. Charles F. Richter published
 his scale in 1935. The power of hurricanes stayed nameless until a
 Miami engineer devised the Saffir-Simpson Scale in 1978.
 In that year, Herbert S. Saffir wrote a report for the United
 Nations on low-cost construction to resist high winds. While
 studying hurricanes all over the world for the project, he devised
 a tabulation to explain the destructive strength of these tropical
 cyclones. The full text spells out the kind of wreckage to be ex-
 pected at each level of wind speed.
 For instance, a Grade One storm is "nominal," with winds only
 74 to 95 miles an hour. The worst kind, Grade Five, would be
 "catastrophic," like the Labor Day Hurricane of 1935 which
 knocked over a railway train in the Florida Keys and drowned
 400 persons with a storm surge that roared over the low islands
 11 to 18 feet higher than the normal level of the sea.
 The narrative part of the Saffir-Simpson Scale gives this
 frightening description of a Grade Five storm: "Winds greater
 than 155 miles per hour. Shrubs and trees blown down; consider-
 able damage to roofs of buildings; all signs down. Very severe
 and extensive damage to windows and doors. Complete failure
 of roofs on many residences and industrial buildings. Extensive
 shattering of glass in windows and doors. Some complete build-
 ing failures. Small buildings overturned or blown away. Com-
 plete destruction of mobile homes. And/or: storm surge greater
 than 18 feet above normal. Major damage to lower floors of all
 structures less than 15 feet above sea level within 500 yards of
 shore. Low-lying escape routes inland cut by rising water 3 to 5
 hours before hurricane center arrives. Massive evacuation of
 residential areas on low ground within 3 to 10 miles of shore
possibly required."


 Saffir gave the scale to the Hurricane Center in Miami for the
use of its forecasters. The director of the center, Robert Simpson,
added the estimates of the height of storm surges, so the table
has been known since then as the Saffir-Simpson Scale.
 Saffir, the head of Herbert Saffir Consulting Engineers in
Coral Gables, has studied and reported on hurricane damage to
structures in many parts of the world for 30 years. He is the au-
thor of the South Florida Building Code's section on wind load
requirements. His work made this code the first in the land to
set design standards based on sound engineering principles.
 Few laymen know that wind gets stronger with height. A three-
story building would feel a 120-mile-an-hour wind at that speed.
The same wind would strike the top of a 30-story skyscraper at
167 miles an hour, according to a widely used engineering for-
mula. On this basis, Saffir recently calculated exactly how strong
buildings must be at various heights to survive hurricanes. Using
these figures, the South Florida Building Code will let one-story
buildings be a little weaker than those 30 feet or more in height;
thus saving construction costs.
 The 120-mile-an-hour wind is Grade Three on the scale one
likely to cause extensive damage once in 50 years. Saffir explains
that building for total resistance to hurricanes would be very ex-
pensive and not practical.
 Saffir's report on a tornado that battered parts of Fort Lauder-
dale on May 24, 1979, was printed for the convention of the
American Society of Civil Engineers at Miami Beach in 1980.
He found that the tornado's wind speeds at touchdown were
those of a Grade Five hurricane, at least 155 miles an hour. He
concluded that the destruction he saw was "the type of damage
that would ensue under hurricane conditions even with a strong
hurricane-resistant code."


The Saffir-Simpson Hurricane Scale


Category Description

 1 Minimal

 2 Moderate

 3 Extensive

 4 Extreme

 5 Catastrophic


Mean wind
speeds (mph)

 74-95

 96-110

 111-130

 131-155


Storm surge North Atlantic &
 (ft.) Gulf examples


4-5- Agnes

6-8 Cleo


9-12

13-18


Betsy

David


Greater than 155 Greater than 18 Camille


FLORIDA ARCHITECT September/October 1985