MIAMI - Herbert Saffir, an engineer who created the five-category system used to describe hurricane strength and warn millions of an approaching storm's danger, has died. He was 90.

Saffir died Wednesday from complications of surgery, said his son, Richard Saffir.

A structural engineer, Saffir created his scale in 1969 - laying out for the first time what kind of damage could be expected from an approaching hurricane. It has since become the definitive way to describe intensity for storms that form in the Atlantic and parts of the Pacific. Before the scale, hurricanes were simply described as major or minor.

Saffir's innovation was ranking storm destruction by type, from Category 1 - where trees and unanchored mobile homes receive the primary damage - to Category 5 - the complete failure of roofs and some structures. The five descriptions of destruction were then matched with the sustained wind speeds producing the corresponding damage.

Saffir's scale was expanded by former National Hurricane Center director Robert H. Simpson and became known as the Saffir-Simpson scale in the 1970s. The scale is now so well known that many coastal residents toss off shorthand like "Cat. 1" and few need to be told that it refers to Saffir and Simpson's creation.

Simpson said the system helped him communicate the power of an approaching storm.

"We had a lot of requests before the scale: how many resources of what kind would be needed to deal with the storm," Simpson said during a phone interview earlier this year. "I couldn't tell the Salvation Army, for example, how much and what materials they should be shipping. The scale gave them a much better handle on that."

Simpson added possible storm surge heights for each category, and the hurricane center staff made a small adjustment to the scale's wind speeds. Simpson, 95, now lives in Washington, D.C.

Saffir was born in New York in 1917. He graduated from Georgia Tech with a degree in civil engineering in 1940 and then served in World War II, later moving to South Florida to become a county engineer.

Because of the area's vulnerability to hurricanes, Saffir quickly became an expert in how hurricane-force winds affect buildings. He helped write and unify building codes in South Florida.

Saffir began working on an intensity scale in 1969 as part of a United Nations project. He had been asked how the U.N. could lessen hurricane damage to low-cost buildings worldwide. To help officials understand the full range of hurricane damage, Saffir proposed rating storms from one through five. Scales for rating earthquake damage were already well known, and Saffir believed hurricanes needed their own system of ranking.

He presented his system to Simpson, who began to use the rankings internally and later for a weather report meant largely for emergency agencies. The scale was so useful, however, others quickly adopted it.

It was later used for public hurricane forecasts, making the pair's names synonymous with the Atlantic hurricane season.

For storms that originate in the Pacific Ocean, called typhoons, a five-point scale is also used, but it is based on wind gusts, not sustained winds.

While Saffir became known for the scale, he continued to work as a structural engineer at his Coral Gables office past his 90th birthday. He also traveled to inspect storm damage, even producing reports on the performance of structures during 2005's Hurricane Katrina.

Despite devoting much of his life to thinking about and preparing buildings for hurricanes, Saffir acknowledged earlier this year that his own home was not completely protected from a storm with hurricane shutters. He had done studies on the glass in the windows and found it was relatively shatterproof, he said. At the same time, he told The Associated Press, "I confess I only have partial shutters."

Saffir's wife, Sarah, preceded him in death. Besides his son, he is survived by daughter Barbara Saffir.

The Saffir-Simpson hurricane scale of ranking storm intensity

The Saffir-Simpson scale of a hurricane's intensity is used to estimate the potential property damage and coastal flooding. The scale is determined by wind speed, since storm surge sizes depend on the slope of the continental shelf.

- Category 1: Winds 74-95 mph. Storm surge 4 to 5 feet above normal. Damage primarily to unanchored mobile homes, shrubbery and trees. Some damage to poorly constructed signs and piers.

- Category 2: Winds 96-110 mph. Storm surge 6 to 8 feet above normal. Some roof, door and window damage to buildings. Considerable damage to mobile homes, small watercraft, trees, poorly constructed signs and piers. Flooding of coastal and low-lying areas.

- Category 3: Winds 111-130 mph. Storm surge 9 to 12 feet above normal. Some structural damage to small homes. Mobile homes destroyed and large trees blown down. Coastal flooding destroys smaller structures and floating debris damages larger structures. Terrain lower than 5 feet above sea level may flood as far as 8 miles inland. Hurricane Katrina, the costliest natural disaster in U.S. history, was a Category 3 storm at landfall in 2005 after being a Category 5 in the Gulf of Mexico.

- Category 4: Winds 131-155 mph. Storm surge 13 to 18 feet above normal. Wall failures and roof collapses on small homes, and extensive damage to doors and windows. Complete destruction of some homes, especially mobile homes. Major coastal flooding damage. Two 2004 storms were Category 4: Hurricane Ivan, which made landfall near Gulf Shores, Ala., and Hurricane Charley, which hit the Florida Gulf Coast near Fort Myers.

- Category 5: Winds greater than 155 mph. Storm surge greater than 18 feet above normal. Complete roof failure on many homes and industrial buildings. Smaller buildings and mobile homes blown over or completely blown away. Major damage to lower floors of all structures located less than 15 feet above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5 to 10 miles inland may be required. The last Category 5 storm to hit the United States was Hurricane Andrew in 1992. Two Category 5s made landfall for the first time in the same season this year in Central America.

- Source: National Hurricane Center