The Corps of Engineers used safety margins in the design of New Orleans storm protection levees that are just too small. Rather than a typical design margin of 2 to 3 times the specified conditions, the corps decided to use a margin of 1.3 times spec in the New Orleans levees.

Safety margins in design protect the public from errors in engineering, maintenance and use of products and services common to modern life. Over design though expensive is considered necessary to make products safe.

For example a typical lightweight step ladder is rated for a maximum weight of 175 pounds. When new it will support at least three times this weight or it would never make it in the market. If it was designed and built to collapse under 225 pounds when new, just think how it would perform after ten years storage in the garage.

A design margin of 30% above specification may be acceptable in protecting crops and livestock but is it what we expect for a modern American city?