MEPX
Chapter 10 of 12All chapters
  1. 1What engineers do
  2. 2The design process
  3. 3Forces and loads
  4. 4Stress, strain and materials
  5. 5Structures
  6. 6Mechanisms
  7. 7Electrical basics
  8. 8Energy in machines
  9. 9Manufacturing and tolerances
  10. 10Safety factors and failure
  11. 11Testing and standards
  12. 12Responsibility

Chapter 10 of 12

Safety factors and failure

Designing for the day it goes wrong.

Factor of safety

A factor of safety is how much stronger a design is than the load it is expected to carry. A factor of 2 means it should survive twice the expected load, and the number comes from uncertainty rather than optimism.

  • Higher factors where loads are unpredictable, materials vary or failure hurts people.
  • Aerospace uses low factors and compensates with testing and inspection, because weight costs.

Failing safely

Good design decides in advance how something breaks: a fuse blows, a shear pin snaps, a beam bends visibly before it collapses. Sudden failure with no warning is the outcome worth engineering away.