Overview

Accidents don’t just “happen.” They are caused by bad design. Safety Engineers are the people who make sure the machine doesn’t kill the operator. They assume humans will make mistakes, and they design systems to catch those mistakes.

Core Idea

The core idea is Fail-Safe. If the system breaks, it should break in a safe way.

  • Safe: Elevator cable snaps -> Brakes engage automatically.
  • Unsafe: Elevator cable snaps -> Elevator falls.

Formal Definition

The discipline which assures that engineered systems provide acceptable levels of safety. Key Concept: Hierarchy of Controls (Elimination > Substitution > Engineering Controls > Administrative Controls > PPE).

Intuition

  • The Saw:
    • Old Saw: If you touch the blade, you lose a finger.
    • SawStop: If you touch the blade, a sensor detects your skin and stops the blade in 5 milliseconds. You get a scratch instead of an amputation. That is safety engineering.

Examples

  • Airbags: Explosives in your steering wheel that save your life.
  • Dead Man’s Switch: If the train driver has a heart attack and lets go of the lever, the train stops automatically.
  • Poka-Yoke (Mistake Proofing): Designing a plug so it can only fit in the socket one way. You can’t plug it in backwards.

Common Misconceptions

  • Safety is just following rules: Rules (Administrative Controls) are the weakest form of safety because people ignore them. Good safety is built into the design (Engineering Controls).
  • Zero Risk: There is no such thing. There is only “Acceptable Risk.”
  • Swiss Cheese Model: Accidents happen when the holes in multiple layers of defense line up.
  • Root Cause Analysis: Asking “Why?” 5 times to find out why the accident really happened. (It’s rarely just “Human Error”).

Applications

  • Chemical Plants: Designing pressure relief valves so the tank vents instead of exploding.

Criticism / Limitations

  • Safety Third: Mike Rowe argues that “Safety First” is a lie. Getting the job done is first. Safety is a shared responsibility, not just a slogan.

Further Reading

  • Dekker, Sidney. The Field Guide to Understanding ‘Human Error’.