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System Safety FAQ


In System Safety FAQs I will deal with the most commonly searched-for online queries.  This post is also the basis for the First in a new series of monthly webinars I’m running.  I will also be answering your questions: leave them in the comments at the bottom of this post!

What is System Safety?

“System Safety is the application of engineering and management principles, criteria and techniques to achieve acceptable mishap risk within the constraints of operational effectiveness and suitability, time and cost throughout all phases of the system life cycle.”


This definition from NASA is spot on. System Safety is fundamentally about reducing the risks of mishaps (accidents). The NASA Office of Safety and Mission Assurance website is great for practitioners!

The #Systems-Engineering 'V' Model
The Systems Engineering ‘V’ Model

“The system safety concept calls for a risk management strategy based on identification, analysis of hazards and application of remedial controls using a systems-based approach”.[1] 


This Wikipedia article reminds us that safety risk management is a subset of risk management in general.  It also brings in the concept of a ‘hazard’, which is typical for ‘system safety’ – see my free lesson on basic risk concepts for more information.

Where Does Safety Start?

Safety is an ‘emergent property’, that is it comes about by pulling together many different things.  Only leaders and managers can deliver these things; it doesn’t work if you try to do it from the bottom up.

“Safety undoubtedly starts at the top. The people leading the organization are the ones most responsible for its safety. It’s simple.”

I would also say that safety begins at the start of the lifecycle with requirements – see my short video about what System Safety is:

Safe System Approach?

“The Safe System approach adopts a holistic view of the road transport system and the interactions between people, vehicles, and the road environment. It recognises that people will always make mistakes and may have road crashes – but those crashes should not result in death or serious injury.”

This is a great view of a safe system approach, or strategy, from the world of road safety.  Road networks, their commercial and private users, neighbors, regulators, emergency services, etc., form a very complex distributed system.

Why System Safety?

What are the benefits?

“A customised Safety Management System will help you create an environment where all employees are empowered to identify hazards before they become problems, so your business can stay safe without losing focus on growth, profit or innovation.”

I would add that a systematic approach to safety saves time and money in the long run.

System Safety for The 21st Century

Traditional System Safety has its critics, most famously professors Nancy Leveson and Erik Hollnagel.  They have made various criticisms of system safety – some of which I agree with, and some I most definitely do not.

Leveson has proposed new methods:

  • System-Theoretic Accident Model and Processes (STAMP);
  • Systems Theoretic Process Analysis (STPA); and
  • Causal Analysis using System Theory (CAST) – accident analysis.

Hollnagel has written on a wide variety of safety topics including cognition, organizational robustness, and resilience.  He also coined the terms “Safety I” for traditional safety approaches, and “Safety II” to describe the conceptual approach that he and others have developed.

He designed the Functional Resonance Analysis Method (FRAM). 

“THE FRAM is a method to analyse how work activities take place either retrospectively or prospectively. This is done by analysing work activities in order to produce a model or representation of how work is done.”

I have tried FRAM, and even without any training (which is recommended), I found it tremendously powerful.  FRAM can analyse problems that conventional safety techniques just can’t get to grips with.   

From FRAM in a Nutshell by Mohammad Tishehzan at
From ‘FRAM in a Nutshell’ by Mohammad Tishehzan at

Others have also introduced the term “Safety III”, but I’m not sure how useful these labels are.  Perhaps we are now on a trajectory of diminishing returns.

System Safety is a Design Parameter

To save us from all this abstract navel-gazing, let’s get back to practical matters.

“Safety-related parameters are control system variables whose incorrect setting immediately increases the risk to the user.”

Concrete, specific, practical: I love it!  Let’s not forget that we do safety for a reason, and big part of that is to control the machines that make our modern world.  This doesn’t sound very exciting, but automation has enabled huge increases in productivity, wealth, health, quality of life, lifespan and human rights.  Let’s remember that during the current hysteria about Artificial Intelligence (actually Machine Learning).

Safety System of Work

“a safe system of work such as safety procedures. information, supervision, instruction and training on the safe use, handling and storage of machinery, structures, substances and other work tasks. personal protective equipment as required. a system to identify hazards, assess and control risks.”

If we think about it, this ties in nicely with the definition of a system used in system safety, e.g.:

“A combination, with defined boundaries, of elements that are used together in a defined operating environment to perform a given task or achieve a specific purpose. The elements may include personnel, procedures, materials, tools, equipment, facilities, services and/or software as appropriate.”

UK Defence Standard 00-56/1

System Safety in Engineering

There are a number of ways that we could answer this (implicit) question.  Here’s one from the Office of The Under Secretary Of Defense For Research And Engineering:

“System safety engineering involves planning, identifying, documenting, and mitigating hazards that contribute to mishaps involving defense systems, platforms, or personnel (military and the public). The system safety practice aids in optimizing the safety of a system.”

This definition neatly pulls together activities, hazards and accidents, those impacted and the aim of the whole thing.  Phew!

There’s More!


I’m going to be talking about these topics in more depth in a webinar on EventBrite.  There are only 25 tickets, which are worth getting for all the extras!  If you don’t get in, then join my email list to get an invitation.

Questions and Comments?

Please leave them below.

Meet the Author

My name’s Simon Di Nucci. I’m a practicing system safety engineer, and I have been, for the last 25 years; I’ve worked in all kinds of domains, aircraft, ships, submarines, sensors, and command and control systems, and some work on rail air traffic management systems, and lots of software safety. So, I’ve done a lot of different things!

Meet the Author

[1] Harold E. Roland; Brian Moriarty (1990). System Safety Engineering and Management. John Wiley & Sons. ISBN 0471618160.