Tag: system-safety-handbook

In this 45-minute video, I discuss System Safety Principles, as set out by the US Federal Aviation Authority in their System Safety Handbook. Although this was published in 2000, the principles still hold good (mostly) and are worth discussing. I comment on those topics where the modern practice has moved on, and those jurisdictions where the US approach does not sit well.

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System Safety Principles: Topics

• Foundational statement
• Planning
• Management Authority
• Safety Precedence
• Safety Requirements
• System Analyses Assumptions & Criteria
• Emphasis & Results
• MA Responsibilities
• Software hazard analysis
• An Effective System Safety Program

System Safety Principles: Transcript

Hello and welcome to The Safety Artisan where you will find professional pragmatic and impartial educational products. I’m Simon and it’s the 3rd of November 2019. Tonight I’m going to be looking at a short introduction to System Safety Principles.

Introduction

On to system safety principles; in the full video we look at all principles from the U.S. Federal Aviation Authority’s System Safety Handbook but in this little four- or five-minute video – whatever it turns out to be – we’ll take a quick look just to let you know what it’s about.

Topics for this Session

These are the subjects in the full session. Really a fundamental statement; we talk about planning; talk about the management authority (which is the body that is responsible for bringing into existence -in this case- some kind of aircraft or air traffic control system, something like that, something that the FAA would be the regulator for in the US).

We talk about safety precedents. In other words, what’s the most effective safety control to use. Safety requirements; system analyses – which are highlighted because that’s just the sample I’m going to talk about, tonight; assumptions and safety criteria; emphasis and results – which is really about how much work you put in where and why; management authority responsibilities; a little aside of a specialist area – software hazard analysis; And finally, what you need for an effective System Safety Program.

Now, it’s worth mentioning that this is not an uncritical look at the FAA handbook. It is 19 years old now so the principles are still good, but some of it’s a bit long in the tooth. And there are some areas where, particularly on software, things have moved on. And there are some areas where the FAA approach to system safety is very much predicated on an American approach to how these things are done.  

Systems Analysis

So, without further ado, let’s talk about system analysis. There are two points that the Handbook makes. First of all, these analyses are basic tools for systematically developing design specifications. Let’s unpack that statement. So, the analyses are tools- they’re just tools. You’ve still got to manage safety. You’ve still got to estimate risk and make decisions- that’s absolutely key. The system analyses are tools to help you do that. They won’t make decisions for you. They won’t exercise authority for you or manage things for you. They’re just tools.

Secondly, the whole point is to apply them systematically. So, coverage is important here- making sure that we’ve covered the entire system. And also doing things in a thorough and orderly fashion. That’s the systematic bit about it.

And then finally, it’s about developing design specifications. Now, this is where the American emphasis comes in. But before we talk about that, it’s fundamental to note that really we need to work out what our safety requirements are.

What are we Trying to Achieve?

What are we trying to achieve here with safety? And why? These are really important concepts because if you don’t know what you’re trying to achieve then it will be very difficult to get there and to demonstrate that you’ve got there – which is kind of the point of safety. Putting effort into getting the requirements right is very important because without doing that first step all your other work could be invalid. In my experience of 20-plus years in the business, if you don’t have a precise grasp of what you’re trying to achieve then you’re going to waste a lot of time and money, probably.

So, onto the second bullet point. Now the handbook says that the ultimate measure of safety is not the scope of analysis but in satisfying requirements. So, the first part – very good. We’re not doing analysis for the sake of it. That’s not the measure of safety – that we’ve analyzed something to death or that we’ve expended vast amounts of dollars on doing this work but that we’ve worked out the requirements and the analysis has helped us to meet them. That is the key point.

Safety in Different Jurisdictions

This is where it can go slightly pear-shaped in that this emphasis on requirements (almost to the exclusion of anything else) is a very U.S.-centric way of doing things. So, very much in the US, the emphasis is you meet the spec, you certify that you’ve met spec and therefore we’re safe. But of course what if the spec is wrong? Or what if it’s just plain inappropriate for a new use of an existing system or whatever it might be?

In other jurisdictions, notably the U.K. (and as you can tell from my accent that’s where I’m from, I’ve got a lot of experience doing safety work in the U.K. but also Australia where I now live and work) it’s not about meeting requirements. Well, it is but let me explain. In the UK and Australia, English law works on the idea of intent.

So, we aim to make something safe: not whether it has that it’s necessarily met requirements or not, that doesn’t really matter so much, but is the risk actually reduced to an acceptable level? There are tests for deciding what is acceptable. Have you complied with the law? The law outside the US can take a very different approach to “it’s all about the specification”.

Not Just the Specification

Of course, those legal requirements and that requirement to reduce risk to an acceptable level, are, in themselves, requirements. But in Australian or British legal jurisdiction, you need to think about those legal requirements as well. They must be part of your requirements set.

So, just having a specification for a technical piece of cake that ignores the requirements of the law, which include not only design requirements but the thing is actually safe in service and can be safely introduced, used, disposed of, etc. If you don’t take those things into account you may not meet all your obligations under that system of law.

So, there’s an important point to understanding and using American standards and an American approach to system safety out of the assumed context. And that’s true of all standards and all approaches but it’s a point I bring out in the main video quite forcefully because it’s very important to understand.

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