Introduction to System / Product / Design Safety Concepts

What do we Mean by ‘Safe’?

Hi everyone and welcome to the Safety Artisan. Whether you want to know how safety is done or how to do it, I hope you'll find today's session helpful.

So, let's get started. Well, we're going to talk today about System Safety concepts. What does it all mean? We ask this question because the answer is not obvious, as we will see.

If we look at a dictionary definition of the word safe, it's an adjective. To be protected from or not exposed to danger or risk. Not likely to be harmed or lost. There are synonyms – protect, shield, shelter, guard, and keep out of harm's way. They're all good words, and I think we all know what we're talking about. However, as a definition, it's too imprecise. We can't objectively say whether we have achieved safety or not.

What we need is a better definition: a more practical definition. I've taken something from an old UK Defence standard. Forget about which standard, that's not important. It's just that we're using a consistent set of definitions to work through basic safety concepts. And it's important to do that because different standards, come from different legal systems and they have different philosophies. So, if you start mixing standards and different concepts together, that doesn't always work.

OK so whatever you do, be consistent. That's the key point. We will use this set of definitions from the U.K. defense standard because they are consistent. In this standard, ‘safe’ means: “Risk has been demonstrated to have been reduced to a level that is ALARP, and broadly acceptable or tolerable. And relevant prescriptive safety requirements have been met. For a system, in a given application, in a given Operating Environment.” OK, so let's unpack that...