> There is a fundamental difference between "we have assessed the risk and here it is below some threshold where we are confident that no further safety measure

> There is a fundamental difference between "we have assessed the risk and here it is below some threshold where we are confident that no further safety measures are required" and "this place is safe, no accidents can happen here." But that is not what was asked in the comment. What was asked is how you know if something is unsafe. > A lockout would have done nothing. You state that very confidently. Do you have insider information you are privy to? Computers controling valves can go bad. Valves can stuck open or closed. Open wider than they were meant to. Open faster than they meant to. You take a diagram of the aparatus and go through all the possible way a valve can misbehave on all possible computer controlled valves and ask: “what would be the consequence of that?” You realise that there is a possibility that a system in question goes rapidly to a high pressure state. You then ask what harm that might cause? You realise that it might blow parts of. Or at least you are not confident that it can’t. So you ask an engineer what is their mitigation for that. If they say “oh we just know it is dangerous, we would never stand by the pipes when the test is running” then you ask them to employ a lockout system. Look. I don’t know anything more about the test they were running than what is written in the article. You are assuming that he was in a safe place, but suddenly it was not a safe place anymore. How does that happen in your opinion? Did the pressure just suddenly teleport in? It is a ton of work to validate control software. Much easier to just stand in a place where even if the controls go haywire you will be okay. I’m reading the same sentence differently from you. To me it means that he shouldn’t have been there during a test. (And also the test shouldn’t have blown up the valve.)