Emergency stop buttons with different functions


Thread Starter


A panel already has two emergency stops - for two diesel engines powering an alternator and hydraulic pumps- and requires a third for the actual control system. The original two are legacy, the latest is new (don't ask).

My gut feeling is that more than one emergency stop mushroom in a single location is dangerous, if they affect different systems- in a panic, the operator can't know which is the right one to push. On the other hand, it's not obvious that killing the whole power system is necessarily the safest thing to do. For example, if someone is trapped in the machinery, the machinery has to be made "safe", but killing the alternator power would kill all but the emergency lights, and the machine operates mainly at night. And killing the hydraulic power might lead to uncontrolled movement of the machinery as it falls back to the no- pressure position.

Has anyone had to treat emergency stops where a panel controls different systems with conflicting requirements?

James Ingraham

Tough situation. Generally, when we run into this we use "Section Stops" for each piece of equipment, and "Emergency Stop" shuts everything down. Since all of you Section Stops are in one place you will still have the "which one do I push" problem, even if you add an E-Stop button for everything. Especially since that would actually mean FOUR pushbuttons in your case. We use a blue mushroom head for Section Stop and reserve red for E-Stop, so that differentiates them. We also sometimes use an over-sized mushroom head for the E-Stop to make it even clearer.

Off hand, I'm not sure there's a great solution to your problem.

-James Ingraham
Sage Automation, Inc.
Multiple emergency stops that do different things would not be allowed where I am. You *can* have multiple "stop" buttons so long as they don't look like an e-stop button and they are not intended to be safety devices. You should have one and only one genuine emergency stop button on a control panel however. I don't know what the laws and regulations are where you are, but I suspect that the same principles would apply.

Furthermore, an emergency stop is a button that you press if there is an emergency and you need to make the equipment "safe". If pressing an emergency stop will *create* a safety hazard, then there is a larger safety design issue present. If killing the power can cause machinery to fall on someone then there is a serious problem. What if a fuse blows on the pump? What if a hydraulic hose or fitting breaks? What if an engine stalls? For that matter, what *should* an operator do in an emergency?

I think the whole machine needs a serious design review, and I also think the problem is not primarily one of controls design. This sort of problem sounds like something the mechanical designer(s) should be taking the lead on, as sticking a bunch of big red buttons all over the machine isn't by itself going to make it any safer. If leaving the power on is dangerous and turning the power off is dangerous, then the machine as it stands now has a design problem.