E-Stops and protection against unintended operation.

Tharon

Member
T
Join Date
Jan 2007
Location
Other
Posts
1,430
I've noticed that depending on who inspects your plant, the OSHA requirements seem to change.

Recently we had an inspection and we were told that a few of our Emergency Stop buttons which were guarded against unintended activation using manufacturer supplied guards were a violation. Usually for the small little differences in code interpretation, I don't care and just do it to make the inspector happy. But guarding an E-stop against unintended activation is important when it comes production at times. I'm not sure how I should handle this. The guards that some manufacturers sell are just rings around the outside that stop you from bumping into them and activating them. From what I can gather, guarding E-stops is fine as long as it doesn't stop you from operating it.
 
I'm curious... what OSHA codes cover the guarding of E-stop buttons? Can you post a code reference?
 
I can't, at least not without researching. I just have the piece of paper from the inspector telling us what needs to be fixed.

Edit:
I always thought that while OSHA didn't cover everything they included phrasing about following local regulations which would include things like the various NFPA rules into OSHA's list of musts.
 
Last edited:
Tharon said:
I always thought that while OSHA didn't cover everything they included phrasing about following local regulations which would include things like the various NFPA rules into OSHA's list of musts.
Click to expand...
Yes, I've found that the OSHA codes really don't go into any detail whatsoever except for specific kinds of equipment like punch presses. We are told to "follow local regulations," but in my experience I've never seen any codes dealing with guarding of E-stop buttons. Unless perhaps the inspector is concerned about general accessibility of the button.
 
NFPA79 10.7.1.1:
"Stop and emergency stop pushbuttons shall be continuously operable and readily accessible."

EDIT: This is 2012 version
 
NFPA79 section 10.7 is what I would go to, but the old copy on my desk doesn't address collars or guards.

I think the argument would come around 10.7.1.1: "Stop and emergency stop pushbuttons shall be continuously operable and readily accessible".
 
I don't think there is anything in that statement that precludes the use of a guard against inadvertent operation of an E-Stop.

After all, they have put e-stops in the same classification as ordinary stop buttons, and most makes of those are the recessed type where the button cannot (or is difficult to) be pressed "by accident".

I would ask the inspectorate to quantify the violation by stating what code has been violated. I'm guessing this is just one guys interpretation of a loosely worded requirement.

I cannot see any reason why manufacturers would continue to make and sell E-Stop shrouds that violated any safety codes.
 
I've been meaning to get a copy of NFPA 79. While we're on the topic. What code books would you recommend an Electrical Engineer keep handy in an automotive factory environment in the United States? Currently I just have the NFPA 70. Been meaning to get NFPA 70E and NFPA 79.
 
I went to a safety design seminar and the speaker told us guards on E-Stops violated code. From the language of the code itself, it seems that the key phrase--"readily accessible"--is really up to the interpretation of the inspector. To me, "readily accessible" means out in the open and not hidden behind a pile of boxes or inside the control panel or something. The argument against guards would be if someone were to slap their palm against a guarded E-Stop (which is instinct for most people), it might not go in. I could definitely see how an inspector could interpret the "readily accessible" clause to apply to guards like that.
 
Here we go again. It is hard to write a rule that is clear to all who read it and apply it. No wonder we have so many lawyers. Terms like readily accessible are guaranteed job security for lawyers.

I have backed into E stops and shut a machine down - quite easily done - and results in a typhoon in a teacup with production. Putting a shroud around it makes some sense yet the shroud does require more effort ie better eye and hand coordination to activate the E stop.

Many were the times when I did OSHA type inspections for State of Ore we were told it is a judgement call. So what happens is we have the judgement of many individuals design engineers, installer, operator, Safety Guy (in plant) and Safety Guy (compliance inspector). Whose judgement is the final and correct one?

I think I would challenge this one.

Dan Bentler
 
In my opinion, when you have an E-Stop button that gets inadvertently actuated, you should relocate the button rather than install a shroud around it. It is better to make it less likely to be actuated by mistake than to make it harder to actuate.
If it is getting actuated by people leaning over or leaning on the control desk, move it away from the edge. If it is getting actuated as people pass by it, move it a little further out of the traffic pattern.
 
Steve Bailey said:
In my opinion, when you have an E-Stop button that gets inadvertently actuated, you should relocate the button rather than install a shroud around it. It is better to make it less likely to be actuated by mistake than to make it harder to actuate.
If it is getting actuated by people leaning over or leaning on the control desk, move it away from the edge. If it is getting actuated as people pass by it, move it a little further out of the traffic pattern.
Click to expand...

Have seen E stops mounted on front of machine at waist height - seems silly to me. Agree that they should be mounted out of walkway etc.

Dan Bentler
 
brstilson said:
The argument against guards would be if someone were to slap their palm against a guarded E-Stop (which is instinct for most people), it might not go in. I could definitely see how an inspector could interpret the "readily accessible" clause to apply to guards like that.
Click to expand...

leitmotif said:
...Putting a shroud around it makes some sense yet the shroud does require more effort ie better eye and hand coordination to activate the E stop.
Click to expand...

In my opinion, the inspector may not be just looking at...

NFPA 79: 10.7.1.1: said:
"Stop and emergency stop pushbuttons shall be continuously operable and readily accessible."
Click to expand...

but also...

NFPA 79: 9.2.5.4.1: said:
"Emergency stop functions provided in accordance with 9.2.5.3 shall be designed to be initiated by a single human action."
Click to expand...
The inspector may also be interpreting the guard as an obstruction to the "single human action" required to operate the emergency stop.

We have some guarded emergency stops, just to protect them from top or side impact from large objects, such as fork-trucks. But the emergency stop stalk is longer and so is proud of the guard so it can be seen and easily activated.

If the guard is deeper than the emergency stop, that's where they tend to have an issue. It's not accessible enough and may not be activated at the first attempt. Also, if the person cannot see the emergency stop from the side, this could be a breach.

Tharon,

In your opinion, do you think the guarding obscures the emergency stop from sight and could possibly prevent that required single action?

G.
 
Now just to muddy the waters, from ANSI/RIA R15.06, applicable if you're using a 'robot':
"4.6.3 Emergency Stop device design
Push-buttons that activate an emergency stop circuit shall be:
a) red in color with a yellow background;
b) unguarded;
c) palm or mushroom head type;
d) the type requiring manual resetting;
e) installed such that resetting the button shall not initiate a restart. (emphasis added)"

On the other hand, from ISO 13850 Safety of machinery -- Emergency stop -- Principles for design:
"4.4.2 An emergency stop device shall be located at each operator control station, except where the risk assessment indicates that this is not necessary, as well as at other locations, as determined by the risk assessment. It shall be positioned such that it is readily accessible and capable of non-​​hazardous actuation by the operator and others who could need to actuate it. Measures against inadvertent actuation should not impair its accessibility. (emphasis added)"

This would certainly indicate that preventing inadvertent actuation is allowable if it doesn't impair intentional activation.

Now comes the difficult (read: impossible) task of convincing your OSHA inspector that the guards do not impair intentional operation.

It all comes down to his interpretation of "readily accessible." Or to whoever handles the appeal when you get fined. Or to the judge (jury) that hears a possible lawsuit when someone gets injured using the machine.
 
I don't think a "palm-operated" button, once shrouded, can be operated with the palm of the hand.

However, if you go for "mushroom" head, there is no requirement to operate it with the palm - and pressing in a button with your fingers is still a "...single human action".

Probably best to put a small HMI next to each E-Stop, which prompts "Are you Sure ?" if the e-stop is actuated... (only kidding !!).
 

Similar Topics

K
Emergency stops
Hey guys. currently running an automation system that includes 60 Panasonic servo drives with STO function. Omron PLC tied into the safety system...
2
Replies
20
Views
941
JLand
J
O
Alarm when Analog Signal stops moving
Hello, I have a compact Logix plc and I have been task with configuring alarms into our SCADA when an Analog signal stops moving. The analog...
Replies
6
Views
238
Ones_Zeros
O
R
L83ES stops communicating to ABCIP IO server
Have a customer that has a running 1756-l83es, communicating to redundant ABCIP IO servers for Wonderware 2020. This configuration has been...
Replies
7
Views
875
robertmee
R
N
IGS stops reading booleans after firmware upgrade
Hi. I'm trying to update the firmware on some ControlLogix's. They're being polled by an IGS driver. After the upgrade, my floats and integers...
Replies
5
Views
1,383
harryting
H
P
Micro870 CCW: Signal stops before coil, coil does not get energized
Hi all. This is my first time working with the CCW software, and I'm using the CCW developer edition version 21. The PLC is a Micro870...
Replies
4
Views
1,503
5618
5618
Back
Top Bottom