Bypass guarding through software?

I have been asked by our customer to bypass the machine guarding by using a password button in the HMI, instead of a key switch. Is this ok?

I wouldn't think so. Espescially in an engineered safety system. I am suprised that you CAN do it with a key switch. Is this normal? I have seen this but it was some time ago and I think since all instances of bypasses were removed.

Hi R_c

I would just say carry out a risk assessment, do the paper work, but unless its in a safety plc I would not carry this out as it will come back to you if someone gets hurt. I would also carry out the safe for a key switch bypass function,
carry out a risk assessment, detail the reason and whom can do this only if your risk assessment comes up the the findings that it is ok to do this, contact the machine maker to see have they a system for doing this and if so why.
Its not impossible ( like some robot cells for set up but NOT normal operation )to have this function on SOME machines for SOME tasks but it needs to be taught out correct, good documents to back it up and remember YOU will be the person that will have to stand over this not the person who requested it.

Donnchadh

Donnchadh said:

Hi R_c

I would just say carry out a risk assessment, do the paper work, but unless its in a safety plc I would not carry this out as it will come back to you if someone gets hurt. I would also carry out the safe for a key switch bypass function,
carry out a risk assessment, detail the reason and whom can do this only if your risk assessment comes up the the findings that it is ok to do this, contact the machine maker to see have they a system for doing this and if so why.
Its not impossible ( like some robot cells for set up but NOT normal operation )to have this function on SOME machines for SOME tasks but it needs to be taught out correct, good documents to back it up and remember YOU will be the person that will have to stand over this not the person who requested it.

Donnchadh

Click to expand...

Thanks Donnchadh.
Can you point me in the direction of some kind of documentation that explains this?

NO! Osha rules and regs specifically state what can and cannmot be done. Even a key switch to bypass machine guarding is a big if. as far as i know a key switch has 2 contacts, bypass and to keep the machine from running in autonatic.

bypassing safety guards is a no no.

any time you bypass safety guarding, you are setting yourself and your company up for an eventual lawsuit. someone always forgets to turn the system back on.

if the customer insists, you need to get with legal department and draw up a legal document stating that no one ( you or your company is liable for any injuries / deaths resulting from the changes). but there is always OSHA to deal with after that.

regards,
james

Hi James

This is for Europe not sure about the far side of the pond but I would say have a look at your USA standards.

Here is some light reading

http://ec.europa.eu/enterprise/sect...n_directive_2006-42-ec-2nd_edit_6-2010_en.pdf


Donnchadh

I wouldn't touch it with a ten foot hot stick.

"I have been asked by our customer to bypass the machine guarding by using a password button in the HMI, instead of a key switch. Is this ok? "

Eh, no......

Why is the guard there? To keep personnel safe while the machine is running.

"OK, let's bypass it to carry out some maintenance. Oops, there goes the phone - another issue elsewhere...off we go and forget to take off the bypass."

Operator starts up the machine, realises an issue inside, opens up the guard, gets pulled into the machine and severely injured..... who gets jailed?
The operator? No
The Engineer? maybe, most likely
The Managing Director? maybe, most likely

Do not bypass a safety system with a passworded button .......

Even having the keyswitch to bypass a guard seems like a very, very, very VERY bad idea! Unless this is some abberration where there is some obscure loophole in the OSHA regulations (highly doubtful. those guards were put there for a reason) that allows you to do this, I would stay away from it. If only from a liability standpoint. If someone gets hurt on that machine after you change it, the legal avalanche will come down on you.

Donnchadh,

since this is for across the pond, it's not only no but NO!

you must full fill all European directives, (3 sections)
do an inhouse risk assessment.
have the customer do an in house risk assessment.
and lots more paperwork.

the software bypass will not be allowed unless they changed something recently.
their rules about safety are more strict than the USA.
i can't remember all the rules.


you couldn't pay me enough for that.
the legal red tape and legal battles is worse than in the USA.
regards,
james

The big question before everything else is: WHY?

Make sure they have a legitimate reason why. Inconvenience is not a legitimate reason.

Second, without that safeguard in place how is safety maintained?

It may be permissible to do so.

This is based on ANSI/RIA 15.06-1999 Industrial Robots, so it may or may not be specifically applicable to your machine. This standard allows bypassing of safeguards if "alternate safeguards are provided which provide an equivalent level of protection from the hazard (10.4.4)." Also, important to note with regard to bypassing or muting is that "the bypass control shall be designed and installed consistent with the circuit reliability of the device being bypassed (10.4.4)."

In other words, the bypass has to provide the same SIL or PL of the safety function you just bypassed and there must be some other way to keep people safe when it is bypassed.

In your case, you have to prove that a dangerous failure of the HMI is as likely as a failure of the safety function itself.

Hi James

I don't disagree with you but " I know says he but"
Here in Europe under ce and the new machine directive it would be possible in something like a robot cell with a safety plc and then the robot can only run a 10% of its max speed. I also stress that this would depend on a risk assessment and the findings of this. I did also suggest to contact the machine maker and ask them have done it as they would have to be informed any way.
I am not saying that r_c should bypass them I am only saying that he has to carry out the paper work which may actually show he should not do it, but I did also stress that he would have to stand over it.

Donnchadh

One part of the hazard assessment is "likelihood of avoiding the hazard" or something to that effect. If the bypass also alters the operation (for example, slowing it dramatically, limiting range of operation etc.) the actual hazard level may be lowered enough to allow no or minimal guarding of the process.

Now, whether a software switch can be trusted to ABSOLUTELY limit the process is probably the main factor that has to be taken into account - besides the resultant lowered hazard level. I have no experience with "Safety PLCs". The normal ones I use I wouldn't trust with my life.

bernie_carlton said:

One part of the hazard assessment is "likelihood of avoiding the hazard" or something to that effect. If the bypass also alters the operation (for example, slowing it dramatically, limiting range of operation etc.) the actual hazard level may be lowered enough to allow no or minimal guarding of the process.

Now, whether a software switch can be trusted to ABSOLUTELY limit the process is probably the main factor that has to be taken into account - besides the resultant lowered hazard level. I have no experience with "Safety PLCs". The normal ones I use I wouldn't trust with my life.

Click to expand...

Thanks for all the replies!
The machine has several pneumatic cylinders. The customer would like to be able to put the machine in manual mode and bypass doors switches, to actuate the cylinders for adjustment purposes.

Hi

Again this is only my take on the europe machine directive and please remember I dont claim to know anything about the USA standards.
Now again I say the only way to know the risks is to carry out a RISK ASSESSMENT.
If the cylinders could cause serious harm to some one then I do not have to say anything you have the answer and only you among us here can say as only you know the machine.
I would get some one to carry out a risk assessment and please dont take this the wrong way I dont think that should be you R_C based on the questions you are asking here as there is options on the air which I cant comment on as I dont know the machine.
I did push this tread a little ( ok a lot) further than I normally would but you can see its a position must people will not put them selves in so i would go back if it was me and tell you client some of the findings you have found and say that its better to get the safety person on site to talk it over with a company that carries out machine risk assessments and /or talk to the machine maker.

Donnchadh