Upgrade E-stop system ?

Does anyone know if it is a requirement that when you make a control system upgrade (new drives, PLC, HMI, etc.) are you required (and by whom)to meet certain safety standards, specifically an upgrade to an outdated Emergency stop system?

It depends on where you are at.

In Europe, there are safety regulations that have the force of law; you must follow them under the penalty of criminal prosecution even if no one was ever hurt. In North America, it is mostly the area of civil jurisdiction so although there is no mandatory statutes, your customer and possibly you may be held liable in case someone does get hurt. Which usually means lots of money in fines in compensations.

Therefore, it is always a good idea to suggest upgrading the safty system as well. And to get some kind of written waver in case your customer refuses to pay extra costs for the upgrade.

Clear, but not clear-cut.

It's a BIG topic, and as noted differs a lot depending on your location. Your profile doesn't say.

Since I'm in the United States, I start with the Occupational Safety and Health Act of 1970: OSHA.

Here's a nice readable overview of how OSHA 29 CFR 1910 is the umbrella under which all national, state, and local codes huddle:

http://www.grainger.com/images/US_Safety_Standards.pdf

The question you're really asking is "how much do I have to change about a machine before I should do a safety analysis" ?

And I don't know.

I've discussed this with customers and co-workers in the past, and it always ended up that because we were altering the components of a machine that controlled its movement, that we also needed to reconsider the safe control of that movement, so we did a hazard analysis from the beginning.

I know in our company if we change out something and notice that it does not meet current safety requirements, we are required to bring it up to code. Checking out the laws in your state and OSHA requirements is a good ideal. It could save you from a costly lawsuit later on.

If you modify the system in any way, then you are at risk of being held liable in civil court for any accidents subsequently associated with the equipment.

I once worked for a company that was named as a defendant in a lawsuit simply because we applied 480 VAC power to an OEM system that was later involved in a workplace injury. We weren't found liable, but we had to go to court nonetheless.

The machinery needs to be current to the relavent standards when there is a change performed.
Hydraulics/Pneumatics included.
this seems to be in All OHSA standards.