Mike Mln said:

how does everyone else manage when they come across the edge case that would make applying the standard less effective

You apply for a derogation. Or, in human speak, you present evidence that what you are doing achieves the same effect that the standard was trying to achieve, and - importantly - achieves the same level of risk.

Remember standards aren't laws, they're standards. You don't have to comply with them. But if you don't, and there's an accident, you have to have a good argument as to why you didn't. Like most of the Highway Code - you don't have to comply to it, but if you don't and then you have an accident the fact that you didn't could be seen as negligent.

I can imagine that your problem might be, who do you get to sign off that your alternative (your derogation) is ok. If there is someone competent (end client, licensing authority etc), and particularly if they required you to work to that standard in their contract, then its a process of presenting them the argument and them accepting it, that's pretty usual.

But otherwise it's much tougher, you have to take the risk of making the decision yourself, and getting your evidence ready in case you ever get challenged - which will probably be after an accident, and the challenge will happen in court. Which won't be nice.

Also, remember that your legal responsibility is to reduce the risk "as low as is reasonably practicable". So for example you might need to show that it's not reasonable to accept the number of nuisance shut offs - that the cost of that is disproportionate to the benefit. If the emergency shut off is positioned there in the standard to prevent the risk of someone dying (i.e. the benefit is that you save a life in the lifetime of the system) then that might be hard to prove.

I don't suppose that's completely helped, because  it depends so much what sort of contract you're working on, but hopefully it's made it a bit clearer.

Really good question.

Thanks,

Andy

further to that, and again without seeing the standard or understanding the exact situation, these are some things to inform that discussion -

1) Who is expected to operate the E-stop,   and when would they be expected to do so ?

Presumably not the local drunken youth coming back from a night out, but perhaps emergency services, or technicians coming in to service it or night watchmen or caretaking staff if there is a warning light on somewhere ?

2) Where are the things being cooled/ heated, where are the other controls and who has access to them - would there be a better place?

3) How serious would an unplanned switch-off be ?

Or one could imagine a double door/ internal or external porch or corridor type arrangement to meet the letter of the rules but unless there already is one, it might rapidly get a bit silly. 

Mike,

which needs to be outside the room

Being a little pedantic, but does it say where outside the room? (e.g. immediately outside, within sight of the entrance door, or such like). Otherwise, logically, anywhere beyond the room is outside the room - e.g. inside some other room even in another building, might comply.

  - Andy.

Hi Andy,

This is really helpful.

As I have never really had to depart from the standards, learning about derogation and how it can be utilised for the job, is quite useful to know.

Hopefully I can get everything together and come up with a suitable Risk Assesment, it might come to nothing in the end, but I have got new knowledge I can use where needed.

Thanks

Mike

Hi Mike,

mapj1 said:

1) Who is expected to operate the E-stop,   and when would they be expected to do so ?

This is a tough one to answer in a way, as the room is for authorised people only, you would think it would be for them.

I dont know when they would be expected to do so, as for a lot of the standard it is about more Toxic and harmful refrigerant than is being used in the heat pumps we are using, so in those cases, there are requirements for leak detection and beacons and alarms, but the ones we are using dont require those features. So knowing when they would use this switch in that case I dont actually know, as there would be no outward indication that it needed to be hit.

mapj1 said:

2) Where are the things being cooled/ heated, where are the other controls and who has access to them - would there be a better place?

The system is replacing the gas boilers for the site, so it will be doing both Domestic hot water (DHW) and space heating, so it is acting as a second stage heat transfer onto the exisitng pipework that runs through the whole building.

The control panel/BMS for the system is located in the same room, the interfaces would also be for authorised personal only.

mapj1 said:

3) How serious would an unplanned switch-off be ?

As a threat to life, none existant, essentially the building would lose all heating and hot water. The hot water system has backup immersions, but if it stayed off too long, they would burn out. So really damage to equipment would be a worry, plus if it happens often there would be a worry of legionnaires' in the hot water system.

Thanks

Mike

Hi Andy,

As I am at home now, I dont have the exact wording, but it makes it sound like it is immediately outside next to the door to the room. I dont believe you could have it in a different room or another building, due to it needing to comply with EN ISO 13850, which part of it mentions locations and it needing to be suitably close to what the switch is controlling.

Thanks

Mike

Mike Mln said:

This is especially odd in this case as the stop would not serve to avert or reduce hazards to people or damage to machinery, which is what the emergency function is intended for.

I'm no expert in such things, but I can imagine that a faulty cooler could catch fire and leak refrigerant averywhere.  I wouldn't want to be the person who has to go into that room to hit the emergency stop button.

Hi Simon,

I would say that a fire is not an situation where an emergency stop would be effective as by pressing it wouldn't stop the fire (the main hazard in that case). The emergency stop function in the standard suggested reads more like averting hazards by stopping movement based devices (reads like it is intended or based on conveyor systems).

The reason I think it is ok to omit in this case, is it is an unoccupied room with no through ways, so the only reason to be in there is maintenance of equipment. When maintenance is being done the management system would turn off the system function, then parts that need maintaining would be isolated as required.

The refrigerant is contained inside of the heat pump enclosure, so if it leaks it isnt spraying across a whole room, it is into its enclosure. If it does leak an emergency stop wont stop it from leaking. The only other risks are from the characteristics of the refrigerant itself, but in this case, it is low toxicity and low flammability and the size of the discharge is low enough to not displace enough O2 to be considered hazardous.

The heat pump itself also has measures built into its design, to reduce risk.

I am not against having emergency switches available for the system itself, it is just the one instance where it would be placed in public access, the standard for emergency switches also says to not place in areas where it can be activated unintentionally.

The standard also calls for another switch just inside the room, which I have no issues with.

Mike