Hello all,

Hope you are all enjoying the sunshine (short-lived though it will surely be!).

I work in the HE sector and we have many chemical fume cupboards in our facility that are used to protect empoyees from being exposed to harmful chemical agents that they are using. Last week we had a report that one such cupboard had stopped working just before someone needed to use it. The person who was called to it could see that the power to the fume cupboard was off and it seemed "dead". They called the Estates guys, who sent up electricians to investigate. Their analysis showed that the trip on the cupboard had activated and they said that this was because a faulty piece of equipment had been plugged into one of the 13 amp sockets attached to the cupboard. They reset the trip and the cupboard duely started working again. They left, after telling the staff in the area that they had to check the equipment used with the cupboard to ensure it was electrically safe.

I heard about this second hand and was immediately horrified that plugging in a faulty piece of electrical equipment would cause the entire cupboard to stop working. Thankfully, in this case the work had not actually started and people had simply been preparing for the work. However, if the cabinet had failed during the work, the operative and others could have been exposed to dangerous substances. I wrote an email to various people about this and insisted that this had to be investigated immediately to see if it was true that tripping the sockets would stop the entire fume cupboard, whether other cabinets were similarly affected and, if so, take action to rectify this.

An independent check by a qualified electrician determined that the fume cupboard was indeed set up to stop completely if something tripped out the sockets. However, a senior Estates manager has written back to say that this behaviour is likely to be a design feature to cause "total isolation" in the event of a fault and that they would not alter such an installation because "it could risk falling foul of the Electricity at Work Act". We are still awaiting a reply from the cupboard manufacturer about this, but my question is:

1. What aspect of the EAWA exactly would we "fall foul" of if the cupboard were set up with independent trips for the sockets and fan? I cannot really think of any, but I am willing to be corrected.

2. Not withstanding any EAWA issues, I feel that the current design does reflect a very poor design principle (ie failing to danger) and does mean we are breaching our responsibility to protect employees AFAIRP under HSWA,COSHH,IRR & PUWER. I think the design might also breach the EU machinery directive.

Surely it has to be safer for a fault on the sockets not to stop the entire cupboard. I think the Estates manager is looking too narrowly at one aspect of safety.

What are peoples' thoughts?

I also work in the HE sector, and this gives me pause for thought - I wonder if I have the same problem!

I agree with you absolutely, a fault that trips the associated sockets should not trip the fume cupboard itself. I would challenge the view of Estates - this cannot be right.

Paul - these sockets are usually on the panels just outside the booth, along with gas taps, water taps, air flow indicators etc. My particular problem when some of mine were installed was that ajacent cupboards were on different phases, leading to sockets less than 15cm apart on different phases! I got it changed.

Obviously 3 phase equipment is, well, 3 phase, so is not relvant to the discussion.

I disagree with you on the proximity of different (single) phases, particularly in a lab environment. The age of the variac is not quite over. I have discussed this with one of the specialist HSE inspectors whose verdict was that putting two phases in close proximity is extremely bad practice.

This is quite an old tale but I tell it because it seems relevant...

When we were designing and building our new radio studio (1992) we needed separate phases in each room because we wanted audio equipment to be on its own phase to reduce the possibility of line noise, for example if a cleaner plugged a vacuum cleaner into a mains socket: The electrical engineer designing the install told us we couldn't have different phases on sockets in the same room, and suggested there was a reg against it.

As the engineer later married my sister I know him quite well and consider him trustworthy in knowing his stuff!

Having said that I have seen in some places (public loos in the university for example) warning that there may be 415 volts between adjacent equipment, which I guess is caused by the same thing, so maybe it's become acceptable more recently? Even if so, I would support Jane's view that using specific equipment might mean that adjacent different phases cannot be allowed in certain circumstances...

Paul, I believe that in an earlier edition of the Wiring Regulations it was stipulated that two phases were not to be placed within 6 feet of one another unless there was a physical barrier (such as a wall).

Johnman - yes, if there is a power cut the fume cupboard user may have a serious problem. They may have more than one problem!

All,

Thanks for the replies. Very informative.

Regarding the issue of what happens if the power fails during an experiment, yes this is a problem. Users are instructed of correct procedure (stop work immediately, close sash, vacate area, report). The fume cupboards are not on UPS systems, which would be an added layer of protection, but I expect was either not considered when cabinets were being procured or it was considered and decided not necessary or would cost too much. Given the limitations of what is in place vs what would be an "ideal" setup, all your answers show that the linking of a critical safety circuit to a non-critical circuit and placing both under the same trip is not sensible to say the least. This is exactly what I thought and I thank you all again for your input. I have some very interesting discussions ahead with the manufacturer and Estates I suspect!

I'm aware of the following good practices that are perhaps not being followed for the fume cupboards in question.
1. Inlet and outlet air flows to the room need to be balanced to get the right face velocities for each fume cupboard, so often there's an inlet HVAC fan as well as the outlet fan on each cupboard. So tripping the outlet fan without doing anything about the inlet air doesn't make sense.
2. I would have expected the outlet fan possibly to be 3-phase as it needs a fair bit of power for a normal fume cupboard. If so, it will be separately wired from the sockets and the Estates guy is talking nonsense - though the supplier may well have wired the trip to operate like that.
3. If the fumes are significantly harmful, there should be a low air flow alarm. However, in many cases fumes are 'nuisance' rather than 'hazardous', in which case the consequences of lost air flow are not as serious as Nick-H suggests re legal duties. For such cupboards, if there's no fixed alarm, small 'tell-tale' paper strips at the bottom of the sash, and awareness by users of the purpose of these are perhaps sufficient?