Advice on designing an electrostatic-proof building please.

[Mark42]

I’m converting a steel Portacabin-type box into a lab for static-sensitive equipment and materials.

If there are any ESD gurus on here, I’d appreciate any advice please!

I’ve ripped out all the vinyl, floored it with aluminium treadplate, clad the walls in painted aluminium sheets, and left the ceiling in the original painted steel.

Worktops will be in Trespa anti-static material, there’s a metal fume cupboard, and metal cupboards and shelving. Everything is bonded together, and earthed TT. Earth impedance is good.

I’m also intending to run a bonded metal (copper or maybe ali) strip all round the worktops, with little sockets for plugging in flying earth leads for loose equipment, wrist straps and so on. Conductive shoes will be worn, and no plastics or other insulators allowed in the building.

But this is all new to me: have I missed anything? The most dangerous errors are those you don’t know you’ve made!

And one specific question please:

Is it OK to use 10mm John Guest plastic plumbing pipe (Polybutylene), tucked away under the worktops? I need to run ring mains of mains water, Type 2 pure water, vacuum, and gas. There are no great flow velocities. It’s so much nicer to install, and easier to amend. Is a little bit of plastic pipe which will never be touched really a problem?

 

[pc1966]

You might find the floor is mostly wood over some steel cross-beams, so make sure the building is Earthed to the ground immediately below to keep ant E field down from that source.

Keep the place humidified (within reason) to lower any charge build up of stuff you have not thought about.

Folk moving about are a significant source, so you will have to take care of the types of clothing worn (i.e. keep to natural fibres like cotton/wool and not polyesters, etc) or have semi-conductive overalls.

If worried about the pipes (and flow in an insulators is a risk) then look to screening them by having a mesh cover under the worktops or possibly look at conductive paints, but they won't stick terribly well to plastic, etc. To be honest going for copper pipes and equipotential bonding them is a far safer choice if you need to keep E fields down through materials like wood, or anti-static plastics that are barely conductive (static dissipative), etc.
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Doh, just re-read and you have conductive floors already!
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If it is more than just low electric fields (i.e. you are trying to avoid sparks, etc) then you need to look also at tools and those tend to be expensive for stuff made from beryllium-copper alloys.

Same applies for electrical switches, motors, etc, you would need to look at intrinsically safe ones designed for explosive atmospheres.

There are probably some folk with experience in the oil industries who can tell you more about such standards & practices.
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Also for wiring you would be looking at stuff in metal trunking, metal conduit, SWA cable, or far simpler to handle using Flexishield cable so all circuits are within an earthed shield. Strip lights, etc, might need to have CPC-bonded wire mesh over them depending on how much field you can tolerate.

 

[DPG]

Speak to a company called Vermason.

Consider air ionisers. Also they will need to regularly test things like foot straps and wrist straps, so a tester will be needed. Probably down to them that though.

 

[Pete999]

I’m converting a steel Portacabin-type box into a lab for static-sensitive equipment and materials.

If there are any ESD gurus on here, I’d appreciate any advice please!

I’ve ripped out all the vinyl, floored it with aluminium treadplate, clad the walls in painted aluminium sheets, and left the ceiling in the original painted steel.

Worktops will be in Trespa anti-static material, there’s a metal fume cupboard, and metal cupboards and shelving. Everything is bonded together, and earthed TT. Earth impedance is good.

I’m also intending to run a bonded metal (copper or maybe ali) strip all round the worktops, with little sockets for plugging in flying earth leads for loose equipment, wrist straps and so on. Conductive shoes will be worn, and no plastics or other insulators allowed in the building.

But this is all new to me: have I missed anything? The most dangerous errors are those you don’t know you’ve made!

And one specific question please:

Is it OK to use 10mm John Guest plastic plumbing pipe (Polybutylene), tucked away under the worktops? I need to run ring mains of mains water, Type 2 pure water, vacuum, and gas. There are no great flow velocities. It’s so much nicer to install, and easier to amend. Is a little bit of plastic pipe which will never be touched really a problem?

Have the electrical supply isolated from the mains, M/A set or Isolating transformers. insulate both inside and outside, use wave guides for any entry point to the building.
Raise the building floor from the main floor, air condition to a70deg and 50% RH or as near as possible, use DP mcbs etc.

 

[DPG]

Have the electrical supply isolated from the mains, M/A set or Isolating transformers. insulate both inside and outside, use wave guides for any entry point to the building.
Raise the building floor from the main floor, air condition to a70deg and 50% RH or as near as possible, use DP mcbs etc.

I wouldn't have thought that most of that would be needed for an anti static environment.

 

[Mark42]

You might find the floor is mostly wood over some steel cross-beams …

Exactly correct. It’s pretty rubbish construction actually. I’m adding 25mm Celotex, then a 3mm ali treadplate floor glued down, with bare aluminium wires laid underneath the sheets, all terminated at a main bonding point. I’ve no idea if this is a standard way of doing things, I made it up.

… Keep the place humidified (within reason) to lower any charge build up of stuff you have not thought about. …

Great idea.

… have semi-conductive overalls …

Yes, we’re doing that.

If it is more than just low electric fields (i.e. you are trying to avoid sparks, etc) then you need to look also at tools and those tend to be expensive for stuff made from beryllium-copper alloys.

Exactly correct. It’s all about preventing sparks. The lab is for sensitive explosives.

Same applies for electrical switches, motors, etc, you would need to look at intrinsically safe ones designed for explosive atmospheres.

I think there’s no need for that as it’s for solid explosive materials sitting on a desk on in a flask, not explosive atmospheres, which is an entirely different thing.

Also for wiring you would be looking at stuff in metal trunking, metal conduit, SWA cable, or far simpler to handle using Flexishield cable so all circuits are within an earthed shield.

Flexishield is a great idea. Thanks. It appears you can’t buy cut lengths so I’ve ordered one roll of 2.5 which I’ll use for everything (inc lighting!)

The easiest installation would be one run of dado-rail multi-compartment trunking around the walls, terminating directly into the DB. I’m researching this today. It appears a metallic version is very difficult (and expensive!) to source. Or I'm thinking quality 100 x 50 metal trunking, with accessories cut into the lid, which is economic enough and fully shielded, but would look a bit sh!te

Strip lights, etc, might need to have CPC-bonded wire mesh over them depending on how much field you can tolerate.

I was going to use 3 No. LED IP-rated strips, the type with all the electronics in a metallic enclosure.

I need to keep the cost down so I’m not looking at intrinsically-safe equipment unless I really need to.

… If worried about the pipes (and flow in an insulators is a risk) then look to screening them by having a mesh cover under the worktops or possibly look at conductive paints, but they won't stick terribly well to plastic, etc.
To be honest going for copper pipes and equipotential bonding them is a far safer choice if you need to keep E fields down through materials like wood, or anti-static plastics that are barely conductive (static dissipative), etc.

Agreed but there are other reasons why copper is not a good idea, chemically. Many of the regs for this kind of thing were written sometime in the Cretaceous (probably by actual dinosaurs), before plastic pipework existed. I’ll do some research on the static properties of John Guest pipes, which are either polybutylene or polyethylene first.

I like your metal cage idea, that’s cheap and easy to fabricate.

Thanks for the excellent advice!

I'll post photos once it's done in a few weeks ...

 

[DPG]

Ah, in your OP you said it was for static sensitive equipment. I assumed they were repairing electronic equipment. I see it's actually explosion risk you are looking at. That's a whole different ball game with it's own regulations.

 

[Mark42]

... If worried about the pipes (and flow in an insulators is a risk) then look to screening them by having a mesh cover under the worktops ...

Any idea how dense a mesh cover needs to be to provide electrostatic screening? Would something as simple as bonded mesh cable basket hung on wall clips, directly over the runs of plastic pipes work?

Very easy to buy and fit. If cut into short modules, easy to unclip to make changes to the push-fit pipework.

It would also prevent touching, so even if the pipes carried an electrostatic charge, it can't go anywhere?

I do like simple solutions

 

[pc1966]

I think there’s no need for that as it’s for solid explosive materials sitting on a desk on in a flask, not explosive atmospheres, which is an entirely different thing.

I have a strong suspicion that is likely to be a rather controlled occupation. Getting advice from a bunch of randoms on an internet forum is not something you can depend upon!

Flexishield is a great idea. Thanks. It appears you can’t buy cut lengths so I’ve ordered one roll of 2.5 which I’ll use for everything (inc lighting!)

It is half way between SWA and normal round cable to work with. It tends to stay in place when you bend/set it. It is not "flexible" - it is intended for fixed wiring. However, unlike SWA where you need to carefully fit a gland for the outer armour/CPC, for Flexishield you can use a normal IP68 style plastic gland so far easier to use.

Read the stripping instructions, basically you score the outer sheath and then bend it to split the plastic and aluminium foil, then pull it off. With gloves, and some force.

You can score with a knife if careful, but this sort of tool is far safer & repeatable:

RS PRO Triple Action Wire Stripper, 4.5mm Min, 29mm Max | RS

uk.rs-online.com

The easiest installation would be one run of dado-rail multi-compartment trunking around the walls, terminating directly into the DB. I’m researching this today. It appears a metallic version is very difficult (and expensive!) to source. Or I'm thinking quality 100 x 50 metal trunking, with accessories cut into the lid, which is economic enough and fully shielded, but would look a bit sh!te

Unitrunk make covers for the 100mm and 150mm wide trunking pre-punched for single and double switches/sockets:

Products | Total Cable Management Solutions - trunking, cable tray and ladder: Unitrunk

www.unitrunk.co.uk

While trunking is hard to work with, it is touch and long-lasting. Just remember to use grommets and/or glands for cable in and out, and to ensure it is bonded to your MET.

As you found, also massively cheaper than metallic dado rail style options.

Agreed but there are other reasons why copper is not a good idea, chemically. Many of the regs for this kind of thing were written sometime in the Cretaceous (probably by actual dinosaurs), before plastic pipework existed. I’ll do some research on the static properties of John Guest pipes, which are either polybutylene or polyethylene first.

I like your metal cage idea, that’s cheap and easy to fabricate.

Or wrap it in aluminium self-adhesive tape.

Thanks for the excellent advice!

I'll post photos once it's done in a few weeks ...

We look forward to seeing it.

Also we can discuss where you are likely to appear next:

• Derek Lowe's blog "Things I Won't Work With"
• The Darwin Awards

Ladies, gentlemen, and internet randoms, place your bets

 

[Pete999]

pc1966 there a lot of "RANDOMS" on this forum that have a lot of knowledge, judging from your reply you think are insignificant, chose your wording carefully.

 

[pc1966]

pc1966 there a lot of "RANDOMS" on this forum that have a lot of knowledge, judging from your reply you think are insignificant, chose your wording carefully.

Sorry if I offended anyone, that was not my intention.

It was more the point that if the excrement were to impact on the air-moving apparatus, standing up in a court and saying "But the folk on forum XYZ said this was safe!" is not going to go down well.

 

[davesparks]

Is this a licenced explosives factory?

If it is then I know what the OP means about the rules being antiquated, our fireworks business has a factory licence, the explosives factories act of 1875 is the appropriate law. Although it has been updated a few times since then!

 

[pc1966]

Just to add I consider myself as one of the "internet randoms" here.

 

[DPG]

Just to add I consider myself as one of the "internet randoms" here.

I'm proud to be an internet random. Is there a badge for it?

 

[davesparks]

Just to add I consider myself as one of the "internet randoms" here.

I'm pretty random myself.

 

[Mark42]

Is this a licenced explosives factory?

If it is then I know what the OP means about the rules being antiquated, our fireworks business has a factory licence, the explosives factories act of 1875 is the appropriate law. Although it has been updated a few times since then!

Close. The Explosives Act 1875, AKA 'The Green Book' written by the rather splendid Col. Majendie. I've had my copy for over 40 years. Beautiful, precise law which nearly all made sense. Now almost entirely repealed and replaced by a succession of European-inspired Acts and Statutory Instruments which are impenetrable, daft in parts, and contain typos.

And yes, this is an authorised explosives site, it's what I do. (Electrickery is an adjunct, primarily for personal use).

You're in the fireworks business? We must know of each other. CBI EIG? IExpE?
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Unitrunk make covers for the 100mm and 150mm wide trunking pre-punched for single and double switches/sockets

Brilliant. Well-found! Doesn't look too bad either. A bit of etch primer and a coat of paint and it will both look pro, and save me a few quid . Thanks for the tip.

Or wrap it in aluminium self-adhesive tape.

Good idea. Or stainless cable braid as used on vehicle fuel hoses. And I just found this:

Metallised spiral wrap for use in the food industry. I've e-mailed the manufacturer to ask it it's actually conductive and hence anti-static.
Would be dead easy to install.

... Also we can discuss where you are likely to appear next:

Derek Lowe's blog "Things I Won't Work With" ...

Is that the bloke with the azidoazides which go off if you 'look at them in a funny way'?

Ha Ha, bloody amateur. Here is me enjoying destroying heavily peroxidised Tetrahydrofuran found earlier this year in a Kent lab. A fine day out. Yeah, and now I'm waiting for a chorus of, 'All the gear but ...'

I do rather enjoy my work.

 

[Mark42]

... Getting advice from a bunch of randoms on an internet forum is not something you can depend upon!

Wrong.

I have much more respect for people like those on this type of forum who, like me, actually build stuff than for any number of supposed 'experts' who have done little but read the manual. And I often find those enforcing regulations read the manual only yesterday.

And advice sought does not always have to be taken

 

[static zap]

I know photon energy gets involved in some unstable reactions ,maybe we can include quantum mechanics for if some-one was actually looking/filming ..satellite passing over !
(when a good conductor can meet another conductor )-- 500k -1 M in all sockets could reduce arc from a hand held metal object waved too near a socket... always a compromise between discharge time and reducing current in any small arc ! -- I'm no expert but was wary of being personally earthed
with anything lower than 1MOhm.

 

[pc1966]

Good idea. Or stainless cable braid as used on vehicle fuel hoses. And I just found this:

Metallised spiral wrap for use in the food industry. I've e-mailed the manufacturer to ask it it's actually conductive and hence anti-static.
Would be dead easy to install.

Good ideas in both cases.

Is that the bloke with the azidoazides which go off if you 'look at them in a funny way'?

Yes, his articles are both informative and amusing, with the ones on hideous chemicals usually the best of both:

In the Pipeline by Derek Lowe | Science | AAAS

Derek Lowe’s editorially independent blog on drug discovery and the pharma industry.

blogs.sciencemag.org

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Wrong.

I have much more respect for people like those on this type of forum who, like me, actually build stuff than for any number of supposed 'experts' who have done little but read the manual. And I often find those enforcing regulations read the manual only yesterday.

And advice sought does not always have to be taken

As long as you understand things and filter the advice it is fine!

This forum has a policy of avoiding step-by-step guides for DIY and being very cautious about any advice on the USA forum, etc, to avoid it coming back to bite them if it all goes horribly wrong and things get litigious.
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Also to add you probably will need the building to have a lightning conductor arrangement, at least all explosive stores I have seen have that.

And relating to that is having SPD fitted to the incoming distribution board. With a lighting conductor in use it should be a Type 1+2 to deal with the much higher surge energy in the event of a direct hit (not just induced spikes) and they cost a lot more (single phase in the £300 region, not the £70 region for Type 2 only). Examples include:

DV M TN 255 | Dehn, DV Modular Surge Protector 255 V ac Maximum Voltage Rating 50kA Maximum Surge Current Lightning Arrester | RS

uk.rs-online.com

Type 1+2 Lightning Current and Surge Arrester (KM1+2-25-1+1 SC) - Kingsmill Industries

System: Single Phase TT/2 Pole Nominal Voltage: 230V AC

www.kingsmillindustries.com

Type 1+2 Lightning Current and Surge Arrester (KM1+2-12.5-1+1 SC) - Kingsmill Industries

System: 1 Phase TT/2 Pole Nominal Voltage: 230V AC

www.kingsmillindustries.com

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I'm no expert but was wary of being personally earthed with anything lower than 1MOhm.

Quite right, most ESD wrist earth straps are of the order of 1M for that very reason! For example:

RS PRO ESD Grounding Wrist Strap & Cord Set With 10 mm Socket, 10 mm Stud | RS

uk.rs-online.com

Also in such environments it is not uncommon to use 10mA RCDs as well just to lower the risk further.

 

[DPG]

Close. The Explosives Act 1875, AKA 'The Green Book' written by the rather splendid Col. Majendie. I've had my copy for over 40 years. Beautiful, precise law which nearly all made sense. Now almost entirely repealed and replaced by a succession of European-inspired Acts and Statutory Instruments which are impenetrable, daft in parts, and contain typos.

And yes, this is an authorised explosives site, it's what I do. (Electrickery is an adjunct, primarily for personal use).

You're in the fireworks business? We must know of each other. CBI EIG? IExpE?
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Brilliant. Well-found! Doesn't look too bad either. A bit of etch primer and a coat of paint and it will both look pro, and save me a few quid . Thanks for the tip.



Good idea. Or stainless cable braid as used on vehicle fuel hoses. And I just found this:

View attachment 59918
Metallised spiral wrap for use in the food industry. I've e-mailed the manufacturer to ask it it's actually conductive and hence anti-static.
Would be dead easy to install.

Is that the bloke with the azidoazides which go off if you 'look at them in a funny way'?

Ha Ha, bloody amateur. Here is me enjoying destroying heavily peroxidised Tetrahydrofuran found earlier this year in a Kent lab. A fine day out. Yeah, and now I'm waiting for a chorus of, 'All the gear but ...'

View attachment 59920

I do rather enjoy my work.

Looks interesting!

Did you buy the suit off the guy from Boney M?

 

[Mark42]

Did you buy the suit off the guy from Boney M?

No.
I sold him my spare one.

 

[pc1966]

Fun fact (well, not for him) is that Bobby Farrell died in St. Petersburg on the anniversary of Grigori Rasputin's death.

Oh those Russians...

 

[DPG]

Fun fact (well, not for him) is that Bobby Farrell died in St. Petersburg on the anniversary of Grigori Rasputin's death.

Oh those Russians...

Always a source of good information this forum.

 

[Mark42]

OK, that's enough reminiscing . I'm ordering trunking to use as dado rail today.

Unitrunk looked excellent, until I looked at the price: 100 x 50 x 3m is £193! I though it was a typo.

Very similar Tamlex 100 x 50 x 3m from CEF is £24.17.

I'd have to cut my own holes in the Tamlex, but for an overall saving of £1,012 (!) I think I'll get the jig saw out

 

[pc1966]

Unitrunk looked excellent, until I looked at the price: 100 x 50 x 3m is £193! I though it was a typo.

That is the list price. Most electrical trade places will give you discounts of the order of 70-90% on that if you ask the right folk.
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If your company are doing a lot of this sort of work (internally, not as electrician services, etc) it might be in your interests to apply for a trade account with one or two of the local wholesalers.
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Is the trunking just for a set of 13A sockets? you might find it easier to use the likes of these and glands/Flexishield between them:

MK Electric K2946ALM Metalclad Plus 2 Gang Double Pole Switchsocket With Surface Mounting Box 13A - Shop4 Electrical

Buy MK Electric K2946ALM Metalclad Plus 2 Gang Double Pole Switchsocket With Surface Mounting Box 13A. Shop today.

www.discount-electrical.co.uk

 

[KennyKen]

If you have explosive material or potential to become explosive then you’ll first need to follow Hazard area classification depending on what chemical or potentially explosive Material you are using. Normally cabling would Have to be intrinsically safe ie the use of shunt diodes or enclosures would have to be EX rated depending on the application. EX D is flameproof, EX P is pressurisation of an enclosure. EX E is extra protection and so on. Zoning is generally 0,1 and 2 and that basically goes on your LRL & URL limits.

 

[Mark42]

If you have explosive material or potential to become explosive then you’ll first need to follow Hazard area classification depending on what chemical or potentially explosive Material you are using. Normally cabling would Have to be intrinsically safe ie the use of shunt diodes or enclosures would have to be EX rated depending on the application. EX D is flameproof, EX P is pressurisation of an enclosure. EX E is extra protection and so on. Zoning is generally 0,1 and 2 and that basically goes on your LRL & URL limits.

Thanks for the ideas, but those regs are for explosive atmospheres, as often found in chem plants, or offshore. It has nothing to do with explosive substances. It's a very frequent confusion, especially among regulators.

Think about it - a sparky switch would definitely ignite a gas/air mixture permeating the whole area, but the same sparky switch would not jump across a room and set off a pile of nitrocellulose propellant sitting on a lab bench. It's only static protection which is important to consider in the latter case.
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That is the list price. Most electrical trade places will give you discounts of the order of 70-90% ...

Yeah, it's stupid isn't it? Like arguing with Travis Perkins. We do have trade accounts and I'm good at getting best prices, but not many places advertise the Unitrunk stuff, so it's perhaps too much effort.

Update: I just checked, it appears Unitrunk only sell direct from their own places, and there's no central tel number, only published (massive) list prices and an email form. They appear to be one of those companies which makes it hard to buy from them. Marketing people call this having a 'customer prevention department' I can't be bothered! cf. Two clicks on CEF and Tamlex product can arrive tomorrow ...

Is the trunking just for a set of 13A sockets? ...

No, it's for power, data, telelphone and a DC lab supply as well. Hence the flexibility of using trunking.

 

[Julie.]

I take it that using nitrocellulose propellant, you are loading ammunition, anything interesting?

 

[Mark42]

I take it that using nitrocellulose propellant, you are loading ammunition, anything interesting?

Not exactly, but yes, interesting. Do you shoot? or maybe ex-forces?

 

[Julie.]

Not exactly, but yes, interesting. Do you shoot? or maybe ex-forces?

Yes I shoot, also section 5

 

[Mark42]

Yes I shoot, also section 5

S5 is rare, well done! Anyone who can deal with the Home Office and retain their sanity deserves respect .

 

[Julie.]

S5 is rare, well done! Anyone who can deal with the Home Office and retain their sanity deserves respect .

Scottish Government!

Also who said I retained my sanity?

 

[KennyKen]

Three types of Hazardous Areas are recognised as follows:
• Group II - Hazardous Areas (gas or vapour) in which an explosive atmosphere is present, or may be expected to be present, in quantities such as to require special precautions for the construction, installation and use of the equipment.
• Group III - Hazardous Area (dust) in which combustible dust in cloud form is, or can be expected to be present, in quantities such as to require special precautions for the construction and use of equipment in order to prevent ignition of an explosive dust/air mixture.
• Explosives Hazardous Areas – An area in which explosives material/substances of Explosives Ordnance are exposed to the atmosphere such that they require special precautions for the construction and use of equipment in order to prevent ignition of an explosives material/substance.

sound suspiciously like the material your working with... These rules don’t just apply to the Oil & Gas and offshore industries mate.

 

[pc1966]

Update: I just checked, it appears Unitrunk only sell direct from their own places, and there's no central tel number, only published (massive) list prices and an email form. They appear to be one of those companies which makes it hard to buy from them. Marketing

Some others also do socket fittings. You might have more luck with this:

Cable management - overhead | Legrand United Kingdom

www.legrand.co.uk

I found it easy to get the Unitrunk stuff from Holland House (oddly enough a Scottish electrical trade suppler, one of the oldest).

 

[Mark42]

Three types of Hazardous Areas are recognised as follows:
...
• Explosives Hazardous Areas – An area in which explosives material/substances of Explosives Ordnance are exposed to the atmosphere such that they require special precautions for the construction and use of equipment in order to prevent ignition of an explosives material/substance.

sound suspiciously like the material your working with... These rules don’t just apply to the Oil & Gas and offshore industries mate.

Eh? Where did that badly-written rubbish come from?

I've been working with this stuff for 40 years but have never read that before.

I can't believe that's from a UK or European document. Whichever genius wrote '... explosives material/substances of Explosives Ordnance are exposed to the atmosphere [sic] ...' clearly has no experience of working with energetics.

That is a fine example of exactly the kind of nonsense that gets into the literature, then is parroted by an enforcing authority without understanding. I'm not having a go at you, mate, but I've been dealing with this 'legislative' cr@p for decades and it irritates me

In the UK we have the HSW Act, and the subsidiary SI 2014 No. 1638 The Explosives Regulations 2014.

In essence they require you to take reasonable precautions, considering all the circumstances of each case. Therefore the requirements are very different if you wish to set up a nitroglycerine factory producing 1000 tonnes a year, and if you want to hold a few grams in an experimental lab for a day.

Excuse the rant, but essentially my policy is to identify actual risk (in this case static sparks) then to use common sense.

Only rarely do flames shoot out of 13A sockets. Or at least from those which I wired they don't.

So far

 

[KennyKen]

Well that’s straight from the compEX list of definitions. A standard used by every global Hazardous area company, and no offence I know which argument I would believe. OK. Your dealing with “Grams” irrespective of large factories. Your Duty of care is to ensure that your install ensures that the risk is ALARP. I wouldn’t be reliant on a 13amp B&Q socket for that.

 

[static zap]

..Do have a vague memory of an Electrostatic Field detector .. that would would wail with big field changes , down side was it used handpicked CMOS inputs
left in a ZAPABLE open circuit state + attached to paddle antennas ..
(but I'll have to trawl internet history from pre 1998 )
( Moving any midly conductive object in an electric field --Can add energy to its stored charge - An induction technique )
... capacitively detecting any charges moving about nearby .... assuming no strong AC fields upset it.
(any missing -r-s due to iffy keyboard.)

 

[Mark42]

Well that’s straight from the compEX list of definitions. A standard used by every global Hazardous area company, and no offence I know which argument I would believe. OK. Your dealing with “Grams” irrespective of large factories. Your Duty of care is to ensure that your install ensures that the risk is ALARP. I wouldn’t be reliant on a 13amp B&Q socket for that.

Oh well, I tend to believe the opinion of someone who’s actually worked with live explosives for 40 years and still has all appendages attached. Now where would I find one of them?

I’m interested by what mechanism you believe the presence of an empty and shuttered quality 13A metallic socket could cause the ignition of say 5g of nitrocellulose in a crucible a metre away. If there’s something I don’t know I genuinely want to learn. I’m a scientist by nature and training: the only thing a scientist knows for certain is that he or she doesn’t know much.

I accept that many guidelines are there to be idiot proof. Eg exclude sockets so no fool can plug in a soldering iron or fan heater. But I will be excluding not only static from my lab, but fools as well.

ps. What’s compEX? I’ve never heard of it.

 

[pc1966]

Oh well, I tend to believe the opinion of someone who’s actually worked with live explosives for 40 years and still has all appendages attached. Now where would I find one of them?

As Derek Lowe put it:

Hexanitro? Say what? I’d call for all the chemists who’ve ever worked with a hexanitro compound to raise their hands, but that might be assuming too much about the limb-to-chemist ratio.

I accept that many guidelines are there to be idiot proof. Eg exclude sockets so no fool can plug in a soldering iron or fan heater. But I will be excluding not only static from my lab, but fools as well.

That is a factor for this forum - what sort of load(s) are you planning?

To my untrained eye with explosives, keeping the opportunities for electrical incidents down is a starting point, and then taking steps to limit the worst-case let-through energy if there is a fault, the second step.

For example, if you have no loads above 5A or so, you might chose a few radial sockets with 10A MCBs for your "13A" sockets, and have the whole system backed up by, say, a 32A BS88 fuse as an ultimate energy-limiter compared to MCBs at high fault currents.

 

[Mark42]

Well that’s straight from the compEX list of definitions. A standard used by every global Hazardous area company, and no offence I know which argument I would believe. OK. Your dealing with “Grams” irrespective of large factories. Your Duty of care is to ensure that your install ensures that the risk is ALARP. I wouldn’t be reliant on a 13amp B&Q socket for that.

Tell you what though, I’d be with you when it comes to major storage magazines. I’ve just watched a video from Beirut today. That was one astounding bang, the shockwave created its own meteorological effect. I reckon that was tens, if not hundreds of tonnes of HE, all going off at once. Not ideal.

 

[pc1966]

Tell you what though, I’d be with you when it comes to major storage magazines. I’ve just watched a video from Beirut today. That was one astounding bang, the shockwave created its own meteorological effect. I reckon that was tens, if not hundreds of tonnes of HE, all going off at once. Not ideal.

Sad to see, as if Beirut has not suffered enough already

 

[Mark42]

UPDATE
For anyone who might be interested in this thread in the future, I'll document my 'As Built' progress. I've finished most of the structural and plumbing stuff now so am installing the electrics.

I gave up all thoughts of dedicated dado power strip, and went with a run of 50 x 100 Salamandre galvanised trunking (From CEF, £7/m).

This meant cutting the lid manually, but avoids the multiple lid joints in the commercial systems. Inserting MK panel mounting plates, in what I think is the wrong place, ie behind the panel (lid), works well and will allow completely flush installation of accessories.

Also for wiring you would be looking at stuff in metal trunking ... or far simpler to handle using Flexishield cable ...

Thanks for the tip. I hadn't used Flexishield before and it's brilliant stuff. As is the recommended RS 262-0151 circular cable stripper. It makes T&E feel a bit Neanderthal

It sits nicely in the trunking, and stays where you put it.

As I can't use compartmented trunking as it would foul the accessories, I'm sleeving the ELV stuff: alarm, dc power supply, data, etc with braid, then tying it off at the top of the trunking. As this in non-standard, I'm not entirely sure if this satisfies current separation requirements but can't see why it's not OK electrically.

The picture below shows one dc power point, none of which will be close to any mains accessory.

The yellow socket is one of what will be multiple points at which to plug in (resistored) ESD wrist bands, or to ground items of portable lab apparatus.

To be continued
[automerge]1598748353[/automerge]

Three types of Hazardous Areas are recognised as follows:
...

• Explosives Hazardous Areas – An area in which explosives material/substances of Explosives Ordnance are exposed to the atmosphere such that they require special precautions for the construction and use of equipment in order to prevent ignition of an explosives material/substance.

sound suspiciously like the material your working with... These rules don’t just apply to the Oil & Gas and offshore industries mate.

I researched these regs, of which I knew nothing, in detail.

As I suspected it's all about explosive atmospheres - eg gas/air, solvent vapours, flammable dusts - not Class 1 explosive materials sitting on a bench.

The statement '... An area in which explosives [sic] material/substances of Explosives Ordnance are exposed to the atmosphere' does not mean the general atmosphere of the Earth, it means any explosive atmosphere to which the ATEX regs apply.

But it's unclear why anyone would want or need to break open items of explosive ordnance while surrounded by an explosive atmosphere. It would be an extraordinarily reckless thing to do

 

[pc1966]

UPDATE
For anyone who might be interested in this thread in the future, I'll document my 'As Built' progress. I've finished most of the structural and plumbing stuff now so am installing the electrics.

Great to see an update! No matter what the matter or problem discussed, I think we all like to hear how it was resolved, etc.

I gave up all thoughts of dedicated dado power strip, and went with a run of 50 x 100 Salamandre galvanised trunking (From CEF, £7/m).

This meant cutting the lid manually, but avoids the multiple lid joints in the commercial systems. Inserting MK panel mounting plates, in what I think is the wrong place, ie behind the panel (lid), works well and will allow completely flush installation of accessories.

That looks like a good way to do things.

Thanks for the tip. I hadn't used Flexishield before and it's brilliant stuff. As is the recommended RS 262-0151 circular cable stripper. It makes T&E feel a bit Neanderthal

Yes, I'm a recent convert as well!

Also it shares the SWA attribute of being shielded in the electrical safety sense - so if punctured it will trip the MCB, etc, and disconnect safely. (OK in your case the resulting spark might not be good, but at least there is little electric shock risk).

As I can't use compartmented trunking as it would foul the accessories, I'm sleeving the ELV stuff: alarm, dc power supply, data, etc with braid, then tying it off at the top of the trunking. As this in non-standard, I'm not entirely sure if this satisfies current separation requirements but can't see why it's not OK electrically.

Off hand I don't know if there are very specific requirements for separation, but certainly having an adequate air gap under any realistic cable movement, and the presence of the braid (and shield on the Flexishield cable) would satisfy me.

Just one point, how are you earthing the added braid for the DC and signal cables?

The picture below shows one dc power point, none of which will be close to any mains accessory.

I guess they are all current-limited so low risk of any significant spark or even thin wire overheating if accidentally shorted out?

 

[Lucien Nunes]

As per the above post, you need to look at the configuration of the braid and insulation of the ELV stuff in the areas around mains accessories where only basic insulation is present.

Consider a broken / faulty mains socket that exposes some live component to the interior of the trunking; unlikely but I've seen a line terminal break out of the back when the socket was hit at the front. If that component contacts the exposed braid, will it reliably witshtand the fault current in the way that the trunking would? Will it blow through and allow contact with the ELV circuit? I would rather have seen it insulated, perhaps by running plastic mini-trunking along the back of the steel trunking.

 

[pc1966]

One aspect I mentioned earlier was the issue of fault energy and trying to keep it to a practical minimum by choice of MCB / backup-fuse / etc. That would also help a bit with the braid fault ratings.

Also worth asking if there are any plans for emergency lighting if power should fail? You would not want to knock some of those chemicals off the bench in the dark by mistake!

 

[davesparks]

Why would you use flexshield inside trunking?

Where are the back boxes for the sockets?

It looks like the kind of thing that Diyers come up with in their sheds/garages, just on a neater/bigger scale.

 

[pc1966]

The steel trunking that offers socket outlet plates like Legrand or Unitrunk don't provide back boxes either, so it is no different (just cheaper but more work).

 

[davesparks]

The steel trunking that offers socket outlet plates like Legrand or Unitrunk don't provide back boxes either, so it is no different (just cheaper but more work).

No it isn't any different, the products you mention also aren't, in my opinion, suitable for use in trunking where there are ELV cables and terminals exposed.

Just because a manufacturer makes a product it does not automatically make its use safe and compliant in all situations, especially not non-standard situations.

 

[Mark42]

This job is now done. Thanks for all the help and advice.

For anyone who was following, or may come across, this thread in the future here are the completion updates, 'as built.'

Someone asked how I earthed the braid. Solder and shrink fit:

Braid is used over any plastic plumbing to provide earth continuity to the ESD ground:

For those interested in these things, the waste plumbing is in 'Vulcathene', which is acid-resistant and highly recommended.

There were comments on the non-desirability of having 13A sockets exposed behind the work benches, which may hold exposed hazardous materials. I don't believe this is really a problem, but I used floor sockets to keep them covered up when not in actual use:

The DB installation is now finished. As this is potentially a portable building, it's fed from a 5 pin appliance inlet externally:

The incoming device provides 30mA protection to the whole installation.

The two small relays top left are for security lighting (common to the whole site) which activate internal and external lighting in case of alarm activation.

The PSU on the shelf provides ELV lab power.

The 'greenhouse' thermostat controls a single oil-filled radiator, and can be left at 4C for frost protection.

As far as possible all internal fittings are metallic, and bonded together and to earth.

The walls are clad in painted aluminium sheet from Aalco, with stainless steel jointing strips.

 

[Mark42]

For those who like seeing the finished job at the end of an interminable thread, here it is.

Everything in there is my own work, with most major components from EBay ?. It was two months' work.

All I need now is a chemist ?