Is velcro use acceptable in explosive environments?
Is velcro use acceptable in explosive environments?
(OP)
A colleague wants to use Velcro to attach cables to a robot arm in a paint booth that is classified as Class I Division 1. The only threads I see about this are from NASA in the 1970s. I see some people make anti-static Velcro straps for ESD controlled environments. I'm sure they work, but are they needed?
Thanks,
Z
Thanks,
Z





RE: Is velcro use acceptable in explosive environments?
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx
RE: Is velcro use acceptable in explosive environments?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Is velcro use acceptable in explosive environments?
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Is velcro use acceptable in explosive environments?
But I'm like Gunnar, I think you'll get paint buildup either way. Maybe not due to electrostatic attraction, but the powder will have plenty of places to accumulate in the fabric of the Velcro.
-tg
http://xternal.me
RE: Is velcro use acceptable in explosive environments?
Z
RE: Is velcro use acceptable in explosive environments?
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx
RE: Is velcro use acceptable in explosive environments?
Mike Halloran
Pembroke Pines, FL, USA
RE: Is velcro use acceptable in explosive environments?
Z
RE: Is velcro use acceptable in explosive environments?
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Is velcro use acceptable in explosive environments?
Mike Halloran
Pembroke Pines, FL, USA
RE: Is velcro use acceptable in explosive environments?
There are all sorts of wiring methods, devices etc. which are approved for Div 1 or Div 2 that can be made unsafe by maintenance happening at the wrong time or done incorrectly. From a health and safety perspective alone, it seems to me that you wouldn't want people (probably in supplied air respirators) to be doing maintenance on this thing while it continues to spray paint.
Is the concern that the maintenance will be happening while other, adjacent robots are still operating? Or is there something else in the area making this location Div 1 other than just the paint spray?
Unless you're concerned about the Velcro coming loose due to motion of the robot and that motion causing a static-electric ignition spark, it would seem to me that you're making a mountain out of a molehill.
The point about the Velcro gluing together with overspray is a good one too of course.
RE: Is velcro use acceptable in explosive environments?
Z
RE: Is velcro use acceptable in explosive environments?
Mike Halloran
Pembroke Pines, FL, USA
RE: Is velcro use acceptable in explosive environments?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Is velcro use acceptable in explosive environments?
RE: Is velcro use acceptable in explosive environments?
> Some sort of rubbing/contact motion event -- but this requires two dissimilar materials, one that strips electrons and one that accepts electrons. It would seem to me that Velcro pretty much has similar materials on either side of the rubbing event, so both sides are either trying to strip electrons or both trying to accept electrons, resulting in a net nothing
> One side has to be reasonably conductive -- a balloon can generate static charge, but it doesn't really generate discharges because it's not conductive enough to get all the generated charges into a single location where they can then jump to the other side of an arc. You never see carpets as part of a discharge, nor your shoes rubbing the carpet, nor the body of the door itself, only your finger and the door knob do anything, because they're both conductive
In general, if you're concerned about the Velcro loosening, then it's not the right solution, regardless of the ESD possibilities. And if it's on a robot, why does it need Velcro? Are the cables that bad that you need to replace them so often that you want Velcro and not cable ties? My impression is that cables on a robot arm are pretty much permanent installations, unless someone breaks the cable, or the entire arm.
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx
RE: Is velcro use acceptable in explosive environments?
Sounds like this is about the dust jackets that wrap around the whole robot body, and close around the connectors, too, not just follow a single harness of cables.
Strips of magnetic tape are useful for closing seams and being easy to re-open. You can get it with a self-adhesive backing to stick to the jackets, or sew-on tabs if you prefer. The material is likely to have a high content of ferrite (that is what is magnetized) so I don't think it can retain much ES charge.
Many things release static-electric discharges when they are separated. An example that I noticed last week is the wrapper on band-aids. Peel one in a dark room sometime if you don't believe me.
STF
RE: Is velcro use acceptable in explosive environments?
The user wants to remove the sensor when they clean the robot, so removing the "cable ties" needs to be part of the SOP.
I expect they can use the same thing that they use to hold the dust jackets in place. Unfortunately I'm at least four levels away in the contact chain from the user, so I'm looking for the most complete info that I can give when I hear the middle links talking about Velcro.
Thanks for all the insight.
Z
RE: Is velcro use acceptable in explosive environments?
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx
RE: Is velcro use acceptable in explosive environments?
RE: Is velcro use acceptable in explosive environments?
I like the magnetic cable mount idea. As long as the robot arm isn't aluminum! This may take this thread off topic, but does anyone know why aluminum is acceptable in a Class I Div 1 environment in the USA (i.e. UL regs?) but not in the EU (i.e. IEC regs)? There must be some history there why the two standards diverged.
Z
RE: Is velcro use acceptable in explosive environments?
RE: Is velcro use acceptable in explosive environments?
I was involved in a discussion about EDM in bearings some time ago. This was in a refinery and everyone was thinking Ex with different numbers and letters attached. So it wasn't easy to focus on what was going on in the innards of the bearings and I nearly left the room when one of the more influential guys said that the motor's paint seemed to be too thick.
It took some time to get him off that track.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Is velcro use acceptable in explosive environments?
How did you avoid laughing?
RE: Is velcro use acceptable in explosive environments?
He was very confused and told me that thick paint could get charged when brushed against. Probably true.
The problem was the ground grid. It hadn't been checked since it was buried in 1973. Sulphuric acid, salt water.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Is velcro use acceptable in explosive environments?
Why isn't aluminum prohibited in ATEX Zone 1? Isn't IEC 60079-0 a requirement for ATEX Zone 1?
Or is 60079-0 still showing 'the way we used to do it' and people have realized that the aluminum/steel 'thermite' spark is so improbable that it is rarely a concern? Perhaps it is a requirement only for those extreme cases?
Thanks,
Z
RE: Is velcro use acceptable in explosive environments?
• for Zone 0
10 % in total of aluminium, magnesium, titanium and zirconium, or
7,5 % in total of magnesium, titanium and zirconium;
• for Zone 1
7,5 % magnesium;
• for Zone 2
no requirements except for fans, fanhoods, and ventilating screens which shall comply with the requirements for Zone 1.
ATEX Zone 0 is an environment where an explosive atmosphere is frequently or continuously present, so I guess the even the minute risk of a thermite reaction between iron and aluminium is unacceptable. Zone 1 is an environment where an explosve atmosphere is likely to occur occasionally in normal operation, so the risk of an incendive spark and an combustible atmosphere being simultaneously present is consderably lower.
There is a further line in Clause 8.1.2 which allows use of light metals in Zone 0 subject to the user determining that there is very little risk of an incendive spark due to impact or friction, which gives some idea as to the origin of the requirement.
RE: Is velcro use acceptable in explosive environments?
RE: Is velcro use acceptable in explosive environments?
RE: Is velcro use acceptable in explosive environments?
RE: Is velcro use acceptable in explosive environments?
RE: Is velcro use acceptable in explosive environments?
Not so long ago the UK had a massive coal industry - although you would barely know it now - and there have been more than a few explosions in British coal mines which were attributed to aluminium and rusty steel coming in to contact. Some of the first accidents where the link was recognised occured at Horden Colliery in 1953 and at Glyncorrwg Colliery in 1954. Here's the link to the investigation into the Horden accident: http://www.dmm.org.uk/reports/9399-10.htm
RE: Is velcro use acceptable in explosive environments?
RE: Is velcro use acceptable in explosive environments?
"We know where were goin'. But we don't know where we've been". That Talking Heads lyric is making so much more sense these days!
Z
RE: Is velcro use acceptable in explosive environments?
It was also scary, because nominally minor items like 'enclosures', whatever you choose that word to mean, are almost never designed or selected under scrutiny of any engineer, much less one who would be aware of the special risks of explosive atmospheres.
Mike Halloran
Pembroke Pines, FL, USA
RE: Is velcro use acceptable in explosive environments?
RE: Is velcro use acceptable in explosive environments?
The flammables in a plant environment aren't likely to be as benign as methane from a health/personnel chemical exposure perspective for one thing. And it's tough to imagine an enclosure being a source of ignition, irrespective of what metal it's made of, unless personnel are working in or around it.
The usual situation is that zone 0 or zone 1 are selected as a means of being extra diligent and protective (i.e. for CYA reasons). As an example, gasoline dispensing outdoors. The filling stations are all Div 1 (don't know if it's zone 0 or zone 1 in this case because I have nothing to do with designing filling stations) for the first 3 feet above grade and any space below grade, because the vapours are denser than air. However, vehicles with non-Div 1 electrics and burning hot brakes and exhaust manifolds and emission control catalysts are being operated with in that zone- with all those parts being within 3' of grade.
RE: Is velcro use acceptable in explosive environments?
The more risks I can eliminate the better.
RE: Is velcro use acceptable in explosive environments?
I totally understand your point of view- I'm just pointing out the limitations of focusing on ignition source elimination as a means of protection against fire, in an environment which has hard process needs for sources of ignition such as hot pipe and fired equipment, to be present within the plant boundaries. This seems to be rather easily forgotten or overlooked when setting out a design for fire risk mitigation. Area classification is often used out of context because it is an easily understood set of rules, rather than because it is an effective risk mitigation means. As a consequence, other means of risk mitigation are sometimes ignored or overlooked. I've seen clients who wanted a plant designed for class 1 zone 2 but then wanted the electric heaters "exempted" because they must operate above 80% of the autoignition temperature for the process to work...it's just plain crazy.
RE: Is velcro use acceptable in explosive environments?
RE: Is velcro use acceptable in explosive environments?
Mike Halloran
Pembroke Pines, FL, USA
RE: Is velcro use acceptable in explosive environments?
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx
RE: Is velcro use acceptable in explosive environments?
The only way to be sure would be to mechanically rip apart some sample velcro in a chamber with your hazardous dust. We do the equivalent exercise in methane chambers regularly whenever we have a new material/design/arrangement and need to get it Ex approved. If it goes bang, it's a no go.
For those incredulous at the requirements of hazardous area certification, be assured it is real and on-going. Contraband is a serious issue in underground mines in Australia - no aluminium, no watches, no phones, nothing that could release enough energy to ignite methane. It's hard to believe that people could work in such hazardous environments, where the mere presence of aluminium is a concern, but it works. Lots and lots of study goes into setting the limits and manufacturers manage (through quite extreme constraint) to comply. The problem with aluminium in an underground mine is that things are always bumping into other things, including mobile machines into boring old enclosures. Aluminium is known to be a problem, so we do without it.
Which reminds me - another avenue of investigation might be your customer - if they have a site rule that says employees can't wear velcro strapped watches then there's your answer.
RE: Is velcro use acceptable in explosive environments?
Scotty, that's some nice history you dug up there. Kudos to you!
Z
RE: Is velcro use acceptable in explosive environments?
RE: Is velcro use acceptable in explosive environments?
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.