Hazardous area & static electricity - polypropylene tank
Hazardous area & static electricity - polypropylene tank
(OP)
I'm looking at a design drawing for an ATEX zone 2 hazardous area release point on a polypropylene tank and a question has been raised about static as an ignition source. Polypropylene is one of the worse materials for building up static. The material is not carbon-loaded and is therefore insulating. Surface coatings are unlikely to be effective because they won't adhere to polypropylene. There's a motor-driven agitator on the vessel top which is earthed to the main earth bar.
The vessel content is a horrible brew, but for argument's sake lets call it diesel fuel as this is comparable in flashpoint. Any thoughts on whether this is a problem and if so some ideas on solving it would be welcome.
The vessel content is a horrible brew, but for argument's sake lets call it diesel fuel as this is comparable in flashpoint. Any thoughts on whether this is a problem and if so some ideas on solving it would be welcome.
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If we learn from our mistakes I'm getting a great education!





RE: Hazardous area & static electricity - polypropylene tank
1) Ground probe in the fluid.
2) Wrap the tank in wire mesh, fencing, or screen.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Hazardous area & static electricity - polypropylene tank
A hole is drilled through the fill pipe near the top of tank so it breaks any syphon.
In another case where liquid flows through glass lined pipe at every flange joint a grounding ring is installed.
Roy
RE: Hazardous area & static electricity - polypropylene tank
ht
RE: Hazardous area & static electricity - polypropylene tank
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If we learn from our mistakes I'm getting a great education!
RE: Hazardous area & static electricity - polypropylene tank
I think the Earthrite is just a device for checking that a tanker truck ground wire is connected.
As I said don't just let the product fall into the tank, run it to the bottom.
Have a grounding ring or use metal pipe for the fill connection.
If your fill connection is non metalic figure out a way to insert a ground rod inside it.
Roy
RE: Hazardous area & static electricity - polypropylene tank
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If we learn from our mistakes I'm getting a great education!
RE: Hazardous area & static electricity - polypropylene tank
1. Surface resistivity less than 10^9 ohm
2. (tiny) surface area
3. bonding
4. minimal charge transfer
5. minimal capacitance
6. conductive coating
7. documentation for fixed locations
There are lots of details and fine print regarding all of these.
On your last question regarding the spark potential, as you dig into the standard definition you might find you'll meet the requirements for diesel. Although I don't see diesel fuel called out in the standard tables, so that may get back to your question of is this valid?
This link may be useful:
www.efsec.wa.gov/oplarchive/oplpft/Cca/jpw-2a.pdf
John D
RE: Hazardous area & static electricity - polypropylene tank
I've been throught the nightmare that is BS EN 60079 - a series of documents surely written by lawyers - and options 1-6 are all infeasible in this instance. The tank is pre-existing, about 6' diameter and the surface resistivity is going to be 'high'. Which leaves 7, so I can defeat the static buildup with a sea of paper.
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If we learn from our mistakes I'm getting a great education!