Explosive zone around pump shaft

[MikiBg]

Greetings to all.
We have defined Ex zone 1 within inlet pumping station quadratic shaft on WWTP. Flammable gas present is methane. Since shaft cover isn't gas-tight, the Engineer requires that Ex zone 2 needs to be defined around the cover. The shaft is outside the building, i.e. open space is around it.
Is there any exact rule about the shape, position and dimension of zone in this case?
Thanks.

 

[bimr]

NFPA 820: Standard for Fire Protection in Wastewater Treatment and Collection Facilities contains the information that you are looking for.

http://www.nfpa.org/catalog/services/onlinepreview/online_preview_document.asp?id=82012#

Not sure what you are describing, but if you look at the NFPA 820, the area classifications are well defined. One would think that the areas outside of the building will generally be defined as unclassified. The building classifications depend on whether the building is ventilated.

 

[MikiBg]

Thank you for the reply. My description is in European (IEC,ATEX) language, so maybe someone from that part of the world will understand it more clearly and provide some references based on European norms?

 

[bimr]

One would think that many would have problems with the description. Was referring to "quadratic shaft"? What is that? What type of pump, submersible, centrifugal, vertical?

Is this a wet well lift station with a vertical pump with the motor mounted above?

What is the capacity? Is this a municipal or industrial wastewater?

Is there a building associated with the pump station, or just the lift station?

 

[MikiBg]

I meant to say vertical covered shaft (manhole, duct) of rectangular shape. Pump and motor as well are submersed in it. Four shafts and pumps of that kind form a inlet lifting pumping station of municipal WW. PS is outside the building. You can see drawing attached.
The question is: If there is a Zone 1 under the cover, what is the shape and volume of Zone 2 above the cover? Attached file gives an example, but I don't know on what grounds.
According to Wikipedia, American equivalent to "Zone 1" is "Class I Division 1" and equivalent to "Zone 2" is "Class I Division 2".

 

[bimr]

For a project located here, based on the NEC code and NFPA 820, the areas (in the wetwell) with exposed wastewater are considered a Class I, Division 1 hazard.

Since the wetwell cover is not sealed, the leakage should be considered to be similar to a vent. A vent has a Class I, Division 1 classification within 3 feet of the vent and Class I, Division 2 classification from 3 feet to 5 feet from the vent.

 

[MartinLe]

In our projects, we define Ex-Zone class 2 3m around potential sources of gas. The shape is not a box as in your drawing, draw a quartercircle in your drawing around the edges to get the shape there.
But I did not find where the 3m are defined.
Our projects are biogas plants in german, so DIN & EN norms, EU bylaws and their national applications and specific rulings for biogas are relevant.
I don't know if this is helpful in your area.

Where (in what documents) is Ex-protection handled in your neck of the woods? Can you get such a document?

 

[MikiBg]

It should be ATEX directive, but I doubt that there will be so detailed descriptions. I will try, anyway.
Thanks for help.

 

[MartinLe]

Do you access to the paperwork and planning from other WWTP in the area reagarding EX-Zones, or at least from other plants? That could give you some ideas.

Over here, the owner/operator of a plant has to supply a statement ("Explosionsschutzdokument") about ex-protextion including detailed drawings ofthe ex-zones. This is necesary to get the permit and is also needed to design external lightning protection etc. I menat, try to get something like this.

 

[miningman]

Every post here seems to refer to a regulatory distance, ad the fact that there seems to be significant uncertainty should tell all designers something. Perhaps what is more relevant is that methane is not just imflammable but extremely explosive at certain, rather low % mixtures with air . Personally I wouldnt want to be within 10 metres of a relatively small sized manhole if there was any liklihood of an ignition source somehow initiating a burn / detonation of the methane.