Information on explosive atmospheres

[flyingsparks]

I am currently tendering for work at a milling plant, which is under 'category 22' for dust and the risk of explosion. As far as I can see by looking online this means electrical switchgear and luminaries are to be IP5X or better, or is there more to it than this?
Anyone have experience in this area?

 

[bernardgreen]

There is more. IP5X permits dust ingress, in small fixed, portable or hand held items this is unlikely to be an explosion hazard but in a control cabinet with cooling fans moving the air inside the cabinet then dust inside the cabinet can create the hazard of a rapid combustion inside the cabinet. It might also be an explosion source. Hence for large items IP6x would be prefered ( no dust ingress ).

My experience in dusty food production areas was that some control cabinets were operated under positive air pressure to reduce the risk to acceptable levels.. ( Also curry powder does a lot of harm to electronics ).

There also working practises to comply with to ensure no sparks can be created while dust is present. ( hob nail boots on steel surface was beleive to have been the ignition source in a flour mill fire )

 

[flyingsparks]

Cheers Bernard.
It is a new build so no dust will be present during the wiring of the plant.
So if you went with IP6X throughout, then that is all that would be required for switchgear etc? The control cabinet will be located in a clean area so this is not an issue. I have heard of Atex too, but not sure if this is a different classification?
What I'm getting at I guess, is if IP6x is installed and someone came in afterwards and inspected is the IP6x classification ok, or are they looking for some other symbols on the products?

 

[Adam_151]

http://www.compex.org.uk/generic.aspx?pageid=63

You could be looking at EX rated fittings rather than something simply graded on the IP scale

Also check your insurance and NICEIC/ECA registration are appropiate for this work

BS7671 requires RCD protection to all circuits where stored or processed materials present a risk of fire, but this does not necessarally have to be 30mA

I'm guessing this would be design and build? I'd be careful... if you price it properly you'll probably loose it to someone who hasn't...perhaps best just steer clear of it for when the animal waste products impact upon the air circulation device

 

[ericmark]

The risk assessment seems to control many items and where I worked all production lines were connected to the dust extraction system and if the dust extractor failed all other machines auto shut down.

I have seen the results where dust has ignited how only one guy was injured I don't know. No sides panels left and even some RSJ's were bent as a result for the blast. Working on another job it seems to design the systems one needed qualifications in EX systems. I could do as told but could not design as I did not have the qualifications required.

It seems this is a very specialised subject my limit was enough to know not to get involved.

 

[scousespark]

Are you looking to take full responsibility for this installation? This is a specialized job and may be beyond your experience.

 

[conny]

We used to get EX motors for repair from places like flour mills, wood mills, petrol refineries etc.

Unless you had been on a five day intense course you were not allowed to work on them. All your checks were inspected and signed off by a senior technician. When my certificate ran out after 3 years I didn't bother doing the refresher as the responsibility was too great.

 

[securespark]

Worked briefly in a dairy. One of my jobs was in the SMP plant.

It gets everywhere!

All the switchgear was IP rated, but I can't remember the rating. Plus, I'm going back to the 80's.

 

[stillp]

There's an awful lot more to explosive atmosphere work than just the IP rating. Check out the HSE web pages: http://www.hse.gov.uk/search/search...c.tab=0&gsc.q=explosive atmosphere&gsc.page=1

 

[john4703]

My knowledge is totally out of date but I wonder if the rules are still as stupid as in 1964. I was told to go and do some work at a refinery, basically it was threading conduit by hand as no power threading tools were allowed on site and apprentice labour was cheap, some had threads 12 inches long to seal into boxes. What I could not understand is that about 6 feet away, the other side of a chain link fences was a railway signal illuminated by a paraffin lamp with no protection. I reckon in those days Heath & Safety were clever and educated fumes to stay inside the fence.

 

[stillp]

That's not so stupid. Even if there's no explosion risk in some areas, such as adjacent to a fence, many companies still have a site-wide ban on use of anything that could cause ignition, since it's easier to enforce a blanket ban than to restrict the use of powered equipment to safe areas.

 

[john4703]

That's not so stupid. Even if there's no explosion risk in some areas, such as adjacent to a fence, many companies still have a site-wide ban on use of anything that could cause ignition, since it's easier to enforce a blanket ban than to restrict the use of powered equipment to safe areas.

I agree it is far easier, and safer, to have one rule to cover te whole of a site.