Playing devil’s advocate here, why can’t we make up our own extraction system? For some meat on the question assume a scenario where there is a leak of a flammable gas which is lighter than air in the workplace. The workplace has an apex type roof which would contain the explosive atmosphere. The leak is very unlikely due to other controls, but still possible.

Now because it is lighter than air there are options, 1) put a louvered grill in the roof 2) put fans in the roof, 3) put some ducting inside the apex and a fan that takes the gas out the pine end of the building. All these options would be activated by a sensor for the particular gas and any electrical items in the area ( zone 2) would be made intrinsically safe.

We have concerns about option 1 and 2 icing up / clogging up with snow. But if we go for option 3 what legislation would be the issue with us doing this ourselves.?

As I said I’m playing devils advocate here and I don’t think it is a good idea (but I’m no expert), ref Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 1996. Also been through L138 and called, so called experts in to discuss.

 Why couldn’t we buy the necessary components ie ducting, intrinsically safe duct fan, external stack (not china man’s hat type). Then fit ourselves?

Chris

Just one point, extraction to remove (potentially) hazardous emissions from machinery is specifically included in the annexe to the Machinery Directive, as is equipment for own use, so they are both captured under the MD< and thus, would require CE marking.

I would be very careful about hazardous area equipment, and the design and manufacture of such, as there are directives around that also.

As far as high level fans go, I would fit a wall fans into the apex personally, and hopefully by this time it should not be at a level such that would require any considerations for flammable or explosive atmospheres.  That way no issues with snow/icing as they ar not in the roof space, I have never heard of fans suffering like this.

Flesh out the details a bit more and we can guide you a bit more, or drop me an email/PM if you like.

HTH,

Paul

Set the sensor well below the hazard level

HI Chris,

I think that I recall your industry and I can suspect the reason for the potential release.

Can you confirm that the gas is lighter than air please?

As far as I can remember/check at this point in time many are heavier, it's only these that I could drum up as lighter:

hydrogen, acetylene, hydrogen cyanide, ammonia, methane, carbon monoxide, and ethylene

Now I think one of those leaking and  cloud forming in the roof with the potential of flammability would be pretty low on your list! ;)

I would be cautious about a ducted system, because you are creating a system, and that will require additional assessment to provide proof that it complies.  Also if the gas is evolved under pressure, then it will have strem energy that may not be captured by a hood.

If you use high level wall fans, I am guesing that in the event of a release one of the prcautions will be to open main doors in the area to allow as much ventilation, then you would need exhaust only, yes, these would possibly need to be correctly rated, but they would be sold as a single unit CE marked for the purpose, with installation instructions, so would not necessarily need further assessment.

It depends on I think whether you want legal minimum, or a bit more.

There are standards out there which would help with compliance think EAWR/BS7671 links...

I am cautious about discussing too much about your company on the open internet tbh.

With self contained wall fans the shutters can be passive, or active, if wall mounted I would not worry about icing, especially as they will be at roughly the highest points in the building, they will be kept warm by thermal convection, whis is why I said wall, not roof.

If you are going to extract, you are going to loose heat from the building, that cannot be avoided, but, hopefully it's not going to be a common occurance, with good shutters and maintenance, yes the fan will bea  cold spot, if your building is well insulated but it won't be a massive area.

I would suspect you have compressed air on site, so a secondary shutter pneumatically driven internally would help to conserve energy.

You do need to consider the SIL pr PL of the system though really, as it is hopefully going to be very low demand (i.e. never) but if you need it, then it must work!

Yes, Paul you are correct it is one of those gasses and it is lighter than air. (Explosion group IIA, gave it away)

No, Steve it is not the same issue as 3 years ago. We did not allow that scenario to happen in the end, it turns out others were also not keen on it either. Your help was appreciated in that issue. My job keeps touching on this subject and I have wondered about getting more training in the subject, but not sure what to look for.

There is only 6L of gas, but at 350 bar, so will form just over 2 cubic metres at atmospheric pressure very quickly (energetically). This will mix with the air and rise into the apex of the roof (some may make it out the roller doors which are often open, but not much will make it.).

We will not be able to capture this gas at source with a hood, so it will end up in the roof area where we will have a LEL of 42 cubic metres. It will then just sit there as there is no way out.

Would just a wall fan, mounted near the apex actually drag the gas from a distance? I have been led to believe that wall fans and roof fans have a relatively small capture area. This is why we thought it / they would need to actually be in the roof.

Yes, losing heat will not be an issue as we intend to have it only operating via a gas sensor, specific to the gas, which will hopefully never be needed.

One of the problems I have is that in a past life I was in engineering and certainly the courses I did covered fluid mechanics. So perhaps I see this as less of a problem than others, and so have some difficulty when it comes to explaining to the MD why not, as I have to convince myself as well as him.

I would prefer to pass the problem onto a company who are competent in this area. Sadly, it seems to be becoming harder and harder to find trustworthy competent suppliers in all areas.

I know both of you know where I work and can probably guess where the source is, so thank you for keeping those facts discrete.

Chris

Thanks, I see what you mean, but sadly the other side is a fire wall and some offices. I intend a general discussion with MD tomorrow, So I will see where that goes.  

See what I mean though, put a fan in a wall ok, but put a metal tube on either side and its LEV.

I’m so old fashioned I remember when factories had things called tool rooms that made fixtures, jigs and what would now be described as machines.