Re: Atex And Dust Explosion Hazard
For ATEX to apply the following must be fulfilled
1) a potentially explosive atmosphere must be present
2) the atmosphere must consist of flammable substances mixed with air
3) the atmosphere is under atmospheric conditions
4) the product (equipment) must have its own potential source(s) of ignition
The employer has to carry out a risk analysis of his site to establish if a potentially explosive atmosphere may be present :
Never, so ATEX does not apply
Zone 22, not likely in normal operation, but if it does only for a short period
Zone 21, likely in normal operation occasionally
Zone 20, continuously, or for long periods or frequently
Note the use of 'potentially explosive' in describing the atmosphere containing the dust.
So it would seem that at the site to which you deliver someone has determined that the area at which you discharge is at best Zone 22. Is this realistic? That's the $64,000 question.
Did the risk analysis take place when you were actually discharging so the true conditions could be seen?
Is the area you stand when discharging in an enclosed room?
Is there a lot of dust around?
Do you create a lot of dust around you when discharging?
The site should at least be telling you what are their areas of concern, what they consider are the possible sources of ignition that makes them concerned that a dust explosion may occur.
If they are sure that an ATEX zone is appropriate for your unloading area then maybe the introduction of a Safe System of Work would overcome their concerns.
In all of this it should not be forgotten that explosive concentrations of dust clouds are VERY dense. ■
Re: Atex And Dust Explosion Hazard
Peter
Thanks for the reply. In answer to some of your questions:
There is no dust actually present during the discharge due to the enclosed nature of our delivery system. The reason they seem to be complaining is that there is one section of the system that is a 300 micron polyethylene liner neck that the product flows through and the appear to be saying that this is not strong enough in the event of an explosion. This is a fair point but we cannot see where there is the risk of explosion from in the first place!
- The area we discharge into is at worst Zone 22.
- The risk assessment took place under normal operating conditions. In fact every discharge we have ever done using our system is assessed under normal operating conditions.
- The discharge area is outside next to a bank of silos. There is nowhere for there to be a buildup of dust.
- There is no dust around.
- A small amount of dust is created when discharging, but this is collected before it can get into the atmosphere and passed through a sealed pipe back into the container where the dust settles and the air is vented.
For your information the dust concentration explosive limit is 60g/m3.
Thanks
Guy ■
Re: Atex And Dust Explosion Hazard
Is your vehicle actually in a Zone 22 area when it discharges. Would not of thought a road going vehicle would be approved for any ATEX zone?
As to your problem, where's the source of ignition to cause an explosion?
Not on the trailer.
Inside the liner where the material is, probably not unless there is a possible risk of a spark from static electricity. You could always make sure that everything is well earthed.
In the rotary valve, surely not its full of material.
In the conveying pipeline, well maybe, so earth it against static and change your rotary valve to one approved as suitable for explosion isolation. If an explosion were to occur in the pipeline then it would not be communicated back into the container.
Although if I understand your system correctly, the inlet to the rotary valve is always flooded with material which would itself block an explosion.
It sounds as if your site is over reacting. ■
Re: Atex And Dust Explosion Hazard
No there is no zone 22 area designated. They are saying that when we discharge we are making a zone 22 classified area...centred on the rear of the trailer. But we don't actually make any dust where there is a spark risk. Its all a bit confusing.
Unfortunately the company has stopped us delivering to the site until we do something about it. Its a bit difficult as we don't know what we are doing wrong?!
I was just after a bit of reassurance from people in the know! You're all doing a great job thanks! ■
Untitled
From your last description I would say is that if you are unloading outside in a windswept area then this is a safe un-zoned area even if you make a little dust, not even Zone 22 should apply. The dust concentrations that result from your unloading will be many orders of magnitude below any explosive concentration.
Its important to critically look at individual situations as the consequences of "over zoning" can be dire! ■
Re: Atex And Dust Explosion Hazard
Ok thanks a lot!
I will take things up further with them.
Regards
Guy ■
Citric Acid Powder
http://www.hvbg.de/e/bia/fac/expl/
Open the database at this site. It has stored within it many tests conducted on dusts and powders.
Citric Acid powder is a medium range nasty (St1). Check the database for more information.
Cheers
Paul Spresser ■
ATEX and dust explosion hazard
Good Afternoon.
I work for a company that delivers bulk container loads of Citric Acid powder to a customer in Europe. We use a lined shipping container mounted on a discharge chassis to unload using a pneumatic transfer system operated by a diesel engine.
We have made over 200 deliveries to this site and the customer has just informed us that we cannot deliver to the site as we have no provision against dust explosion. IE the trailer has standard electric items such as lights and electric start engine.
As our system is a closed conveying system, the product leaves the container liner and enters a rotary valve that transfers the product to the blowing line, and the trailer is outside in the open atmosphere during operation am I right in thinking that even if there were a dust leak, as there is no enclosed space for dust to get concentrated that there is no explosion risk? This company also keeps quoting the ATEX regs at us but we cannot see how this affects us due to the nature of the process.
Any advice on this would be greatly appreciated!
Best Regards
Guy Martin ■