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Posted By GavinR
This may sound like a really stupid question but if you have the Lower Explosive Limit and Upper Explosive Limit for a flammable liquid produced in the MSDS how do actually measure that information in real terms? If a LEL is 0.6% and UEL is 10.0% how do you actually determine if those % will be reached?
It is the same issue i'm struggling with regarding dust LIT, MIE, MIT. I am in the process of getting dust samples A/B Tested that will lead to the above tests being required if identified A. Now some guys on this forum previously mentioned to me that you can search for this info online without the tests. But again i am unsure how you measure the explosive and ignition values given and relate this to the actual situation.
Maybe i'm being a total fool, but strugglin to get my head round this one. Any help will be much appreciated!
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Posted By Flic
It's not an easy question to answer at all.
You can approach it in a number of ways. The likelihood of reaching an explosive atmosphere depends on the volatility of the liquid and the LEL, and the former depends on temperature.
There is also a British Standard, BS EN 60079, which deals with this formally.
What might help is to work out the volume of the space you have and work out how much you have to render airborne for it to be a problem. I did this for flour dust in my kitchen, and it came to approximately 1.5kg.
If you want to make contact off forum, we can try to do some arithmetic to see what we can find.
Flic
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Rank: Guest
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Posted By Peter How
Gavin
First flammables
Only when you are in between the Lower explosive limit and the Upper explosive limit can the vapour or gas burn. Just like and old car if the mixture is too rich it wont burn (>UEL), if it is too weak (LEL) it won't burn. In between of course it burns well or certainly does in a car engine cylinder.
For flammable liquids you can only get vapours evaporating off the liquid surface fast enough to support combustion if the temperature is above the Flash point FP of the liquid. So in normal conditions at 20dc petrol will be within the flammable range and diesel won't be. The issue is of course that for any source of release of a gas or vapours, very close to the source you will probably be above the UEL, as you move away and dilute you will enter the flammable /explosive range, (be careful here!!) and further way you will be below the LEL. This is why Zoning according to BSEN60079-10 is carried out to identify potentially flammable areas.
Dusts
Generally handling small quantities of flammable dusts is not a problem, 25kg sacks or even some 1Te bags. All organic dusts can potentially burn, but you must have small particle sizes [large surface area to mass of particle] same principal as you can light kindling wood, but not a tree trunk, with a boy scout single match . Inorganic powders cannot burn. There are some isues with light metals eg magnesium and aluminium.
Practically only worry about grains and feedstuffs, wood, light metals and plastics /rubbers. these are the plants that have blown up due to dust explosions. If you have dustraction units on your site they will usually have a plastic sheet explosion relief panel as mitigation. It is almost impossible to prevent all sources of ignition in dust areas as it is in flammable areas, as tramp metal and stones are usualy present in natural materials.
Dusts are more complicated than flammables, but were largely ignored outside major manufacturers until Dsear came along.
Chilworth technology have a good site for dusts
hope this helps a bit
regards
Peter
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