Try Childworth Technology, Beta House, Chilworth Research Centre, Southampton. SO16 7NS

Tel.44 (0)23 8076 0722 Fax 44 (0)23 9076 7866 www.chilworth.com. ■

ben,

please go in touch with mr. roland bunse @ rembe, brilon.

email: bu@rembe.de

phone: 0049 2961 74 05 - 40

postal: REMBE GmbH SAFETY + CONTROL,

Gallbergweg 21, 59929 Brilon - Germany.

stefan

PS:

do also visit: http://biaonline.hvbg.de/EXPLO.htm and an

english version under http://www.hvbg.de/d/bia/fac/expl/exple.htm

- push "OPEN DATABASE" - there you will find the search engine.

for further queries you can also contact me directly! ■

Unfortunately there is not a universal dust law similar to that for gases. Dusts behave in more random ways and there are several factors that influence the explosive behavior of any given dust. Particle size distribution, chemical structure, moisture content, suspended dust cloud concentration, strength and duration of the ignition source, and homogeneity of dispersed dust cloud to name some. Since these variables are constantly different, the only safe thing to do is to have your dust tested.

You say you have over 100 different dusts so it is obvious that having separate data for every one would be a very expensive proposition. Can you separate them into broad groups based on chemical composition for example? If so, then take the finest particle size distribution sample from each group and test only it. In this way you would have a set of data for the group that should represent a near worst case. Other dust in the group that are chemically similar but are comprised of overall larger particle sizes can be considered to be similar, but slightly less reactive than the test reference for the group. By using the data for the reference dust for each group it can be presumed that you would be conservative and safe.

The basic data you need in all cases is Kst and Pmax. These values are derived from either a 20-liter sphere test, or a 1-cubic meter sphere test. This data is used to size explosion-vents and other protection schemes.

MIE would only be important for dusts that are very sensitive to ignition. Dusts that are mixed with flammable gases or vapors would be an example. A skilled test person can develop a sense of when a dust might be very ignition sensitive from the 20-liter sphere test. Not every dust needs this data point. Let your chosen lab provide guidance on when MIE testing would be prudent.

MAIT would normally only be important if the dust is being exposed to elevated temperatures such as in a heated dryer for example. MAIT is further complicated because there is a test for dust layers and another for dust clouds. If you are unsure which is appropriate, the layer test provides the lower, safer value. Not every dust is routinely exposed to elevated temperatures and as such, this test is not always useful.

Regards,

Bill ■

The lower explosion limits (LEL) for many substances do not take into account particle size distribution. They are often only stated as so many milligrams per litre or grams per cubic meter of "fines or dust". Dust particle size is crucially important in determining explosivity.

What is often stated is that the particle size being refered to is "less than so many microns". This is an improvement but it is not the particle size distribution. A dust sample containing 50% particulate less than 10 microns is much more sensitive to igniton than one with 90% between 10 and 50 microns and only 10% less than 10 microns. Yet both would fall under the same classification if "less than 50 microns" was used to define the LEL.

In addition, modern investigation has shown that the SHAPE of fine particles can significantly affect the explosivity. This is related to charge concentration at sharp points and edges. Modern measurement techniques are now getting to the point where BOTH particle size distribution and particle SHAPE can be defined and this should lead to a finer definition of LEL's.

But we are not there yet. ■

Your idea is quite interesting, Tominer. The closest thing to what you suggest that I can recall is some work that was done by FM Research several years ago on ways and means to control dust cloud formation inside large silos. This was done for the grain industry.

The technique involves the use of oil to attract and agglomerate dust particles so that they would fall out of suspension. I do not recall if anything was done with static charge in those experiments. But I do know that the technique is viable within certain parameters and I believe is widely used in the grain industry.

Regards,

Bill ■

I agre with Bill , corn oil is used to reduce the airborne dust in grain elevators, I am not sure this is usefull in the plastics industry.

I do not believe you can get away from lab testing .

data bases ar a good reference, but to put all the eggs in the basket of somebodyelses database is not wise.

you should start little by little to build up your own database, set yoursels near term goals and start, soon you will find that you have must of your products characterized.

If yoiu want use the pareto principle first or the ABC, sytem.

Or maybe the MUC (management under crisis) method.

But start today. calibrate the existing databases with your own data , credibility( both, yours and theirs) is enhanced when your data match.

Good Luck.

Marco ■

By the way if your customer does not supply exp data , you might add an item to your contract , billing the Lab cost.

marco ■