We have an operation where we are charging powder from an isolator into a tote bin. The stainless steel charging chute has an EPDM Bellows (Insulator). Previously we would have considered the risk of a brush discharge given the low MIE of the powders (3-5 mJ) but since the available information indicates that brush discharges will not ignite dust mixtures (no flammable vapour present),avoidance of ignition sources would have remained our basis of safety.
A consultant indicated that even though there are no large contacting areas between metal and insulator (chute and bellows), he states that it is possible that the close proximity of even a small section could lead to higher than normal charge density on the rubber surface. Similarly, a conducting object or even person, inadvertently in contact with the outside of teh bellows could lead to a higher local charge debsity than normal. Eitherway the result could be what has been termed an enhanced brush discharge - something between a brush discharge and a propagating brush discharge, and almost certainly incendive to our powders.
My question is - has anyone heard of an enhanced brush discharge and if the risk of powder flowing down the chute (<3m) across the bellows presents a significant risk. We have a number of stainless steel pipes elsewhere connected with bellows and this has not been raised as an issue before. ■
Enhanced Brush Discharge
We have an operation where we are charging powder from an isolator into a tote bin. The stainless steel charging chute has an EPDM Bellows (Insulator). Previously we would have considered the risk of a brush discharge given the low MIE of the powders (3-5 mJ) but since the available information indicates that brush discharges will not ignite dust mixtures (no flammable vapour present),avoidance of ignition sources would have remained our basis of safety.
A consultant indicated that even though there are no large contacting areas between metal and insulator (chute and bellows), he states that it is possible that the close proximity of even a small section could lead to higher than normal charge density on the rubber surface. Similarly, a conducting object or even person, inadvertently in contact with the outside of teh bellows could lead to a higher local charge debsity than normal. Eitherway the result could be what has been termed an enhanced brush discharge - something between a brush discharge and a propagating brush discharge, and almost certainly incendive to our powders.
My question is - has anyone heard of an enhanced brush discharge and if the risk of powder flowing down the chute (<3m) across the bellows presents a significant risk. We have a number of stainless steel pipes elsewhere connected with bellows and this has not been raised as an issue before. ■