I'm in a situation with a process that requires addition of powder to a 250L tank that contains ethanol. About 5 kg of powder is added, in 1kg batches. The issue I have is that the powders are weighed and dispensed in a non-conductive plastic bag, and from reading NFPA 30 and NFPA 77, this is prohibited due to the static buildup risk. NFPA 77 also goes on to say that powder loading should be kept below 25kg at a time.
What I'd like to know is, does this mean that in smaller amounts (ex. 1 kg batch additions) the risk of static buildup and discharge is much lower, and could the process be maintained as-is, without the use of static dissipative bags? Or is the risk absolute and it is unacceptable to dispense these quantities?
If we cannot change the bags (this is a pharmaceutical process and it's a lengthy process to change materials), would a setup where the powder is dispensed to an airlock on the tank with two butterfly valves, where the powder gets to be in contact with grounded stainless steel parts before being dispensed to the tank (while the upper valve connecting to the bag is closed) be sufficient to relieve the static buildup before the powder is added to the tank?