There are numerous types of equipment that can cause the charging of powders. Such equipment includes, but is not limited to:
The processes carried out by such equipment can lead to varying degrees of electrostatic charge generation. By any standard, the voltage generated by an operation that is known to be at the lower end of charge generating capacity can still generate enough potential spark energies to ignite a broad range of combustible atmospheres. If the powder is being discharged into a blender or mixer that contains a solvent, the MIE of the hybrid atmosphere could be much lower such that the initial ignition of the solvent vapour could propagate a combustible dust deflagration.
The safety factor that needs to be borne in mind with these calculations is the assumption that the equipment being “electrified” by the charged powder is not grounded. If the equipment is grounded, there is no risk of the equipment becoming electrified by static electricity.
Static Grounding Protection in Powder Processing Operations
“Grounding”, in its truest form, is the method by which a low resistance electrical connection is made between equipment at risk of electrostatic charging and the general mass of the Earth. This connection is normally described as a “true earth ground”. The actual connection to earth is achieved via purpose designed grounding rods, or building structures, that are buried below ground level. These grounding systems are tested by engineers to measure their true earth ground resistances to ensure they are below values required in standards like NFPA 70 “National Electrical Code®” and EN 62305 “Protection Against Lightning”. Some static grounding systems on the market today will actually verify if the equipment they are providing static grounding protection for have a true earth ground capable of conducting static electricity.
In pharmaceutical operations, equipment like powder conveying systems, micronizers, blenders and sieve stacks all make up multiple component assemblies that can accumulate high levels of electrostatic charge should any of the components be isolated from a true earth ground. Connections made with items like bonding straps can provide an intentional bond between metal components or assembly mating surfaces may provide an inherent bonded connection.
Regular disassembly for cleaning and maintenance can result in bonding connections being missed or not made correctly when the equipment is reassembled. Vibration and corrosion may also degrade assembly connections so it is imperative to ensure that no parts in the assembly become isolated from a true earth ground reference.
The most effective way of ensuring that equipment used in powder processing operations cannot accumulate static electricity is to provide a dedicated static grounding solution that will monitor the ground connection of components at risk of static charge accumulation and alert personnel to a potential hazard should a component lose its ground connection. This is especially important if the ground connection point to the equipment is not readily visible or easily accessible.
This is where the Earth-Rite® MULTIPOINT II comes in.
A specialised static grounding system, like the Earth-Rite® MULTIPOINT II, provides the benefits of eight discrete static grounding systems rolled up into a single package. This gives installers the flexibility of providing monitored static grounding protection for multiple components of powder processing assemblies through a discrete wall mounted monitoring unit with eight ground status indicators for each component being monitored.Click here to read more >>>
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Newson Gale, a HOERBIGER Safety Solutions Company, enjoys an outstanding market position in electrostatic grounding for hazardous areas.Headquartered in Nottingham, United Kingdom, the company is represented in over 50 countries around the globe. Newson Gale has over 30 years of experience in preventive explosion protection, offering its customers ...