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38 / May 2020 powderbulk.com ment using wire, cable, or connectors to equalize the equipment's static charge so that sparks can't occur. The need for grounding and bonding must always be considered when adding an interconnection to a vessel handling a combustible dust or vapor. Rules and regulations One example of how the change process is covered in terms of industry standards, regulations, and safety guidelines can be seen in NFPA 652: Standard on the Fun- damentals of Combustible Dust. This standard is aimed at facilities that handle materials that generate combustible dust and requires that before these facilities implement a change, they must conduct an assessment, or DHA, to review the safety implications of the proposed change. Typically, the EPP system supplier can be consulted to determine if the proposed changes will impact the effi- cacy of the system as currently designed and installed. Even temporary changes must be considered for the potential impact on the safety systems installed. In general terms, a manufacturing process change may be viewed in just the same way as any business change management project. The need to review the process as a whole is pertinent, and there are a wide range of change-management models and toolkits used by consulting firms to assist companies in finding successful outcomes. Any proposed process change or modification, however minor it may seem, necessitates a thorough review of the existing EPP measures. The review will help to ensure the new process characteristics don't render the existing system incapable of providing the required assurance level of safe operation and working conditions. PBE For further reading Find more information on this topic in articles listed under "Safety" and "Static electricity" in Powder and Bulk Engi- neering's article index in the December 2019 issue or the article archive at PBE's website, www.powderbulk.com. David Grandaw (david.grandaw@hoerbiger.com, 331- 212-5003) is vice president of sales for IEP Technologies. He has a degree in fire protection engineering technol- ogy and has been with the company for 34 years. He sits on two NFPA technical committees, including as an alternate on NFPA 652. IEP Technologies Marlborough, MA 855-793-8407 www.ieptechnologies.com Changes to protected equipment. Modification to or even replacement of an existing protected vessel can have an impact on the protection measures originally designed in a system. For instance, if a mill is replaced with another mill that provides a finer grind than the original unit, the result is likely to be an end product with a higher K St and lower AIT — along with the added possibility that the existing EPP system is no longer suitable for the process. New penetrations into a pro- tected vessel, such as newly installed inspection doors for example, must be evaluated to ensure that they can withstand, at minimum, the worst-case pressure (known as the P red ) that might develop in an enclosure during a vented or suppressed explosion. The addition of mechan- ical shock, vibration, or sonic devices to minimize material bridging inside the vessel also need to be dis- cussed with the EPP system provider to determine what testing, if any, should be conducted to help ensure that these devices won't inadvertently activate the system. Changes to interconnections. Often, a plant may need to add a duct, pipe, or chute to a protected vessel for production reasons. These additions are potential flame propagation pathways that must be considered for explosion isolation. The mechanical integrity of these ducts also must be considered, as they must be at least capable of handling the P red from the deflagration protection. The addition of flexible ducting should always be reviewed to ensure that adequate grounding or bonding is in place to prevent a static charge from accumulating on isolated conductive parts, which could lead to potential static discharge ignition. Grounding is the safest way to discharge built up static charge. Grounding, also called earthing, connects the process equipment to the earth via a grounding rod or electrode stuck in the ground. As the electrons are produced, they transfer between the equipment and the earth, which drains the static charge. Bonding connects two or more pieces of conductive equip- Permissive grounding system for batch fluid-bed drying process.