temperature test, whereas fluidized bed dryers are more suited to the aerated powder ignition temperature test. Where the internal surface temperature is not known, the hot air temperature can be conservatively used. 8.5.5 Bearings. 8.5.5.1 This section shall not be required to be applied retroactively. 8.5.5.2* Bearings that are directly exposed to a combustible dust atmosphere or subject to dust accumulation, either of which poses a deflagration hazard, shall be monitored for overheating. A.8.5.5.2 The intent of this requirement is to address bearings that can have accumulations of dust on them or be in a suspended dust cloud. The concern is that if the bearing overheats it can present an ignition source to the dust cloud or the dust layer. Such equipment can include, but is not limited to, the following: Bucket elevator head and boot areas Particulate size-reduction equipment Blenders Belt-driven fans where combustible dust is present In addition to monitoring bearing temperatures directly, precursors to bearing or overheating can also provide early warnings of bearing or shaft deterioration. These precursors include excessive shaft vibration or speed reduction. Monitoring can consist of periodic manual checks, installed devices, or automated monitoring. 8.5.5.3 The owner/operator shall establish frequencies for monitoring bearings in 8.5.5.2. 8.5.5.4* It shall be permitted to eliminate bearing monitoring based on a risk assessment acceptable to the authority having jurisdiction. A.8.5.5.4 The risk assessment should include the potential for propagation of an explosion from an unmonitored unit. 8.5.6 Electrical Equipment and Wiring. 8.5.6.1* The identification of the possible presence and extent of Class II and Class III locations shall be made based on the criteria in NFPA 70, National Electrical Code, Article 500.5(C) and (D). A.8.5.6.1
temperature test, whereas fluidized bed dryers are more suited to the aerated powder ignition temperature test. Where the internal surface temperature is not known, the hot air temperature can be conservatively used. 8.5.5 Bearings. 8.5.5.1 This section shall not be required to be applied retroactively. 8.5.5.2* Bearings that are directly exposed to a combustible dust atmosphere or subject to dust accumulation, either of which poses a deflagration hazard, shall be monitored for overheating. A.8.5.5.2 The intent of this requirement is to address bearings that can have accumulations of dust on them or be in a suspended dust cloud. The concern is that if the bearing overheats it can present an ignition source to the dust cloud or the dust layer. Such equipment can include, but is not limited to, the following: Bucket elevator head and boot areas Particulate size-reduction equipment Blenders Belt-driven fans where combustible dust is present In addition to monitoring bearing temperatures directly, precursors to bearing or overheating can also provide early warnings of bearing or shaft deterioration. These precursors include excessive shaft vibration or speed reduction. Monitoring can consist of periodic manual checks, installed devices, or automated monitoring. 8.5.5.3 The owner/operator shall establish frequencies for monitoring bearings in 8.5.5.2. 8.5.5.4* It shall be permitted to eliminate bearing monitoring based on a risk assessment acceptable to the authority having jurisdiction. A.8.5.5.4 The risk assessment should include the potential for propagation of an explosion from an unmonitored unit. 8.5.6 Electrical Equipment and Wiring. 8.5.6.1* The identification of the possible presence and extent of Class II and Class III locations shall be made based on the criteria in NFPA 70, National Electrical Code, Article 500.5(C) and (D). A.8.5.6.1
NFPA%20652_Second%20Draftv2_Mar14.docx