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Description
| Deflagration Management in Dust Collectors and Fires | |
| John discussed the management strategy of deflation in the context of dust collectors and fires. They explained the process of a deflagration, emphasizing the importance of maintaining a clean air section in the dust collector and the potential for flame extension up the inlet duct. John highlighted the use of deflagration relief vents and the importance of knowing the static release pressure (Pst) for each vent. They also touched on the testing process, the use of vent closures for low strength enclosures, and the need for special design software. | |
| Venting Declarations and Safety Measures in Dust Collectors | |
| They highlighted the concept of venting declarations, the importance of ensuring the flame extension does not exceed a certain limit, and the need for designers to take a safety margin on top of the calculated limit. John also discussed the use of noncombustible blast-resistant masonry walls and flame divergers to reduce the needed personal excision vision area. They pointed out the limitation of NFPA 68, specifically its restriction to vessels with a volume less than 20 cubic meters, and the need for designers to consider this limitation when dealing with larger dust collectors. | |
| Venting Building Compartments for Safety | |
| John explained the importance of venting building compartments during a deflagration to prevent the entire building from collapsing. They clarified that the primary purpose of venting is not to save the occupants within the building compartment, but to reduce the risk to occupants in other parts of the building. They also addressed the measurement of D from the exterior wall of the building and the use of flame arresting dust retention vent systems. John highlighted the combustion products of a declaration, emphasizing the need to limit the temperature of the exiting gas to prevent ignition of adjacent combustible materials. They also mentioned the potential presence of toxic substances such as formaldehyde and acetylene, as well as formic acid, and the need for caution when exhausting these substances into the building compartment. | |
| Designing Safe Devices for Building Occupants | |
| John stressed the need to proactively design devices to calculate resulting pressure and compare toxic constituent concentrations to ensure safety for building occupants. They pointed out that some had been recommending these devices without these essential calculations, potentially exposing employees to hazardous environments. John highlighted the importance of considering the effects of material discharge into the building compartment and using a linear uptake model to predict toxicant doses. They also emphasized the need to consider exposure levels for toxicants, such as carbon monoxide, to ensure occupant safety. John outlined a process for calculating the carbon monoxide mass liberated into a building compartment, the volume of the compartment, and the concentration, before determining the maximum permissible egress time. | |
| Venting Relations With Gases and Dust | |
| John discussed the factors involved in venting relations with gases or dust, emphasizing the importance of a constant, "k". They explained that results must exceed the KST of 50 and mentioned the equivalent test standard, ISO 61, 84, slash, one. John also explained the concept of KSD, the rate of pressure increase divided by the cube root of the vessel volume, and noted that hybrid mixtures can yield higher values. They emphasized the importance of P. Red, or reduced pressure, which is the pressure that exists during the proper operation of venting the system. John explained the calculation method for the maximum allowable working pressure in pressure vessels, stating that the dynamic load factor is assumed to be 1.5, unless there is specific design data available. They also mentioned that the manufacturer provides the maximum pressure that the vessel can withstand, which is then used to calculate the design pressure. John further discussed the calculation of reaction forces and threshold force, and the conditions under which the calculation can be omitted. They emphasized that larger vents allow for a lower design pressure, which is beneficial. | |
| Ventilation in Enclosures: Importance and Design Considerations | |
| John elaborated on the crucial role of ventilation in enclosures. They clarified that the number and location of vents should be determined by the length-to-diameter ratio of the enclosure, and that for large enclosures, multiple vents enhance performance. They explained the calculation of the hydraulic equivalent diameter for vessels with non-circular cross sections and the concept of flame length or H. They stressed the importance of using the worst-case H when there are multiple events and demonstrated how to calculate the effective volume. They emphasized the significance of vent location, the calculation of effective volume and effective area of a vessel, and the necessity of quality control in vent production. Lastly, they discussed the design of closures in accordance with NFPA 68, Chapter 11, and the limitations associated with deflagration flame diverters. | |
| NFPA 68 Venting System Design Limits and Uncertainties | |
| John discussed the importance of adhering to the limits of NFPA 68 when designing venting systems for hazard management. They stressed the need for sensitivity analysis regarding KST and the use of accurate values for this variable, as well as considering the uncertainty in KST test data. They outlined the process of obtaining numerical values for specific input parameters within boundary conditions and emphasized the importance of not skipping any steps in the process. John also highlighted the limitations of KSG and the P stat, and the process of correcting the L over d ratio. They ended by cautioning against relying on a retired graphical alternative method. | |
| Turbulence and Volume Control in Vessels and Buildings | |
| John discussed the issue of turbulence in various types of vessels, such as cyclones, dryers, and mills. They explained the process of correcting for turbulence, which involves calculating an axial velocity and checking if the Vx and V10 velocities exceed 20 meters per second. John also addressed the need to correct for turbulence when applying venting calculations to a building compartment, highlighting the importance of considering turbulence-inducing conditions inside the compartment. They also discussed the need to correct for panel inertia and mass, but noted that this method has only been validated for events with a mass less than 40 kg per square meter. John explained the calculation of threshold mass and the process of making corrections if the mass exceeds this threshold. They also discussed the concept of partial volume declarations, emphasizing the importance of controlling the volume of the deflagration to a specific fraction to reduce the vent area. John discussed the use of partial volume correction strategies in processes involving combustible solvents or vehicles. They also outlined the process of calculating the fill fraction of dust in a space during a deflagration, emphasizing the need to quantify various parameters. | |
| Calculating Entrainment Factors and Vent Area | |
| John discussed the calculation of entrainment factors, emphasizing the use of absolute particle density instead of bulk density. They explained a computational strategy for calculating the threshold velocity and determining the maximum entrainment rate, noting that these equations have not been experimentally validated. They also discussed the correction for Ventz, the calculation of pressure drop due to turbulent flow, and the limitation of pressure effects to vessels with initial pressure less than 0.2 bar gauge. John then explained the process of calculating the vent area for a vessel or duct, emphasizing the importance of strengthening the vessel or shortening the duct if necessary. They concluded by emphasizing that the method can be complex and is often only suitable for extremely strong enclosures. |