Hazard Mitigation Analysis (HMA)
NFPA 855 requires a Hazard Mitigation Analysis for the permitting of stationary ESS. When producing an HMA, Hazard Dynamics gathers information from other analyses in order to produce a broad view of major hazards and corresponding mitigation in place. Input documents typically include explosion control analysis, FMEA (failure mode effects analysis), FRA (fire risk assessment), system drawings, UL 9540A test reports, and more. The deliverable is a report that uses a bow-tie method, which was published by EPRI. The bow-tie analysis evaluates hazards associated with ESS and the associated threats, barriers, and consequences. Finally, Hazard Dynamics provides recommendations for further mitigation to prevent identified hazards.
NFPA 69 Explosion Prevention CFD Analysis
NFPA 69 explosion prevention is often used to meet the explosion control requirements of NFPA 855. This is typically done using an emergency ventilation fan system to bring in outside air and exhaust flammable gases. These systems are usually triggered by gas detectors. In order to meet the requirements of NFPA 69, the average gas concentration within the enclosure must remain below 25% of the lower flammability limit (LFL) at all times. Hazard Dynamics performs computational fluid dynamics (CFD) analysis to show that the designed system is capable of meeting this requirement. This analysis uses system geometry, system equipment specifications, and UL 9540A test results to model gas detection times and gas concentrations before and after emergency ventilation activation. Hazard Dynamics provides a report summarizing details of the system, UL 9540A testing results, model setup, and model results.
NFPA 68 Deflagration Vent Sizing Analysis & Report
NFPA 68 is the Standard on Explosion Protection by Deflagration Venting. Hazard Dynamics can perform calculations of the required deflagration vent area to mitigate for full volume (worst-case) and partial volume (limited gas quantity) deflagrations. These calculations use equations from the NFPA 68 standard. This calculation relies on information about the strength of the container, the geometry of the container and battery vent gas properties from UL 9540A test results. If gas properties are not included in test reports, Hazard Dynamics uses thermodynamic models to estimate these properties using the reported gas composition. The final deliverable is a report and calculations which include gas property inputs, enclosure characteristics, calculations, assumptions used, and a results summary.
Deflagration Consequence CFD Analysis
All battery vent gas releases will result in some portion of the battery enclosure exceeding the lower flammability limit (LFL) and forming a flammable mixture. Often this flammable region is small and very close to the release location. In less favorable circumstances, the flammable cloud may expand to fill a large portion of the enclosure. Hazard Dynamics can model possible deflagration consequences for varying scenarios using the FLACs CFD modeling software. Hazard Dynamics can calculate consequences including overpressures, structural damage, fireball thermal hazards, projectile distances, human injury and whole-body displacement (throwing people). These models use the structural strength of the enclosure, modeled gas dispersion, and vent gas properties as inputs. Hazard Dynamics produces a report that describes model setup, model results and expected consequences for a given scenario.
Fire Risk Assessment (FRA)
Heat and gases released by lithium-ion cells during thermal runaway can lead to a fire. The burning battery vent gas as well as other burning materials in the battery system pose risks to people and surrounding equipment. Hazard Dynamics assesses these risks based on NFPA 551 using UL 9540A test data as well as site and system information. The FRA report will include the methods, calculations, and results associated with the assessment, including expected heat flux levels near the ESS during a fire event.
Heat Flux Analysis (HFA)/Fire CFD Models
Computational fluid dynamics (CFD) models can provide a more robust understanding of fire scenarios and consequences than simple calculations alone. Hazard Dynamics uses UL 9540A test results, site design, and system information to produce a CFD model that evaluates the fire hazards of an ESS system on nearby exposures under varying wind and climatic conditions. Multiple conditions can be modeled with much less time and expense than tests or experiments allow. Results, including heat fluxes and temperatures on nearby exposures, are presented in a deliverable report.
Plume Study
When lithium-ion batteries fail in thermal runaway, they produce a mixture of flammable and toxic gases and particulates. These gases contain toxic components whether or not they ignite. Burning of system components may also add to the toxicity of any gases released. In order to evaluate the spread of toxic gases from an ESS, Hazard Dynamics creates a CFD model using information obtained from documents such as site drawings, UL 9540A test results, and the system FRA. The model is used to estimate the spread of toxic gases in both fire and gas release scenarios and under different atmospheric conditions. A report is issued that summarizes the toxic hazards of ESS, the system, UL 9540A test results, and model setup and results. These results include approximate distances at which IDLH (immediately dangerous to life and health) and AEGL (acute exposure guideline level) concentrations may be present.
Structural Analysis for Blast
When evaluating the consequences of a deflagration, it is necessary to have information regarding the strength of the enclosure or building in which the deflagration takes place. This is used to determine the ability of the enclosure to resist damage from overpressure. In order to calculate the strength of an enclosure or structure, Hazard Dynamics uses material specifications, engineering drawings, CAD models and datasheets for the container, door, hinges, and other key structural elements.