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Prescriptive vs. performance based cook-off fire testing

Tieszen, Sheldon R.; Erikson, William W.; Gill, Walter; Blanchat, Thomas K.; Nakos, James T.

In the fire safety community, the trend is toward implementing performance-based standards in place of existing prescriptive ones. Prescriptive standards can be difficult to adapt to changing design methods, materials, and application situations of systems that ultimately must perform well in unwanted fire situations. In general, this trend has produced positive results and is embraced by the fire protection community. The question arises as to whether this approach could be used to advantage in cook-off testing. Prescribed fuel fire cook-off tests have been instigated because of historical incidents that led to extensive damage to structures and loss of life. They are designed to evaluate the propensity for a violent response. The prescribed protocol has several advantages: it can be defined in terms of controllable parameters (wind speed, fuel type, pool size, etc.); and it may be conservative for a particular scenario. However, fires are inherently variable and prescribed tests are not necessarily representative of a particular accident scenario. Moreover, prescribed protocols are not necessarily adaptable and may not be conservative. We also consider performance-based testing. This requires more knowledge and thought regarding not only the fire environment, but the behavior of the munitions themselves. Sandia uses a performance based approach in assuring the safe behavior of systems of interest that contain energetic materials. Sandia also conducts prescriptive fire testing for the IAEA, NRC and the DOT. Here we comment on the strengths and weakness of both approaches and suggest a path forward should it be desirable to pursue a performance based cook-off standard.

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TYPE Conference YEAR 2010
OSTI

Development of scalable cook-off models using real-time in situ measurements

Kaneshige, Michael; Renlund, Anita M.; Schmitt, Robert G.; Erikson, William W.

Scalable thermal runaway models for cook-off of energetic materials (EMs) require realistic temperature- and pressure-dependent chemical reaction rates. The Sandia Instrumented Thermal Ignition apparatus was developed to provide in situ small-scale test data that address this model requirement. Spatially and temporally resolved internal temperature measurements have provided new insight into the energetic reactions occurring in PBX 9501, LX-10-2, and PBXN-109. The data have shown previously postulated reaction steps to be incorrect and suggest previously unknown reaction steps. Model adjustments based on these data have resulted in better predictions at a range of scales.

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TYPE Conference YEAR 2003
OSTI

Coupled Thermal-Chemical-Mechanical Modeling of Validation Cookoff Experiments

Erikson, William W.; Schmitt, Robert G.

The cookoff of energetic materials involves the combined effects of several physical and chemical processes. These processes include heat transfer, chemical decomposition, and mechanical response. The interaction and coupling between these processes influence both the time-to-event and the violence of reaction. The prediction of the behavior of explosives during cookoff, particularly with respect to reaction violence, is a challenging task. To this end, a joint DoD/DOE program has been initiated to develop models for cookoff, and to perform experiments to validate those models. In this paper, a series of cookoff analyses are presented and compared with data from a number of experiments for the aluminized, RDX-based, Navy explosive PBXN-109. The traditional thermal-chemical analysis is used to calculate time-to-event and characterize the heat transfer and boundary conditions. A reaction mechanism based on Tarver and McGuire's work on RDX{sup 2} was adjusted to match the spherical one-dimensional time-to-explosion data. The predicted time-to-event using this reaction mechanism compares favorably with the validation tests. Coupled thermal-chemical-mechanical analysis is used to calculate the mechanical response of the confinement and the energetic material state prior to ignition. The predicted state of the material includes the temperature, stress-field, porosity, and extent of reaction. There is little experimental data for comparison to these calculations. The hoop strain in the confining steel tube gives an estimation of the radial stress in the explosive. The inferred pressure from the measured hoop strain and calculated radial stress agree qualitatively. However, validation of the mechanical response model and the chemical reaction mechanism requires more data. A post-ignition burn dynamics model was applied to calculate the confinement dynamics. The burn dynamics calculations suffer from a lack of characterization of the confinement for the flaw-dominated failure mode experienced in the tests. High-pressure burning rates are needed for more detailed post-ignition studies. Sub-models for chemistry, mechanical response and burn dynamics need to be validated against data from less complex experiments. The sub-models can then be used in integrated analysis for comparison with experimental data taken during integrated tests.

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TYPE Conference YEAR 2000
OSTI
Results 51–71 of 71
Results 51–71 of 71