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June 2018

BakerRisk Supports Improvement of NFPA 68

With the assistance of the ERC and other industry partners, BakerRisk continues to perform model validation and product performance testing in order to better understand explosion protection system design and the response of structures to large scale vapor cloud explosions. BakerRisk recently published a paper in the Journal of Loss Prevention in the Process Industries comparing vented explosion test data with predictions using standard industry approaches. The test program, funded by the Explosion Research Cooperative (ERC) utilizing BakerRisk’s Deflagration Load Generator (DLG), showed that the current (i.e., 2013) NFPA 68 correlations can be under-conservative for worst case, near-stoichiometric, propane air-mixtures Using these tests, the newly adjusted NFPA 68 correlation is judged to be reasonable for conditions likely to be present in actual accidental vented deflagrations.

The DLG test apparatus is 48 feet wide × 24 feet deep × 12 feet tall and is enclosed by three solid walls, a roof, and floor, with venting through one of the long walls (i.e., 48-foot by 12-foot). The tests were performed with near-stoichiometric propane-air mixtures for various flammable cloud sizes, congestion levels and vent panel configurations. The industry standard in the United States for predicting the peak pressure developed in a vented deflagration is the National Fire Protection Association’s Standard on Explosion Protection by Deflagration Venting (NFPA 68, 2013 Edition).

explosion

The test data were compared with the NFPA 68 vented deflagration peak pressure predictions. The average internal peak pressures were approximately a factor of 2 larger than those predicted by NFPA 68 for three of the four test series. This indicates that the current (i.e., 2013) NFPA 68 correlations can be under-conservative for worst case, near-stoichiometric, propane air-mixtures.

loss prevention chart

Adjustments to the NFPA 68 correlation were investigated to improve agreement with both the current test data and past published data, thus the newly adjusted NFPA 68 correlation gives peak pressures that are approximately 65% to 85% of the measured values for the current tests. This level of agreement between the current test data (i.e., for uniform near-stoichiometric mixtures) and the adjusted NFPA 68 correlation is judged to be reasonable for conditions likely to be present in actual accidental vented deflagrations.

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