Ammonia Vapor Cloud Explosion Testing and Implications for Facility Siting Studies, Consequence Analyses, and Risk Assessments
A.M. (Tony) Downes & Sam Rodgers
Honeywell International, Inc.
115 Tabor Road,
Morris Plains, NJ, 07950
Darren Malik & J. Kelly Thomas
Baker Engineering and Risk Consultants
3330 Oakwell Court, Suite 100
San Antonio, TX 78218-3024
An open question with regards to facility siting studies, consequence analyses, and risk assessments for release scenarios involving very low laminar burning velocity (LBV) fuels (i.e., significantly lower than methane's LBV) has been whether such releases pose an unconfined vapor cloud explosion (VCE) hazard. There are no reports of an accidental unconfined VCE with such fuels, and applicable VCE test data has not been published. One approach taken within industry has been to use methane as a reference for such fuels. This is clearly a conservative approach, as the flame speeds achieved with very low LBV fuels would be expected to be much lower than those achieved with methane in a VCE under the same conditions. An alternative approach taken by some has been to discount the potential for a VCE with very low LBV fuels.
In order to better define the flame speeds and VCE blast loads from very low LBV fuels, Honeywell commissioned BakerRisk to perform VCE tests with ammonia and methane. Ammonia was adopted as a conservative representative of very low LBV fuels. Methane was included as a reference benchmark. The rig used for these tests was 72 feet long, 12 feet wide, and 6 feet high, unconfined, and filled with a high level of congestion made up of a regular array of vertical circular tubes (area and volume blockage ratios of 22% and 5.7%, respectively). A near-stoichiometric quiescent fuel-air mixture completely filled the test rig, which was ignited against a large wall placed at one end of the rig. Blast pressure histories were recorded using an array of pressure gauges within and external to the test rig. Flame speeds were determined via high speed video recordings of the tests.
This paper discusses the tests performed, results obtained, and the implications with regard to facility siting studies, consequence analyses, and risk assessments for release scenarios involving very low LBV fuels.