(51b) Ammonia Vapor Cloud Explosion Testing and Implications for Facility Siting Studies, Consequence Analyses, and Risk Assessments

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

Anthony.Downes@Honeywell.com

Darren Malik & J. Kelly Thomas

Baker Engineering and Risk
Consultants

3330 Oakwell Court, Suite
100

San Antonio, TX  78218-3024

(210) 824-5960

DMalik@BakerRisk.com

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.