The boiling liquid expanding vapour explosion (BLEVE): mechanism, consequence assessment, management.

A framework for risk assessment and decision-making strategies in dangerous good transportation

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The measured blast overpressures from recent tests involving boiling liquid expanding vapour explosions (BLEVE) has been studied The blast data came from tests where 04 and 2 m 3 ASME code propane tanks were exposed to torch and pool fires In total almost 60 tanks were tested, and of these nearly 20 resulted in catastrophic failures and BLEVEs Both single and two-step BLEVEs were observed in these tests This paper presents an analysis of the blast overpressures created by these BLEVEs In addition, the blast overpressures from a recent full scale fire test of a rail tank car is included in the analysis The results suggest that the liquid energy content did not contribute to the shock overpressures in the near or far field The liquid flashing and expansion does produce a local overpressure by dynamic pressure effects but it does not appear to produce a shock wave The shock overpressures could be estimated from the vapour energy alone for all the tests considered This was true for liquid temperatures at failure that were below, at and above the atmospheric superheat limit for propane Data suggests that the two step type BLEVE produces the strongest overpressure The authors give their ideas for this observation The results shown here add some limited evidence to support previous researchers claims that the liquid flashing process is too slow to generate a shock It suggests that liquid temperatures at or above the Tsl do not change this The expansion of the flashing liquid contributes to other hazards such as projectiles, and close in dynamic pressure effects Of course BLEVE releases in enclosed spaces such as tunnels or buildings have different hazards

Blast overpressures from medium scale BLEVE tests

The boiling liquid expanding vapour explosion (BLEVE) has existed for a long time and for most of this time it has been cloaked in mystery. Several theories have been put forward to explain this very energetic event but none have been proven. This paper describes a series of tests that have recently been conducted to study this phenomenon. The study involved ASME code automotive propane tanks with nominal capacities of 400 litres. The tanks were exposed to a combination of pool and/or torch fires. These fire conditions led to thermal ruptures, and in some cases these ruptures resulted in BLEVEs. The variables in the tests were the pressure-relief valve setting, the tank wall thickness, and the fire condition. In total, 30 tests have been conducted, of which 22 resulted in thermal ruptures. Of those tanks that ruptured, 11 resulted in what we call BLEVEs. In this paper, we have defined a BLEVE as the explosive release of expanding vapour and boiling liquid following a catastrophic tank failure. Non-BLEVEs involved tanks that ruptured but which only resulted in a prolonged jet release. The objective of this study was to investigate why certain tank ruptures lead to a BLEVE rather than a more benign jet-type release. Data are presented to show how wall temperature, wall thickness, liquid temperature and fill level contribute to the BLEVE process.

The boiling liquid expanding vapour explosion

Liquid temperature stratification and its effect on BLEVEs and their hazards

There is a significant variation in the blowdown behavior of the pressure relief valves (PRV) commonly supplied on certain commercial propane tanks. Determining how different pressure relief valve characteristics affect the survivability of a propane tank in a fire and the associated hazards, was the goal of these tests.



To determine the effect of PRV blowdown, six 1890 L (500 gallon) propane tanks were exposed to an array of torch fires and thermally ruptured. A computer controlled valve was used to simulate the desired characteristics of a commercial PRV. In all cases the simulated PRV was set to open at 1.9 MPag, and blowdown was varied from 5% to 45%.



The impact of the blowdown was determined by observing the nature of the failure, the time to failure, and the energy stored in the liquid and vapor phases at failure. Blast, radiation, and projectile hazards were also observed and recorded in order to determine the impact blowdown has on these pressure vessel failure hazards.



An important finding of this testing is that the blowdown setting does impact the tank's survivability. It was consistently observed that large blowdown resulted in delayed failure. As a result, the PRV was open for a longer time, with a resulting reduction in hazards because of the lower fill at failure. This is believed to happen because of the lower average stress state in the tank with increased blowdown.

Fire tests to study the effect of pressure relief valve blowdown on the survivability of propane tanks in fires

The 4-metre Multi-Object Spectroscopic Telescope (4MOST) is a fibre-fed multi-object spectrograph for the VISTA telescope at the ESO Paranal Observatory in Chile. The goal of the 4MOST project is to create a general-purpose and highly efficient spectroscopic survey facility for astronomers in the 4MOST consortium and the ESO community. The instrument itself will record 2436 simultaneous spectra over a ∼4.2 square degree field of view and consists of an optical Wide-Field Corrector (WFC), a fibre positioner system based on a tilting spine design, and three spectrographs giving both high and low spectral dispersion. The WFC comprises of 6 lenses grouped into 4 elements, 2 of which are cemented doublets that act as an atmospheric dispersion corrector (ADC). The first lens element is 0.9m in diameter whilst the diameter of the other elements is 0.65m. For the instrument to meet its science goals, each lens needs to be aligned to ∼50µm – a major challenge. This is achieved using contact metrology methods supplemented by pencil beam laser probes. In particular, a novel off-axis laser beam system has been implemented to test the optics’ alignment before and after shipment. This paper details the alignment and assembly methods and presents the latest results on the achieved lens positioning and projected performance of the WFC

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M.H. Cunningham

Papers

The boiling liquid expanding vapour explosion

Blast overpressures from medium scale BLEVE tests

Liquid temperature stratification and its effect on BLEVEs and their hazards

Fire tests to study the effect of pressure relief valve blowdown on the survivability of propane tanks in fires

The assembly and alignment of the 4MOST wide field corrector