Explosion Venting Research Articles

Geophysical events

Mount St. Helens Volcano, Cascade Range, southern Washington, U.S.A. (46.20°N, 122.18° W). All times are local (GMT − 7 h). A major eruption destroyed the summit of Mount St. Helens, projected ash into the stratosphere, devastated the north and northwest flanks, and killed dozens of people last May 18. The initial explosion was heard more than 350 km away. Substantial ashfalls occurred hundreds of kilometers downwind, closing roads, schools, and businesses, and threatening crops in the northwestern United States.Mount St. Helens had begun to erupt on March 27, after a week of local seismicity. During the first 10 days, small to moderate steam and ash explosions ejected ash to as much as 3 km above the summit. A little ash fell as far away as Spokane, Washington, 500 km to the northwest. Small debris flows and cold ash avalanches moved down the flanks of the volcano. By April 12, the two initially separate explosion vents had coalesced into a single crater that was at least 500 m long, 350 m wide, and 300 m deep. Both explosions and ash content decreased in size through mid‐April, then episodic explosions were replaced by continuous steaming late in the month. Explosions, similar to those of early to mid‐April, resumed on May 6 and continued until at least May 14. Several tens of earthquakes per day of magnitude 3 or greater continued to be recorded through May 17. Total seismic energy release remained relatively constant through late April, then declined slightly.

Guidelines in Application of Explosion Vents

This paper is one of those presented at the APCA Specialty Conference entitled “The User and Fabric Filtration Equipment—III”, held in October 1978 in Niagara Falls, New York. It presents guidelines for the application of vents for explosion protection in fabric filter systems. Detailed design procedures will soon be available in the new edition of National Fire Prevention Association Code 68 on explosion venting.

Basaltic ring structures of the Columbia Plateau

Circular structures, defined by arcuate, concentric ridges and scarps that surround hills, mesas, or crater-like depressions, are localized in an exceptionally thick section of the Roza Member of the Yakima Basalt on the Columbia Plateau. Autointrusive dikes are conspicuous in most ridge segments. Palagonite discovered in a few central hills appears genetically related to the ring structures and suggests an origin involving interaction of water and lava. The dikes intruded a crust about 30 m thick, however, so that substantial cooling must have occurred prior to formation of the rings. A plausible explanation for these unusual features may hinge on the disruption of drainage that occurred as a result of the voluminous basalt extrusion. If, after partial cooling, the molten interior of this thick ponded Roza flow were intersected by a rising ground-water table, rapidly accumulating volatiles could have caused explosive venting as well as doming and cracking of the crust, with concurrent emplacement of granulated sideromelane (later palagonitized) and tephra in craters and fractures. Subsidence of the crust after initial venting could have permitted intrusion of melt into fractures predominantly concentric to the focus of pressure release. Subsequent catastrophic erosion by the Missoula floods effectively removed most of the surficial clues to original structure and morphology, leaving the roots of these enigmatic features partly exposed.

The venting of gaseous explosions in spherical vessels. II—Theory and experiment

The computer solutions of Part I [Combust. Flame 32, 221 (1978)] are compared with available experimental data, in terms of the suggested parameters. The use of the vent area to vessel volume ratio is criticised. The reasons for the differences between theoretical and experimental data are discussed. In the light of this evidence, recommendations are made for safe values of the dimensionless ratio, AS0, introduced in Part I, for both initially uncovered and covered vents. It is concluded that uncertainty exists about the effects of turbulence and pressure wave generation.

The venting of gaseous explosions in spherical vessels. I—Theory

A study is made of the required vent areas for pressure relief during explosions with normal flame propagation. Two idealised analyses are presented for what is shown to be the worst case of central ignition in a spherical vessel with venting of unburnt gas: one is simple and for a particular condition, whilst the other is based on a comprehensive computer model. Initial internal and external pressure are taken to be atmospheric. Results are presented in a recommended form of values of maximum pressure rise plotted against AS0, where A is the product of vent area and coefficient of discharge divided by the total sphere area, and S0 is the ratio of gas velocity just ahead of the flame front to the acoustic velocity in the unburnt gas just after ignition. Comparisons are made on this basis with the results of previous workers. Solutions are also presented for burnt gas venting. The gas velocity ahead of the flame front, during venting, is computed and the generation of pressure waves discussed.

Pressure as a function of time and distance in a vented vessel

Rates of fall in pressure have been measured at different positions in a number of differently-shaped vessels vented by means of bursting diaphragms. It is demonstrated that the qualitative features of the experimental pressure histories are predicted by characteristic theory. Attention is drawn to the importance of the reflection of the expansion wave which may partly explain the existence of twin pressure peaks typical of vented explosions and which can result in the reversal of pressure gradients within the vessel.

Recent advances in the relief venting of dust explosions

Relief venting is the principal direct means used for protection of industrial plant and buildings against dust explosions. Information on the design of adequate vents has accumulated over a long period, and this early work has been summarized.More recently, a considerable amount of further data has become available and is reviewed, together with a description of the methods used to obtain it. The majority of data relate to explosions in compact enclosures, i.e. the three dimensions of comparable size, but some data are also reported for ducting and for specific plant units. The effect of vent covers on explosion pressures is also given some attention.The importance of obtaining an adequate theoretical background to the empirical data is stressed, the present situation discussed, and future requirements commented upon.

Volcanic Activity at Deception Island in 1967 and 1969

Eruptions, apparently associated with the caldera fault zone, have created a new island and a new 5 km fissure. Several explosive vents along the fissure caused a rift in the overlying glacier releasing a flood of water carrying ice blocks.

A Crater Formed by Gas Erosion of a Nuclear Explosion Vent

Abstract The PALANQUIN experiment was a 4.3 kiloton nuclear explosion detonated at a depth of 280 feet (85.3 m) in layered trachytic volcanic rocks at the Nevada Test Site. The resulting apparent crater had an unusual conical shape and dimensions of 119.1 feet (36.3 m) radius, and 78.8 feet (24.0 m) depth. The crater volume was 46,800 cubic yards (35,570 cubic meters).

The venting of pentane vapour-air explosions on a large vessel

Experiments have been carried out on the venting of pentane vapour-air explosions in a 60 ft 3 vessel. The effects of bursting disc operating pressure and vent size were investigated for both stationary and turbulent gas mixtures. For the turbulent mixtures experiments were also carried out on the effect of degree of turbulence on maximum explosion pressure. It was found that turbulence had a profound effect on maximum explosion pressure. In explosions of stationary gas mixtures the bursting of the disc itself caused turbulence and affected the maximum explosion pressure for a given vent size, while for explosions of gas mixtures which were turbulent initially, pressure increased with increase in degree of turbulence. For the smaller vent sizes explosion pressure reached a maximum value with increase in degree of turbulence, but this maximum was not reached for the larger vents with the existing equipment. The operating pressure of the bursting discs was found to vary with rate of application of pressure, and under explosion conditions all the discs used burst at a higher pressure than their static rating.

Crankcase Explosions: An Investigation into Some Factors Governing the Selection of Protective Devices

Remedies which have been suggested for crankcase explosions include the use of warning devices to detect over-heating in the crankcase, and the provision of relief vents to limit the explosion pressure to a safe value. Data were obtained experimentally at the Thornton Research Centre for the conditions necessary for the ignition of mists of lubricating oil in air in order that the margin of safety offered by a detector of overheating might be more fully assessed. The venting of explosions was also studied both on a rig scale and in the crankcase of a Diesel engine of 1,100 h.p. The results indicated that it would not be practical to provide sufficient venting area on an engine of this size, to limit the maximum explosion pressures to a safe value for the more violent explosions which might occur. For venting to provide complete protection, it would seem necessary to take measures to prevent the flame from spreading throughout the whole crankcase.

The Potash Ankaratrite-Meleleucocitite Lavas of Nabagando and Mbuga Craters, south-west Uganda

The Katwe-Kikorongo volcanic field, near Ruwenzori in the Western Rift of Africa, is morphologically a typical area of tuffs and multiple explosion vents. The ejectamenta include rocks and minerals derived from ( a ) highly cafemic and potassic volcanic materials; ( b ) biotite-pyroxenite and related cognate sub-volcanic types; and ( c ) the crustal materials through which the vents were drilled. Only four small occurrences of lava flows are known, discovered by the late A. D. Combe in the walls of Nabugando and Mbuga craters. One of these, a truncated pile of at least six flows, is thought to represent the infilling of a deep vent in a tuff-cone now largely destroyed by explosions. The others are the truncated remnants of flows that were probably erupted from the flanks of the same volcano. The lavas and the corresponding ejected blocks are classified as potash ankaratrites (containing potash-rich nepheline), leucite-ankaratrites and melaleucitites, all of which are rich in pyroxenes and black ores; further subdivision is based on the presence or absence of phenocrysts of olivine and/or perovskite. The lavas are briefly described by reference to the twelve types so distinguished. Fourteen chemical analyses of these rocks are presented, twelve of them being new, together with several additional alkali determinations. Following up a hypothesis already proposed to account for the mode of origin and peculiar composition of katungite (a potash-rich melilite-olivine volcanic rock), it is suggested that the silica and alk-aluminous constituents of the volcanic and sub-volcanic products were provided by sialic crustal rocks such as granite (G) and that the cafemic constituents and TiO 2 (C) were introduced by a carbonatite fluid. Reactions between the latter and, say, granite are considered to have generated biotite-pyroxenite (B.P.) and the magmas of potash ankaratrite and its associates (KA), together with vast quantities of highly compressed gases (mainly CO 2 ) which would be available for the explosive work of crustal perforation and tuff formation. The hypothesis, which can be qualitatively expressed as KA+B.P.=G+C, is shown to be quantitatively reasonable and geochemically adequate.

EXPLOSION TESTS ON GLASS WINDOWS, EFFECT ON GLASS BREAKAGE OF VARYING THE RATE OF PRESSURE APPLICATION*

AbstractTests were made to determine whether or not glass windows would be of value in preventing building damage from internal explosions involving combustible dusts or vapors It was found that the effective strength of glass panes increases in an approximate linear ratio with increased rate of pressure application. It was concluded that window glass is of dubious value for explosion venting purposes, except possibly for explosions of high pressure but of very short duration, such as those that might occur if small quantities of high explosive were placed relatively near the windows.

Explosion vents for fume hoods and a method for testing them.

Explosion vents for fume hoods and a method for testing them.

Volcanic Centers of the Sunlight Area Park County, Wyoming

The Sunlight area is located in the northern Absaroka Mountains of northwestern Wyoming. The rocks are dominantly Tertiary pyroclastics and basalt flows which rest on flat-lying Paleozoic limestones. The pyroclastics were thrown out from a large number of vents in explosive eruptions and were later modified by mud flows. Two major volcanic centers and one small explosive vent have been found in the Sunlight area. Intrusions of stocks, laccoliths, plugs, cone sheets, and radial dike systems are closely related to the volcanic centers. The radial dikes were formed by magma moving horizontally outward from the intrusive centers in vertical cracks. The Sunlight centers are similar in many respects to the Scottish Tertiary volcanoes. The rock types in general show a normal differentiation series from olivine gabbro and basalt through diorite and andesite to sodic syenite and trachyte. Several unusual orthoclase-bearing basalts, known as the absarokite series, are also present.