Archive for March 2007

Timing Aerial Shell Bursts for Maximum Performance and Safety

K.L. and B.J Kosanke

The time chosen for the interval between a shell firing and its burst is sometimes given less thought than it deserves. By carefully choosing the delay interval provided by the time fuse, it may be possible to produce undistorted bursts, with a higher level of safety. When an aerial shell bursts, while it is nearly stationary, its stars are propelled outward, each experiencing nearly the same aerodynamic drag.

Thus the symmetry of the burst is determined only by the construction of the shell, and the pattern will appear to be suspended in the air for its duration. That is to say, a properly made peony will appear as an expanding, near-perfect sphere and will seem to hang motionless in the air as it spreads. See the left column of Figure 1, which is intended to appear as a timed sequence of the burst and expanding pattern of stars from a near stationary spherical shell. On the other hand, if the same shell were to burst while it was in rapid motion, the star pattern would be distorted. This is because the spreading stars would be subjected to a little different aerodynamic force depending on which way they were traveling relative to the motion of the shell. The star pattern will appear smaller and somewhat elliptical. Also the star pattern will be slightly more sparse on the bottom than on the top. Perhaps, most noticeably, the developing star pattern will move in the direction of the original shell motion, and will appear to expand from a point which is not at the center of the pattern. See the right column of Figure 1 for an illustration of the case where the upward motion of the shell approximately equals the burst velocity of the stars. (Readers wishing to learn more about star ballistics are referred to Reference 1.) Thus there are aesthetic reasons why aerial shells are normally intended to burst near their apogee, when their upward motion has essentially stopped.


Ref: Selected Pyrotechnic Publication of K.L. and B.J Kosanke, Part 3, (1993-1994), pp 1-3
(K3_1)
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Fireball Characteristics as Determined in a Test Simulating the Early Stage of a Fireworks Truck Loading Accident

K.L. and B.J Kosanke

A few years ago there was an investigation and analysis of an accident thought to have been initiated by the ignition of a case of spherical aerial shells in the cargo area of a truck. It was thought that the case of shells had been dropped or thrown to the floor of the truck during the course of its loading. (Note that some of the facts of the matter may be in dispute.) As part of that investigation, it was thought that a simple test would aid in establishing the likely sequence of events during the early stages of the accident. Accordingly a test was performed to estimate the extent and rapidity with which the initial fireball would develop from the ignition of a case of spherical aerial shells. Because the information developed by the test is of general interest to persons working with display fireworks, this brief article has been written.


Ref: Selected Pyrotechnic Publication of K.L. and B.J Kosanke, Part 6, (2001-2002), pp 103-106
(K6_103)
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Pyrotechnic Burn Rate Measurements: Strand Testing

K.L. and B.J Kosanke

Background: Burn rate is one of the most fundamentally important properties of pyrotechnic materials. While burn rate may be measured as a mass burn rate (mass of pyrotechnic composition consumed per unit time, e.g., g/s), linear burn rate is most commonly used. Linear burn rate can be defined as the distance the burning surface of a pyrotechnic composition advances inwardly (perpendicular to the burning surface) per unit time, and typically would be reported as inches per second (or mm/s). Even for a specific pyrotechnic material with a defined composition (including prescribed particle size and shape) there are a number of factors that will effect its burn rate.[1] Generally the most important factors, ranked roughly in order of importance, are: ambient pressure, loading pressure (composition density), temperature, and burning surface area. Accordingly, for burn rate measurements to be most useful, they must take each of these additional factors into consideration.


Ref: Selected Pyrotechnic Publication of K.L. and B.J Kosanke, Part 6, (2001-2002), pp 100-103
(K6_100)
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“Impossible” and Horrific Roman Candle Accident

K.L. and B.J Kosanke

[Authors note: This article includes a number of notes with ancillary information. This information is not essential to the primary purpose of this article. Accordingly, it is suggested that the reader might wish to initially ignore the notes, and then subsequently, if additional information is desired, read any notes of interest.]

Introduction: In May of 2000 in Queensland Australia, a most horrific accident occurred involving large bore (2-in., 50-mm) Roman candles, which had generally and widely been thought to have been impossible. Because the set of conditions leading to this accident could occur again, and because requirements in the national fireworks standards (in both the US and Australia) should be modified somewhat to help mitigate the potential for future injuries, a series of articles derived from this accident and its investigation are being written.

To facilitate their publication, the length of these articles will be limited such that only a portion of the overall subject will be addressed in each. This first article begins with a brief discussion of common Roman candle malfunctions. The bulk of the article presents the basic facts of the accident. Subsequent articles will present: a discussion of the Roman candle characteristics that caused the powerful explosion; partial summaries of the results of the many and in-depth scientific investigations undertaken to elucidate and confirm the cause and course of this accident; recommendations of some changes to the safety procedures for the use of large bore Roman candles; and warnings regarding the manner of manufacture of large Roman candle stars.


Ref: Selected Pyrotechnic Publication of K.L. and B.J Kosanke, Part 6, (2001-2002), pp 95-99
(K6_95)
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Aerial Shell Burst Delay Times

K.L. and B.J Kosanke

If you have ever wondered how long the shell burst process takes after the time fuse burns through to the interior of the shell, this article may be of interest to you. Although rapid, the process is not instantaneous. A flame front must advance through the burst charge and an amount of combustion gas must be produced that is sufficient to pressurize the shell casing beyond its burst strength. Some time ago, as part of a study of the possible cause of muzzle breaking aerial shells, we needed to determine approximately how long this process takes.[1] That burst delay time data is summarized below.


Ref: Selected Pyrotechnic Publication of K.L. and B.J Kosanke, Part 6, (2001-2002), pp 93-94
(K6_93)
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Aerial Shell Burst Height as a Function of Mortar Length

K.L. and B.J Kosanke

[This article is augmented with a number of text notes, indicated using superscript letters. While it is hoped these provide useful information, they are not essential, and the reader may wish to ignore them unless further information is desired.]

From time to time over the years there has been discussion of the effect of mortar length on the burst height  achieved by fireworks aerial shells. However, rarely has burst height versus mortar length data been presented, [1,2] even then the data has been of limited value. In one case, the results were predictions using a ballistics model where only the maximum possible height reached by aerial shells was presented, not the measured height at the time of their actual burst.[a] In the other case, only a one shell was fired for each mortar length, and the method of determining the height of the shell burst was rather imprecise. The study being reported in this article is more useful in that actual burst heights were reasonably accurately measured and there were several firings from each mortar length. Unfortunately, this study only examined the effect of mortar length on 3-inch (75-mm) spherical aerial shells. While it is expected that similar results would be found for other shell types and sizes, that cannot be assured.


Ref: Selected Pyrotechnic Publication of K.L. and B.J Kosanke, Part 6, (2001-2002), pp 90-92
(K6_90)
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A Rule for Improving Manufacturing Safety

K.L. and B.J Kosanke

Over the years there has been an almost continuous series of accidents involving people using energetic materials, too many of which involve fireworks, their manufacture or their preparation for use. There are important lessons that can be learned from these accidents; unfortunately most of these come too late for the people suffering those accidents. Even more unfortunately, many of the same factors have combined to produce similar accidents again and again.


Ref: Selected Pyrotechnic Publication of K.L. and B.J Kosanke, Part 6, (2001-2002), pp 88-89
(K6_88)
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DOT Exemption for Display Fireworks with Electric Matches Attached

K.L. and B.J Kosanke

Background: Several years ago the US Department of Transportation granted an exemption[1] that, undercertain conditions, “authorizes the transportation in commerce of Division 1.3 and 1.4 display fireworks with igniters (electric matches) attached to either the fuse or the lift charge.”  Because of concern regarding one of the specific provisions of that exemption, a brief study was undertaken. This short article discusses that concern and reports on the results of the study. (A restatement of the full set of conditions that must be met is beyond the scope of this article, see reference 1.)


Ref: Selected Pyrotechnic Publication of K.L. and B.J Kosanke, Part 6, (2001-2002), pp 85-87
(K6_85)
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Sodium/Potassium Ratio and Hygroscopicity of Civil War Era Black Powder

K.L. and B.J Kosanke

Several years ago a sample of Black Powder, which had previously been recovered from US Civil War era cannon balls (ca. 1865), was made available for analysis. This made possible a brief comparative study of the Civil War era sample and one representing currently produced Black Powder. That study found the performance of the Civil War era powder sample to be roughly comparable to current production Black Powder.[1] Following that initial study, a very brief study was conducted regarding the purity of the potassium nitrate used in the Civil War era powder sample. Specifically, the molar percentage of sodium to potassium was determined, and those results were compared with the results from two more recently produced powders. This was of interest because it was speculated that the potassium nitrate in the Civil War era Black Powder might have been of lower purity with regard to the amount of sodium present (potentially as sodium nitrate). If that were the case, it might contribute to the susceptibility of the powder to absorb moisture, potentially leading to its degraded performance under battle field conditions.


Ref: Selected Pyrotechnic Publication of K.L. and B.J Kosanke, Part 6, (2001-2002), pp 82-84
(K6_82)
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Studies of Electric Match Sensitiveness

K.L. and B.J Kosanke

ABSTRACT: The sensitiveness of a collection of ten electric match types, from four suppliers, was determined under conditions intended to reflect their actual use to ignite fireworks displays. The measurements included determinations of impact, electrostatic discharge (ESD), friction, and thermal sensitiveness. The ESD tests considered discharges both through the bridgewire and from the bridgewire through the composition to ground. When safety shrouds were provided by the manufacturer, additional impact and ESD (through the composition) testing was performed with the safety shrouds left in place on the electric match tips. (Note that users often remove the protective shrouds for convenience during use.) To simulate conditions during use, additional impact and friction testing was performed with Black Powder prime composition in the presence of match tips. It was found that there was a wide range of electric match sensitiveness, that the presence of the shrouds provided significant decreases in sensitiveness, and that the presence of Black Powder prime did not significantly affect sensitiveness.

Keywords: electric match, impact sensitiveness, friction sensitiveness, thermal sensitiveness, electrostatic discharge sensitiveness, ESD, sensitiveness testing


Ref: Selected Pyrotechnic Publication of K.L. and B.J Kosanke, Part 6, (2001-2002), pp 61-81
(K6_61)
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