State-of-the-art research on fireworks and pyrotechnics

Kosanke – Part 6

Selected Pyrotechnic Publications of K.L. and B.J. Kosanke,

Part 6. (2001 and 2002)

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Titles and Abstracts (Part 6)

Fire Sculptures Using FireRope

Fire sculptures are not a true pyrotechnic effect, being produced simply by the burning of a liquid fuel in air. Nonetheless their use can contribute rather nicely to firework displays that include ground effects. Fire sculptures form continuous images in yellow fire that burn for 10 minutes or more. This is in contrast to lance work images, created using a series of points of variously colored fire that burn for about a minute. As with lance work, it is probably more common for fire sculptures to form images of objects, ships or buildings, than lettering.

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Electric Matches: Physical Parameters

A major study of electric match sensitiveness was recently completed. This article continues that work and presents a compilation of the physical parameters (as measured and/or provided by the suppliers) for the same collection of 10 electric match types as in the previous article.

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Electric Matches: Ramp Firing Current

A major study of electric match sensitiveness was recently completed. This article presents the results of a test to reveal aspects of the firing characteristics for the same collection of 10 electric match types as in the previous articles.

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Pyrotechnic Reaction Residue Particle Identification by SEM / EDS

Today the most reliable method for detecting gunshot residue is through the combined use of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) of the resulting X-rays. In recent years, this same methodology has found increasing use in detecting and characterizing pyrotechnic reaction residue particles (PRRPs). This is accomplished by collecting particulate samples from a surface in the immediate area of the pyrotechnic reaction. Suspect PRRPs are identified by their morphology (typically 1 to 20 micron spheroidal particles) using a SEM, which are then analyzed for the elements they contain using X-ray EDS. This will help to identify the general type of pyrotechnic composition involved. Further, more detailed laboratory comparisons can be made using various known pyrotechnic formulations.

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Hypotheses Regarding Star-Shell Detonations

Fireworks star shells occasionally explode upon firing while they are still inside the mortar. Most often, this occurs with approximately the same level of violence as when the shell explodes after having left the mortar, and often even relatively weak mortars survive the experience intact. While unnerving to the firing crew, this represents relatively little hazard for crew or spectators. However, on rare occasion, the in-mortar star shell explosion achieves a level of violence substantially greater than normal. These more powerful explosions represent a potentially life-threatening hazard for both the firing crew and spectators. Unfortunately, the cause for these more violent explosions has not been definitively established, and without knowing the cause, relatively little can be done to prevent them from happening. In this article, two hypotheses are suggested as possible explanations for these dangerous malfunctions. Basic information and some empirical evidence are presented in support of two potential theories.

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Chlorate Compositions in Quickmatch

After the 1999 PGI convention, the authors were told about a type of quick match that had been sold at the convention and which was suspected of being made using a chlorate oxidizer. The individual’s suspicion was based on his perception of its extremely fast burn rate. Subsequently, a sample of that fuse was spot tested and found to contain a nitrate but not a chlorate. Sometime later, the authors were given a sample of quick match thought to be of the same type. The burn rate of the quick match was observed to be most vigorous; however, there was not a sufficient amount for the authors to make a usefully quantitative measurement of its burn rate. Small amounts of the composition were removed from the black match portion of this fast burning quick match, and two tests for the presence of chlorate were performed. The first test was the concentrated hydrochloric acid test, in which a few drops of the acid are placed on the composition. The presence of a chlorate is revealed by a modest rate of chlorine dioxide gas production, with its characteristic color and odor. The second test was the analine-HCl spot test, in which some of the composition is dissolved in a tiny amount of water, the water is decanted and treated with a drop of analine-HCl test reagent. The presence of a chlorate is revealed by the appearance of first a red then blue color. Again, both test results were negative for the presence of a chlorate. Accordingly, another possible explanation for the vigorous burn rate of the quick match was sought.

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Faversham’s Gunpowder Mills

Recently, while in the United Kingdom and between teaching pyro-chemistry short courses, we took a side trip to visit the restored Chart gunpowder mill. This is the only restored mill from what was once a collection of approximately ten powder mills near the town of Faversham in Kent county. When operating at their peak in 1792, these mills produced over 25,000 barrels of powder.

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 Floating Dud Aerial Shells

Over the past 25 years, the percentage of spherical aerial shells that fall to the ground as duds after firing has substantially decreased. (This is especially true for shells from China.) Obviously this is a good thing, and it is a result of such things as improvements in the quality of the time fuses being used and the methods of their priming, and because of the near universal adoption of redundant fusing techniques. However, the improvement has not been so great as to reduce the percentage of dud shells to zero. Nonetheless, the reduction in the number of dud shells, in conjunction with the use of substantially increased separation distances introduced approximately 15 years ago, combine to afford a high level of spectator protection from dud shells during typical displays. Further, the increased attention to dud searches both immediately following and at first light on the morning after land-based displays has mostly eliminated accidents resulting from dud shells left behind to be found by children.

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Study on the Effect of Leg Wire Attachment on the Height Attained by Aerial Shells

In many electrically discharged fireworks displays, it is a common practice to securely attach the electric match leg wires to both the aerial shell and to the firing mortar or mortar rack. When this is the case, it is necessary for the aerial shell to sever the attachment to the mortar or rack upon the firing of the shell. Usually this is accomplished by severing (tearing) the leg wires themselves. In this process, some of the kinetic energy of the shell is consumed, resulting in a reduction in the burst height that would otherwise have been achieved. This reduction in burst height will be greatest for those shells possessing the least kinetic energy (i.e., the smallest and lightest of the aerial shells). While experience has shown that the amount of reduction in burst height apparently does not present a significant safety hazard, the question remains as to how much reduction actually results. In a brief study of this question, it was concluded that for even the smallest and lightest aerial shells commonly used in displays (75 mm with a mass of 90 g) the reduction in burst height is on the order of 12%, and this decreases to about 1% for mid-sized aerial shells (150 mm with a mass of 1.1 kg).

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The Effect of Ignition Stimulus on Aerial Shell Lift Performance

It had been speculated that the replacement of fierce burning quick match shell leaders with electric matches might have contributed to the production of a significant number of low breaking aerial shells experienced by a small fireworks display company. A preliminary study of the effect of ignition stimulus level did not supporting the theory that the weaker stimulus provided by electric matches (possibly in conjunction with Chinese lift powder) was the reason for the low breaking shells. However, that study was thought not to be sufficiently conclusive to completely settle the question. Accordingly, a more extensive series of tests were subsequently performed. For these tests, because of the lack of sufficient Chinese lift powder, Goex (USA) Black Powder was used. The result of these tests was that again no effect was observed for the flight times of the test aerial shells. The average flight times for groups of approximately 30 of the 75- mm (3-in.) test shells was 9.65 ± 0.13 seconds and 9.58 ± 0.17 seconds for shells using quick match and electric match firing, respectively.

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The Effect of Mortar Diameter on the Burst Height of Three-Inch Spherical Aerial Shells

A while ago, a small fireworks display company called seeking information about the effect of mortar internal diameter on the burst height expected to be achieved by aerial shells fired from them. It seems the company had received a large quantity of three-inch, high-density polyethylene (HDPE) pipe that they had cut into 18- inch lengths for mortars (including 1.5-inch thick plugs) before having checked the pipe’s internal diameter. When it was checked, the HDPE pipe was found to have an internal diameter of 3.21 inches (i.e., it was significantly oversize). Because it was close to the July 4th holiday season, there was not sufficient time to replace the pipe. Accordingly, the question was, could these mortars be safely used?

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Electric Matches: Effective Thermal Output

A study of electric match sensitiveness and performance has recently been completed, and a summary of the results is being presented as a series of short articles. This is the ninth article in the series and presents the results of tests to determine the effective thermal output for the same collection of 10 electric match types as in the previous articles.

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Factors Affecting the Precision of Choreographed Displays

For maximum effectiveness of tightly choreographed fireworks displays, it is important that shell bursts occur very near their intended times. For the purpose of this article, it is assumed that electrical firing employing a computer or other means of accurately applying the firing current to electric matches is being used. In addition, it is assumed that the choreographer has accurate information about the firing and burst characteristics of the shells being used, and that no errors are made in the design of the choreography or in the loading of the display. In that case, there are two primary sources of variation that combine to affect the overall precision of the shell burst times. First is the preciseness of the shell firings from their mortars; second is the preciseness of the time fuse burning. (In the context of this article, “preciseness” is intended to indicate consistency or reproducibility of events.)

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Studies of Electric Match Sensitiveness

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.

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Sodium/Potassium Ratio and Hygroscopicity of Civil War Era Black Powder

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. 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.

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DOT Exemption for Display Fireworks with Electric Matches Attached

Several years ago the US Department of Transportation granted an exemption that, under certain 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.

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A Rule for Improving Manufacturing Safety Involving the Use of Energetic Materials

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.

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Aerial Shell Burst Height as a Function of Mortar Length

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, 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. 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.

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Aerial Shell Burst Delay Times

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.

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“Impossible” and Horrific Roman Candle Accident

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.

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Pyrotechnic Burn Rate Measurements: Strand Testing

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. 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.

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Fireball Characteristics as Determined in a Test Simulating the Early Stage of a Fireworks Truck Loading Accident

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.

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