Posts Tagged ‘Combustible Dust’

by: Jason A. Sutula

Most people do not think about metals burning when they think about combustion and fire. Yet, metals can combust, especially when the metals are being used within an industrial process or themselves being processed at higher temperatures. Fortunately for the process safety, mining, and other industries, much research on metal combustion has been done over the years. One of the first studies on the burning of metal dusts was published in 1955 by Titman (Titman, 1955).

Titman examined small metal particles and the influence they had on the explosive mixtures of gases. Additionally, the metal dusts themselves were determined to have explosive properties. The hazards of metal dust combustion are similar in nature to those of organic dusts, which were discussed in a previous post of mine (The Creamer Canon). Since metals have a high affinity for oxygen and have the material property of high heats of oxidation, they are capable of producing high temperatures and the liberation of energy in very rapid fashion.

Another seminal, systematic study was conducted by Harrison and Yoffe in 1961 and published in the Proceedings of the Royal Society of London (Harrison and Yoffe, 1961). Harrison and Yoffe conducted their experiments using wires of various metals. These metals included aluminum, iron, magnesium, molybdenum, titanium, and zirconium.

Harrison and Yoffe demonstrated that the process of metal combustion was much more difficult to initiate when the metal was in wire form as opposed to dust. Their results indicated that the explosive hazard associated with the metal dusts were not as much of a concern with larger chunks of metal. Additionally, Harrison and Yoffe discovered that the mode of burning for each metal was determined by the relative melting and boiling points of the metal and the metal oxides (which is formed as the product of the combustion reaction).

Today’s embedded YouTube video selection demonstrates the energetic reaction produced by titanium powder burning. The reaction of the individuals involved is eerily similar to that of the Mythbusters crew as seen in the Creamer Canon video. In addition to providing a means to educate us through videos on the internet, combustible metals do have many other useful purposes. One such is the use of metal dusts to ensure a specific color in commercial firework displays. Titanium, Aluminum, and Magnesium powders are used to make a vibrant white color in the pyrotechnic stars. With that in mind, an argument can be made that the Chinese were actually the first researchers who began walking the path of understanding metal combustion. Have a happy and fire safe 4th of July!

Titman, H., Trans. Inst. Min. Engrs., Lond., 115, 1955.

Harrison, P.L., and Yoffe, A.D., “The Burning of Metals,” Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, Vol. 261, No. 1306, pp. 357-370, 1961.

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by: Jason A. Sutula

Last week, I enjoyed an excellent presentation by a colleague on the explosive power of combustible dust. The presentation started off with several case studies throughout history that all told a similar tale. One of the most interesting cases was also one of the earliest on record: “The Account of a Violent Explosion which Happened in a Flour-Warehouse, at Turin, December the 14th, 1785, to which are added some Observations of Spontaneous Inflammations.” (Printed in its entirety in Eckhoff, 2003) Even more interesting was that this incident was investigated by a local official, Count Morozzo, who took the time to do as scientific of an investigation as was possible for his time. He even wrote an account of his findings.

According to Count Morozzo, at about 6:00 p.m. an explosion took place in the house of Mr. Giacomelli, a Baker in the city of Turin. The explosion was powerful enough to blow out the windows and window frames of the building, and produced a noise that was as loud as a “large cracker.” At the moment of the explosion, Count Morozzo reported that a very bright flame was observed that only lasted for a few seconds. Further investigation revealed that the “inflammation” had started in the flour warehouse, which was located in the rear of the structure over top of the bakery shop. A boy was stirring flour in this area while using the light from a lamp. As a result of the fire, the boy sustained burns to his face and hands, and his hair had been burned off.

Without the benefit of chemistry and modern fire and explosion dynamics, Count Morozzo was able to use logical arguments to piece together many of the components that led to the incident. He correctly deduced that the flour needed to be in the air (dust suspended in air), that atmospheric air was mixed with the flour (oxidizer), that the event was confined within a small room in the bakery (confinement of the dust cloud), and that the ignition occurred from the light next to the boy (heat source for ignition). These are four of the five components necessary for a dust explosion to occur. The remaining component is the dust itself (the fuel). Count Morozzo was unable to link this component to the event because fuel chemistry was not understood at the time, and he believed that “inflammable air” was confined within the flour and could be released without changing the makeup of the flour itself.

The good news is that the boy recovered from his injuries within a fortnight (14 days). The bad news is that even with Count Morozzo’s account, the process industry did not learn from these types of case studies until more recently in the modern era. It can also be argued that there is still plenty of work left to do today.

In an effort to demonstrate what that poor boy in Mr. Giacomelli’s Bakery must have experienced, take the time to watch the above YouTube video. Mythbusters produced this non-dairy creamer cannon demonstration for Season 07, Episode 03. It is the perfect visual for understanding the power of a dust explosion.

Eckhoff, Rolf, Dust Explosions in the Process Industries, Third Edition, Boston, Gulf Professional Publishing, 2003.