Historical foreword to explosion proof products
1815 the miner safety lamp, invented by
|The explosion of firedamp in mines caused by the flames of oil lamps, was the cause of many accidents and caused hundreds of deaths. This explosion had a double danger: methane gas and coal dust. When the methane exploded, the explosion was generally followed by a much more violent explosion of dust (the dust explosion) produced by inflammation of the cloud of coal dust produced by the initial explosion.
The oldest listed, but certainly not the first tragedy, was the one of the pit of the Barbeau de Wez, near Liège in Belgium, which caused 94 victims in 1514.
The first solution was to hire minors, volunteers and paid more to ignite the gas every day.
Firedamp was “lit” before the miners arrival. For this purpose, a worker called penitent (because of the suit which he was clothed) or gunner, covered with wet leather or fabric clothes, face protected by a mask equipped with glass windows and carrying a lighted candle, was responsible for igniting the gassy pockets, mostly located in the upper parts of galleries.
Alphonse Meugy describes how to operate in his book, “History of the Mines in Rive-de-Gier” (1848):
“Two workers called gunners used to go down to the mine a few hours before their peers, with strong canvas clothes, and covered with a kind of head cap.
They were moving at a certain distance of the working faces and while one of them was hiding in a nearby gallery, the other one, armed with a pole bearing a burning wick at its end, was approaching by crawling until the flame of the wick was beginning to grow. He then was laying, face to the ground with his clothes soaked and was lifting the pole to the top of the excavation. This was producing a detonation which often had the effect of seriously injuring the gunner. He was rescued by his colleague.”
Ponies carrying a lit candle were also used. They were watered then sent to the galleries in the hope of creating tiny explosions.
After many accidents, the English Humphry Davy discovered in 1815 that a flame enclosed in a very fine mesh does not ignite firedamp. Miners lighting became safer.
The practice of the “penitent” or “gunner” was gradually outlawed in the mines around 1835, after the Davy lamp being almost universally used in France since 1823.
This lamp, which was called ”the Davyne” in France, seemed likely to provide all the necessary safety guarantees against ignition of firedamp but after many explosions occurred in coal mines where this lamp was used, it was soon demonstrated it was not flawless, and that it could only reduce the chances of explosions, without preventing them in all cases. In particular, it had the following defects:
– The inflammation of a mixture of air and carbon hydrogen can occur through the metallic canvas, in galleries where there is a quick airflow, because then, the lamp flame blushes the mesh or passes through.
1842 The Mueseler miner lamp
|-The slightest shock can deform or even tear open the mesh, and thus render the lamp ineffective.
– The metal-mesh in contact with the oil reservoire,is soon greased and traps fuel dust, thus forming a paste which can be ignited, both inside and outside.In 1842 the Liège Mathieu-Louis Mueseler invented a lamp that had the following advantages:
– It is quickly extinguished when there is plenty of explosive gases, even in a mixture with pure hydrogen.
– It shines best and can be placed away from the worker and free tools, and best suited in galleries having strong air streams.
– The wire mesh, being remote from the tank , do not permeate to oil. Only a dry dust can stick but it is easily removable.
– It is provided with two wire meshes, one horizontal and the other vertical, so that one remains intact when the second is to be torn.
– Finally , the air flow to activate the combustion is from top to bottom instead of being laterally, provision that gives the inestimable advantage over all other safety lamps, of turning off suddenly when the air is charged with sufficient carbon hydrogen to provide an explosive mixture.
This lamp spread in the basin of Seraing and other coal centers in Belgium and, in 1864, its use was prescribed by the Belgian Government. It was then adopted in a number of mines in France and England.
Lighting miners became safer. The use of these lamps, however remained linked to the respect of safety, and there were many accidents resulting from human carelessness. Here is an example, one of my ancestors, Auguste-Joseph Jumeau , was one of the victims :
On Saturday, March 6, 1852 , at the pit ” Ferrand ” at Elouges in The Borinage (Belgium), the morning shift just came down in the galleries, it was the last day of work in this mine, as it should be closed to allow upgrades and safety works. The pit had a small diameter and allowed a two buckets traffic only (large casks used to bring the coal up to the surface and the movements of people) attached to hemp ropes.
1862 Electrical miner lamp
|At 20 meters of the hanging point, at the entrance of a gallery, was a tank containing water for the mine horses. Around 10 AM, the worker in charge of treating horses went there to draw water. As the lamp did not light enough (probably a Davy lamp type), he imprudently opened it. As soon as the flame in contact with the atmosphere, an explosion rocked the mine. The horse trainer was thrown against a wall and was horribly burned. He survived nevertheless.
His many companions were less fortunate: 63 miners, men, women and children were killed.
A risk still remained to be solved: the ignition of the lamp, which forced to back it out of the well if accidentally extinguished. In the 1890’s, when kerosene replaced oil in lamps, electric ignition systems for miner lamps were tested, having enclosures that did not let the flame out (Patent by William Ackroyd, Morley, England).
The first electric portable lamps with batteries offered at the Academy of Sciences of Paris en1862 by MM. Dumas and Benoit, did not definitely meet safety requirements, unlike earlier expectations that set forth their lighting tube enclosed in a sealed tube as not fearing the ignition of firedamp (featured in the Journal of Industrial Engineering, July 1863).
1884 Cad electrical lamp
|In 1884, English Theophilus Cad, from Forest Gate, England, invented an electric lamp whose switch was enclosed in what can be considered the first electrical flameproof enclosure (British Patent No. 806 of 5 January 1884).
Timidly used from 1890, electric lamps grew very slowly between 1920 and 1930.
But shortly after the introduction of electricity in coal mines, it was also discovered that lethal explosions could be initiated by fixed electrical equipment such as lighting, signals or motors.
Around 1910, 12 volts DC signaling systems considered safe appeared.
However, in October 1913, took place the largest explosion of British mines, that of Senghenydd Colliery, where 439 miners perished. It was suspected an alarm system, consisting of two
parallel bare wires running along the galleries, which allowed any miner wishing to report a problem to the surface to make it by contacting momentarily the two wires with a metal tool.
But the bell inductance coils caused a spark, which was probably the cause of the explosion. It was then determined that these products might be secured by a careful design, the forerunner of the “intrinsic safety”. Following this disaster, the miners demanded the withdrawal of the electrical equipment of pits. Then began the development of electric devices called “explosion proof”, which inevitable sparks could only occur in a protective envelope preventing from igniting the surrounding gas.
Historically, the topic of Hazardous (Classified) Locations first appeared in the National Electrical Code (NEC) in 1923, when a new article entitled “Extra-Hazardous Locations” was accepted. This article addressed rooms or compartments in which highly flammable gases, liquids, mixtures or other substances were manufactured, used, or stored. In 1931, “Classifications” consisting of Class I, Class II, etc., for the hazardous locations were defined.
In the investigations leading to approval of loading and conveying machines the bureau is guided by the provisions of Schedule 2C. issued on February 3, 1930. This schedule classified the various electrical parts according to their liability to sparking and specified the type of enclosure to be used for each class. As required by the schedule, a part that may produce sparks during normal operation must be enclosed in an explosion-proof casing; that is, an explosion of gas in such a casing must not ignite the gas surrounding the casing or discharge flames from any joints, bearings, or lead entrances. The object of the bureau’s investigations is therefore to determine by test and inspection whether or not the enclosures are suitable to the purpose for which designed. The explosion-proof qualities are demonstrated by tests in which gas is exploded within the casings. Other tests are made to check the adequacy of electrical clearances and insulation. In addition to the tests, a detailed inspection of parts, including a careful check against drawings and specification is made. These drawings constitute the chief record of the equipment investigated and therefore must be complete in detail to cover adequately the construction to be approved. A description of test equipment and methods followed in conducting these investigations is given in Bureau of Mines Bulletin 305, Inspection and Testing of Mine-Type Electrical Equipment for Permissibility, published in 1929.
In Europe, the first German standards on “The protection of electrical installations in hazardous areas ” were published in 1935, and gave guidelines for the installation of electrical equipment in hazardous areas. In 1938 appeared a fundamental change dividing the installation requirements (VDE 0165) and the design requirements of products (VDE 0170 / 0171 ).
Standards of product design included the types of basic protection against explosions such as flameproof enclosures, immersion in oil and increased safety. Components were designed to be protected against explosions and housed in industrial type housings that were resistant to weathering. This led to the development of flameproof components mounted inside increased safety housings. Devices designed to this standard were marked with the symbol (Ex). During the 1960’s, the European Community was founded to establish a free trade area in Europe. Consequently, the European Organisation for Electrotechnical standardization (CENELEC) was created. A new set of European standards describing devices for explosive environments (EN 50014 – EN 50020) was published in 1972. In 1975, the first EU directive for devices used in hazardous areas, known as “Directive on the protection against explosions “, was published. In 1978, the first edition of European standards was published by CENELEC which covered installation techniques.
To reach this goal, technical standards needed to be harmonized
|IEC standards currently in force in 2014 for equipment for explosive atmospheres are:
IEC 60079-1: Flameproof enclosures “d”,
– IEC 60079-2: Envelopes internal pressure “p”,
– IEC 60079-5: Powder filling “q”,
– IEC 60079-6: oil immersion “o”,
– IEC 60079-7: increased safety “e”,
– IEC 60079-11: intrinsic Safety “i”,
– IEC 60079-15: Type of protection “n”,
– IEC 60079-18. Encapsulation “m”.
|They are supplemented by the following equipment standards:
– IEC 60079-25,
– IEC 60079-26,
– IEC 62013-1,
– IEC 62086-1.
At their transcription into European standards, the IEC prefix is replaced by EN.