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Armament Depot Layout, Quantity Distances and Explosives Classification

Introduction

The layout of an armament depot like RANAD Newington is the result of cumulative planning decisions taken over many years and in response to varying military needs, economic circumstances, and technical knowledge of explosion effects. In times of emergency, expediency also emerges as a planning variable, as when brickworks kilns were taken into use for storage during World War 2.

In January 1853, Henry David Thoreau was in the vicinity when a gunpowder mill near Concord, Massachusetts, blew up. On the ground shortly after, he described the scene in his Journal, concluding with the observation "Put the different buildings 30 rods (30 rods is equal to 165 yards) apart and then but one will blow up at a time."

This layman's observation encapsulates one of the basic principles on which the layout of explosives sites rests, and which is given expression in what are known as "tables of distances", "safety distance" or "quantity distance" tables. (The latter terminolgy is used hereafter, in accordance with current practice.)

These tables, in their modern form, specify the minimum distance required between a potential explosion site (PES), such as an explosives storehouse, and an exposed site (ES), which could be another explosives facility, an administrative facility, a public traffic route or an inhabited building outside the boundary of the armament depot.

Early British Practice

As early as 1772, legislation was enacted in England to regulate the manufacture of gunpowder. It imposed limits on the quantity of gunpowder that could be processed in one batch, stipulated the materials to be used for construction of gunpowder magazines, and set down a 50 yard minimum separation distance between magazines and process buildings. It is likely that this legislation produced changes in the layout of gunpowder mills, resulting in more and smaller process buildings. (Wayne D. Cocroft, Dangerous Energy, 2000, pp. 27-28).

By the late 18th century, William Congreve's Marsh Works was utilising earthwork traverses or embankments to separate process buildings (Wayne D. Cocroft, Dangerous Energy, 2000, p. 35). Traverses (also known as revetments, barricades or blast walls) are an enduring feature of quantity distance tables, as they enable reduced separation distances where either the PES or ES is constructed with traversing. Traverses may behave as interceptor traverses, where they surround the PES, or receptor traverses, where they shield the ES. Traverses exist in many forms, including natural landforms; in earlier periods dense vegetation was regarded as a traverse.(The ability of traversing to mitigate the effects of an explosion of mass detonating ("high") explosives is described in an account of explosion trials below.)

In 1864, there was a large accidental explosion of gunpowder at magazines at Erith on the Thames River in the United Kingdom. In his report on this accident, Lieutenant Colonel Boxer, R.A., the head of the Royal Laboratory at Woolwich, provided a comprehensive account of the damage that had occurred at differing radii from the explosion site. For example, at 5 miles radius "Sir Thomas Wilson's house at Old Charlton, five miles from the site of the magazine, sustained considerable injury in the way of broken windows"". (Appendix No. 17 to Copies of the Reports of Lieutenant Colonel Boxer, R.A. and, of Correspondence Relating to the Explosion of Gunpowder at Erith, and the Condition of Magazines and Manufactories of Gunpowder, The House of Commons, 6 May 1865)

UK Explosives Act of 1875

In 1874, Major Majendie, the Home Office Inspector of Gunpowder Works, prepared a report on the inadequacy of the existing legislation for regulating explosives, including the "inadequacy of the regulations for localising, and protecting the public from, the effects of possible accidents". His report contains a detailed listing of the deficiencies of the act. (Vivian Dering Majendie, Major, Royal Artillery Reports on the Necessity for the Amendment of the Law Relating to Gunpowder and Other Explosives, with Suggestions for a New Act. Her Majesty's Stationery Office, 1874)

These deficiencies were reiterated in proceedings before the House of Commons Select Committee on Explosives Substances, which was established on 16 April 1874. The report of this committee resulted, in 1875, in a new explosives act for the United Kingdom (Explosives Act, 38 Vict. Ch. 17). The first schedule of this act provided some more detailed quantity distance rules to be applied to non-military storage of explosives. For example:

"(6.) Every person keeping or using any mill for the making of gunpowder shall have (in addition to the expense magazines) agood and sufficient factory magazine or magazines, situate (unless otherwise authorised by a certificate of the Secretary of State under the Gunpowder Act, 1860) at least one hundred and forty yards distant from the mill or mills and every press house and other house or place used for or in the making of gunpowder, such magazine or magazines to be well and substantially built with brick or stone, and situate in such place as may have been lawfully used or duly licensed by justices before the commencement of the Gunpowder Act, 1860, and not made unlawful by that Act, or may have been after the commencement of that Act duly licensed under the Gunpowder Act, 1860."

Tables of Distances

At about the same time, the first "tables of distances" came into use. Whilst giving evidence at a conference on proposed new Canadian explosives legislation, Captain Desborough, H.M. Inspector of Explosives, gave evidence as follows:

"The principle we use in England regarding the licensing of factories depends on what we call the table of distances. That is, the maximum quantity, of explosive allowed to be in any building depends on the distance it can maintain from other buildings connected with the factory, and also from certain prescribed buildings and works outside the factory. These distances are shown in two tables of which I have copies here. One is called the table for outside distances, and the other is what we call the intra-factory distance table. I will just give you one instance here. Take a blasting explosive. We should be prepared to allow 30,000 pounds in a building, provided it was adequately mounded, and was at a distance of 65 yards from other buildings. If the mound were not erected, then we should cut down the quantity to 6,000 pounds. It shows the great trust we put in mounded buildings." (Conference on Proposed Legislation to Regulate the Manufacture, Importation and Testing of Explosives Held in Room 16, House of Commons, Ottawa, Sep. 23 and 30, 1910)

Elsewhere, Captain Desborough stated that these tables had been in use for about 30 years ( A report on an accidental explosion in 1893 contains an appendix (XIV - Table of Distances between Danger Buildings Enforced by the Home Office) which is a "Table Showing Distances from Protected Works for Magazines and Other Danger Buildings". ( First Report of the Committee Appointed to Enquire into the Accident of the 13th December, 1893, at the Royal Gunpowder Factory, Waltham Abbey, and into the Construction,&c., of the Danger Buildings at Waltham Abbey and the Royal Arsenal, Woolwich together with Minutes of Evidence and Appendices( Her Majesty's Stationery Office, 1894). This is a recognisably modern table of distances, containing distances to a variety of both internal and external exposed sites. Whilst the Explosive Substances Act did not apply to the Crown, it is likely that similar rules were being observed by the Army and Navy.

British Quantity Distance Table

British Table of Distances - circa 1890 (From: Oscar Guttmann, The Manufacture of Explosives, Vol. II, Whittaker & Co., 1895, p. 379)

Here are some other accounts of quantity distance rules roughly contemporary with the foundation of RANAD Newington in 1897:

"If it can be avoided, gunpowder and high explosives should never be stored in the same magazine; nor for obvious reasons should high explosives be stored within the main work of a fortification, nor within the radius of 500 yards of other buildings.

If any considerable quantity of these explosives is to be stored, it is advisable to erect a special magazine for the purpose in the most unfrequented place, and to mark it plainly so that its dangerous character may be recognized.

It is also advisable to store not more than 1200 or 1500 pounds of high explosives in a single magazine. Such an amount of explosives may be stored in a magazine 14 feet long by 9 feet wide by 9 feet high, interior dimensions."

(Willoughby Walke, Lectures on Explosives, John Wiley & Sons, 1897, pp. 382-383)
"In Austria-Hungary the buildings of an explosives factory are divided into several groups ... Magazines holding 2000 kilogrammes must be placed at 100 metres from each other, and those with a maximum capacity of 10,000 kilogrammes at least 200 metres from each other. Tie buildings of the first four groups must be placed apart from each other and surrounded with mounds of earth at least 1 metre wide on the top, and as high as the ridge of the roof. All parts of the factory where there are explosives at any time must be at least 500 metres from any buildings outside the factory area, when consent in writing has been obtained from the owner, and the same distance from unfrequented paths and roads. From inhabited houses, when written consent has not been obtained, and also from railways, water-ways, country-, county-, and district- roads, and from much-frequented footpaths they must be at least 1000 metres off."

(Oscar Guttmann, The Manufacture of Explosives Volume II, Whittaker & Co,1895, p.378)

In New South Wales

In NSW, the Gunpowder and Explosive Consolidation Act, 1876 did not refer to Tables of Distances but it did provide that:

"41. The Governor shall at all times have and exercise the following powersó
(I.) He may from time to time make and publish regulations not being inconsistent with this Act for the management and control of all magazines now or hereafter proclaimed and especially for the quantities of explosives which may be stored in every such magazine."

It is likely that the Ordnance Storekeeper would have been aware of the UK Explosive Substances Act of 1875, and of any Tables of Distances used by the inspectorate in administering that Act.

A Sounder Basis to the Tables

In 1909 the Bureau of Explosives (of the American Railroad Association) and the Association of Manufacturers of Powder and High Explosives made an intensive study of the effects of explosions world-wide, which resulted in the issue of the American Table of Distances in 1915. According to Mark Aldrich:

"Those who had agitated for the bureau focused on dangerous manufacturing and shipping practices, but they had not thoroughly appreciated the dangers of storage magazines. Bureau inspectors soon discovered that there were thousands of such magazines, which were dangerous because many contained old, leaky dynamite and also because they were often located within a few feet of the tracks. In 1909, the bureau, along with the conference of explosives manufacturers, studied other countries' regulations governing the location of magazines, and in 1910 came up with its own American schedule that related the amount of explosive stored to a minimum distance from surrounding buildings." (Mark Aldrich, Regulating Transportation of Hazardous Substances: Railroads and Reform, 1883-1930, The Business History Review, Vol. 76, No. 2 (Summer, 2002), p. 287)

This table was adopted by the US Government in 1928 following the Lake Denmark accident; at the same time the Dept of Defense Explosive Safety Board (DDESB) was established:

"The Department of Defense Explosives Safety Board (DDESB), formerly called the Armed Forces Explosives Safety Board, was established in 1928 by the Seventieth Congress after a major disaster occurred at the Naval Ammunition Depot, Lake Denmark, New Jersey in 1926. The accident virtually destroyed the depot, causing heavy damage to adjacent Picatinny Arsenal and the surrounding communities, killing 21 people, and seriously injuring 53 others. The monetary loss to the Navy alone was $84 million. As a result of a full-scale Congressional investigation, Congress directed the establishment of the Board to provide oversight of the development, manufacture, testing, maintenance, demilitarization, handling, transportation and storage of explosives, including chemical agents on DoD facilities worldwide." (http://www.ddesb.pentagon.mil/ - accessed 21 May 2010)

Aldrich also asserts that Charles B. Dudley, who drew up the Pennsylvania Railroads explosives transport rules that formed the basis for the American Railway Association rules and Interstate Commerce Commission regulations, was influenced by contemporary British practice:

"In 1895, these events led management again to focus on ways to improve the safety of transporting explosives. For guidance, Dudley turned to Britain, which had regulated explosives since 1875. He corresponded with the British inspectors and obtained copies of their annual reports. British experience, and his own investigations of the physical properties of black-powder containers, led him to develop company regulations similar to those in force in Britain." (Mark Aldrich, Regulating Transportation of Hazardous Substances: Railroads and Reform, 1883-1930, The Business History Review, Vol. 76, No. 2 (Summer, 2002), p. 273)

The counterpart of the DDESB in the UK until 1939 was the Classsification of Explosives Committee of the War Office, later the Explosives Storage and Transport Committee (ESTC) of the Department of Supply, which made its first quantity distance prescriptions for both military and civil use in 1943.

Following World War 2 considerable study was made in both the UK and the US using bomb damage data, results of other explosions, and trials to refine the existing tables. Amongst the trials were those conducted on Heligoland on 18 April 1947 when some 4,100 long tons of surplus explosives were detonated. New quantity distance tables were adopted by the ESTC in 1948 and by the DDESB in 1955.

Quantity Distance Table for Explosives

Portion of a Modern Table of Distances (NATO) - Pictographs are Used to Represent Differing Types of Potential Explosion and Exposed Sites

Research for refinement of the tables had been continuing ever since. The NATO standards for inhabited buildings are based on work reported by the United Kingdom in 1959. In this work the data were derived from bomb damage by air blast to buildings during World War 2. Trials have been conducted in Australia (at Woomera) in recent times to validate quantity distances for specific designs of explosives storehouse.

The following extract describes trials carried out by the UK ESTC in the 1950s to validate assumptions about the effectiveness of traverses in reducing separation distances:

"If missiles can be arrested, then the distances quoted above can be reduced considerably. Various types of traverse (revetment) have been suggested, ranging from the earth traverse of Burlot to a water tank. The most usual although not necessarily the cheapest or easiest to maintain is the earth traverse.

A series of trials analogous to those last described was carried out to determine if the presence of an earth traverse between stacks would reduce the safety distance. The base width of the traverse was 21 ft in all cases: the crest width was 3 ft, and the height varied from 5 to 6 ft, being at least 2 ft higher than the stacks of bombs or depth charges.

In the first trial, 231 bombs filled with Minol 2 were arranged with axes horizontal and parallel and 31 ft from a similar stack. The traverse was erected midway between the stacks. All bombs in the primary stack detonated and all in the secondary stack were undamaged but displaced for about 8 ft to the rear. The traverse disintegrated completely and buried a number of bombs.

The second trial was a repeat with a filling of pentolite, a stack-to-stack distance of 35 ft, and 7 ft between bombs and foot of traverse. Results were similar, with a displacement of the secondary stacks of 2 ft. The traverse was demolished, but the primary crater was rather less and only extended two-thirds the width of the traverse.

In the next two trials, the primary stack was increased to 80,000 lb at 36 ft from the secondary, the distance to the traverse being 7 ft from the respective bomb stacks. The secondary stack in Trial 3 was made up of similar quantities of pentolite bombs, and in Trial 4 amatol in light-cased high-capacity bombs was used. In neither case did the secondary stack detonate, and the only damage was to the tail covers of the pentolite-filled bombs; the light-cased bombs were displaced 7 ft to the rear, the heavier bombs only four feet. The traverses had completely disintegrated.

Two trials with depth charges were then carried out, with 78,000 lb of torpex in primary and secondary stacks at 60 ft distance with intermediate traverses of sand. Neither secondary stack detonated; both were displaced 2 ft to the rear and covered with sand, but the depth charges remained serviceable after cleaning.

These trials emphasized the role of missiles in causing propagation and showed that if they can be intercepted, the safety distances required from the blast effects are very small for Z category weapons (2). In fact, three of the secondary stacks were situated within the crater of the primary stack and survived. It was not thought, however, that this could be considered as good practice and the safety distances accepted for adequately traversed Z were increased ..." (D.E. Jarrett, Derivation of the British Explosive Safety Distances, Annals of the New York Academy of Sciences, Volume 152, 28 October 1968)

Traverses and Barricades

The earth banks (formerly known as traverses) or concrete walls (known as barricades) surrounding explosives buildings are often misunderstood by the layman as being intended to contain an explosion.

In more recent military usage, the term "barricade" has been adopted for all such structures intended to mitigate the effects of an explosion. Heritage architects may sometimes use the term "berm" for traverses.

Generally, it is only possible to contain explosions of comparatively small quantities of explosives.

The primary role of a barricade is to protect the building it surrounds from an explosion elsewhere. A secondary role, when the explosion is within the barricade, is to mitigate the effects of the explosion on nearby buildings and sites.

A barricade may, at any given location, have one or more of the following functions:

Effective barricading of buildings reduces the separation distance required as compared with unbarricaded buildings, resulting in a more economical use of space.

Classification of Explosives

In 1977, the United Nations Classification System for explosives was adopted by the United States, United Kingdom and many NATO countries, and a NATO Standard for quantity-distances was adopted. (Manual on NATO Safety Principles for the Storage of Ammunition and Explosives, 1977, AC/258-D/258.) Australia adopted the NATO Standard in 1981.

Prior to this, the RAN used the systems of classification promulgated by the War Office and later the United Kingdom Explosives Storage and Transport Committee (ESTC). In 1904, the classification provided for 2 Groups (I & II), according to whether the explosives required Magazine storage conditions or not. Within each Group were Divisions which represented groupings of compatible explosives that required separation in storage from those of other Divisions. A copy of this Classification, from the Regulations for Army Ordnance Services (Provisional Edition), War Office, 1904, can be read or downloaded in PDF format (109KB).

In the years between World Wars 1 and 2, there were at least 13 groups, denoted by Roman numerals, that were derived from considerations of compatibility in storage. For example, Group II covered incendiary ammunition, whilst Group III covered bulk cordite and BL cartridges without means of ignition. These Groups are clearly incompatible. Provision was also made for 3 safety distance categories. The latter were revised early in World War 2, due to them being somewhat confusing (Ammunition Bulletin No. 4 for Inspecting Ordnance Officers, October 1939 issued by the Chief Inspector of Armaments). The new categories were:

Safety distance Category Z was subsequently subdivided into Categories "Z" and "ZZ", with the latter being for mass detonating explosives that did not produce significant missile effect (e.g. plastic explosive).

Immediately prior to the adoption of the United Nations Classification System, the ESTC prescriptions included:


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Robert Curran
borclaud @ tpg.com.au