EXTREME CONDITION PROCESSING
esign and Construction of Barricades R. L. PORTER, Aufoclave Engineers, Inc., Erie, Pa. P. A. LOBO, Continental O i l Co., Ponca Cify, Okla. C. M. SLIEPCEVICH, Univ. o f Oklahoma, Norman, Okla.
T
HE most important factor in processing under extreme conditions is adequate safety for operating personnel. The
usual safeguards should include:
1. Specially trained ersonnel 2. Well designed a n t engineered equipment 3. Proper safety devices such as relief valves, automatic shutoffs, explosion- or vaporproof fixtures, and remote control switches 4. Barricading Although all four of these items are extremely important, with trained personnel heading the list, this discussion is limited t o the design and construction of barricades. Many and varied types of barricades have been used in the long history of experimental work involving hazardous reactions, but as yet no standards are available for selecting the most appropriate barricade for a given application. The types of barricades that have been used in the past range from pits into which the equipment is lowered, sand bags piled around the equipment, and steel or rope matting hung between the equipment and operator. to the more modern types of barricades composed of steel or concrete fortification-type walls. From the standpoint of modern design, these latter types of barricades find most frequent application. Figure 1 is a sketch of a barricaded cell which incorporates most of the emential safety features.
Another improvement over the single steel-plate design is to back up the plate with a layer of wood about 2 inches thick. The wood supposedly absorbs the energy in the shock wave and also slows down the projectile t o the point where i t cannot penetrate the steel. Where the wood is used in the barricade walls, it should be fireproofed. Another type of barricade which has been used frequently, particularly on temporary installations, is rope or steel matting. This type, which is available commercially, is fabricated by weaving manila rope or wire cable, ranging in diameter from '/e t o 1 inch, into a closed-mesh mat. The barricade is hung from the top in much the same way as a curtain. Because this type has freedom of movement, it has proved very effective against flying missiles and in absorbing the energy in shock waves.
BLOW-ou WALL
Types of Construction Probably the simplest and most commonly used barricades consist of boiler plate (in some cases, armor plate) mounted on a self-supported structure which surrounds the equipment. I n the literature, the recommendation will be found t h a t boiler plate should not be less than inch in thickness t o provide adequate protection (2). The real basis for this recommendation has not been established. I n all probability it was influenced by an explosion which occurred in one of the industrial laboratories t h a t pioneered high pressure research (1). I n this instance, a '/(-inch thermocouple tube was blown from its silver-soldered connection t o the reactor, passed through a a/16-inch steel plate, and produced a dent in another steel plate located 9 feet away. I n any case, where a steel plate is used as the only protective barrier, the thickness of the plate usually ranges between '/4 and */, inch. The plate is either tack-welded or bolted t o a selfsupporting angle iron framework in sheets ranging from 3 t o 6 feet in width. Most of these structures have a rectangular floor plan, but in some instances the plate consists of a curved section which is placed between the equipment and the operator. I n these cases, the top portion of the plate is curved inward toward t h e equipment and acts as a deflector. This type lends itself t o use as a temporary or portable barricade. A variation from this design is the use of two steel plates spaced a slight distance apart. Based on some field tests performed by t h e Ordnance Department of the U. S. Army, it was found that two spaced plates are 20 to 3070 more resistant t o penetration by a projectile than a single plate whose thickness is equal t o the two steel plates.
May 1956
Figure 1.
Typical barricaded room
For permanent installation, block houses built of concrete reinforced on both faces and ranging in thickness from 1 foot to, in some instances, over 30 feet, are probably the most popular form of construction. I n high pressure studies, on relatively small scale equipment, the concrete is usually between 1 and 2 feet in thickness. Aside from being structurally strong, a concrete barricade possesses a psychological advantage in t h a t i t creates the impression of unlimited strength. I n recent years, the steel sandwich type of construction has gained considerable popularity, This construction consists of two steel plates, ranging in thickness from I/, to l / 2 inch, separated 4 to 6 inches. The space between the steel plate is usually filled with sand, but in some instances, cotton batting, rope, or wood has been used, A modification of this type of construction consists of a steel plate on the outside wall and wood, 1 to 2 inches thick, on the inside wall, and with a sand filler between. I n order t o retain the sand, tongusand-groove wood joints are recommended. There is some evidence that the wood on the inside
INDUSTRIAL AND ENGINEERING CHEMISTRY
84 1
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT wall can absorb some of the shock of flying missiles more effectively than steel by virtue of its "cushioning" property. The sand filler also serves to reduce the shock against the outside steel wall,
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I/.. P L A T E
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Figure 2.
Construction of typical barricade walls
Figure 2 shows a cross-section detail for three types of construction-boiler plate, reinforced concrete, and sandwich construction.
Comparison of Various Barricades As mentioned before, there is not sufficient evidence to support one type of construction in preference to the other. From the standpoint of a practical ultimate in safety, the concrete or sandwich type construction appears to be the best. It is interesting t o compare some of these types from the standpoint of weight and cost. Weights are shown for five different types of barricades for a cell 10 X 10 X 10 ft. It is assumed t h a t the barricaded cell consists of three walls with an open ceiling and open rear wall.
Steel blasting mat, "8 inch Boiler plate, I/z inch Sandwich (2 tons of steel, 3 tons of sand, 1 ton of wood) Sand bags Reinforced concrete, 12 inches
Weight, Tons 2.5 3.5 6 6.5 7.5
It is evident t h a t the barricade walls constitute a substantial weight factor, which may be of importance where the cell is constructed inside a building where floor loading may be a limiting factor. It is rather difficult to assess a definite cost figure t o the various types of construction since numerous refinements are possible. Construction costs will, of course, vary quite widely depending on location and whether the barricaded cell is part of a new building or is constructed within an existing building. However, it is believed that the values given cover the range of costs as estimated from several existing installations and computed on the basis of the cell alone. The cost figures range from sand bags on the low side to reinforced concrete on the high side:
Sand bags Steel blasting mat, 5/8 inch Boiler plate Sandwich Reinforced concrete
Dollars/ Cubic Ft.
