COLLAPSE SEARCH AND RESCUE OPARATIONS: TACTICS AND PROCEDURES
Part 9: Shoring Support Systems
When entering into building collapse operations, it is imperative to observe as many safety precautions as possible. The stabler you can make the remaining structure, the safer your operations will be. Rescue shoring in collapsed structures is an inherently risky business, and you must do everything possible to put the safety factors on your side. One of the fastest ways to accomplish this is through the use of specially designed support systems.
Several different types of mechanical and pneumatic shoring systems available today have been adapted for use in rescue operations. One system, although designed for use in trench shoring situations, has been used in other operations as well. The shore is constructed of aluminum and has a hollow shaft perforated with holes every several inches. After the shore has been extended, an aluminum locking pin is inserted by hand into a set of these holes and a collar is twisted under the pin to hold the shaft tight. This system consists of two types of shores—the standard shore, which has two rigid bases, and the swiveltype, which has two movable bases that swivel up to 15 degrees.
One relatively new system in particular is very versatile and can be used in various building collapse situations as well as for several other shoring and rescue operations—a big plus for departments with limited budgets. The system affords rescuers a choice of securing devices: the Acme thread strut or the self-locking strut. Following is a description of the components and features of this system.
The self-locking strut. The system contains self-locking struts of three sizes: 24 ½ to 36½ inches (12-inch stroke); 36 ½ to 58 inches (21 ½-inch stroke); and 55½ to 91 inches (35Vi-inch stroke). Each strut is made of three-inch aircraft aluminumalloy tube with a solid 2‘/i-inch aircraft aluminum-alloy movable grooved shaft. These struts normally are extended by hand for building collapse operations but can be activated by air, carbon dioxide, or nitrogen if the need arises.
The distinctive feature of the self-locking strut is that it locks automatically in an extended position; its special locking feature, a double-row ball-lock coupling, does not require a member to manually lock it in place, and there are no safety locking pins to install by hand—a greater inherent safety factor. The hands-free locking feature allows the rescue team to extend and lock the strut from a remote location, if necessary.
Taking down and repositioning the strut can be accomplished more safely than the same operation with some other types of struts. The locking mechanism can be released by removing the load pressure and pulling a release ring. If for some reason the load shifts or if further collapse occurs, the rescue team member need only let go of the release ring and the strut immediately will lock in place again, stopping debris from shifting further.
The Acme thread strut. This system contains Acme thread struts of three sizes: 24¾ to 36½ inches (11 ¼-inch stroke); 36½ to 58½ inches (22-inch stroke); and 58 to 90 inches (32-inch stroke). These struts are constructed of the same aircraft aluminum alloy as the self-locking strut and also consist of three-inch aircraft aluminum alloy tube with a 2’/2-inch solid aircraft aluminum alloy Acme threaded shaft. Like the self-locking variety, they can be extended manually or from a pressure source such as air, nitrogen, or carbon dioxide. However, locking the strut is a manual operation.
The distinctive feature of the Acme thread strut in this collapse rescue support system is that it allows for extremely soft placement in most collapse rescue operations—it can be brought to and ently tightened at any point under a load, unlike pneumatic shoring systems that require locking at specific points.
The strut is secured in place with a large hut, which extends with the shaft, that the iser manually screws down and locks against the tube. Taking down the Acme thread strut can be accomplished as safely as taking down the self-locking strut: Reniovc the load pressure and manually fwist the Acme nut, and the locking nut will be released. If debris shifts while the 6trut is being lowered, the firefighter simply lets go of the Acme nut; and the shore will lock in place, resupporting the oad.
Strut extensions. The system also contains three rigid strut extensions—12-, 24-, and 36-inch — that are constructed of Three-inch aircraft aluminum-alloy tubing. These extensions were designed to allow fescue personnel to add length to either strut type, multiplying support capabilities and applications in building collapse situations. Each strut extension can be used as a rigid support device if necessary.
Low-clearance supports. The low-clearance support system is a series of four solid extensions constructed of the same material as the Acme and self-locking strut shafts, in one-, three-, five-, and seven-inch lengths. The system is designed for rescue work in close quarters, and the extensions can be used with a variety of bases.
Capacity. The self-locking and the Acme thread struts have been tested by an independent company and have an axial crush strength of more than 50,000 pounds, well above the average for any of the other pneumatically operated shoring devices. Each of these struts has an axial working load capacity of 20,000 pounds, making them excellent choices for initial safety shoring and for working in tight void areas.
Activation force. The activation force is the amount of pressure needed to raise the shaft of the rescue strut. As the activation force is increased, the support force of the strut increases proportionally. For example, if a pressure of 50 psi is exerted against the shaft, the strut is capable of exerting 245 pounds of force. If a pressure of 350 psi is placed on the strut, the strut will exert a force of 1,700 pounds. These shores have limited lifting capabilities and generally should be used only as stabilizing tools, especially in collapse operations where any additional movement could be detrimental to rescue personnel.
BASES AND FITTINGS
‘ITianks to a specially designed adapter called the extension converter, any of the system’s bases and end plates may be attached to either end of the strut extensions to create a strong and rigid support device. Numerous bases and connectors are available for the rescue strut systems discussed above, making them very versatile systems. They can be used tor building collapse, trench rescue, and automobile extrication, just to name of few of the operations for which they are suited.
The three-inch standard base. This is a simple three-inch-diameter cap two inches high with a Ivinch pull-and-twist locking pin. Covering both the strut base and the end of the shaft, the standard base protects the strut ends during simplebracing operations.
Rigid base. A sixby six-inch rigid base with a nonskid grooved surface was developed to provide greater stability than a standard base. This base works well on solid surfaces.
Swivel base. A fitting with a sixby sixinch square base that can swivel 20 degrees in any direction, the swivel adds approximately 3½ inches to the length of the strut. It was developed for use in cases where the items to be braced are not in direct alignment. This base can be used in many situations.
Cone base. The cone base basically is the standard base with a ¼-inch pointed cone in its center. It is used primarily for holding the struts at a slight angle against smooth surfaces such as the sheet-metal skin of an automobile.
Spring-loaded connector. A fitting developed especially for use with the selflocking strut, the spring-loaded connector., keeps the strut compressed even if slight movement occurs. The spring is activated? at roughly 200 pounds and has a travel length of approximately ½ inch.
Adjustable connector. The adjustable,, connector is designed for use where any forceful movement can be dangerous—a4 it car be in building collapse shoring^ operations. Manufactured from a l/t-inch threaded aluminum shaft, it can be finely adjusted up to ½ inch. It is excellent for use with the self-locking strut in collapse^ operations where supporting the collaps^ load is the primary function.
Hinged base plate. Designed to be used with the rescue strut system, the hinged base plate rotates 90 degrees in one direction, making the struts available as an initial safety rake shore at 45 degrees.
Four-by-four “U” bracket. This bracket, specially designed for shoring operations, can be used on the base of the strut or the end of the shaft. It locks onto a 4 X 4, to which it can be anchored with nails or screws. The bracket is six inches long, 2¾ inches high, and 3½ inches wide and is designed to fit snugly to the shoring lumber.
Six-by-six “U” bracket. This bracket was designed for heavier lumber opera-, tions. It is utilized the same way as the 4 x 4 bracket.
“V” bracket. A 3by 3-inch cylindrical fitting with a 90-degree “V” approximately one inch deep in its center, this bracket is used for stabilizing anything with an angle or a corner, such as a tractor trailer leaning after an accident or a beam with a square edge in a building collapse.
“1″ bracket. This L-shaped fitting has a 1 ’A-inch lip that can be used to hang the strut for hands-free operation. Such a situation may occur in a trench cave-in, where the whalers have to be rebraced before personnel can enter the excavation.
The hydraulic ram. A recent addition to the system is a 10-ton hydraulic ram with a four-inch lifting stroke and a separate power pack with a six-foot hose. The ram can he utilized in several collapse situations as well as in a retrieval system for shores under pressure. A coupling on the bottom of the ram accepts any of the rescue struts, and a fitting on the top accepts all available bases and connectors. It is small enough to be easily maneuvered in a collapse void and used as a temporary support for damaged or unstable structural elements. In special cases, it may be able to gently lift certain collapse debris pinning a trapped victim, freeing the victim from the rubble.
RESCUE STRUT SYSTEM USES
The system described above has many uses in building collapse situations. Following are a few examples of when and where the system can be quickly and safely used.
Window shore. In some instances, entry into a collapsed building may be most easily achieved through a window opening. Generally, the window shore is installed to hold up or stabilize loose headers or lintels that have lost their integrity, to make the access point safer for rescue personnel.
The sill plate and header are installed as usual (see “Collapse Search and Rescue Operations: Tactics and Procedures Part 6: Window and Interior Rake Shoring,” Fire Engineering, October 1993); however, the rescue support struts are used where the 4×4 wood posts would be installed. Using the “U” brackets on both the base and shaft of the strut, first install the base bracket to the sill plate. By hand, raise the shaft of the strut with the top bracket under the header and securely hand-tighten the nut. If any shimming of the sill plate or header must be done, place it directly in line with the rescue struts, to transfer full bearing properly.
The smalland medium-size struts are adequate for the window openings normally encountered. Two of the major advantages of utilizing the rescue struts are that they are considerably stronger than the average 4×4, and they can be installed quickly. It is not necessary to measure posts or install wedges; therefore, the operation time is shortened considerably.
Door shore. The door shore is erected in a manner similar to that used for the window shore. Use the largest size struts where possible; however, medium-size struts with strut extensions also can be safely used. Using the adjustable connector and the 4×4 “U” bracket, either the self-locking or the Acme thread struts can be used in this operation.
Vertical “dead” shore. When the shoring officer has determined that a vertical shore should be erected, some type of initial safety shoring generally needs to be ⅞ constructed. The rescue support struts in conjunction with the “U” brackets can be*’ raised quickly under a 4 X 4 or 4 x 6 ^ header for an initial safety factor, if necessary. The struts can support a substantial amount of weight, making it safer to conduct additional shoring operations. * Another advantage of the system is that it,, can be taken down quickly and easily and reassembled when additional shoring is to * be erected, making each operation safer^ Void shoring. Some of the most dangerous and unpredictable situations you may, encounter as a firefighter are the void search operations in a structural buildings collapse operation. As the search for trapped victims is begun, shoring must be erected to stabilize the area in which you»j will be operating. This initial safety shoring is another case where solid stmts can be* used. The stmts can be installed in tight^, void openings to support structurally unstable bearing elements, giving personnel a { safe area in which to operate while additional shoring is erected, if necessary. The solid stmts can be used in conjunction with various bases and connectors and, for even more versatility, with wedges.
