SECURING, LOADING, AND STOWING HAZARDOUS CARGO
9-1. FUNDAMENTAL SECURING PROCEDURES. Shifting cargo presents hazards such as damage to the vessel or explosions. It is important that all precautions be taken to protect cargo from shock, fire, high temperature, moisture, or any other hazards that could lead to a catastrophe. In transit, repairs to dunnage or resecuring shifted cargo are difficult and dangerous. The term securing describes the procedures by which military explosives are effectively blocked, braced, and tommed aboard merchant-type ships. Securing is done to resist forces generated by vessel response to sea conditions and includes various wooden structures. It also includes any straps or webs that are used to restrain cargo stowed in the holds and on the weather deck of a ship. The terms blocking and bracing describe more specifically the securing process. The terms are closely related, although each function is distinctly different.
a. Blocking. Blocking is the act of attaching solid pieces of wood, or blocks, to a deck, bulkhead, or overhead, so that these pieces lean directly against the cargo to prevent its movement. Blocking must be braced, shored, or tommed to be effective. Figure 9-1 shows the basic technique of blocking from which more complex securing structures are developed. Additional bracing would be required to secure the item adequately. Pieces of wood measuring 2 by 4 inches are doubled instead of using single 4- by 4-inch pieces to make nailing and securing to the deck possible. The 2- by 6-inch blocking extends the full width of the unit load. Since blocking may be nailed directly into the wooden deck, the load may be secured in any location in the hold without the need for extending pieces to permanent ship's structures for bracing. Since it is very difficult to drive nails into a metal deck, 4- by 4-inch lumber must be extended to the bulkhead to provide necessary bracing.
b. Bracing. Bracing is the act of installing a wood piece or structure so that it extends from a deck, bulkhead, or overhead to the stow. This technique strengthens the blocking by supporting it in a horizontal direction. Figure 9-2, shows a basic method of bracing. Kickers are relatively short lengths of lumber nailed horizontally. They add rigidity to the uprights and braces and are either nailed to the deck or wedge-fitted to a bulkhead. In both cases, the structure extends slightly higher than the unit load and along its full width.
c. Shoring and Tomming. Shoring, which includes blocking and bracing, is the process of securing cargo to prevent side-to-side movement by supporting it from the side. Shoring may also be used to prevent downward movement by supporting cargo from below. Tomming is the securing of cargo to prevent upward movement. Personnel secure the cargo by running lumber from the ship's overhead structure down to the cargo either vertically or at an angle.
9-2. PRELOAD SECURING. After inspecting and cleaning the hold as required for loading explosive cargo, personnel begin prestow preparation and loading. Considering the stowage requirements of the type of cargo being loaded, structures such as heat bulkheads or sheathing are installed.
a. Sweatboards (or sweatbattens) are lengths of lumber, usually 2- by 6-inch stock, installed in hangers or bolted over the ship's structural stiffener beams (see Figure). They are used to prevent damage to the cargo or ship caused by contact of the cargo with the ship's structure and hull. Contact with moisture condensing on the hull plate is also prevented, hence the name "sweatboards." Before placing the cargo, personnel should replace all missing or damaged sweatboards from the ship's stock or use 2- by 6-inch lumber cut to the required length.
Figure 9-2. Basic bracing for
Figure 9-3. Hanger
b. Sweatboards bolted in position are more difficult to replace. Personnel must drill holes to receive bolts mounted on the stiffener beams. Sweatboards are not generally used as load-bearing members in the block stow technique. They are used extensively as bearing surfaces for distributed loads transmitted through strip sheathing when the sweatboard-to-sweatboard method is used.
c. After preload securing, crew members must consider the requirements for bulkhead construction. Heat or nonheat bulkheads are constructed wherever loads are stowed along the ship's athwartship structural bulkheads. Heat bulkheads are tightly constructed to prevent radiated heat, such as heat from engine rooms, bulkheads, uptakes, or casing, from reaching the cargo. Figure 9-4 shows typical completed heat and nonheat bulkheads.
Figure 9-4. Heat and nonheat bulkheads
d. In compartments where hull contour is absent or minimal, extensive preload securing is unnecessary. Responsible personnel only need to protect minor obstructions such as latches, pipes, or conduit. In cases such as these, spacer material is installed before stowage. The spacers are constructed of uprights of a size necessary to obtain adequate clearance. Normally, 4- by 4-inch stock is used for this purpose. Obstructions are boarded over with 3-inch minimum lumber.
e. The final requirement that responsible personnel should consider in basic prestowage securing is the boarding over or encasement of stanchions, ladders, kingposts, vents, pipes, or beams that could otherwise contact the cargo (Figure 9-5). Complete encasement has been almost totally abandoned with the introduction of palletized cargo; however, paragraph 9-2 gives one instance of its use.
- Container failure or evidence of leaking of liquid components.
- Unusual appearance of the container, such as dampness, molds, or stains, indicating internal defects in the absorbent material.
- Defective ammunition and/or packaging.
a. Rail cars or trucks are subjected to visual inspections en route to the loading area to ensure that the cargo has not been damaged in transit. After the rail car or truck has been opened and its contents inspected, cargo is transferred by forklift truck to designated spotting points for each hatch. When handling loading, or unloading military explosives, cargo handlers should use equipment made especially for this type of cargo.
b. Inspectors visually scan explosives positioned for hoisting to detect defects in strapping or packaging. All metal strapping should be tight. The items that make up the unit load should be undamaged. Broken or loose banding of explosives on pallets requires that the defective pallet of explosives be removed, separated from the others, and corrected before loading. Responsible personnel should immediately report defects in banding to the supervising authority for evaluation of the banding and possible on-site rebanding. If damage is evident, workers should transfer the load immediately to an area away from normal loading activity and wait for further instructions.
c. If any of the following conditions exist, cargo handlers should not load the explosive item for transportation or stowage on board any vessel:
d. Personnel must remove explosive cargo with any of these problems from the loading area, isolate the cargo, and process it in accordance with safety regulations.
e. At the spotting location, riggers/hook handlers place the appropriate sling on the load and check pallet balance and construction for lift capability.
f. To eliminate excessive drift, responsible personnel should use slings that are as short as possible when handling military ammunition or other explosives. A cargo safety hook is used almost all the time for hoisting loads of military explosives aboard merchant-type ships. Bomb slings (see Figure 9 -6) made of manila or wire rope are used to hoist single bombs aboard the vessel. When the sling is attached to the load and secured to the hook, the signalman signals the winchman to hoist the load. Personnel should be careful not to exceed the weight limits when hoisting drafts. They should lift drafts in a single, smooth motion, clearing the rail and hatch coaming by at least 3 feet. If the activity within the hold restricts the lowering of the load, personnel must return the load to the dock or lower it within 6 inches of the ship's deck until loading begins again.
g. Personnel move the load from the square of the hatch to the stowage position by forklift. Wedge-point bar adjustments allow final positioning for a tight stow. Crew members may use pallet trucks or transporters to stow loads in areas of difficult access. Personnel must stow all loads right side up on their pallets or skids.
h. As the loading of each compartment is completed, the ship's master or his authorized representative certifies the stowage using a cargo stowage inspection record.
- Last-on, first-off loads which interfere with access to the hatch.
- Items that are too large to fit through the hatches, such as completely assembled missiles or rockets.
- Items that are relatively bulky compared to their weight, such as bomb fins and empty incendiary bombs.
- Flammable liquids, solids, or oxidizing poisons, and combustible liquids (including rocket engines containing a liquid propellant and fuels in containers for guided missiles and rockets).
a. Magazine - Class A. Responsible personnel should isolate magazines when stowing cargo because they are highly sensitive to shock and ignite very easily by sparks or friction. Any class of ammunition requiring magazine stowage, Class A, is not to be overstowed with any other kind of cargo. The type of explosives stowed in magazines must be compatible. Personnel should stow portable magazines in a hold or on deck.
b. Ammunition. Military explosives should be stowed in a cool location. The best place is in a lower tween-deck hold or lower hold. Personnel should use the same priorities for selecting locations as those used for magazines.
c. Chemical. Chemical agents also require a cool location for stowage; a deep tank or lower hold is preferred. Because of the hazards associated with leakage, cargo handlers should take precautions during the dunnaging operation to seal the pump suctions, hatch covers, and ventilators.
d. Special. Responsible crew members should stow classes of military explosives authorized for special stowage in ventilated space protected from the elements. They will ensure that the space does not contain vessel stores, machinery, or navigation equipment. The space should be located so that it can be closed off from traffic while at sea. Personnel should avoid stowing in locations such as deckhouses, mast houses, and mast lockers. Crew members should use dunnage to protect the explosives from contact damage with the ship's structure.
e. Pyrotechnic. Cargo handlers should stow pyrotechnic ammunition the same way as they stow ammunition and special stowage. It should be protected from moisture and heat. Except where permitted, personnel should not stow pyrotechnic ammunition in holds or compartments with other military explosives.
f. Deck. Most classes of explosive cargo can be stowed on the weather deck. Typical cargo stowed on deck includes the following:
(1) Cargo handlers should never stow dangerous items such as flammable or combustible liquids on deck above a hold containing ammunition.
(2) The dockside handling procedures for cargo to be stowed on deck and the same as those previously described for cargo stowed in the hold. Often, crew members position the cargo on deck with the hoisting gear and then manually stow it. Proper placement of cargo is as important for a tight stow on deck as it is in the hold, and the unit loads should touch one another as much as possible. Figures 9-7 and 9-8 show stowing methods for single-item and palletized unit loads.
Figure 9-7. Palletized unit load
Figure 9-8. Single-item load
9-5. STOWAGE GROUPS. The explosives loaded aboard merchant ships are classed generally as rectangular or round. For stowing and securing purposes, cargo handlers group loads as rectangular unit loads which are items unitized on wood pallet, metal pallets, or skids, or as round, single-item loads which are large items loaded individually. Explosives are stowed below decks using either of the methods listed below.
a. Block Stowage. In block stowage, personnel stow loads in the form of tight blocks between both sides of the hold or confine the loads by other loads or wooden bulkheads if the size permits. Block-stow techniques are best because undesirable empty areas within the stow are kept to a minimum (see Figure 9-9).
Figure 9-9. Typical block stowage, lower hold number 1
b. Sweatboard-to-Sweatboard Stowage. Sweatboard-to-sweatboard stowage uses the most space within a hold but results in a greater number of small empty spaces than block stowage. These features become more pronounced in compartments with severe hull curvature. In rectangular shape areas, the technique resembles block stowage. Using the sweatboard-to-sweatboard stowage method in compartments with severe hull curvature requires considerably more manpower and time than does a straight block stow.
a. Personnel can stow bombs using an electric forklift. A 2- by 4-inch board extends downward at a 45 degree angle (tomming). Also, 4- by 4-inch and 2- by 4-inch boards provide support in open spaces between rows (blocking and bracing). Separation boards (dunnage) are placed between the heads of one row of bombs and the tails of another row of bombs. A head-to-tail configuration is best for stowing bombs, as it results in better space usage and less carpentry in securing. Tail-to-tail stowage of bombs is acceptable, but results in loss of space and requires more extensive securing between the heads of bombs.
b. Proper bracing must be provided in areas where bombs are stowed near the bulkheads or the sides of the ship. Similar precautions should also be taken around the hatch ladder and stanchion.
c. Boards used for all blocking and bracing operations should be at least 2 inches thick, though they may be any width.
d. Bombs weighing 2,000 pounds are individually stowed by three basic methods.
(1) First method. Cargo handlers should-
(a) Place two 4- by 4-inch timbers athwartship in the hold to form tracks on which the bombs can rest. These timbers keep the rolling bands free of the deck.
(b) Roll the bomb across the deck of dunnage and place them on the tracks, band to band (see figure 9-10).
(c) Block and brace bombs securely to prevent movement.
(d) Separate the second row from the first by dunnage as shown in Figure 9-11 to protect the head and tail fins of the bombs.
(e) Prepare a track ((a) above) to use on top of the first row of bombs for loading succeeding tiers. No floor of dunnage is required between the tiers.
(f) Place the rolling bands of the second tier of bombs directly above those of the first (see Figure 9-12).
Figure 9-12. Band-to-band method of
(2) Second method. Cargo handlers should-
(a) Start the first row directly on the dunnage floor.
(b) Brace the bombs in the outboard row against the side of the hold.
(c) Place dunnage between rows to protect the head and tail fins.
(d) Lay 2- by 4-inch timbers athwartship to clear the rolling bands of the first tier.
(e) Lay a floor of dunnage over the athwartship timbers and continue the second tier in the same manner as the first.
(3) Third method. In this method, cargo handlers interlock the rolling bands and turn every other bomb end for end so that the tail of one bomb is adjacent to the head of the adjoining bombs.
e. Although the methods described in "d" above deal only with fore and aft stowage, personnel may stow bombs athwartship to fill in unused space (Figure 9-13).
f. The large assortment of missile components creates unusual problems for transportation terminals. Careful planning, special caution, and complete information regarding the characteristics of missile cargo are necessary for its safe, successful, and efficient handling.
(1) Terminal receipt of cargo. Cargo operations personnel must obtain advance information concerning the size, weight, characteristics, packaging data, and peculiarities of the missile components to be handled. The depot originating the shipment may provide this information in the form of writing, photographs, and conferences with representatives of organizations involved in the movement. Using this information, terminal personnel prepare instructions for handling components for cargo handlers and other units concerned with the cargo handling.
(a) On receipt of missile components, cargo handlers must inspect the condition of components to determine whether the terminal should accept the shipment for export.
(b) Sometimes personnel must wear special protective clothing when handling missile propellants and oxidizers.
(c) Certain components are shipped in special containers that have temperature, pressure, or humidity gages attached to them. Responsible personnel should check these gages to ensure they meet allowed tolerances given in the instructions from the terminal.
(d) Cargo operations personnel should reject all material received at the terminal which is damaged or unacceptable for export. This material should be turned over to the technical service representative for disposition.
(2) Handling, loading, and storage. Special slings and lifting devices for transferring and loading missile components at water terminals usually accompany the shipment. Standard materials-handling equipment and watercraft can handle missile components. With the improvements in missile container design and the incorporation of transportation features in the construction of components, the problems associated with shipping this type of cargo are diminishing. Nevertheless, cargo planners must always carefully plan and use special caution. Standard cargo tie-down equipment, consisting of the usual bracing, shoring, lashing, and tomming is fully effective in securing the missile components.
(3) Temporary storage of missile components. Cargo handlers should-
(a) Ensure the storage area is clean, level, and well drained. They should provide some form of shelter if components are subject to weather or temperature limitations.
(b) Store dangerous and hazardous components away from overhead power lines and in areas free of combustible material.
(c) Stack cargo as instructions specify.
(d) Use the type dunnage specified in governing instructions.
(e) Restrict activity in the storage area to receiving, inspecting, and discharging cargo.
(f) Post guards and display signs for dangerous, hazardous, or classified cargo.
(g) Frequently inspect cargo to determine its condition. Also, check gages on sealed containers periodically.
(h) Comply with commodity distance tables.
(i) Ensure decontamination squads and firefighting teams are readily available where special weapons are stored.
(4) Cargo discharge. Discharge problems with missiles are generally comparable to those of other munitions.
a. Decking. Decking is used to prevent metal-to-metal contact between the deck and the unit load. If not used, a fire or an explosion could result. Personnel should lay decking over metal decks or tank tops to protect military explosives. Decking is not required when decks or tank tops are coated with the right kind of nonmetallic materials, such as mastic. Since the entire exterior of Class A magazines is wood, they must be completely floored.
(1) Strip decking. Since the primary purpose of decking is to prevent metal-to-metal contact between the deck and the unit load, it is necessary to install, as a minimum, strip decking. Responsible personnel should install strip decking in compartments where metal pallets or the strapping of wooden skids bound with metal straps would otherwise contact the deck. Figure 9-14 shows the use of strip decking, also referred to as strip flooring. Since the strip decking bears only compressive loads, 1- by 6-inch lumber is adequate for stripping purposes. Work crews should cut the stripping to appropriate lengths and place it under the skids of the unit load. Crews should position the stripping crosswise to the pallet skids to minimize any possibility of the unit loads being displaced from the stripping in transit.
(2) Full decking. Full wood decking is made of lumber not less than 1 inch thick by 10 inches wide (Figure 9-15). Smaller lumber is more readily displaced and damaged by the wheels of forklift trucks. Two layers of lumber are used to construct full decking provided the bottom layer is not less than 6 inches wide and the top layer not less than 10 inches wide. Decking is laid in crosswise layers if located within a Class A magazine. This technique is preferred whenever two-course decking is used. Workers should ensure the decking is fitted tightly, edge-to-edge and butt-to-butt. However, they should leave adequate space at the hull to permit drainage of condensation runoff.
(a) Flooring in the between-deck holds can be made using a single layer of 2- by 10-inch lumber. The floor is laid directly on the deck, edge-to-edge and butt-to-butt. Boards are laid fore and aft or athwartship. The athwartship orientation is preferred if the entire hold is to be floored, or if flooring is required only at the curve of the hull. Flooring laid in this manner will closely follow the hull contour with a minimum of exposed metal deck. If obstructions on the deck prevent workers from laying a flush flooring surface by obstructions on the deck, they may lift the flooring on a foundation of 4- by 4-inch runners (Figures 9-16 and 9-17). Runners are laid fore and aft or athwartships. However, spacing must not exceed 10 inches center-to-center. The work crew should leave enough space between runners and the shell plating to allow for condensation run-off.
(b) Inspection covers and fill caps often protrude above the deck surface in the lower holds in which the tops of deep tanks form the deck. Items not requiring wood flooring, such as unit loads on wooden pallets, are loaded directly on the deck around the obstruction. Workers should construct a void table block of 4- by 4-inch lumber around the obstruction and the void block. This unit load will be higher than the remainder of the loads stowed directly on the deck which creates an uneven surface for flooring. This method is used only when compartment height or characteristics of the cargo do not require that a floor be installed. If a floor is necessary above this or other tiers, workers must make the stow as level as possible. The surrounding unit loads are stowed in block fashion around the obstruction. A void table (Figure 9- 18) is constructed to support the next tier on the floor.
(c) In some cases, it is difficult to work around obstructions; personnel will construct flooring of two 2-inch planks laid on the metal deck (Figure 9-19). All decking (and runners) should be laid to sufficiently cover any area where forklift truck wheels can reach. However, the decking must not overhang the runners. Runners are not necessary where the tank top surfaces are level and the flooring is laid directly on the tank top, as required. When used as a stowage area for military explosives, deep tank bottoms are floored over, as required, using the same procedures prescribed for the holds.
(d) In certain holds or compartments, raised hatch edges make the installation of elevated flooring necessary in an area next to the outline of the hatch (Figure 9-20). This flooring is used only in an area large enough to provide a smooth level surface for the safe operation of forklift trucks while stowing unit loads of cargo in an area next to the hatch level. Unit loads stowed fore and aft of the hatch and in the wings of the hold are stowed on the deck or on strip decking a short distance from the brow plate or hatch level to permit safe operation of the forklift truck.
(e) At this point, the forklifts are removed from the compartment and elevated flooring is installed. The flooring is usually laid fore and aft at the same level as the hatch. It extends from the brow plate or hatch level to the previously stowed unit loads in the wing and between the unit loads forming the alleyway. Forklift equipment can now complete the brow plate or hatch level in transferring loads from the square of the hatch to the final stowage position on the elevated flooring.
(f) Depending upon the type of cargo being stowed, a space assembly with face boards is required between the unit loads stowed on deck and those on the elevated flooring, due to the difference in height. Loads which need a space assembly usually have exposed, unsupported strapping and include items such as bombs on metal pallets, and irregularly shaped unit loads or containers.
(g) With the increased use of power-operated folding hatch covers on merchant ships, personnel will seldom encounter break-bulk ships using between hatch boards (see Figure 9-21). However, vessels using hatch boards are still in operation under foreign flags and must be considered. In most cases wood pallets are loaded directly on the hatch boards. Cargo handlers should ensure that all working surfaces can support the weight of the vehicle and load. Hatch covers, truck plates, or other temporary surfaces should not shift under pressure or because of vehicle movement. Cargo handlers must install, as a minimum, a double layer of 1- by 6-inch lumber over the hatch boards. The top course should be laid crosswise to the bottom layer and nailed to prevent movement. Personnel may use plywood of a minimum 3/4-inch thickness or a single layer of 2-inch lumber. In all cases, the bottom layer of 1-inch plywood or the single layer of 2-inch material will be laid lengthwise in the direction of the centerline of the vessel.
(h) Additional space can be gained for stowing explosives in lower holds bisected by the shaft alley, provided flooring is installed. A foundation of 4- by 4-inch lumber pieces is supported at the center by the shaft alley and at the ends by 4- by 4-inch uprights on 3-inch centers. Double uprights are provided to gain additional lateral clearance with the alley. The cargo floor would extend wing to wing.
(i) When cargo is tiered to the height of the operating range of forklift trucks and additional overstow is intended, the cargo is covered over with a tier deck or machine floor. This floor is made up of two layers of 2-inch lumber. The top layer is not less than 10 inches wide, laid edge-to-edge and butt-to-butt. The lower course is at least 6 inches wide and spaced at intervals of approximately 3 inches. Certain loads, such as explosive bombs, may overhang the pallet or skid so that when loaded nose to nose, a space exists between the tops of the loads. In such cases, the lower course of decking is laid lengthwise across the narrowest dimension of the space. As the first course is laid, dunnage such as short 4- by 4-inch pieces cut at random lengths is placed on the loads at points where the decking would otherwise bear on an uneven foundation. Figure 9-22 shows how short lengths of 4- by 4-inch dunnage are placed where the unit loads would not support the decking. The top layer is laid crosswise to the bottom course and nailed securely to make sure it is stable.
(j) Bombs are often loaded nose to butt. A lower course of 4- by 4-inch lengths of lumber is laid in the same direction lengthwise of the unit loads. The position of the 4- by 4-inch pieces is clearly shown in Figure 9-23. Each is placed directly over the bombs to span the void between unit loads. Cargo handlers should never place runners between bombs. This action would cause compressive loads on parts of the unitized pallet not intended to be pressure-bearing surfaces. The machine floor is particularly important in the stowage of explosives since it forms the foundation for more than one load. It must withstand the concentrated loads of wheeled forklifts while retaining stability. Cargo handlers should ensure that voids under the flooring subject to bending are kept to a minimum. They should make provisions for the load to be moved through uprights, particularly when using the block-stow technique.
b. Dunnage Flooring. When two classes of noncompatible explosives are stored one above the other in the same hold, federal regulations specify that dunnage flooring must be installed to separate the classes. Dunnage flooring is classified as either Type A or Type B.
(1) Type A. The Type A floor is made of two layers of 1-inch thick lumber not less than 4 inches in width placed edge-to-edge and butt-to-butt. The top layer is laid crosswise to the lower layer. A single layer of 2-inch thick lumber of widths not less than 6 inches is fitted tightly edge-to-edge and butt-to-butt. When using 2-inch thick lumber over hatch boards, workers should lay the lumber in a fore-and-aft direction.
(2) Type B. Type B dunnage floor is made of a single layer of commercial 1-inch thick lumber not less than 4 inches wide. It is fitted tightly edge-to-edge and butt-to-butt.
Figure 9-23. Tier decking for nose-to-butt bomb stowage
c. End Bulkheads. End bulkheads, which must be in place before placing loads within the stow, can be either the heat or nonheat type. The type used will depend on the location of the stow with respect to heat-radiating surfaces such as engine room bulkheads.
(1) Heat bulkheads. Heat bulkheads are recognized by tight, unbroken face boarding constructed at least 1 foot off the ship's permanent bulkhead. The smooth side of the bulkhead must always face the stowage of explosives or ammunition (see Figure 9-24). A minimum separation of 12 inches must be maintained between the boarding of the heat bulkhead and the ship's bulkhead.
(a) Sheathing is constructed of 2-inch lumber, preferably not less than 10 inches wide. Federal regulations require 4- by 6-inch uprights spaced not more than 30 inches apart in the tween or shelter deck, or 6- by 6-inch lumber spaced not more than 24 inches apart in the lower hold. Since 4- by 6-inch and 6- by 6-inch lumber is not readily available, personnel may use the more abundant 4- by 4-inch stock for bulkhead construction. When workers use 4- by 4-inch uprights, they should space them at intervals not exceeding 24 inches on the between decks or on the shelter deck, or 16 inches in the lower hold. Lumber that is 2- by 6-inches is used as necessary for headers and bearers. Bearers are optional if wood flooring already covers the metal deck. Uprights are fastened at the top and bottom to horizontal stringers of suitable size to obtain a 12-inch separation from the upper and lower stringers.
(b) Figure 9-25 shows a heat bulkhead. Uprights (minimum of 2- by 4-inch lumber) are fitted against the stiffeners. Headers are not generally required. Bearers need to be laid only if the metal deck has not been floored over. If the ship's permanent stiffener beams exceed a center-to-center spacing of 30 inches, dunnage should be built up to match the stiffeners, or 2 1/2-inch boarding can be used. It is, however, more common and faster to build up dunnage between stiffeners since the 2 1/2-inch material is not readily available in many areas. The uprights are sheathed with 2-inch lumber. The lumber should preferably be 2- by 10-inch or 2- by 12-inch stock, or 1/4-inch plywood sheets. As an alternative method of heat bulkhead construction, crew members may use jacks to provide the necessary support for the 2-inch boarding. This type of bulkhead is used either on the smooth side or on the stiffener side of the ship's bulkhead.
(2) Nonheat bulkheads. Nonheat bulkheads are made in the same manner as heat bulkheads except that the boarding need not be fitted edge-to-edge (see Figures 9-26 and 9-27).
(a) The bases and tops of palletized unit loads that are tiered two-high are properly supported by 2-inch boarding. Several fundamental techniques of securing nonheat bulkheads also apply to structures other than bulkheads. In general, boarding should be vertically spaced to provide a bearing surface for the top and bottom of each unit load in the tier. The space between the centers of uprights should not exceed 24 inches in tween deck compartments or 16 inches in the lower holds. Nonheat bulkheads constructed on the stiffener side of the ship's bulkhead are fastened together (Figure 9-28). Uprights of 2- by 4-inch minimum stock are positioned on each stiffener. Boarding is vertically spaced in such a manner as to maintain two-point contact with each unit load.
(b) When stowage ends in an area of a hold where there is no permanent ship's bulkhead to support, an end (nonheat) bulkhead is secured by the use of A-frames (see Figure 9-29). The hatch coaming and deck are used as support points for 4- by 4-inch main braces. Braces and kickers provide the required bracing of the uprights. Work crews should construct braces and kickers of 4- by 4-inch stock, cut to fit. The structure is securely laced with 2- by 3-inch lumber. Cleats under the kicker are 2- by 4-inch material.
(c) In cases where the cargo is too far from the coaming to make A-framing practical, the bulkheads are braced (see Figure 9-30). Braces bear on the bulkhead at the same level as the top of the cargo. These braces are secured with 2- by 12-inch runners, which are nailed to the deck or wedge-fitted to the ship's solid structure. The length of the bracing member is determined by maintaining a 3:1 ratio (3-foot run to l-foot rise) when possible. Uprights are extended to the overhead to provide rigidity.
(d) Stowage extending to the level at the hatch edge is secured by nonheat bulkheads (see Figure 9-31) commonly known as fences. They are constructed of 4- by 4-inch uprights securely wedged to the overhead, and bearing against the hatch level and coaming. Boarding of 2- by 6-inch minimum stock is secured to the uprights as required by the type and size of the unit load.
(e) Nonheat securing structures are installed in lower holds against the shaft alley (see Figure 9-32). Uprights of 2- by 4-inch lumber with 30-inch maximum centers are cut level with the top of the shaft alley, over which flooring is laid to provide additional stowage space.
d. Partition Bulkheads. Personnel construct partition bulkheads when it is necessary to separate military explosives by type or weight, or because of differences in the packaging construction (see Figure 9-33). This type of bulkhead is constructed of 2- by 4-inch minimum uprights not exceeding 30 inches in separation. Boarding material should be a minimum of 1- by 4-inches secured alternately on both sides of the uprights and spaced not more than 4 inches apart.
e. Division Bulkheads. If there are not enough explosives to fill the hold or compartment completely, personnel load general cargo in the remaining area. In this case the explosives must be completely separated from the general cargo by means of a division bulkhead (see Figure 9-34). This bulkhead requires commercial 2-inch boarding secured on 4- by 6-inch uprights spaced not to exceed 30 inches center-to-center for between-deck compartments or holds. Also, 6- by 6-inch uprights are spaced not more than 24 inches center-to-center in the lower holds. General shortages of 4- by 6- or 6- by 6-inch stock often dictate the use of 4- by 4-inch uprights in construction of the division bulkhead. Boarding may be of random widths, although 2- by 12-inch lumber is preferred. A smooth surface formed by edge-to-edge and butt-to-butt fitting of the boarding always faces the explosive stowage. When use of 4- by 4-inch uprights is necessary, spacing must not exceed 24 inches on the tween decks or 16 inches in the lower holds.
Figure 9-33. Partition bulkhead
Figure 9-34. Division bulkhead
f. Encasement. In order to prevent contact of the cargo with the ship's structures such as beams, air vents, conduits, pipes, stanchions, or ladders, these structures must be covered with or surrounded by wood material. Encasement is either complete or partial. Requirements for complete encasement have been almost completely eliminated with the introduction of palletized cargo, but is required by federal regulation if the structure is located within an area intended for magazine stowage Class A.
(1) Complete encasement (see Figure 9-35). If a metal stanchion or ladder is located within a Class A magazine, it must be completely encased with wood of minimum 3/4-inch thickness secured with nails or countersunk screws.
NOTE: All encasement lumber is 3/4-inch thick minimum, with widths to suit particular applications.
Figure 9-35. Typical complete encasements
(2) Partial encasement. Provided the obstruction is not located in a Class A magazine, partial encasement is used to protect the cargo (see Figure 9-5). Encasement procedures vary slightly, depending upon whether the sweatboard-to-sweatboard method or block stowage is being used.
(a) In the sweatboard-to-sweatboard method, obstructions such as ladders and stanchions are first encased as shown earlier in Figure 9-5. Unit loads are then stowed against the encased structure. Uprights are spaced around the obstructions. Each upright should provide a bearing surface for the cargo. Kickers of similar size stock, spaced not more than 36 inches apart, are used to secure the uprights and unitize the structure. Work crews should not construct partial encasement higher than the adjacently stowed unit loads. However, the structure or ladder should remain accessible and available for use if necessary. If adjacent stowage of rectangular unit loads is intended, uprights and kickers are constructed of minimum 2- by 4-inch stock. Overhanging unit loads are accommodated by securing boarding of minimum 2- by 6-inch lumber to the uprights at intervals the same as those of the exposed surfaces of the cargo. Finally, work crews should ensure the unit load is stowed tightly, contacting the encased structure. Figure 9-36, depicts a typical partial encasement of a stanchion and ladder with a rectangular type of unit load and a partial encasement of an air vent.
(b) When block stowage methods are used, compartment obstructions such as ladders or stanchions are not partially encased before placing the unit loads. Instead, personnel stow cargo in block form around the obstruction and shore at a later time in the operation. In actual practice, stowage of additional unit loads would continue before installation of shoring to achieve minimum stowage rates. Neither the ladder nor the stanchion bears any cargo weight that might result from ship motions. Instead, all forces are transmitted to the ship's structures through the 4- by 4-inch kickers. The ship's structures, regardless of appearance, might not be structurally efficient for support of cargo loads. All stanchions and posts must be examined carefully and protected with full-block shoring if necessary. In no case should access ladders bear cargo loads of any type. Ladders are not intended to be load bearing structures, and failure under load could result in serious degradation of the stow.
Figure 9-36. Partial encasement
with rectangular load
g. Class A Magazines. Federal and Coast Guard regulations specify that certain classes of explosives be stowed in special portable or nonportable structures known as Class A magazines. This is to ensure adequate segregation and protection of the stow. These magazines may be constructed of either steel or wood, depending on the quantity and compatibility of explosives to be stowed in it.
(1) Nonportable Class A magazine. The complete boarding over (encasement) of all metal surfaces or structures is a basic requirement of magazine construction to eliminate the possibility of metal contacting metal and causing a spark. The interior of magazines constructed of steel must be entirely protected by wood that is a minimum of 3/4-inch thick. All ship's structures within magazines constructed entirely of wood, including overhead beams or hatch coamings within 12 inches of the top of stowed explosives, will also be boarded over. Bare steel decks within the magazine should be covered with a wooden floor consisting of at least two crosswise layers of commercial 1-inch boarding not less than 4 inches wide. Existing decking is covered with only one course of dunnage. All flooring should be fitted as close as possible edge-to-edge and butt-to-butt.
(a) Figure 9-37 shows details for the framework of a Class A magazine constructed along the side of the ship. The horizontal braces (kickers) extend to the hull plate or to strip sheathing secured over the sweatboards. Spacing of the braces must not be over 36 inches. Regulations governing the separation of the class of explosive from the ship's skin determine the length of the braces. Uprights will not be stepped directly onto a metal deck. Instead, personnel fit a 2- by 4-inch header between the overhead and the tops of the uprights.
(b) During construction, workers must ensure that nails do not penetrate the magazine and that the interior boards are fitted and finished to form a smooth surface. When a metal stanchion, post, or other obstruction is located within the interior of the magazine, workers must cover it completely with wood of at least 3/4-inch thickness. Then it may be secured with nails or countersunk screws.
(c) Bulkheads forming the sides and ends are constructed of commercial 1-inch lumber, 3/4-inch tongue-and-groove sheathing, or of 3/4-inch plywood secured to uprights of at least 3- by 4-inch but preferably 4- by 4-inch stock spaced on 1-inch centers. Uprights are spaced on 24-inch centers if 3/4-inch plywood is used.
(d) When a Class A magazine measures more than 40 feet in any direction, personnel will install a partition bulkhead to divide the stowage area approximately in half. The bulkhead should extend from the deck at least to the top of the stow. Boarding should be spaced not more than 6 inches apart, alternately, on both sides of the uprights.
(2) Portable Class A magazine. Portable magazines are made for stowage of certain classes of explosives (see Figure 9-38). These magazines are constructed of wood or metal lined with wood of 3/4-inch minimum thickness. No more than 100 cubic feet plus 10 percent of explosives (gross) should be stowed in a portable magazine.
(a) When constructed of wood, the general materials and dimensions for these magazines will not be less than those required for a nonportable Type A magazine. It is recommended that only 4- by 4-inch uprights be used in construction of the magazine runners, uprights, and cover support members. Workers should ensure that spacing of uprights is not more than 24 inches on centers if 4- by 4-inch material is used. The magazine shell is constructed of minimum 1-inch commercial lumber, although 2-inch material is recommended for added rigidity. Plywood sheathing that is 3/4-inch in width or 3/4-inch tongue-and-groove sheathing is also acceptable for construction of the shell. All inner surfaces of the shell should be smooth and free of nails, screws, or other projections.
Figure 9-38. Portable Class A magazines
(b) After completing the basic magazine, workers protect the magazine interior and cover with a moisture barrier of polyethylene or waterproof paper at least 0.004 inch thick. The barrier material should be installed as a single piece; however, overlap of pieces is sometimes necessary. Personnel direct water runoff toward the magazine exterior by overlapping the bottom piece over the top piece. Portable magazines stowed in holds where protection from the weather is not a factor do not require moisture-barrier construction.
h. A-Frame Tomming. Light items easily bump each other in heavy seas and therefore require overhead securing, known as tomming. Tomming is accomplished by tying down overhead structures to the cargo. Overhead bracing frequently uses the A-frame to provide vertical securement. Strips of lumber are laid on the stowed items and serve as the foundation for the A-frames which also prevent items from bumping together.
(1) Figure 9-39, shows construction details for A-frame tomming. To prevent excessive flexing of frame members as the height of the frame increases, personnel increase the required lumber similarly. In most cases, 2- by 6-inch stock is used to construct the A-frame. When the height of the overhead exceeds 10 feet, legs of the frame should be constructed of 4- by 4-inch lumber. The angle of the frame, as measured between legs at the highest point (vertex), should not exceed 45 degrees. Legs of the A-frame greater than 3 feet in length must be joined with cross members. When the length of the leg does not exceed 6 feet, workers may use a single cross member. They should secure this piece an equal distance from the end of the joined legs. Legs greater than 6 feet in length will be joined by two cross members secured at points one-quarter of the length of the leg from either end. The frames are fastened to double 1- by 6-inch or single 2- by 6-inch lumber strips placed over the cargo. Adjacent A-frames may be unitized by means of 2- by 6-inch or 2- by 3-inch horizontal lacers.
Figure 9-39. Overhead A-frame
(2) Figure 9-40 shows construction details for A-frame tomming under between-deck hatch beams. Load-bearing sections of the A-frame are constructed of 2-inch lumber. However, 1-inch material is acceptable for stripping purposes.
(3) Figure 9-41 shows tomming of cargo stowed in the square of the hatch. After stowing, personnel must lock the hatch cover in place to provide the overhead support for the tomming structure.
i. Stepping-Down Structure. In some cases, particularly in the upper tween decks when the vessel loading is nearly complete, it may be necessary to reduce the number of tiers or layers of cargo as the stow progresses toward the center of the compartment. This technique is known generally as stepping down. Normally the stowing process will proceed at the same time from the fore and aft bulkheads and the wings, with the crew working toward the center of the hatch. If the stepping-down procedure is to be used, a securing structure similar to a partition bulkhead is built. Workers position 4- by 4-inch uprights against the tiered unit loads near each end and lace these with 2- by 3-inch or wider material. They then place the unit load against the uprights. Crew members complete the stowage by loading the central area last with remaining smaller or irregularly shaped unit loads. Full block securing is used to shore any void remaining in the stow. It may be necessary to brace the structure with diagonal pieces of lumber for added support depending on the volume or weight of the cargo in the multiple tiers behind the step-down structure. Effective preload planning is necessary to efficiently use the deck space in the center of the compartment for the remaining cargo.
j. Open-Hold Guardrail. Military explosives are not loaded or unloaded in the hatch at the same time that other cargo is being worked in any hold served by that hatch. In addition, all tween-deck hatch covers must be in place before the cargo can be worked in a compartment above stowed military explosives. In some cases during the loading of a ship, however, personnel must assemble prefabricated structures or install preload dunnage while loading operations are proceeding in the next lower level. To protect the personnel, a guardrail is made across the open tween-deck hatch (see Figure 9-42). The guardrail extends the full width of the hatch. It is located a minimum of 2 feet from the edge of the open hold and requires minimum rail height of 42 inches above the hatch boards. The double 2- by 10-inch plate at the base of the bracing acts as a positive stop for forklift trucks so they cannot move toward the open hatch.
k. Deck-Stow Securing. Unit loads stowed on deck must be protected from direct sun and exposure to the elements. If the explosive's container provides adequate protection, an open deck-stow structure is permissible. Personnel should stow more sensitive items in closed structures. Construction sites on deck must not be within 20 feet of an incinerator, ash hoist, or any other heat or spark-generating source.
(1) The closed deck-stow structure (see Figure 9-43) is made primarily of 2-inch lumber. It is securely braced to adjacent permanent ship structures. Workers first lay random-length lumber of 1- by 6-inch minimum upon the metal deck to elevate the entire structure slightly permitting deck water to drain. Runners of 4- by 4-inch stock laid directly on the deck boards form the foundation of the structure. Construction proceeds in a similar manner to that of a portable Class A magazine. Workers lay a course of 2- by 10-inch minimum flooring and securely nail to the 4- by 4-inch runners. The walls of the structure are constructed of 2- by 6-inch minimum lumber secured to 4- by 4-inch uprights. Workers use suitable waterproof barrier material to line the interior of the structure. After placing the cargo and making a final covering with barrier material, they lay a single course of 2- by 6-inch minimum runners spaced at intervals not exceeding 6 inches on top of the barrier material. The top of the structure, constructed of 2- by 10-inch minimum lumber, is installed and securely nailed to both the side structures and the 2- by 6-inch runners. Finally, a catwalk, if required, is constructed for access to either side of the stowage area. After fixing enough 4- by 4-inch blocking to adjoining coamings or bulwarks, workers place the entire structure upright, put it together by means of 1/2-inch wire rope cables passed over the construction, and secure it with turnbuckles. Workers must use appropriate padeyes or lashing points for this purpose; guardrails or other structures not designated as lashing points will not be used.
Figure 9-43. Closed deck-stow structure
(2) Cargo packaged in containers providing adequate protection from the environment can be stowed in open deck-stowed structures. Open-type construction consists of 2- by 10-inch minimum horizontal stiffeners and 4- by 4-inch uprights. Bearing plates of 1- by 4-inch stock are laid along the uprights at the deck to provide a surface to which 4- by 4-inch bracing pieces may be extended as in the closed structure. This construction permits deck wash drainage. The interior of the stowage area need not be floored if the unit loads have been palletized on wooden skids. For metal pallets, workers nail 2- by 10-inch minimum flooring to 4- by 4-inch runners laid on 10-inch centers.
(3) Another type of open deck stowage is used for items packaged in a specially designed container treated with a protective (heat-resistant) paint that cannot be penetrated by salt spray. The container is equipped with attachments designed just for securing. Before loading the item, risers made of a double thickness of 2- by 10-inch minimum boarding are placed on the metal deck athwartship to have direct and full contact with the container skids. The containers are tiered two high, strapped together before loading, and placed on the deck in groups separated from adjacent groups by a minimum distance of 3 feet. This spacing permits ready application of the various securing materials and is a requirement for stowing these types of items.
(4) As each tiered unit load is positioned, workers place spacers adjacent to the lifting bracket near each end of the container and lace them together with 2- by 4-inch minimum material. These spacers are constructed of 4- by 4-inch uprights cut to a length extending slightly above the height of the unit load. After workers place the final unit load, they lay a single thickness of 2- by 10-inch minimum lumber, of sufficient length to span the entire grouping, across the top at each end of the container. A suitable barrier material is placed on the unprotected sides of the container at the point where the banding would cause chafing of the container. Workers bank the whole group together with 2-inch banding material on the center of the 2- by 10-inch lumber and barrier material. They install uprights and braces of 4- by 4-inch stock and lace them together. The 1/2-inch lashing cable is attached last.
|Join the GlobalSecurity.org mailing list|