Recovering objects from the bottom is divided into two divisions, light and heavy. Light objects are those that can be pick up by the recoverer himself. These objects present little hazard. The key to light recovery is that for the added weight. No matter how light the object recovered is the diver must maintain neutral buoyancy. When this is not done the diver must compensate by using muscle and this creates undue fatigue. When the object is heavy enough that neutral buoyancy cannot be maintained and the diver is excessively negative then the object should be lifted by a lifting device, and becomes heavy recovery. Many divers feel that the use of the pocket lift bag is a waste of time. The thinking is just because the object is heavy does not mean I cannot bring it up alone without a bag. These divers believe that the BCD is a lift bag. All they do is grab the object and hit the inflate button until they start to go up. This is extremely dangerous and leads to uncontrolled buoyant ascents. A BCD can be used for lifting but not when a diver is attached to it.
When recovering an object with a lift bag the buoyancy capacity should only slightly exceed the weight of the object. To use a larger bag than necessary might end with the bag making too rapid an ascent. Rapid ascents can cause air spillage when reaching the surface and subsequent uncontrolled descent.
All lifts with bags should be considered basically uncontrolled ascents, even when they have bleed valves. Bleed valves are good for reducing volume at the surface. Trying to use one to slow an ascent may result in dumping too much air.
To properly inflate a lift bag the diver delivers small squirts of air at the edge of the bag. Never use your primary second stage, use a safe second. For large operations bring down an extra tank and regulator just for filling lift bags. After each burst of air, check the object for movement. Sometime the bottom suction must be broken. Do not over inflate the bag to overcome suction.
Suction can be overcome be several methods. First is rocking. Once the lift bags are secure and partially inflated, a diver or two starts to rock the object of the lift as the bags are filled. The divers doing the rocking should not be over the top of the object. Another method is to use pry bars or shovels to try to break suction. Digging around the object also may be used. A sand sucker can break suction around a large object quite rapidly. Whatever method used all have the same hazards. These are that the object may break lose and rapidly shoot to the surface. Another is that once suction starts to break or once a method is employed, visibility can drop to zero. Always know where you are in relation to the object to be lifted.
An important part of recovery is planning. Imagine anything that can go wrong, will. Train for every problem and always expect the unexpected.
Extended time of immersion can weaken or decay any object, upon reaching the air again, the deterioration may accelerate. Field preparations and forethought should be given to recovery. Items found around the house is all that is needed to guard recovered items until they can be properly handled. Any kind of plastic wrap works well to avoid exposure. For large items keep a drop cloth. These take up little space and may be cut to the size needed. Sandwich and freezer bags also are handy for recovery of small items, as are trash bags for larger items. Some large lawn size trash bags can make a good field expedient body bag when needed.
When recovering an object use the simplest method. That is pick it up. Stoke's basket is a good recovery tool. They can be loaded and lifted by multiple divers very easily. They make underwater body recovery and extrication a simple task.
Use Archimedes' principle for lifting. Find out the water displaced to determine the amount of lift needed. Do not use the technique of filling lift bags until the object starts to move. Use planning and forethought.
There are several types of lift bags but using them is basically the same. Buoyancy compensators are not lifting devices. Pocket bags may be used a single diver or buddy team, while larger bags may require four or more divers.
When using bags without a relief valve extra care is needed to insure that the bag will not pop out of the water upon reaching the surface. When this happen air can spill out resulting in the lifted item returning to the bottom.
The safest lift bags are those with relief valves. When using a bag with a relief valve assign one diver to control the valve. Rigging a home made bags must be predetermined in training. Home made bags are oil drums and inner tubes.
Never is anyone to be under the bag or the object being lifted.
Care must be taken to insure that the object to be lifted is secure. Objects can be secured with ropes, straps, and chains. When securing the object take your time and think it out. Let the water do the work for you, do not muscle an object from the bottom. If it is too heavy, use more lift bags. Multiple bags for large objects such as boats and cars is better, and safer, than sling loading under one large bag. Balancing the object requires practice and skill.
Securing a cylinder is not to difficult to perform. Use a barrel sling and practice.
Use of guide lines to control ascent. No diver should hold on to the object being lifted. Prior to the lift assign a diver to each corner of the object. This dive then attaches a guide line to his corner. His job upon lift is to keep the object from swinging by maintaining tension on the line. If the object swings too much, or starts to fall or ascend to fast the diver can let go of his guideline and avoid being taken with it.
Once the object is lifted it has to be removed from the water. This requires moving the object near shore so it can be hoisted out. Moving an object as large as a car may seem like a large task but in realities quite easy. First remember that the water does the work. Keep the lift bags just under the surface. Then by attaching more guidelines or using the existing ones divers can swim along the surface pulling the object to shore. This must a slow swim ensuring that the lift bags do not spill. Try to avoid pushing the object from the rear. Once near shore the object can be lowered by releasing air and a hoist applied.
Hoisting an object is an option that should be considered in certain situations, first. It can be employed with or without lift bags. To hoist an object a power winch, manual come-a-long or a rope hoist can be used. Hoisting is only useful near shore. Tow trucks are very useful in removing boats and cars.
If the dive team is used to place a car, or boat in the water, the opposite of the lift is used. Movement is the same. Once the desired location is reached the bags are deflated and lowered, the same as being raised. Only use bags that can be deflated when lowering an object.
Keep in mind that the two most dangerous times in a lift operation is when the object is first lifted and at the surface. Surface work with a heavy object suspended by lift bags is extremely dangerous. Use cation and care. Never rush. Remember the Divemaster in the water is in charge follow directions and use care.
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