Using a lifting bag, often in the context of scuba diving, is a technique for raising heavy or bulky objects from the seabed to the surface in a controlled manner.
Lifting bags are specialized inflatable devices used to provide buoyancy for lifting submerged objects. Their use requires proper training to ensure safety and control during the ascent.
Here's a general guide on how lifting bags are typically used:
Steps for Using a Lifting Bag
Using a lifting bag involves several key steps, from preparation underwater to handling the object at the surface.
1. Preparation and Attachment Underwater
Before attempting to lift an object, assess its weight, shape, and the best point(s) for attachment.
- Ensure the lifting bag is in good condition with no leaks and functional valves.
- Securely attach the lifting bag's strap or line to the object. Use appropriate knots or fasteners designed for underwater use. The attachment point should be balanced so the object lifts evenly.
- Position the bag above or alongside the object, ready for inflation.
2. Controlled Inflation
This is the critical step where buoyancy is added.
- Use a low-pressure inflator hose from your scuba cylinder or exhale air directly into the bag's opening (depending on the bag type and the required buoyancy).
- Add air in small, controlled bursts. The goal is to add just enough buoyancy to make the object neutrally buoyant or slightly positively buoyant.
- Avoid over-inflating, as this can cause an uncontrolled, rapid ascent.
3. Managing the Ascent
Once the object starts to move, managing the ascent is crucial for safety.
- Maintain control of the line attached to the bag, allowing it to ascend slowly.
- Be prepared for the air inside the bag to expand as it rises due to decreasing water pressure. This will accelerate the ascent if not managed.
- Vent excess air from the bag using its dump valve to maintain a slow, controlled ascent rate.
- Stay clear of the ascending object and bag to avoid entanglement or being struck.
4. At the Surface
Once the lifting bag reaches the surface, the task transitions to handling the object and managing your own buoyancy.
- According to the provided video snippet, once the lifting bag reaches the surface, you should then inflate your BCD. This helps ensure you have adequate buoyancy at the surface after the lifting task is complete.
- Secure the object (to a boat, shore, or marker) as needed.
- Recover the lifting bag and prepare it for storage or reuse.
Safety Considerations
- Always use a lifting bag appropriate for the weight of the object.
- Practice with lighter objects in controlled environments before attempting heavy lifts.
- Ensure the ascent path is clear of obstacles and other divers.
- Be aware of potential hazards like entanglement or rapid ascent.
- Ensure proper training in lifting bag usage from a certified agency.
Using a lifting bag effectively allows divers to recover objects safely and efficiently, but it requires practice and a thorough understanding of buoyancy control and ascent management.
