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| ADCI Industry Informational
Update #2009-05 |
February/2009 |
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TO: ADCI General
Membership and Industry Stakeholders
The following items of
information are provided to bring your attention to
recent industry developments, initiatives,
or safety notices. If you do not wish to
receive future Industry Updates, please use the
unsubscribe option, located at the bottom of this
update. |
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ADCI UNDERWATER AIR
LIFT BAG OPERATIONS
GUIDELINES |
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No standard can cover all
potentialities that might be encountered. JSA's
common sense, and extra attention to detail by the
entire dive team are to be considered essential
components for approaching operations of this
nature. JSA's should be updated as work
progresses, to reflect the current
conditions.
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| Purpose |
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1. The purpose of this guideline is
to identify potential hazards and recommend safety
precautions when working with underwater air lift
bags.
2.
This recommended procedure is applicable for all sectors
of the commercial diving community, both inland and
offshore. |
| Precautions |
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1. When performing
tasks underwater, divers are often required to move or
lift objects, using the assistance of underwater air
lift bags.
2. Using underwater
air lift bags can pose a threat of uncontrolled ascent
to the diver.
3. Extra precautions
should be taken through the performance of pre-dive
safety assessments.
NOTE: Underwater air lift
bags are not like other forms of lifting devices.
The lifting action is produced by the displacement of
water when the bags are filled with air. A diver
must be aware of the position of his umbilical at all
times to avoid fouling. Hose management is
essential to prevent entanglement with the underwater
air lift bag rigging or the object to be
lifted. |
| Definitions |
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Anchor Point: (also referred to as
dead man anchor or DMA)- a point where the anchor line
is attached to the underwater air lift bag to restrain
the load. Anchor points must have a mass in excess
of the maximum lift capacity of the underwater air lift
bag.
Dump
line: line attached to the dump
valve inside of the lift bag. It should be
distinguishable from any other line. The dump line
controls deflation of the lift bag by the dive.
(Some lift bags are also fitted with an extra length
line, which can allow the diver to operate dump value
from a safe distance.)
Dump
Valve: Valve located inside of the
lift bag for deflation of the lift bag, which is
controlled by the diver through the use of the dump
line.
Inversion
Line: line attached to the load
and to the top of the lift bag, to ensure that the bag
inverts and deflates the air in the event of any failure
of the lift bag's rigging.
Main Lifting Lines:
this is the standard rigging, which
is attached to the lift bag,in either a two or four
strap configuration. These lines are normally
shackled to the top of the object to be
lifted.
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| Responsibility |
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The Dive Supervisor is
responsible for the welfare and safety of the dive
team. The diver is responsible for ensuring that
he is familiar with the principles outlined in the
document. The diver is also responsible for
ensuring that he is performing his tasks in a safe
and responsible
manner. |
| Potential Hazards Associated with
Underwater Air Lift bag Operations |
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- Over-inflation of the lift
bag
- Accidental deflation of the lift
bag
- Failure of the rigging or
lift bag straps
- Failure of lift bag
fabric
- Utilization of a lift bag not
rated for the load
- obstructions in the path of the
lift (water column or surface)
- Possible disruption of DP system
during deflation of lift bags
- Possible entrance of deflated air
into the diving bell
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| Recommended Ways to Mitigate
Potential Hazards Associated with Underwater Lift bag
Operations |
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Situational Awareness on the part
of the diver and topside personnel
- Proper education and
training (Boyle's Law / Archimedes Principle /
Hydrostatic Pressure / Absolute Pressure, see ADCI Formula
Sheet)
- Ensure that an anchor /
restraining line is present (when applicable) with
sufficient strength to remain attached to the load and
dead man anchor (DMA)
- Proper inspection of the lift bag prior to use,
testing, and certification
- Ensure that dump lines are distinguishable from
all other lines
- Ensure that diver's personal equipment and all
other tools are not in a position to get fouled with
the drum line
- Proper maintenance, inspection, and testing of
the lift bag and its rigging
- Lift bags should be washed after use and free
of debris, which can compromise the integrity of the
valves, bag fabric, or its
straps
- Attachment of an inversion line to the top of
the lift bag, and ensure that it is secured to a DMA
or other object on the bottom
- Proper education and training, combined with
visible markings to indicate the ratings of the
lift bag and the units of measurement used to
express its rating (lbs / kg). It is
important to utilize lift bags that have a lift
capacity which is close as possible to the weight of
the object, to prevent the potential for accidental
lift on ascent.
- A complete assessment and survey of the area
must be performed, prior to initiating lift (inflation
of the bag)
- On a DSV / DPV; the volume of air escaping from
the lift bag during the deflation phase may affect the
vessel's DP system; prior notification of the bridge
should be made before initiating
deflation
- It is important that lift bags are not
deflated in the area directly underneath the diving
bell, as this could pose a hazard to personnel inside
of the bell
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| Operational Considerations when
Using Underwater Air Lift Bags |
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- Weather and
Environmental Conditions
Factors to be considered include:
- Current
- Seabed
Obstructions
- Seabed
Condition
- Details of the object
to be lifted and its position in the water
column
- The composition; what
the object is made of and its approximate center of
gravity
- Assessment of the
object's exact position and its
stability
- Determine the objects
lifting points
- Perform all necessary
calculations to determine the object's weight, taking
into consideration the object's submerged weight,
stability, and its approximate center of
gravity
- When making your
calculations, it is important to assess the best
position and number of lift bags required to avoid
damage to the object (bending or buckling).
Determination of the inflation sequence, (when using
multiple lift bags), is important towards
establishing a safe and damage-free
lift.
NOTE: Extreme caution must be
used when inflating underwater air lift bags. Do
not use excess buoyancy to "Break out" or "Free" a load
from the seabed.
Remember: in shallower water,
air entering the bag will experience a greater
percentage of change in volume as it rises, than at
deeper depths. Underwater air lift bags inflate
more rapidly at shallower
depths. | |
This Information was
sent to further the communication of all industry
stakeholders. Safety is the primary concern of the
ADCI. Remember: a real time Job Safety
Analysis is important, but nothing can replace good
common sense.
Sincerely,
Phil
Newsum
Association
of Diving Contractors
International
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