User Manual: Generic Section
Section: Introduction 0-4
Revision: 00
Page
20 of 21
11
DISMANTLING SUB-SEA EQUIPMENT
All sub-sea equipment fitted with pressure housings are subject to a vast range of externally applied
pressures and may have an internal pressure rise if a leak occurs or the unit’s battery destructs. Internal
pressure is
dangerous situation and all applicable safety measures must be enforced. Fumes given off by
deteriorated batteries, particularly lithium based types, are health hazard. Use all applicable safety
precautions.
There is likely to be no indication to the presence of internal pressure. First indications will be the end-cap(s)
of the unit forced out of the housing under pressure during the dismantling process.
Indications of high internal pressure are as follows:
a)
Equipment that failed when deployed, in transit or storage
b)
Equipment stored for a long time with batteries connected
c)
Equipment suffering from physical damage.
When a unit has leaked it behaves like a valve, i.e. water pressure causes a rise in internal pressure which
cannot then escape as the point of leakage becomes sealed. Complete removal of an end-cap’s retaining
mechanism means that it becomes unconstrained and therefore free to be discharged from its housing under
high internal pressure a potentially lethal situation.
CAUTION
Do not transport equipment which is internally pressured.
11.1 INSTRUMENTS FITTED WITH SPRUNG VENT PLUGS
Pressure Vent Plugs are fitted into all subsea equipment housings containing batteries and have a
green bung with two O rings with a vent hole behind the second O ring. The vent plug is designed so
that it can be partially withdrawn using a M4 screw so its relief hole, positioned inboard of the second
O ring, becomes open to atmosphere and allows the internal pressure to dissipate. The vent plug
cannot be totally removed because a retaining spring holds the red or green bung in place.
A normal unit may emit an audible rush of air when the vent plug is retracted, but it will only last for 1
second maximum. A longer rush of air/gas indicates a pressurised unit, ventilate the area, and let the
remaining pressure out of the unit. Internal pressure dissipates to atmosphere in a short time and may
be accompanied by water, debris, noise etc. Only authorised personnel may enter the vicinity of the
work.
11.2 PRECAUTIONS (INSTRUMENT FULLY FUNCTIONING)
The techniques for retaining end-caps in the pressure housings differ from product to product, and
detailed instructions on opening the pressure housing are given in the servicing section of the
individual product manuals.
11.3 PRECAUTIONS (INSTRUMENT KNOWN OR SUSPECTED TO BE PRESSURISED)
If an instrument is known, or suspected to be internally pressurised through water ingress or battery
venting use the safety precautions that follow:
Remove the instrument to a well ventilated location away from other personnel.
Wear the applicable protective clothing, safety glasses and gloves, and refer to battery manufacturer’s
Material Safety Data Sheet (MSDS).
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