Quantcast Tunnels and Manholes

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2.4.6 Tunnels and Manholes.  M e c h a n i c a l ventilization is often provided for
tunnels to remove obnoxious gases that might accumulate, to carry away
m o i s t u r e saturated air, and to facilitate maintenance through better ambient
conditions for `workmen.  Mechanical ventilation can be provided permanently by
e x h a u s t fans installed in the generating plant to create a slight negative
d r a f t in the tunnel.  Atmospheric air enters the tunnel through the manhole
v e n t s , circulates through the tunnel, and is discharged to the atmosphere by
the exhaust fans.  Often temporary ventilation is obtained by fans arranged to
force air into the manholes.  Perform inspections according to the following
Inspect manholes and check operation of the
( a ) Monthly Inspection.
draining equipment.
( b ) Quarterly Inspection.  Inspect and tighten the packing of conduit
gland seals.  The friction caused by the movement and the heat conducted from
the pipe shortens the life of the packing. Repack the gland before a
d e f e c t i v e packing permits water to enter. Gland seals on lines that are
frequently turned on and off require more maintenance than those installed on
lines operating on longer cycles.  The inspection frequency depends on the
particular  installation.
( c ) Yearly Inspection.  Make a general overhaul of sump pumps and team
ejectors after the heating season.  Inspect manholes for water leaks and check
c o n d i t i o n of ladders, waterproof covers, e l e c t r i c a l f i x t u r e s a n d i n s t a l l a t i o n ,
and vents.  C h e c k supports, guides, expansion joints, and all auxiliary
2 . 4 . 7 Inspection of Cathodic Protection Systems. Consult specific
instructions furnished by the manufacturer or designer of the system for the
p a r t i c u l a r  i n s t a l l a t i o n .  NAVFAC MO-306, Maintenance and Operation of Cathodic
Protection Systems and )40-307, "Cathodic Protection Systems Maintenance" give
specific guidance for the inspection and maintenance of cathodic protection
systems.  I n general, the following inspection schedules apply:
* Impressed current Systems:  Read and record rectifier settings and
outputs monthly.  Record information on NAVFAC Form 9-11014/17B.
Notify EFD (Code 102) if inconsistent readings are observed.
* Galvanic Anode and Impressed Current Systems: Make
S t r u c t u r e - t o - E l e c t r o l y t e Potential readings at selected test points
Record information on NAVFAC Form 9-11014-17B.  Notify EFD
(Code 102) if inconsistent readings are obtained.


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