On the morning of the accident, the chief mate indicated to his watchstanders
that he intended to check out the inoperable draft sensors
in the bottom of ballast tanks No 4P and 4S.
The C/M directed two AB's to install air blowers on the tank openings.
When he tasked the seamen top install the ventilators,
the C/M did not advise them to follow any special precautions
or be alert for the smell of fumes,
Neitehr the C/M nor the Master was on the main deck
during the tank opening operations
and they did not oversee the ventilation of the ballast tanks.
According to eye witness accounts,
the actions of the master and C/M indicate that they probably
became aware of the contamination in the 4S ballast tank
whenthey initially looked into the tank.
Although the master and the C/M recognized that the tank atmosphere
was not safe for entry without a breathing apparatus,
witnesses did not see anyone test the tank atmosphere
for flammability or safe levels of oxygen.
After one descent intothe tank, the C/M retruned to the deck.
He and the master then removed the fans
and used mirror(s) to reflect sunlight into the tank
in an attempt to locate the naptha leak
The naptha leak into the No 4S ballast tank begain sometime
between February 18 and 22, 1990,
after the liquid hydrocarbon was loaded into cargo tanks
Nos 5S, 5C, and 6C and/or during the tank ship's passage through the Persian Gulf.
Enough naptha leaked intot he starboard ballast tank
so that when the vapors mixed with the air injected into the starboard ballast tank,
the naptha atmosphere reached the explosive range.
Naptha could only have entered the 4S
as a result of either a failure in the ballast system piping
or a failure in a ballast tank bulkhead.
Post-accident examinations conducted by the CG revealed
that the weld around the ballast pipe penetration into 4S,
the ballast piping, and the branch valve was tight;
no evidence of naptha was present.
Thus, the ballast system piping did not provide a path for naptha
leakage into the tank.
The Safety Board also considered fractures resulting from metal fatigue,
stress concentrations, corrosion, and laterally symmetric damage
in the No 4P and 4S tanks as a source of naptha entry into the tank.
Testimony indicated that in the Surf City, [fatigue] working
appears to have had the greatest effect inthe No 4P and 4S ballast tanks.
The conditions of bulkhead and structural strength members
in the No 4P and 4S ballast tanks, as reported by Coast Guard inspectors
and ABS surveyors before the accident,
indicate that the aft area of the ballast tanks
was an area of concentration within the cargo block.
The Coast Guard hull inspector testified that the fractures he found
in the transverse web frames, longitudinal stiffeners,
and the upper horizontal girders were stress fractures.
When the former Chief Mate inspected the Surf City's ballast tanks
in Jauary, he reported numerous new stess fractures,
some along previous weld repairs,
in the girders, frames and stiffeners in 4P and 4S.
These new fractures had occurred less than 1 year
following the previous ballast tank inspections and shipyard repairs
in February, 1989.
He also found a previously unreported unreported bulkhead patch
in the NO 4S ballast tank on the aft bulkhead
in an area corresponding to the bulkhead fracture found in the 4P ballast tank.
The testimony and reports from the previous chief mate,
teh AB's, and the Coast Guard indicate that the type and locations
of fracturing found in the 4P were laterally symmetrical
to those found in 4S.