1984 - Puerto Rican

From October 1 to 8, 1984, the U.S. chemical tanker Puerto Rican docked at five different terminals in Louisiana and Texas. Caustic soda was loaded at two ports.

On October 8, the Puerto Rican sailed from Louisiana, via the Panama Canal to San Pedro, California, the first of three West Coast ports at which it was to discharge the caustic soda. The vessel docked at San Pedro on October 21.

The following day, after about 16 hours of discharging caustic soda from three tanks, a discrepancy was noted in the amount left in tank number 5CP, indicating there could be leakage. The master of the Puerto Rican determined that the discrepancy was due to a recording error.

Nevertheless, all double bottom and void spaces around 5CP were sounded, with the exception of 6CV. The adjacent cargo tanks were also checked for leakage of caustic soda from 5CP. No evidence of leakage was found.

The master maintained that he had been told that 6CV had been inerted with nitrogen, and that he and others looked for a means of sounding the void for liquid. They could not find any sounding tubes for 6CV, although there was a fixed-eductor system for the void. The piping for this system had a removable blank where it penetrated the main deck. The system was not used to check for the presence of liquid in 6CV.

On the morning of October 24, the vessel sailed for the San Francisco Bay area, where it was scheduled to call at four terminals. While the vessel was en route, 5CP was washed and made safe for entry. The master and chief mate then inspected it for cracks or holes, which they did not find.

Several cargoes were loaded in the vessel at the various terminals, including 1,661 cubic metre barrels of Alkane 60 (alkyl benzene) which was loaded in tank number 5CP. On October 29, 5,691 cubic metres of caustic soda, the remainder known to be carried as cargo on the voyage, were discharged.

Cargo discharge and loading were completed on October 30.

The vessel passed underneath the Golden Gate Bridge at about 3a.m. the next day, October 31, and proceeded out to the main channel towards San Francisco.

About 20 minutes later, speed was reduced to approximately five knots as the vessel approached the point where the pilot was to disembark to the pilot boat.

At approximately 3.24a.m on October 31, the tankship S.S. Puerto Rican suffered fires and explosions in number six centre void (6CV) and the adjacent wing tanks. The ship was 8.5 miles west of the Golden Gate Bridge, San Francisco, California.

At the time of the explosion, the pilot, a third mate and a member of the crew were standing on the port side of the main deck over the number four port forward wing tank (4PF), which was adjacent to number 6CV. They were waiting for the pilot boat to come alongside, which was about 90 metres off the port quarter at the time. At the time of the explosion, no one was smoking and nothing was dropped on deck, nor did the pilot make or receive any communications on his portable radio, which was turned off. No one was using a flashlight.

The deck area over number 6CV and adjacent wing tanks was lifted, and blown directly forward, landing in an inverted position on the deck immediately forward of its original location. The explosion severed the firemain piping and the water/foam fireline about 14 metres forward of the deckhouse. Isolating the breaks in the piping delayed bringing the primary firefighting equipment to bear on the fire.

The remaining 26 people onboard the vessel abandoned ship safely at intervals following the incident. The majority of those onboard departed from the stern of the tankship and boarded commercial towing vessels.

The last person to leave was the master, who boarded a tug from the stern of the vessel about two hours after the explosion.

From October 1 to 8, 1984, the U.S. chemical tanker Puerto Rican docked at five different terminals in Louisiana and Texas. Caustic soda was loaded at two ports.

On October 8, the Puerto Rican sailed from Louisiana, via the Panama Canal to San Pedro, California, the first of three West Coast ports at which it was to discharge the caustic soda. The vessel docked at San Pedro on October 21.

The following day, after about 16 hours of discharging caustic soda from three tanks, a discrepancy was noted in the amount left in tank number 5CP, indicating there could be leakage. The master of the Puerto Rican determined that the discrepancy was due to a recording error.

Nevertheless, all double bottom and void spaces around 5CP were sounded, with the exception of 6CV. The adjacent cargo tanks were also checked for leakage of caustic soda from 5CP. No evidence of leakage was found.

The master maintained that he had been told that 6CV had been inerted with nitrogen, and that he and others looked for a means of sounding the void for liquid. They could not find any sounding tubes for 6CV, although there was a fixed-eductor system for the void. The piping for this system had a removable blank where it penetrated the main deck. The system was not used to check for the presence of liquid in 6CV.

On the morning of October 24, the vessel sailed for the San Francisco Bay area, where it was scheduled to call at four terminals. While the vessel was en route, 5CP was washed and made safe for entry. The master and chief mate then inspected it for cracks or holes, which they did not find.

Several cargoes were loaded in the vessel at the various terminals, including 1,661 cubic metre barrels of Alkane 60 (alkyl benzene) which was loaded in tank number 5CP. On October 29, 5,691 cubic metres of caustic soda, the remainder known to be carried as cargo on the voyage, were discharged.

Cargo discharge and loading were completed on October 30.

The vessel passed underneath the Golden Gate Bridge at about 3a.m. the next day, October 31, and proceeded out to the main channel towards San Francisco.

About 20 minutes later, speed was reduced to approximately five knots as the vessel approached the point where the pilot was to disembark to the pilot boat.

At approximately 3.24a.m on October 31, the tankship S.S. Puerto Rican suffered fires and explosions in number six centre void (6CV) and the adjacent wing tanks. The ship was 8.5 miles west of the Golden Gate Bridge, San Francisco, California.

At the time of the explosion, the pilot, a third mate and a member of the crew were standing on the port side of the main deck over the number four port forward wing tank (4PF), which was adjacent to number 6CV. They were waiting for the pilot boat to come alongside, which was about 90 metres off the port quarter at the time. At the time of the explosion, no one was smoking and nothing was dropped on deck, nor did the pilot make or receive any communications on his portable radio, which was turned off. No one was using a flashlight.

The deck area over number 6CV and adjacent wing tanks was lifted, and blown directly forward, landing in an inverted position on the deck immediately forward of its original location. The explosion severed the firemain piping and the water/foam fireline about 14 metres forward of the deckhouse. Isolating the breaks in the piping delayed bringing the primary firefighting equipment to bear on the fire.

The remaining 26 people onboard the vessel abandoned ship safely at intervals following the incident. The majority of those onboard departed from the stern of the tankship and boarded commercial towing vessels.

The last person to leave was the master, who boarded a tug from the stern of the vessel about two hours after the explosion.

Puerto Rican had drifted to within 7kms of the shore by 6.30a.m., when a towing vessel secured a towline to its stern and started towing it seaward. The fire on the tankship was not extinguished until the early evening of November 1.

On November 3, nearly four days after the explosion, the stern section separated from the forebody at roughly the middle of number 6CV. This section sank in about 450 metres of water, 68kms southwest of the nearest point at shore.

Number 6CV contained a large independent cargo tank which floated free and was towed to a ship repair yard in Oakland, California, on November 4. The forebody was towed to a dock in San Francisco on November 18. After the remaining cargo was removed and the tanks cleaned and freed of gas, the forebody was sold for scrap.

Following are some of the conclusions arrived at through the Coast Guard investigation of the casualty.

The breaking in half, sinking of the stern section and total constructive loss of the Puerto Rican resulted from explosions and fire occurring in 6CV and four adjacent wing tanks on October 31.

The proximate cause of this casualty was the failure to repair a concave shaped indent through the stainless steel cladding on the bulkhead separating 5CP and 6CV. The indent was most probably made while the tank was being constructed.

The indent exposed the mild steel bulkhead behind it, which then corroded due to repeated exposure to caustic soda. The corrosion process created a hole that fully penetrated the 5CP after the bulkhead (Figure 1) sometime before the vessel's arrival in San Pedro on October 21. Approximately 2,500 to 3,000 barrels of caustic soda leaked through the hole from 5CP into 6CV, creating a liquid level height of about half a metre.

The caustic soda reacted with the zinc-rich epoxy coating on the bulkheads and tank supports as well as with the zinc galvanized layer on the piping, consuming the zinc and liberating hydrogen gas. No other flammable gas was in 6CV at this time.

Approximately 175 cubic metres of the Alkane 60 loaded into 5CP on October 28 also leaked into 6CV through the hole in the 5CP after bulkhead (see Figure 1). Alkane 60 has a flashpoint of approximately 138ºC. It is less dense than caustic soda solution, and therefore, remained on top of the caustic soda in 6CV, raising the liquid level to one and one-half metres.

Sufficient hydrogen gas was generated in 6CV by the reaction of the caustic soda with the zinc-rich epoxy and galvanized piping to cause the atmosphere in the void to be in the flammable range. This flammable mixture was ignited shortly before the explosion which inverted the main deck section on October 21.

The most probable ignition source was a spark within 6CV, either from metal-to-metal contact or due to an electrostatic discharge.

Contributing to the cause of this casualty was the failure of the master to use all reasonable means to account for the caustic soda discrepancy from 5CP after being notified of it on October 22.

The indent and the stainless steel cladding in the 5CP after bulkhead, and the corroded area behind it, existed and was not detected during a number of internal inspections of this tank by various inspection personnel before the corrosion fully penetrated the bulkhead.

The fact that this hole was never detected during any inspection of 5CP before the casualty illustrates practical limitations inherent in the inspection of large, complex tank vessels by visual methods, rather than a lack of adequate inspection requirements.