MAIB publishes ENNERDALE propane leak report
Into the incident 17th October 2006 when 66 tonnes of propane was released at Fawley terminal

 

On 17 October 2006, the Hong Kong registered gas carrier Ennerdale experienced a major leak of liquefied propane, while cargo sampling operations were taking place, alongside Fawley Marine Terminal (FMT).

The leak was sealed 29 hours later, after an estimated 66 tonnes of propane had been lost to atmosphere.

The fully pressurised gas carrier Ennerdale arrived at FMT’s No. 2 berth
at 2300 on 15 October 2006, to load liquefied propane. Preloading
checks were conducted and loading commenced shortly after. At 1830
on 17 October the loading operation was halted, approximately 2 hours
before cargo loading was due to be completed, to allow a ‘freeze’ test to be conducted. A
cargo surveyor came aboard and attached his cargo sampling equipment to the sampling point
of tank No. 1. The cargo was then circulated for 2-3 minutes. The process was repeated for
tank No. 2. With the test results satisfactory, cargo loading continued and completed at 2100.

The cargo surveyor returned to the ship and went straight to the sampling point of tank No.
1, where the chief officer was already preparing. The cargo surveyor used a thread adapter
to connect the sampling device to the ship’s sampling connection. The chief officer then
circulated the cargo, using the deep well pump, to ensure a good representative sample was
obtained. The cargo surveyor flushed the sampling device through three times before filling it.
He repeated the process, taking four samples in total, before moving aft to the sampling point
of tank No. 2. While the chief officer secured tank No. 1, the cargo surveyor prepared to fit his
equipment to the sampling point of tank No. 2. As he turned the sampling connection towards
himself, the sampling valve assembly came off in his hand.

The chief officer saw and heard a leak and activated the emergency shut down (ESD) valves.
Attempts were made to refit the sampling valve but the 11 bar pressure of the cargo, and the
formation of ice on the connection, made it impossible. It soon became apparent that the ESD
valve adjacent to the tank on the same line as the sampling connection was not completely
shut.

The emergency services were alerted soon after the accident and the ship was doused in
water sprays to disperse the gas cloud. At 2200, the port of Southampton was closed to all
traffic. All ships at FMT were evacuated at 0000. At 0530 on 18 October, with the situation
stabilised, traffic restrictions were reduced to a 400 m exclusion zone around Ennerdale, which
allowed the port to reopen to traffic.

After several options to stop the leak had been considered, it was decided to hot tap the
cargo pipework and inject a sealing compound to stop the leak of gas. Furmanite, a company
regularly used at Fawley refinery, successfully drilled into the pipework at 1408 on 18 October.
The sealing compound was then slowly injected into the pipework, enabling the leak to be
sealed and capped at 0240 the next morning.

Ennerdale then sailed and anchored in the Solent, awaiting clearance to sail which was
contingent upon class approval of the repair and the discharge port agreeing to accept the
vessel. This completed, she sailed at 1814 the same day.

The assembly used for gas sampling was designed as a drain point for the cargo pipework
system, but had come to be used for cargo sampling when the original arrangement provided
for this was deemed unsuitable. The regulatory requirements for gas carriers include very
little guidance on cargo sampling, with no unified standard employed. Industry guidance on
sampling was also lacking. Guidance, published in 1989 by the Society of International Gas
Tanker and Terminal Operators (SIGTTO), appeared to have been overlooked as industry
inspections of Ennerdale had not highlighted any concerns with the sampling arrangement.

Inspection of the ESD valve, which failed to close and contain the leak of liquefied propane,
revealed that it had been jammed open by a small burr. Although ESD valves onboard
Ennerdale were tested to ensure their closure rates were acceptable, there was a false
assumption that the valves were indicating that they were closed. Although some ESD valves
appeared to have been pressure tested by ship’s staff, those on the cargo discharge lines
were not, as there was no readily available method to do so. There were no records of when
the faulty ESD valve was last inspected, tested or overhauled. Furthermore, there is no clear
regulatory requirement for ESD valves to be tested or internally examined at periodic intervals,
or industry standard for regularly testing of ESD valves in service.

Due to the nature of the leak, the ship’s crew were unable to secure the leak themselves.
Although the emergency response by the ship, FMT, and local emergency services was good,
liaison between ship’s staff and the FMT was not ideal.

Recommendations have been made to SIGTTO, Chemical Distribution Institute (CDI) and Oil
Companies International Marine Forum (OCIMF) with regard to providing industry guidance on
sampling arrangements and procedures. Lloyd’s Register has been recommended to take two
proposals to IACS regarding the standard of sampling connections, and ESD valve design and
periodic testing.

For copies of the full report, see:
http://www.maib.gov.uk/publications/investigation_reports/2007/ennerdale.cfm