By Tom Guldner, President of Marine Firefighting Inc.
What measures are in-place to protect them and prevent emergencies aboard LNG ships and at LNG facilities.? Let’s start with a little history of the LNG ships themselves…
The marine transport of LNG has had a stellar record for safely transporting its cargoes for many years. The industry takes safety seriously and that is the main reason there have been no major incidents involving the marine transport of LNG.
Early LNG ships were merely large thermos bottles. The product they carried, LNG, had to be maintained at approximately minus 260 degrees F for it to remain a liquid. It was not stored under pressure.
Any heating of the product would cause some of the cargo to return to its gaseous state which would be referred to as “boil off gas”. This gas would expand to 600 times its size when changing from a liquid to a gas. If allowed to remain inside this thermos bottle the gas would cause a pressure rise which would in-turn cause more heating of the product and therefore more gas and pressure. The tank was not designed to handle this pressure.
In the early days, this “boil off gas” would just be sent out to the atmosphere through risers located on deck. This prevented over pressurization of the cargo tanks, but it also permitted a loss of cargo. Not something the gas owner appreciated!
Eventually, someone came up with the idea of using this highly valuable and volatile gas to actually fuel the engines of the ship. This led to dual fuel LNG ships with steam engines which could burn either the boil-off gas from the LNG cargo tanks, or its usual bunker fuel. It was a very expensive way to fuel the ship, but seeing that it had previously just been discarded, it was a viable solution. Unfortunately, the ship was still delivering less cargo at its destination than it took on initially. This was still not a good option for the cargo owner.
The next innovation was an on-board re-liquefaction plant. This would take the boil-off gases, cool them back into a liquid, and then put the liquid back into the cargo tanks. These re-liquefaction plants can be found on the rear decks of some of the newer and largest LNG ships, the Q-Flex and the Q-Max vessels. Because the engines on these vessels no longer needed to burn two different fuels, conventional diesel engines could be used.
Preventative Fire Safety
When an LNG carrier ties up at the facility to transfer its cryogenic cargo, shipboard detection and emergency shut down systems (ESD) and those on shore are connected together so that they act as part of an integrated system. If anything goes wrong either on the ship or in the facility, alarms will sound and the loading or off-loading procedure will be automatically shut down.
Both the vessel and the facility have gas sensors which will detect the presence of natural gas and also the lack of oxygen. Other sensors will detect changes in temperature. Heat detectors will alert everyone to a fire while cold temperatures will indicate a LNG leak to trigger an alarm and the (ESD).
Other sensors will monitor the tension on the mooring lines from the vessel to the facility dock. Any surge in tension that might part the lines (such as from the surge of a passing ship) would send the alarm and trigger the (ESD).
The large product loading arms have a quick disconnect device built in. These Powered Emergency Release Couplers (PERCs) (photo right) will close ball valves on both sides of the coupler thus shutting down flow. The coupler will then separate allowing the loading arms to retract away from the vessel while leaving the other half of the PERC valve attached to the vessels manifold. Both halves of the PERC will now have a closed ball valve at the end of the piping to prevent any flow.
Sensors are also continually monitoring the cargo. Any rise or fall of the liquid level in the ship’s or facilities tanks, when pumping is not going on, will indicate a leak and cause an alarm.
In addition to all of these automatic shut down procedures, anyone either on the ship or in the facility can manually institute an ESD whenever needed.
If a leak or fire occurs
Water will not extinguish an LNG fire. Firefighting water does have its uses in an LNG fire such as keeping a vapor cloud away from a source of ignition, but the extinguishing agent used for LNG fires is Dry Chemical. Within the facility there may also be High Expansion Foam Generators to flood LNG retention areas with a blanket of foam. That foam may reduce the flames intensity or reduce the volume of vapor, but extinguishment is achieved with dry chemical. In many cases, it may be advisable to allow small LNG spills to burn themselves out.
In the facility the Code of Federal Regulations (CFRs) requires certain dry chemical firefighting equipment and supplies be installed……
§ 127.609 Dry chemical systems.
(a) Each marine transfer area for LNG must have a dry chemical system that provides at least two dry chemical discharges to the area surrounding the loading arms, one of which must be—
(1) From a monitor
(2) Actuated and, except for preaimed monitors, controlled from a location other than the monitor location.
(b) The dry chemical system must have the capacity to supply simultaneously
or sequentially each hose or monitor in the system for 45 seconds.
(c) Each dry chemical hose station must have at least one length of hose that—
(1) Is on a hose rack or reel; and
(2) Has a nozzle with a valve that starts and stops the flow of dry chemical.
[CGD 78–038, 53 FR 3376, Feb. 7, 1988, as amended at CGD 88–049, 60 FR 39796, Aug. 3, 1995]
The International Maritime Organization (IMO) sets the requirements for firefighting equipment aboard LNG ships. The IMO requires
Fixed dry chemical powder is fitted for firefighting in the exposed cargo area with at least two hoses or monitors capable of reaching the manifold area. (Photo left.)
Monitors have a discharge rate of not less than 10 Kg/sec and a range of 10 to 40 meters depending on capacity
Hoses have a discharge rate of at least 3Kg/sec with the rate designed so one man can operate
Consists of two independent systems with remote control monitor to cover manifold area and sufficient powder storage for a minimum discharge time of 45 sec.
In addition to this, several areas aboard ship will have gas inerting systems to flood enclosed spaces in the event of a leak.
Water mains aboard LNG ships must operate on a higher than normal pressure to give a better water spray pattern to protect and cool exposures.
In previous articles I have also discussed the massive 10,000 gpm fire pumps and monitors which must be available on the tugs which escort the LNG ships in and out of harbors.
Both LNG facilities and LNG ships are required to have extensive training. Facilities are required to have an extensive printed Emergency Response Plan. In addition to periodic drills, yearly full scale drills must also occur to test the effectiveness of the training.
My company has played a role in the LNG and firefighting training of the tug crews and the facility staff. We have also lead the yearly drill scenarios at an LNG facility.
So, we see that there are quite a few measures to prevent an LNG incident from occurring in the first place and also measures to mitigate any small scale emergency if one should occur.
The LNG industry is currently going through many changes both in the design of the ships and facilities but also in the direction of flow. Massive gas reserves recently discovered in the USA will lead to LNG being exported out of US port instead of being imported into them.
Hopefully the exemplary safety record of the LNG industry will be maintained through the changes and innovations in the future. And hopefully, we will not have to rely of the previously mentioned emergency extinguishing measures in place.
Tom Guldner is a retired Lieutenant of the New York City Fire Department’s Marine Division. Tom held a US Coast Guard License as a Ships Master and is certified as a Fire instructor both within New York State and Nationally in the USA.
He is currently a participating member of the Society of Naval Architects and Marine Engineers (SNAME) Fishing Vessel Operations and Safety panel and also their Small Working Vessel
Tom’s company Marine Firefighting Inc. is involved in consulting and training mariners and land-based firefighters in all aspects of marine firefighting. Visit his web-site at www.marinefirefighting.com or E-mail Tom at [email protected]