In the first part of this article, which appeared in the May 2019 issue, we discussed how LNG is not only being transported on ocean-going ships but is now fuelling those same ships and now also some smaller vessels. In this second part of the article, we look at some of the safety measures that must be in place during LNG bunkering operations.
First though, let’s look at some of the ways bunkering can be achieved via several methods as shown in Figure 1, which shows a fixed land-based operation: (1) shows LNG being supplied to a vessel from a fixed storage tank on land. Many bunkering operations are currently being supplied by trucks (2) delivering the LNG to the vessel’s dock where it is then transferred to the vessel’s fuel tank. Some ports without fixed LNG bunkering facilities have resorted to having an LNG supply vessel or bunkering barge (3) brought alongside the vessel requesting fuel and then transferring the LNG from vessel to vessel.
In the graphic, an alternative means of supplying LNG fuel is via the use of ISO Cryogenic containers. The LNG fuelled vessel exchanges ISO containers when it needs to refuel much as you would exchange an LPG or propane barbecue tank.
The International Maritime Organization (IMO) has kept abreast of all the new LNG bunkering technologies and has written detailed standard operating procedures (SOPs), which must be followed during any bunkering operation. The SOPs should standardize the practices as well as the safety equipment that must be provided. Much of the regulatory information is found in the International Code of Safety for Ships using Gas or Other Low Flashpoint Fuels (IGF Code), which addresses the use of LNG as a fuel aboard vessels.
Let’s first look at some of the safety equipment. LNG is merely natural gas which has been liquefied. Due to this liquefaction there is no odorant added so if the liquid is exposed to air and vaporizes there will be no odour to detect the leak. To counter this problem, there will be fixed gas meters (Figure 2) at each bunkering site.
If increased amounts of methane are detected, alarms will sound and in many cases the LNG transfer operation will be stopped automatically with an Emergency Shut Down (ESD) process. There may also be temperature detectors which could also trigger an alarm.
We are all in the fire service, so we know about heat detectors. However, these detectors not only alarm when dramatic increases in heat are found, they also warn of major drops in temperature.
Remember, LNG is stored at -162°C. Regardless of where in the world you live and how cold it gets there, if the temperature drops to those cryogenic temperatures then something is drastically wrong.
These detectors may also activate the ESD. Due to the extreme cold temperatures, any metal that may encounter the LNG must be stainless steel or other safe metal (Figure 3).
Another issue that might activate the ESD would be any sudden movement of the vessel which might cause undo strain on the bunkering hose and/or the hose connection. During this ESD, in addition to the shutdown of flow, the ‘breakaway’ bunkering connection may separate, leaving one part of the connection on the vessel and the other half at the end of the hose with closed valves at each end.
There is also the problem with the extreme cold of the LNG. If the liquid encounters any ferrous metal, such as the deck of the vessel, then the metal may become brittle.
To counter that, all drip trays under the bunkering connection must be made of a high-nickel-content steel or aluminium, which can handle the extreme cold. In fact, all LNG piping and the inside of LNG tanks must also be made of such metals.
If there would be danger of the drip tray filling, then a trough is added to allow any spilled LNG to be discharged into the water over the side of the vessel (Figure 4).
Many LNG-fuelled vessels will have a protective water curtain flowing over the side of the vessel just below the bunkering station. This would prevent any spilled LNG from causing damage to the ship because it would drop onto the surface of the water and be washed over the side. This feature has been used on the large LNG tankers which have been transporting the product around the world for many years. In my previous articles dealing with the properties of LNG I have mentioned that LNG is lighter than water and will therefore float on the surface of this water curtain and thereby not affect the metal deck.
A permanently installed fire-extinguishing system will typically be fitted at the bunker station and drip trays. These systems can discharge automatically upon an alarm and/or be operated manually.
During all vessel bunkerings, access to the area must be restricted by setting up mandatory Safety Zones around the entire bunkering operation. These zones are designed to keep unauthorized personnel from creating a source of ignition. The zone would also restrict any hazardous, non-intrinsic operation to outside the zone (Figure 5). Current regulations might permit ‘simultaneous operations’ whereby other vessel operations might be carried on during the bunkering. This would include the loading/unloading of cargo. These Safety Zones would be extremely important on any passenger vessel as the passengers are not familiar with posted safety measures. In the US, simultaneous operations are only permitted by the US Coast Guard on a case-by-case basis.
Training for the crews aboard LNG-fuelled vessels is something that is also covered by international regulations. Two levels of training are outlined in the IMO guidelines. Everyone aboard an LNG-fuelled vessel must undergo a basic course of training dealing with safety and firefighting. Additionally, all crew members who take an active role in the bunkering, storage and use of the LNG fuel must undergo an advanced course of training in addition to the basic-level training.
These crew and facility training programs are designed to keep the LNG inside the piping and storage tanks. If it remains inside with no openings, the LNG cannot reach its flammable range. The flammable zone for LNG is between 5% and 15% mixture with oxygen. If the LNG is never exposed to the air, there will be no oxygen and therefore no fire.
In summation, LNG is a product that we in the fire service will have to deal with in the marine environment but also on our roads and railways. It may just be transported on vessels and vehicles, but it may also be fuelling these vessels, trucks and locomotives.
In the future there will be an article dealing with LNG being transported on our roads and also fuelling the vehicles.
The safety record of LNG being transported via ships over the past 60 years is excellent. If the same safety standards are applied to LNG as a vessel and vehicle fuel, we can continue that excellent record.
However, those of us in the fire service must be prepared for the worst. To quote Murphy’s Law: ‘Anything that can go wrong will go wrong, and it will go wrong at the worst time.’ Those in the fire service who Fail to Train are Training to Fail.
Until next time; Stay Safe.
For more information, go to www.marinefirefighting.com