Safety first in the dash for gas
As more vessel types take up the cost and environmental benefits of gas-powered shipping, it is becoming increasingly important that crew are trained properly in its use
GAS-fuelled ships are one way forward to reduce air emissions. But in the dash for gas we must ensure that lower emissions don’t mean less safety. Carrying and using gas at sea requires a culture that is present on gas carriers, but which is not found on most other ship types. We need to take great care when we extend gas power to other ship types. Substantial changes are needed to the structure and outfit of the vessel, and the crew need to be trained to understand the new fuel and its risks.
RINA is not the only classification society which has rules and requirements for the use of liquefied or compressed natural gas (LNG or CNG) on board ship as an alternative to traditional fuels. These rules give the industry a regulatory tool to ensure that the arrangement and installation on board of machinery using this type of fuel are such as to provide a level of integrity, from the point of view of safety and reliability, equivalent to that of a conventional installation.
These class requirements are aimed at structure and outfit. They do not address two big issues facing owners looking at using gas fuel. One is crew training, the other is the supply of gas bunkers. These issues are outside the remit of class; we are here to keep things safe and efficient from the structural and outfit perspectives. But the issues are linked, because the crews of passengerships and cargo ships are not used to handling gas, and not used to LNG ship-to-ship transfers, and both of these will become common once gas is in greater use.
We know the many advantages in the use of gas as a fuel in terms of reducing air emissions – a total reduction in sulphur oxide emissions, a considerable reduction in nitric oxide emissions, a 20% reduction in carbon dioxide emissions, and competitive prices at current costs and estimates for the near future. But there is a cost in terms of new outfit, new design, operational flexibility and crew training. All of these will be covered in the new IMO Code for Gas Fuelled Ships, but that is not going to be ready before 2014.
The starting point for the equivalency of safety is to recognise that gas as a fuel has a very much lower flashpoint than marine fuel oils, and also that it is stored as a liquid at very low temperatures or as a gas at very high pressure. Swapping oil for gas is not a direct equivalent, and attention has to be paid to where it is stored, how it is distributed, and, above all, who is handling it and how they understand the new risks.
If there is any escape or leakage, there is both the possibility of explosion and the possibility of the extreme cold liquid gas causing structural damage. Tanks and gas piping must be located so as to minimise the risk of collision damage. So you need a lot of space for gas carriage. Prismatic tanks used for liquefied gas cannot withstand the pressures which build up in a tank of LNG over even a short storage period without using it. A cylindrical tank is required, and even then it will have to be used within two weeks if pressure is not to become too high. On a tanker you can see that such tanks can be mounted on the open weather decks forward of the accommodation. For bulkers it is a much harder design issue, as a hold, or a big part of a hold, could be lost from the cargo spaces.
Machinery spaces with gas distribution must use double wall pipes or there must be emergency shutdown systems automatically activated in case of gas leakage in the machinery space and, consequently, a double redundant engine room set-up. You can see how the design consequences of a decision to build in LNG as a fuel multiply. Estimates of the space penalty vary but, depending on the ship type, the amount of space needed for a liquid gas fuel installation compared to a conventional oil one is in the order of three to four times as much.
The space issues can be overcome, but owners will have to invest in crew training. We will not see a lot of small fixed LNG terminals for fuelling ships. I expect the fuelling will be done by smaller LNG tankers, and that means ship-to-ship transfer of very cold LNG. At the moment, ship-to-ship LNG transfer is carried out only by experienced gas carrier crews. So we will need to see a big effort to train the crews of other ships using gas as a fuel. The training will have to mirror that of gas carrier crews and focus strongly on ship-to-ship transfers.
We know about gas, and we believe in it as a fuel. Italy is a major gas importing and distribution hub for Europe, and RINA has been heavily involved in the development of onshore, offshore fixed and the world’s first offshore floating LNG terminals. So we have hands-on experience. Our job now is to take the hype out of the rush to fuel ships with gas and make it a safe, practical and economic reality.
Head of Machinery Sector at RINA
This article appeared in Lloyd’s List on 26 July 2011.For more information visit www.lloydslist.com