design considerations for aluminum hull structures - Ship Structure ...

.65-Machineq Spaces - Reference (68) lists 24s fire casualties on allclasses of ships, of which only four were on bulk carriers. Three of thefour fires originated in themachineryspaces and one in the accommodationspaces. Of those occurring in the machinery spaces, two were the resultof fuel oil fires while combustible materials restite’din the accommodationspace fire. This agrees with the expected assumption that these two t~esof combustibles are the primary sources of incipient fires, and that theselocations must therefore be provided with the maximum protection againstfires.Within the machine~ space, the most serious problem is the protectionof the exposed aluminum structure to prevent the passage of smoke and flameand to restrict the maximum temperature of the aluminum to 400 degrees Ffor the required one hour time interval. The overriding requirement is themaximum temperature restriction in the presence of fire, since if this canbe accomplished, the structure will prevent the passage of smoke and flame.One potential solution might be the use of sprinklers to form water wallson the vertical surfaces and the underside of the flats. However, thismethod is incompatiblewith an oil fire. A fixed fog system might be consideredbut to date there have been no physical tests to evaluate the timetemperatureresults of either of these proposals. A simple solution wouldbe to constmct the machinew space enclosing structure of stieel. This,however, poses additional problems of added weight, connection of incompatiblemetals, and differential coefficients of expansion. For many localstructures, such as machinery flats and small tanks, the use of steel inlieu of protected aluminum would appear to offer significant cost savingswithout a major weight penalty. Various types of fire-retardant intumescentpaints are available, but these are p~imarily used to retard the sPread offire rather tha to restrict the temperature rise on the surface to whichthey are applied for any appreciable time duration.Of all the methods considered, the one chosen to best provide thedesired protection to vertical surfaces and the crown of the machinery boxis the application of a suitable thickness of insulation, sheathed with metalto protect the insulation against injury and abrasion.The surface of tank top, while still requiring the same degree of protection,presents a rather different problem due to personnel access and abrasionfrom the movement of equipment. Of all the available materials considered, acomposite construction consisting of an approved cellular glass incombustiblematerial, expanded metal, .%bkote No. 1 and a magnesia aggregate topping similarto MIG-11-2313Lhas been selected as the optimum after due consideration ofweight, cost. abrasion, resistance, oil spillage, good housekeep~ng and otherconstraints.Table 13 gives the approximate areas in each category together withthe anticipated approximate added weight to protect the aluminum.While not considered in detail at this time, other items that must bedealt with are structural stanchions and webs in the machine~ spaces,together with exposed areas of main and auxilia~ machine~ foundations.It is also necessa~ to offset the deleterious effects of heat tramfer,