The Flash Point of a fuel is the temperature at which vapor given off will ignite when an external flame is applied under specified test conditions. A flash point is defined to minimize fire risk during normal storage and handling.
The minimum flash point for fuel in the machinery space of a merchant ship is governed by international legislation and the value is 60C. For fuels used for emergency purposes, external to the machinery space, for example the lifeboats, the flash point must be greater than 43C. Even when residual fuels are at a temperature below their measured flash point, they are capable of producing light hydrocarbons in the tank headspace, such that the vapor composition may be near to or within the flammable range. Hence all residual fuel oil headspaces should be considered to be potentially flammable.
At all times the temperatures in the fuel oil system should conform with recognized codes of practice and excessive local temperatures should be avoided. Particular care should be taken to ensure that any flame screens/traps are in good condition on the various fuel oil tank vent pipes, and that there are no ignition sources in the area immediately surrounding the venting system.
The reason for this is that when tanks are being filled, the tank headspace gas will be displaced through the vent pipes. When filling empty or near empty tanks, it should be ensured that the heating coils are shut down and cool. Fuel oil contacting hot exposed heating coils could lead to a flammable atmosphere being rapidly generated. All residual fuel oil tank headspaces should be classified as "hazardous" and all electrical equipment within the space must meet the appropriate safety standard.
All operations, such as ullaging and sampling, should be carried out to avoid any hazards associated with static electrical charges. These precautions would, for example, include ensuring that metallic sampling equipment and ullaging equipment is properly earthed or bonded to the tank structure. When tanks are opened, it is important not to stand downwind of the tank and to ensure that there are no sources of ignition within the vicinity of the tank hatch.
