The general terms ‘oil’ and ‘petroleum products’ cover a very wide variety of cargoes. These include ‘black oils’, which would be solid at ambient temperature, and gasses only made liquid under pressure or at a very low temperature, spiked crudes (crudes to which light fractions such as butane have been added) topped crudes, feedstocks and chemicals as well as the more commonly known gasoline, kerosene and gas oil or diesel. The different crude oils vary widely in appearance, consistency and characteristics, not just from country to country but from field to field. They range from pale brown liquids, which flow like water, to viscous semi-solids; from crudes with very few light fractions not far removed from fuel oils to crudes which are highly gaseous; from crudes with a specific gravity of 0.99 to crudes with a specific gravity of less than 0.80. They can be broadly divided into two main classes, the paraffin base crudes which contain varying quantities of paraffin wax and little asphaltic material and the naphthenic crudes which contain little or no wax but have a high proportion of asphaltic material. All crude oils are volatile depending on temperature and therefore are a potential source of inflammable vapours. The flash point of any crude (or product) is the lowest temperature at which enough vapour will be given off to form an inflammable mixture with air. Below that concentration of vapour the mixture is too weak and will not ignite. With a very high concentration (an over rich situation) there will be insufficient oxygen to support ignition. Between the two levels if there is a source of ignition an explosion will follow. Familiarity with handling petroleum in its various forms should never be allowed to lead to over confidence and to cutting corners. All regulations and precautions must be strictly observed.