Comparison chemicals/products versus oil

This manual deals mainly with chemicals. On the other hand there are many more oil spills. It is important therefore to know the similarities and differences between oil and chemical spills to learn which oil spill response techniques and safety precautions can be applied to chemical spills as well.

Crude oils consist of solids, liquids and gases in various percentages. Light crude oils have higher percentages of the lighter compounds (gases and liquids) while heavy crude oils have less of the light compounds and more of the solid compounds in solution, while gases such as propane and butane are produced as LNG (Liquefied Natural Gas). Most crude oils are liquids; though there are also solid oils products such as asphalts.

Crude oils are complex mixtures of hydrocarbons (C-H) of varying molecular weight and structure comprising the three main chemical groups (1) paraffinic, (2) naphthenic and (3) aromatics. The composition of crude oils varies greatly.

These hydrocarbons range from simple, highly volatile substances to complex waxes and asphaltic compounds that cannot be distilled. Oxygen, nitrogen, sulphur, vanadium, nickel and mineral salts etc., may all be present in various combinations. Simple hydrocarbons include methane (1 Carbon and 4 Hydrogen atoms), ethane (2 Carbon and 6 Hydrogen atoms), propane (3 Carbon and 8 Hydrogen atoms), butane (4 Carbon and 10 Hydrogen atoms), pentane (5 Carbon and 12 Hydrogen atoms), hexane (C6H14), heptane (C7H16), and octane (C8H18). Liquefied propane, butane, or a mixture of these is called Liquefied Petroleum Gas (LPG), the transport of which is highly regulated as flammable gas. In fact crude oil consists of various chemicals. Beyond LPG, other products are gasoline (motor spirit), kerosene, gas oils, fuel oils (light, medium and heavy) and lubricating oils, these being refined oils, fractionally distilled to various specific gravities, viscosities and flashpoints depending on intended application. A wide range of additives is used in these oils, many of which are surface-active compounds.

Oil is not only a source of fuel. It is also as a resource for the precursors of most day to day products of the petrochemical industries such as plastics, paints and pharmaceutics.

The products derived from crude oils by refining will have chemical and physical characteristics that depend on the nature of the crudes and the various processes to which they have been subjected. It may be said that the sulphur, vanadium, wax and asphaltenes in the crude are associated with the higher boiling materials. Therefore, although they will appear in the light and middle distillates they will in general become relatively more concentrated in the heavier products, i.e. in the medium, heavy, and residual fuel oils.

Hazards

The hazards of crude oil derive from the individual chemicals of which it is comprised. Thus, for instance, crude oil contains the BTX products, benzene, toluene, and the xylenes. The aromatic compounds (BTX) are described as "relatively toxic" and some aromatics are potentially carcinogenic, but toxicity always depends on exposure concentration.

Also crude oil is explosive and flammable due to the light components such as methane, propane and butane though these evaporate rapidly.

In contrast, weathered oils are non-flammable and less toxic. Thus, other than fire or explosion hazard, the main concern is adhesion to and irritation of the skin on prolonged exposure.

As to adhesion, some chemicals are extremely sticky such as: lube additives, silicone oils and phthalates, while the stickiness of oil affects coastlines and the feathers of birds causing the death of many individuals exposed to oil spills.

As already said the hazards of crude oils are flammability and explosion danger while toxic and carcinogenic effects in the air and in the water column are dependent on exposure concentration. On the other hand, some chemicals are explosive, corrosive and more toxic than oils and unlike oils may be bio-accumulative, though again toxicity and tainting are concentration dependent.

Physical properties

For response to spillage, the following physical parameters are important:

• Density
• Viscosity
• Pour point
• Flash point
• Vapour pressure
• Solubility
• Phase

Most of these parameters determine the behaviour of a substance in the marine environment. The main difference is that the properties (parameter-values) change on release in the water due to evaporation of the volatile compounds and water-in-oil emulsion formation with the non-volatile. Again, evaporation of the volatile components increases density and may change some oils from the liquid to the solid state.

Yet again, biodegradation in longer-term changes the properties of the original pollution as the molecular structure changes en route to the ultimate carbon dioxide and water.

Also reaction with water changes the properties of some chemicals to those of the product chemicals, while water-in-oil formation changes as properties of the oil to that of the emulsion.

Behaviour

Thus, just as individual chemicals can evaporate, float, dissolve, sink exhibit these behaviours in combination, so too can the individual components of oils. Accordingly, the volatile components of oil up to C7 evaporate fast; the non-volatile persistent components (> C15) disperse naturally as droplets, dissolve to a limited extent, or sink to the seabed due to uptake of seawater and sediments. In fact crude oil can exhibit all of the behaviours exhibited by individual chemicals.

Spill size

Crude oil spills can be very large compared to chemical spills, because chemical tank sizes are small (3000 or even only 1250 m3 for the most dangerous substances) while those for crude oil can be as large as (30.000 m3) for wing tank or 50.000 for a centre tank.

Thus, crude oil spills easily release more of an individual chemical than could be released from a chemical cargo tank. For example, a crude oil could contain an aromatic fraction >30% which could contain more benzene than might be onboard a chemical tanker carrying benzene.

Comparison oil spills with chemical spills

While oil spills are much larger than chemical spills they are also occur more frequently. However, with many different chemicals being transported, the risk of any individual chemical being released is very much less than the risk of an oil release.

Oils can evaporate, float, dissolve or sink as their component chemicals dictate Oil spill response is focused on removing the floating oil from the water surface and on minimizing its spread. The large quantities that evaporate, naturally disperse or dissolve are welcomed as being beyond response. (Deep Water Horizon spill 2010). In fact enhance dispersion by dispersant application is one of the oil spill response options that reduce hazard by exposing it to enhanced biodegradation as dispersed droplets in the water column.

However, the floating part of an oil spill is treatable because it is visible by colour differentiation. In contrast, most chemicals are invisible on the water surface.

Again, released chemicals, naturally transferred to the air and to the water column should also be welcomed as untreatable being present in smaller amounts than oil components and just as likely to dilute therein to zero concentration. Yet again, floating, persistent chemicals, if visible with the help of remote sensing techniques, could be treated like oil spills. On the other hand, persistent floating chemicals that remain on the water surface for long enough and which are not more explosive/flammable or toxic than oil could be treated by oil response techniques.

Further to similarities, oil and chemicals could be flammable; Oil and chemicals could be explosive (gas plume); Oil and chemicals could be toxic in air and in the water column subject to exposure concentrations. However some chemicals are intrinsically more toxic than oils, while weathered oil is effectively less toxic but is sticky. As to oil components and chemicals, some are carcinogenic subject to exposure concentrations, while some individual chemicals can be; explosives (IMDG Class 1), reacting substance (IMDG Class 4) corrosives (IMDG Class 8) oxidizing substances (IMDG class 4) and radioactive substances (IMDG class 7), which is never the case for oil.

Chemicals can also be released while still inside a package (drum, container etc.), the more toxic substances being transported in stronger packages, which withstand exposure to the marine environment for longer without losing their content. However, releases from such sources are small and non-recoverable. Therefore, rather than concentrating on released chemicals it is better to focus on chemicals still recoverable in the package before the content is released through corrosion or severe weather.

This being best achieved by salvaging grounded ships, recovering (tank) containers with chemicals inside, and by recovering packages from the sea or the seabed.

Similarly, in incidents involving oil and bulk chemicals, the first priority is to save cargo and bunkers by lightened to another tanker.

Salvage techniques for oil and chemical spills should, therefore, be the focal point in dealing with incidents of both. Only the visible floating chemicals and those which sink to the seabed should be recovered as for oil, the latter being seen as a salvage job.

In fact we can speak about the chemical spill response as we can about oil spill response, the hazards and the behaviours being comparable unless the chemicals need further consideration in respect of some additional radioactivity, corrosiveness, reactivity, and, in case of IMDG class 1, explosion.