Physical
The assessment of the physical properties of crude oils focuses on characteristics such as viscosity, density and pour point and how these change as oils weather at sea.

The evaporative losses of oils during weathering are also calculated, as is the degree of emulsification that occurs.

Weathering is undertaken using a MacKay Nadeau Steelman Tester (MNS), commonly referred to as the ‘MacKay Tester.’ The time period that oils are weathered for can range from an hour to upwards of weeks.

The physical properties of crude oils, and their character during the weathering process can be used to assess the amenability of the oils to various spill response options and to particular items of response equipment.

Chemical
Chemical characterisation can be used to quantify the presence of toxic hydrocarbons and other compounds present in crude oils that could contribute to the overall toxicity, and to fingerprint the oil for future monitoring purposes.

A range of compounds can be examined including, BTEX, polycyclic aromatic hydrocarbons (PAHs), phenolics, paraffinic hydrocarbons and sulphur compounds.

A range of biomarker compounds can be determined, including a range of hopanes, steranes, and isoprenoids. These compounds are resistant to oil weathering processes and are present in ratios which are characteristic of particular oils. The quantification of these compounds and the subsequent calculation of the various biomarker ratios effectively provide a ‘fingerprint’ of the oil. This can be of significant value during post spill assessment work.