Cleaning requirements between one grade and another must be strictly observed and all major charterers have their cleaning tables and special requirements. Various products have their own critical properties. Products may be colour critical or may go off flashpoint or must be lead free. Other factors to be considered include viscosity, octane number, wax and asphaltenes. Chemical carriers operate in a very specialised trade carrying a wide range of chemicals and also a variety of other petroleum products such as aromatics and unleaded gasoline. If any cargo, whether chemicals or otherwise, has specialised requirements which would not be within the knowledge of the owner of the normal type of vessel carrying such cargoes, the charterer has a duty to advise the owner of these special requirements. With chemicals, because of the range of types and because different manufacturers and chemical traders often have different names for the same chemical product, an owner needs to know exactly what the product is and not just its brand name. This is essential for all aspects of cargo care and handling and for the safety of the ship and personnel. However, liquid chemicals in bulk tend to be the province of a relatively small number of chemical producers and an even more limited number of ship operators operating vessels with the sophisticated hardware for carrying such chemicals and both sides have expert knowledge in their own fields. The terminals at which such cargoes are handled are similarly expert and well equipped. There are chemical carriers over 30,000 tons deadweight but the majority of chemicals shipped in bulk are carried in small quantities and so the average size of chemical carrier is small with suitable size tanks and good segregation capability. The nature and high unit value of such products justifies the cost of stainless steel tanks or expensive coatings, separate pumps and lines and extra safety features. The hazardous nature of many of these chemicals, which may be toxic to breathe or in contact with the bare skin, necessitates strict adherence to safe handling procedures and appropriate protective equipment must be worn.