Hazardous substances should be identified and marked accordingly Stores containing one or more substance of the same code should use this sign when cylinders are used for storing the substances The number indicates the type of equipment suitable for fire fighting and dispersing of spillages -In this case "2" indicates water fog - in the absence of fog a fine spray must be used The letters indicate the precautions to be taken: The letter "W" indicates there IS danger of violent reaction or explosion and full protective clothing must be worn and the spillage must be contained to avoid spillages from entering drains or water courses The letter "E" (the third part of the code) indicates that evacuation of people from the neighbourhood of an accident should be considered.