These signs should he used to convey “Do Not” type commands For example, to indicate that smoking is not allowed or that, where a particular material reacts dangerously with water or water should not be used to extinguish a fire. In the workplace they should be used to reinforce instructions prohibiting dangerous activities. Such instructions, however, should also form part of the employees training. Signs prohibiting an activity consist of a circular red band and single diagonal cross bar descending from left to right at an angle of 45 degrees. The background should be white with the pictogram indicating the nature of the command in black.