The technique, however, encourages expensive overdesign that results in unnecessary use of highly fire-resistant materials. In addition to controlling ignition by material selection, the designer may use active or passive fire protection measures, or both. Active techniques sense a primary ignition either manually or by automatic means to evoke a response. Automatic sprinkler systems are the most common. Where they are not desirable, substances that quench flames chemically may he used, for example, halon gases or dry powders.
Carbon dioxide is also effective, displacing the oxygen necessary to sustain fire.
Passive Fire Protection Passive techniques rely on built-in fire protection measures and do not require activation. Fire-resistant compartmentation of rooms, for example, is an important element of the fire protection of buildings. 7 Protective coatings . A very simple technique for protecting combustible material from unwanted ignition is to cover the surface with a non-combustible protection. Metal sheathing is used to protect some combustible insulation products.