This Aerospace Standard covers three basic types of cargo compartment fire detector instruments. Basic Types - Definition of: Type I: Carbon Monoxide, an instrument which will actuate an alarm signal when the concentration of carbon monoxide in air exceeds a specified value. Type II: Smoke Detector, Electronic, an instrument operating on the principle of smoke particles modifying the relationship between a light beam and electronic light sensor which will actuate an alarm signal when the concentration of smoke in air exceeds a specified value. Type III: Smoke Detector, Visual, an instrument which, by visual means, will show in a positive manner the presence of smoke when the concentration of smoke in air exceeds a specified value.