Smoke detectors are designed to identify a fire while in its smoldering or early flame stages. The most common
smoke detectors are spot type units, such as ionization smoke detector and scattering smoke detector, which are
placed along ceilings or high on walls in a manner similar to spot thermal units [4]. They operate on either an
ionization or photoelectric principle, with each type having advantages in different applications. For large open
spaces such as galleries and atria, a frequently used smoke detector is a projected beam unit [4]. This detector
consists of two components, a light transmitter and a receiver, that are mounted at some distance apart. As smoke
migrates between the two components, the transmitted light beam becomes obstructed and the receiver is no longer
able to see the full beam intensity. This is interpreted as a smoke condition, and the alarm activation signal is
transmitted to the fire alarm panel.