HD Horizontal Sidewall Sprinkler is a small, thermosensitive, glass-bulb spray sprinkler available in several different finishes and temperature ratings to meet design requirements. Sprinkler is UL Listed and FM Approved. During fire, the heat-sensitive liquid in the glass bulb expands, causing the glass bulb to shatter. Water flowing through the sprinkler orifice strikes the sprinkler deflector, forming a uniform spray pattern in order to control or extinguish fire. Horizontal sidewall sprinkler is designed for installation along a wall or the side of a beam and just beneath a smooth ceiling.