A fire sprinkler or sprinkler head is the component of a fire sprinkler system that discharges water when the effects of a fire have been detected, Nearly all fire sprinklers are composed of the same components: a sealing assembly or ‘plug’ that prevents water from escaping, a heat-sensitive element that allows water to flow at a given temperature, a deflector that distributes water effectively, and a frame. Fire sprinkler heads feature heat-sensitive parts – either a glass bulb or a fusible link – that cause them to activate at a specific temperature. When a sprinkler head has a glass bulb, that bulb typically contains a glycerin-based liquid.