text: Sprinkler systems are intended to either control the fire or to suppress the fire. Control mode sprinklers are intended to control the heat release rate of the fire to prevent building structure collapse, and pre-wet the surrounding combustibles to prevent fire spread. The fire is not extinguished until the burning combustibles are exhausted or manual extinguishment is effected by firefighters. Suppression mode sprinklers, also known as Early Suppression Fast Response (ESFR) sprinklers, are intended to result in a severe sudden reduction of the heat release rate of the fire, prior to manual intervention.
  Control mode sprinkler systems are designed using an area and density approach. The building use and contents are analyzed to determine the level of fire hazard. The hazard is classified as light hazard, ordinary hazard group 1, ordinary hazard group 2, extra hazard group 1, or extra hazard group 2. After determining the hazard classification, a design area and density can be determined by referencing tables in the 13 National Fire Protection Association standard. The design area is a theoretical area of the building representing the worst case area where a fire could burn. The design density is a measurement of how much water per square foot of floor area should be applied to the design area.
  For example, in an office building classified as light hazard, a typical design area would be  and the design density would be  per  or a minimum of  applied over the  design area. Another example would be a manufacturing facility classified as ordinary hazard group 2 where a typical design area would be  and the design density would be  per  or a minimum of  applied over the  design area.
  After the design area and density have been determined, calculations are performed to prove that the system can deliver the required amount of water over the required design area. These calculations account for all of the pressure that is lost or gained between the water supply source and the sprinklers that would operate in the design area. This includes pressure losses due to friction inside the piping and losses or gains due to elevational differences between the source and the discharging sprinklers. Sometimes momentum pressure from water velocity inside the piping is also calculated. Typically these calculations are performed using computer software, but before the advent of computer systems these sometimes complicated calculations were performed by hand. This skill of calculating sprinkler systems by hand is still required training for a sprinkler system design technologist who seeks senior level certification from engineering certification organizations such as the National Institute for Certification in Engineering Technologies (NICET).
  Sprinkler systems in residential structures are becoming more common, as the cost of such systems becomes more practical and the benefits become more obvious. Residential sprinkler systems usually fall under a residential classification separate from the commercial classifications mentioned above. A commercial sprinkler system is designed to protect the structure and the occupants from a fire. Most residential sprinkler systems are primarily designed to control a fire for a sufficient time to allow for the safe escape of the building occupants. While these systems will often also protect the structure from major fire damage, this is a secondary consideration. In residential structures, sprinklers are often omitted from closets, bathrooms, balconies, garages and attics because a fire in these areas would not usually impact the occupant's escape route.