Eight Facts About Residential Sprinkler Systems - Understand How They Work

The installation of domestic / residential sprinkler systems in homes will extinguish the risk - and prevent the spread - of fire with its fast response. Fire sprinkler systems are designed to protect you and your family from terrible injury or loss of life. Fire can also severely damage or completely destroy the building in which it started, and any neighbouring buildings in close proximity to it.

Residential sprinkler systems are designed to fight fires at the early stage in their development thereby controlling the fire and allowing you to get to safety. The cost of installing a domestic/residential sprinkler system is nothing compared to the safety of you and your family.

Here are eight important facts about residential sprinkler systems:

1. Water Supply - There are three different ways of supplying water to domestic / residential sprinkler systems:
   • A direct connection is a dedicated system supplying water only and directly to the sprinkler system from the mains water supply.
   • A direct and indirect connection that serves both the residential sprinkler system and the domestic water supplies within the building and is controlled by a 'priority demand valve'.
     • If the sprinkler system is activated the priority demand valve ensures that all available water from the mains supply goes to the sprinkler system by closing off the domestic/residential supply.
   • A direct and indirect connection that serves both the residential sprinkler system and the domestic water supplies in the building but without a demand valve.
     • If the sprinkler system is activated water will still be available to the domestic/residential services in the building. It is important therefore to ensure that there is adequate water supply capable of providing the necessary 'pressure and flow rate' for the sprinkler system alone plus an additional flow rate of 25 litres/min for domestic dwellings, and 50 litres/min for residential properties (eg. apartment blocks).
   • Note: If using water from a stored water supply for residential sprinkler systems then it is absolutely important that the storage capacity of the cistern/tank is calculated and installed correctly to provide the right pressure and flow rate to the sprinkler heads (minimum 10 minutes for domestic and 20 minutes for residential properties) according to the manufacturers recommendation. Water can also be automatically pumped to the sprinkler system from a stored supply, a pressure tank or vessel, or an automatic booster pump which can draw water from either the water main or storage cistern/tank. However, the direct connection to the water main where possible is the preferred method. All domestic / residential sprinkler systems rely upon a continuous water supply at the right pressure to operate

 

1. Sprinkler System - There are three types of residential sprinkler systems:
   • The Wet-Pipe system is when the sprinkler system is permanently charged (filled) with water.
     • In the wet-pipe system, water is immediately discharged when the sprinkler heads bursts
   • The Dry-Pipe system is where the sprinkler system is charged with compressed air. This type of system is used in unheated buildings where the temperature may fall below 0^oC and cause water to freeze.
     • In the dry-pipe system there is a time delay as the compressed air is discharged first from the sprinkler heads before the water
   • The Alternate system is when the sprinkler system is filled with water in the summer months and works like the 'wet-pipe system', and filled with compressed air in the winter so works like the 'dry-pipe system'.

    

    

2. Pipe material - Generally copper and stainless steel pipework is used for domestic/residential systems, however, chlorinated polyvinyl chloride (CPVC) pipe is also suitable. The melting point of copper is around 1083^oC - this means copper pipework will not be adversely effected by the heat of a domestic fire.

    

    

3. System Control - A domestic/residential fire sprinkler system should have:
   • A stop-valve which should be locked in the open position to prevent accidental closure of the water supply to the sprinkler system.
   • Backflow protection to prevent contamination of the mains water supply, e.g, non-return/check valves, reduced pressure valve (RPZ), air gaps and ball floats.
   • A priority demand valve where appropriate.
   • A drain and test valve which should be fitted at the lowest point of the sprinkler pipework for testing and for draining the system. The outlet for the test valve should be equal to the smallest sprinkler in the system.
   • A bleed valve for purging air from the system should be fitted at the highest point(s) of the sprinkler system.
   • A water flow alarm that detects the flow of water in the sprinkler system and sounds an alarm. This can be a mechanically driven (water turbine) alarm, or an electrically operated flow switch which will operate an audio-visual alarm both inside and outside the building (these alarms must only be turned off by the fire brigade/department).

    

    

4. Sprinkler Head - Sprinkler heads are the water outlet points from a sprinkler system and they are designed to discharge water in a predetermined pattern. Different types of sprinkler heads produce different patterns.The sprinkler head operates when (depending on type) a predetermined critical temperature level has been reached. This critical temperature is known as the 'temperature rating' of the sprinkler.

    

   For example, in the UK the temperature rating for a sprinkler head under normal conditions will be 57^oC or 68^oC. However, the temperature rating should be at least 30^oC above the anticipated ambient room temperature and a rating within 79^oC to 100^oC if installed under glazed roofs where temperatures can be elevated in the summer months.

   There are two basic types of sprinkler heads:

   • Silica or Quartzoid Bulb, or
   • The Solder Strut type

    

   The silica or quartzoid type bulb is filled with liquid that expands at a predetermined temperature, this expansion breaks the bulb thereby opening the valve in the sprinkler head allowing the water to flow. With the solder strut type the valve is held shut by the solder strut, this solder melts at a predetermined temperature therefore allowing the valve to fall open and the water to flow.

    

5. Maintenance - The maintenance of residential sprinkler systems is the responsibility of the property owner. You must make arrangements for the system to be checked annually and tested by a qualified installer, and you should pay particular attention to the maintenance instructions provided to you by the installer.

    

    

6. General Concerns And Common Misconceptions: Domestic / residential sprinkler systems are not as common as they should be in households and as a result of this there are some misconceptions associated with sprinkler systems. For example:
   • Smoke alarms will provide enough protection - Although smoke alarms do save lives, they do nothing to extinguish a fire nor are they able to protect the young and elderly who may be unable to escape. A sprinkler system is by far the safer option
   • Sprinkler heads can accidentally go off - Sprinkler heads rarely go off accidentally. You have more chance of winning the lottery than having an accidental sprinkler discharge
   • In a fire all the sprinkler heads go off - No. Sprinkler heads go off individually as a direct response to a fire in that location, and almost all fires are controlled or put out by just one or two sprinkler heads. As a result of this quick response fire and water damage is significantly reduced as opposed to an unchecked fire that has to be dealt with by the Fire Brigade/Department
   • Sprinkler systems can cause a lot of water damage - Not as much as the Fire Brigade/Department. A typical residential sprinkler head will discharge 38 to 40 litres of water per minute compared to the 1000 litres per minute from the firefighter's hose. As a general figure a sprinkler system will use between 1/100th and 1/1000th of the water that is used by the Fire Brigade/Department. This is a big difference and in itself can turn a potential disaster into a less costly inconvenience

    

7. The Fire Triangle - A fire can only start and exist if three basic essential ingredients come together, and they are:
   • Fuel - something to burn
   • Air - oxygen for combustion
   • Heat - a naked flame, a chemical reaction, a spark, or radiant heat directly from the Sun

     This is sometimes referred to as the 'Fire Triangle'. If any one side is removed the fire will be extinguished as a result. All forms of fires are extinguished by using this basic principle.

     George Meates-Dennis is a heating engineer who provides easy-to-understand comprehensive information on home heating on his site Home Heating Systems and Solutions, including information on using green energy to heat your home.