Fire Sprinkler Installation

 
Fire sprinkler systems have several different parts that together make up a whole system.

The main parts are –

1. The design and hydraulic calcs
2. Water supply
3. Valves, gauges and pump (if required)
4. Distribution pipe work
5. Sprinkler heads
6. Audible alarms.
7. Certification and on going maintenance.

The actual on site installation can differ slightly depending on the particular property being protected and the requirements of the authority having jurisdiction (AHJ’s), however a system compliant to the current British standard BS9251:2005 must contain all of the above.

Each individual property can be looked at and specified on a case by case basis, if it is a requirement from an AHJ and/or Fire Service that fire suppression is to be installed then the first port of call should always be a member or employee of that authority that can give guidance on the fire risk assessment and what areas of the property are to be protected by the sprinkler system. The BS9251:2005 states under “Extent of sprinkler protection” that all parts of a dwelling should be protected with the exception of bathrooms with a floor area of less than 5m² and cupboards with a floor area of less than 2m². The AHJ may specify that either the whole property requires coverage or in some cases due to there being additional means of escape that only some parts (apartments/rooms) require coverage. A system that is to comply with BS9251 no matter if it has 6 heads or 600 heads must still contain all of the above numbers 1-7.

1. The design

The first thing a sprinkler system needs is its design and specification, after guidance has been given on what areas of a property are to be covered the designer can get to work. Taking into account the size and proposed occupants of the property the designer can determine whether a domestic or residential system is to be specified the main difference between the two being the water supply requirements. A domestic system may only require enough water and flow to supply any 2 heads at any one time for ten minutes where as a residential system may well require enough water and flow to supply 4 heads for 30 minutes running time. The flows and pressures required in either circumstance will determine things like pipe diameter, number of heads and the water tank and pump set specification. The design process is an essential and intricate process with various hydraulic calculations taking place to enable a correct and compliant fire sprinkler system being installed. Tank locations, pipe routes, and room sizes are just some of the different variables that make sprinkler system designs unique to each property.

2. Water supply

A domestic or residential sprinkler system requires water to suppress and in some cases completely extinguish a fire, the BS9251 gives clear guidance on the difference between domestic and residential water supply requirements. A domestic system should be capable of supplying at a minimum 60 litres per minute (LPM) through one head or 42 LPM through 2 heads at the same time in any one room. i.e.. Only one head in room = 60 LPM, 2 heads in any one room = 84 LPM for a time frame of not less than 10 minutes. A residential system requires a minimum of 60 LPM for one head or 42 LPM per head for up to 4 heads in any one room and for a running time of not less than 30 minutes. Clearly if stored water is to be used then the tank sizes can differ massively between domestic and residential. A mains supply can be used if the above flows and appropriate pressures can be achieved at a minimum at the most remote heads, if stored water is used then often most remote coverage increases the flows to the most favourable thus increasing the tank size further. Where a mains connection supplies both the sprinkler system and the property water supply then either a priority demand valve should be fitted or an increase of 25 LPM for domestic or for residential occupancies the design demand or 50 LPM which ever is less should be calculated into the water supply design.

3. Valves, gauges and pump

Various different valves and gauges are installed at different points along the sprinkler pipe network. A pressure gauge is normally installed at the start of the pipe network to enable monitoring of pressure from the water supply and ensure it meets the design requirement at all times (static and flowing). A back-flow prevention device must be installed where there is risk of contamination to the mains water supply and where appropriate an automatic priority demand valve that shuts off all water connections other than the sprinkler system connection in the event of fire. A test valve not smaller in diameter than the sprinkler pipe work should be installed at the most remote point and in some cases the most favourable point to enable flow and pressure testing appropriate to the design requirement and to enable the system to be completely drained of water. Pump sets should be installed to provide the necessary flows and pressures where mains supply fails to meet the design requirement, the pump should be separately electrically fused from after the meter but before the buildings main consumer unit. All electrical cabling used to supply power to the pump must be fire rated.

4. Distribution pipe work

Pipe work is required to supply water from the sprinkler system water supply to the sprinkler heads and test valves. H2O Fire Sprinklers Ltd uses a CPVC pipe that has been specifically designed for use in fire sprinkler systems, the pipe and fittings are made from a thermoplastic known as post-chlorinated polyvinyl chloride. This CPVC pipe will not sustain burning and when exposed to flash ignition temperatures will merely char, it does not drip or otherwise propagate a fire. During the design process the overall lengths and diameters of the pipe are calculated and the positions of the branches or ‘tee’s’ to the heads are established. If any of the pipe work is to be exposed in a room or area then it can be painted using only a water based paint to improve aesthetics, most of the time however the pipe can be concealed therefore painting is not needed. CPVC pipe that is exposed to freezing temperatures must be protected using either pipe lagging/insulation and/or trace heating, when using trace heating care must be taken to ensure the heating tape or cable does not come in direct contact with the surface of the CPVC. This can be achieved by first wrapping the pipe in a foil based insulation product then installing the trace heating along the pipe and covering all with a pipe lagging/insulation.

5. Sprinkler heads

There are several different manufacturers of approved domestic and residential sprinkler heads but it is essential that the same heads specified in the design are used during installation. Different makes and models of heads each have there own spray patterns and coverage and approved heads all come with documentation detailing approval listings and the heads specific characteristics during actuation. Domestic and residential heads come in either pendent or sidewall form and can be exposed, semi-recessed or concealed. They must have a quick response thermal sensitivity rating and be new to the installation, old or used sprinkler heads should not be reused in any installation. The heads will be activated by either a fusible link or a glass bulb, both only reacting when the specific temperature around the head is reached typically in the UK either 57°C or 68°C. Fusible sprinklers should be colour coded somewhere clearly visible on the head and glass bulb sprinklers colour coded by the liquid inside the bulb. During the design process the exact number, location and type of sprinkler heads will be established and no modification to these specifications should be installed before first consulting with the designer and the system design modified to comply with the standard.

6. Audible alarms

The sprinkler system should have an audible alarm which can be clearly heard from anywhere in the building activated by the flow of water from any point along the network of pipe and heads. A flow switch is generally used for this purpose and is activated by flow pushing the switch paddle inside the pipe work and either closing a circuit or opening a circuit (normally open or normally closed), this circuit is linked to a fire panel that detects the circuit change and signals the alarm via attached sounders. It is advised to consult the AHJ with regards to the audible alarms before installation as there may already be a separate alarm system specified i.e. smoke/heat detectors and there is scope to link existing alarms to the sprinkler system.

7. Certification and on going maintenance

After each completed installation a certificate of compliance must be issued detailing the approved installer, address where the system has been installed, BS9251 compliance and any deviations agreed by the AHJ. The sprinkler system should be inspected and tested by qualified engineers at least once a year and certified each year following successful testing. During testing the system pipe work and heads should be visually inspected for damage, leaks and obstruction, if there has been any change in the layout of the property post sprinkler installation action should be taken to ensure complete coverage and compliance. Alarms should be tested and a flow and pressure test carried out at the most remote valve attached to the pipe work for at least 1 minute to ensure the design flow and pressure requirements are achieved.


 

 

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