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:: بهداشت ، ایمنی و محیط زیست در محیط کار ::  

بیان مطالب و مقالات،فیلم و پوستر های مربوط به رعایت قوانین بهداشت،ایمنی و محیط زیست در محیط کار



 

 

Fire Detection Systems & Fixed Installations

 

 

 

 

Firefighting & Rescue Training

 

 

 

for

The National Petroleum Company-Iran

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The Fire Service College

Moreton-in-Marsh

Gloucestershire UK

 

 

FIRE DETECTION SYSTEMS AND FIXED INSTALLATIONS

 

 

 

Contents                                                                                                               Page

 

 

 

1          Key Information

 

1.1       Aims & Learning Outcomes                                                                        3         

 

 

2          Primary Information

 

2.1       Principles of automatic fire detection                                                         4

 

2.2       Types of detector                                                                                          4

 

2.3       Function of sprinkler installations                                                            4  -  5

 

2.4       Types of sprinkler systems and actuating heads                      5  -  6

 

2.5       Practical firefighting considerations                                                       6  -  7

 

 

3          Supporting Information

 

3.1       Reasons for AFD failure                                                                              7

 

3.2       Types of product detected by AFD and the                                           7  -  18

            principles of detection used

 

3.3       Installation and design of sprinklers                                                       19  -  23

 

3.4       Types of sprinkler heads                                                                              23

 

3.5       Rising mains                                                                                             24  -  25

 

3.6       Types of Drencher Systems                                                                        26

 

3.7       Other extinguishing agents                                                                          27

 

 

 

 

 

 

 

 

 

 

                         FIRE DETECTION SYSTEMS AND FIXED INSTALLATIONS

 

1       KEY INFORMATION

 

1.1       AIMS AND LEARNING OUTCOMES

 

 

The aim of this session is to provide students with an understanding of fire detection and fixed fire protection systems found in buildings and firefighting considerations needed when dealing with such systems.

 

 

 

At the end of the session the student will be able to:

 

·        State the function of a fire detection system.

·        State the most common types of detectors found.

·        State the function of sprinkler installations.

·        State the three main types of sprinkler systems.

·        State the two main types of sprinkler head.

·        State practical firefighting considerations. 

 

 

 


 

FIRE DETECTION SYSTEMS AND FIXED INSTALLATIONS

 

2   PRIMARY INFORMATION

 

 

2.1    PRINCIPLES OF AUTOMATIC FIRE DETECTION (AFD)

 

The function of fire detectors is to detect one or more changes in the protected environment indicating the development of a fire condition. 

 

They may operate:

 

·        When the invisible products of combustion are being released;

 

·        When smoke is being produced:

 

·        When the temperature in the vicinity of the fire rises rapidly or reaches a pre-determined figure.

 

 

 

 

2.2    TYPES OF DETECTOR

 

·        Smoke Detectors  -  Ionisation or Optical

 

·        Radiation

 

·        Heat  -  fusible, expansion or electrical

 

The choice of type of detector system has to be based on the type of risk to be protected, the circumstances surrounding that risk, reliability, robustness and lastly, economics.

 

 

2.3    FUNCTION OF SPRINKLER INSTALLATIONS

 

Automatic water sprinklers are the most widely used fixed fire installation.  The system consists of a series of sprinkler heads fitted at intervals, and mounted on a system of pipework installed beneath the ceiling of the area to be protected (depending on the type of risk and installation).

 

Each sprinkler head is capable of opening individually in response to hot gases rising from a fire.  On opening, a spray of water is discharged onto the fire below.


 

Function

 

A sprinkler system is designed and installed to:

 

·             Detect a fire

 

·             Suppress a fire

 

·             Give an audible warning of the fire outbreak

 

·             Restrict the spread of fire.

 

 

2.4    TYPES OF SPRINKLER SYSTEMS AND ACTUATING HEADS

 

Sprinkler Systems

 

There are three main types:

 

Wet System

 

The pipes are kept permanently filled with water.  Used for all locations except where freezing temperatures are likely to occur.

 

Dry System

 

The pipes are normally charged with air under sufficient pressure to hold back the incoming water pressure, until a sprinkler head actuates and pressure is released.

 

Alternate System

 

Usually found in premises where the ambient temperature varies.  It may be kept wet during the summer, then dry during the winter months.

 

 

Sprinkler Heads

 

There are two main types of sprinkler head:

 

Fusible Solder

 

Consists of a metal link held together with fusible solder.  At a pre-determined temperature, the solder melts and the link collapses, water flows from the head onto the distributor plate and falls as a spray.

 

Quartzoid Bulb

 

The valve is held on its seating by a small glass bulb.  The bulb is sealed and contains a quantity of liquid and a small air bubble.  As the temperature rises, the liquid expands until at a pre-determined temperature, the bulb shatters and allows the water from the system to be discharged.


 

 

Fixed Automatic Gaseous Systems

 

These systems are similar to water sprinkler systems, in which they incorporate a detection system, which is linked to an alarm, also activating discharge of the gas into the protected area.  There are two main types of gases used in these installations, they are Carbon Dioxide (CO2) and Halogenated Hydrocarbons (Halon).

The widespread use of this type of installation means that you will inevitably encounter them at some incidents.  They may have operated before your arrival, either due to a fire, accidentally or even maliciously.  In this instance you should be able to recognise that a system is installed, that it has operated and the extent of the area affected.  You should also be aware of the hazards the gases pose and the steps necessary to ventilate the area safely.

 

 

2.5    PRACTICAL FIREFIGHTING CONSIDERATIONS

 

         Initial actions on arrival at a fire involving sprinklered premises

 

On arrival at the premises, a member of the crew is to be sent to the sprinkler control room.  Once access is gained, they must ensure the following:-

 

·             That the main stop valve can be opened if found closed.

 

·             That the valve is not then closed, unless on the strict instructions of the Incident Commander.

 

         Action to be taken during a fire at a sprinkler installed building

·        If a fire service inlet is provided (see Supporting Information) then an established water supply, via fire service appliance, should be connected to support the sprinkler system

·        Do not turn off the sprinklers, so that the fire may be tackled with hose-reels.

·        If additional water is required, it should not be taken from the water main supplying the sprinkler system.

·        Ensure careful examination of the fire incident and scene to ensure it is fully extinguished.

·        If the water supply is unable to be turned off after the fire has been extinguished, then to facilitate damage limitation of water within the premises, delivery hose may be secured to the sprinkler head, facilitating water to be directed out of the premises.

·        The sprinkler system should be reset by the occupiers of the premises, on consultation with a sprinkler engineer or installer.


 

FIRE DETECTION SYSTEMS AND FIXED INSTALLATIONS

 

3   SUPPORTING INFORMATION

 

3.1       REASONS FOR AFD FAILURE

 

When a fire occurs in an area protected by an AFD, after ignition, the fire will grow, probably slowly and irregularly at first, but then at an accelerating rate.

 

Generally products of the fire will be transported to the detector and they will be 'checked' against the prevailing environment.  When the detection system is sufficiently 'sure' that what it is detecting is not an 'environmental fluctuation' it will 'decide' that a fire exists and raise the alarm.  All this appears straightforward but there are many ways in which an AFD system could fail.

 

For example:

 

            Failure to Operate;

 

 

o       Wind or draught fluctuations causing a false temperature reading.

 

o       Obstructions to smoke travel, heat or flame radiation preventing the detector from acting quickly enough.

 

o       The detector may be unable to detect the products of that particular fire.

 

o       A fault in the system may have made the detector inoperative.

 

o       The system may be switched off for servicing (more strictly a maintenance system failure).

 

False Alarms;

 

 

o       In certain areas at certain times insects may trigger false alarms.

 

o       Dust from work processes.

 

o       A detector is calibrated too sensitively for the occupancy of the premises.

 

o       Thunder/lightening storms.

 

 

 

3.2    TYPES OF PRODUCT DETECTED BY AFD AND THE PRINCIPLES OF DETECTION USED
 Types of products

 

Products from fire will travel either by radiation or by physical movement of the atmosphere.  Radiation is fast-moving in straight lines, physical movement is slower but more flexible.  A broad term used for physical transport is 'mass transport' and it is by this that most smoke and heat detectors work.  Flame detectors use radiation.

 

Smoke

 

Smoke consists of a suspension of solid or liquid particles in a gaseous medium.  Its constituents will depend largely on what is burning and how it is burning.  Particles in smoke vary in size from about 1 nanometre to 10 micrometres (see footnote).  As smoke is produced the particles coagulate into larger and larger solids until, eventually, they could precipitate out.  The process of coagulation depends on the source and speed of the combustion.  Slow-burning fires tend to produce larger particles and this, in itself, can have a significance in the choice of detector for a particular risk.

 

FOOTNOTE:  (A micrometer is one millionth of a metre and a nanometre is one thousandth of a micrometre).

 

The optical properties of a particle will affect light by absorption or refraction.  Depending on its constituents, smoke can appear almost white or any shade from that to sooty black.  These effects are due to how much light is being absorbed or 'scattered' by the particles.  This is another aspect, which will affect the choice of detector.

 

Radiation

 

All objects give off thermal radiation.  As the temperature of an object increases, the radiation it emits increases in intensity and changes colour (from red heat to white heat).  Flames also emit radiation, the wavelengths depending on what is burning and how much oxygen is available.

 

These wavelengths, however, can be absorbed by background interference, either natural or man-made.  A major natural interference source is, of course, the sun.  Infrared radiation from the sun is, generally, more powerful than infrared from a fire, so special design has to be incorporated in flame detectors to account for solar radiation.  The usual method is to design the detector to detect flame flicker, This, however, can be simulated by sunlight through the moving branches of a tree, reflection from water surfaces etc, and, where this can happen, it must be modulated out.  External interference may come from welding or tungsten lamps and thought must be given to these sources of false alarms.

 

Ultra-violet radiation is also given off by a fire, and again one natural source of UV radiation is the sun.  However, the ozone layer does filter out a certain band of UV wavelengths and it is this band that can be used by detectors if they are not designed specifically to combat UV radiation.

 

Another source of natural UV radiation is lightning but this is of such brief duration that detectors are easily able to disregard it.  Again, welding and tungsten lamps are examples of external UV radiation and the same precautions need to be taken as for infrared.  Any flame detector needs to 'see' its protection area clearly because, as stated before, radiation travels in straight lines.  Any obstruction, however temporary, could severely limit a detector's capability.

 


 

Heat

 

Heat is transmitted in three ways:  conduction, convection and radiation. Heat detectors rely primarily on convection.

 

The amount of heat produced by a fire depends on the source and speed of combustion, whilst the speed at which it is transmitted to the detector will depend on the ambient conditions.  This latter factor is a particularly important consideration in choosing the most suitable detector. The size and shape of the room, or space, will also need to be taken into account.

 

Since heat, generally, takes longer to evolve in significant quantities than either smoke or radiation, it should not be used as the sole basis for fire detection in situations which demand a high speed response e.g. where there is a life risk.

 

 

Conclusion

 

It can be seen from the foregoing that the correct choice and siting of detectors for the particular risk is essential.  This part describes some of the various systems used.  It examines the principles of the three main types, i.e. smoke, heat and radiation, and describes how these principles are applied to examples of the many current models available.

 

 

Smoke Detectors - Ionisation smoke detectors  -  The Theory

 

What is 'ionisation'?  An atom is made up of protons, electrons and neutrons, the protons and electrons being in balance. If the atom is subjected to radiation from a radioactive source some electrons become detached.  As a result the atom becomes positively charged (i.e. it has more protons than electrons); the 'free' electrons quickly link up with other atoms, which become negatively charged (i.e. more electrons than protons).  These 'new' atoms are called 'ions' and the process that creates them is called 'ionisation'

 

If the atoms of air in a container are subjected to radiation, ionisation will take place in this way, and the ions will move about haphazardly.  If we then introduce a positively charged plate and a negatively charged plate to the container a more orderly and predictable movement of ions will take place; the positive ions are attracted to the negative plate and the negative ions are attracted to the positive plate. This forms the basis of the ionisation detector.

 

The movement of ions between the plates in the chamber reduces the resistance of the air so that a small electric current flows in the external circuit.  The current is small and is amplified so that it can be readily monitored.

 

In a fire condition, smoke particles entering the chamber become attached to the ions because of electrostatic attraction and slow their movement.  This causes a reduction in the current flow.  When the current falls below a predetermined level the amplifier senses it and initiates an alarm.  That is the basic concept of the ionisation detector -- in practice it is a little more sophisticated as can be seen from the following paragraphs.


 

 

The practice

 

An advantage of the ionisation detector is its sensitivity in the early stages of fire when smoke particles are small.  Because of this sensitivity care must be taken in the siting of the detector heads.

 

In some locations such as a garage or kitchen the products of combustion could be present in 'non-fire' conditions.  Siting ionisation detectors in these areas could result in repeated false alarms.

 

It is particularly important that the detectors are not placed near a ventilator or fresh air inlet where a current of clean air can pass over them and inhibit their speed of reaction in a fire situation.

 

Most types of ionisation detector head are designed to be mounted on the ceiling and usually provide adequate coverage for 100 square metres of floor area.  With slight modifications they can be fitted in air ducts for air-cooled machinery and thus give early warning of possible fire damage to intricate and expensive equipment.

 

Ionisation detectors with single chambers have been produced using a capacitor as a replacement for the second (inner) chamber.  They have not been widely used however and the two-chamber type described above is the one most commonly found.

 

The radioactive source used in most ionisation-type detectors is Americium 241, which emits alpha particles and low-energy gamma rays.  It has been proved that these sources present no danger to people even when damaged by fire.

 

 

 

                                  Ionisation type during fire situation

 


 

Optical detector

 

While the ionisation detector responds to the invisible products of combustion the optical detector, as its name implies, reacts to the visible products of combustion, i.e. the particles of carbon and other chemicals which give smoke its characteristic appearance.  An optical detector has two important components, a light source and a photoelectric cell.  It is the amount of light falling on the photoelectric cell, which is the critical factor in the operation of the optical detector.  Some optical detectors are designed so that, in a fire situation, MORE light is thrown onto the photoelectric cell.  These are called the 'light-scatter type'.  Others are designed so that LESS light is thrown onto the photoelectric cell in a fire situation.  These are called 'obscuration type'.

 

The light scatter type

 

 

 

The practice

 

The 'light-scatter type' of optical detector is the more common of the two types previously mentioned. 

 

Smoke entering the detector through the smoke chamber scatters light onto the photoelectric cell.  The small electrical charge produced by this is amplified and actuates an alarm relay.  This raises the alarm and also switches on the indicator lamp on the detector, thus identifying the head that has operated.  Should there be a failure in the power or light supply in the detector, a special relay will signal this at a central point and also illuminate the indicator lamp on the detector head; an actual 'fire' signal is not produced in these conditions.

 

Obscuration type

 

The theory

 

The obscuration type optical detector works on the reverse of the principle just described -- the light is obscured by the smoke.  The resultant reduction in the intensity of light falling on the photo-electric cell causes an alarm signal to be raised

 

The practice

 

 This type of optical detector can be particularly useful for the protection of large areas.  It is possible with only one detector to throw the light beam up to 100 metres with a sensitivity of about 7 metres on either side.  The light source and lens will be housed at one end of the protected area with the photo-electric cell at the opposite end. The principle can also be used in individual detector heads on a similar basis to the light-scatter type.

 

Light emitting diodes (LED’s) are now widely used as the light source in optical detectors instead of tungsten filament lamps.  They consume very little current and provide a more efficient and longer lasting source of light.

 

 

Sampling detector

 

Sampling detectors comprise probe tubes located in the fire-risk zone and they are connected to a monitoring unit, which contains the actual smoke detector.  This monitoring unit continuously samples the atmosphere in the protected zone by drawing air in through the small holes in the probes either by fan or by using a differential in pressure between two probes.  The air is then passed through the detector chamber, which is set to operate when any combustion products reach a certain level.

 

This type of detector is mainly fitted into ducts and must be positioned correctly to operate at maximum efficiency. 


 

Conclusion

 

 The detection of fire by smoke detectors is dependent on a number of factors, e.g. smoke concentration, size, and shape of smoke particles. The wide variety of smoke produced by different materials complicates the situation.  In the early stages of most fires the smoke particles are small, but as the fire develops they tend to conglomerate to form larger particles.

 

The ionisation detector is generally more sensitive to the smaller, normally invisible, smoke particles.  This makes it particularly useful in the early stages of relatively clean burning fires (e.g. of wood and paper).  It will not, however, always operate in the presence of 'cold' smoke.  The optical detector is more efficient in situations where the protected risk is likely to give rise to dense smoke (i.e. larger particles) in the earlier stages of a fire as in some burning plastics.

 

In the main earlier detection can be obtained with a smoke sensitive system than with a heat sensitive one. 

 

 

Siting Smoke Detectors

 

Factors that should be considered are:

 

        i.            They should be sited so as to give the earliest possible warning of fire and allow the occupants the maximum amount of time to escape

 

      ii.            Where smoke will initially gather when a fire happens.

 

    iii.            Allowance for convection and ventilation air currents.

 

     iv.            Siting them in areas which are appropriate, ie not areas where products of combustion and dust are present in non-fire conditions.


 

 

Radiation Detectors

 As well as producing heat fire releases radiant energy in the form of:

 

·        Infra-red radiation

 

·        Visible light

 

·        Ultra-violet radiation.

 

These forms of energy travel in waves radiating from their point of origin and radiation detectors are designed to respond to this radiation.

Obviously the use of the visible light band to activate a detector would present many problems because the detector would not be able to differentiate between the various legitimate sources of visible light and those created by a fire. 

 

In practice therefore these detectors are designed to respond specifically to either:

 

·        Infra-red radiation

 

·        Ultra violet radiation

 

Using a device which is sensitive to one of these sources.

 

Infra-red detector

 

 

The basic components of the infrared detector are shown above.

 

It is obviously necessary to protect the photoelectric cell and electrical components from dirt and moisture but the protective covering must allow the infrared radiation to pass through it.  Not all material is transparent to infrared but quartz is and is commonly used as the protective shield in these detectors.  The lens and filter will allow only infrared radiation to fall on to the photoelectric cell.  On detecting the radiation, the cell will transmit a signal to the filter/amplifier.

 


 

Infra-red Radiation

 

Flame, however, may not be the only producer of infrared radiation in the protected area; there may be a limited number of other producers e.g. sunlight or heaters, but

flame has a distinctive flicker, normally in the frequency range of 4Hz-15Hz.  The function of the filter/amplifier, therefore, is not only to amplify but also to filter out signals not in this range.  If the signal is in this range (4Hz-15Hz) it is then fed to the integrator/timer, which will activate the alarm circuit only if the signal persists for a pre-set period (normally 2-15 secs).  While this small delay may slightly off-set the quick response time of the detector, it is necessary if false alarms are to be kept to a minimum.  Once any signal is rejected the detector goes back on standby.

 

Infrared detectors can provide rapid detection in risk areas where flame is likely to develop at an early stage of combustion.  This is because of the almost instantaneous transmission of radiation.

Unlike smoke or heat detectors which can only be used indoors, the infrared detector can be equally efficient inside or out.  This is because it simply needs to 'see' the flame, whereas smoke or heat detectors have to rely on ceiling or walls to direct combustion products to the sensing device.  This ability makes the infrared detector (especially the scanning type) useful for protection of open storage areas, aircraft maintenance areas (both inside and out) etc.  However, some problems occasionally arise due to sunlight, rippling pools of water, welding etc. but modern detectors incorporate integrated circuits which can filter out these potential false alarms.


 

Heat Detectors

 

Heat detectors are designed to detect fire in its more advanced stages when the temperature in the protected area starts to rise.  Given that the effects of heat are easy to observe it is not surprising that heat detectors were the earliest form of detector to be developed.

 

The effects of heat which provide the basic operating principles for heat detectors are:

 

·        Melting (or fusion) in metals or plastics

 

·        Expansion in solids, gases and liquids

 

·        The electrical effect.

 

Heat detectors using fusible alloys

 

The theory

 

This type of detector is based on the fact that certain metal alloys and plastics melt at relatively low temperatures, the general range available being between 55øC to 180øC.  As the metal/plastic used determines the temperature at which the alarm will sound it will be chosen for the type of risk to be protected and the normal ambient temperature in that protected area.

 

 Heat detectors using the principle of expansion

 

Expansion of a single metal strip

 

A piece of metal will expand when heated; this expansion is most noticeable in a length of metal with its ends unrestrained.

 

If both ends of the metal are secured to a solid base and the metal is then subjected to heat the effect of the expansion is to cause the metal strip to bow If contacts are added, as shown in the diagram, the principle can be used in a detector to complete an electrical circuit when a predetermined temperature is reached.


 

 

Expansion of a bi-metallic strip

The bi-metallic strip is a development of the basic principle of metal expansion due to heat and makes use of the fact that, when heated, some metals expand at a greater rate than others.

If these two metals are bonded together to form a bi-metallic strip and then subjected to heat the strip will bend to accommodate the differing rates of expansion.

 

A simple example of the use of a bi-metallic strip as a heat detector.

 

Power supply

 


 

The advantage of a bi-metallic strip over a single metal strip is the greater movement resulting from a given rise in temperature.


 

Advantages and disadvantages

 

The main advantage of detectors operating on the expansion-of-metal principle is that they suffer no damage from operation and are generally self-resetting.  Where there is likely to be a large but gradual variation in ambient temperature during normal processes, the 'rate-of-rise' detector has the advantage of giving a quick response to any sudden abnormal temperature rise whilst minimising the number of false alarms.

However, where a rapid rise in temperature is a normal result of work processes, the fixed temperature detector is to be preferred.  In this type of situation it is less prone to false alarms than the 'rate-of-rise' type.

 

A fixed temperature detector will take longer to respond in a cold area than in a warm one.  This is because of the longer time needed for the ambient temperature to reach the operating temperature of the detector.  A 'rate-of-rise' type on the other hand will take the same time to respond in both situations -- it reacts to the relative rise in temperature.

 

 

 

Expansion of Liquids - Sprinkler Systems

 

The liquid filled quartzoid bulbs used in sprinkler systems are probably the most common form of heat detector operating on the expansion of liquid principle.

 

Many of the detection systems discussed in these notes are, in practice, linked with sprinkler or other extinguishing systems.  Once activated the detector not only raises the alarm but also causes the sprinkler system to release extinguishing agent into the affected area.

 

This is covered in more detail later in this note.


 

3.3    INSTALLATION AND DESIGN OF SPRINKLERS

 

Installation and design requirements

 

There is currently (August 2000), no national legislation compelling owners of property to install a sprinkler system in a building.  Under local legislation in some areas, plans of certain types of building will only receive approval if adequate provision for sprinklers is made.  Insurance companies encourage the installation of sprinkler systems by giving substantial reductions in premiums for property so protected.  They, through the Loss prevention Council (LPC), lay down the minimum standards necessary.

 

Sprinkler systems are designed in accordance with:

 

(i)  British Standard 5306 Part 2

 

(ii)  LPC rules for Automatic Sprinkler Installations.

 

Sprinkler systems are used to protect a very wide range of premises and there are very few buildings which are totally unsuitable for sprinklers.  Where parts of a building contain materials of processes for which water would be unsuitable as an extinguishing medium, these areas can be isolated by fire resisting construction and the remainder protected by sprinklers.

 

Details of particular supplies

 

  • Town mains

 

The mains water supply must be fed from both ends by mains, each of which must be capable of sustaining the required pressure and flow.  The main at each end must not directly be dependent on a common trunk main in the town main system, and this must be fed from more than one source.  The main must be capable of furnishing, at all times of the day and night, the minimum pressure and flow requirements for the appropriate category of risk.

 

  • Suction and booster pumps

 

If a water supply is available with no head or only under limited pressure, a pump may be used to feed water into the installation at the required pressure.

 

  • Elevated private reservoir - minimum supply capacity

 

This is defined as similar to a ground reservoir but situated at a higher level than the premises to be protected.  Certain conditions regarding capacity must be complied with before this type of reservoir can be used as a source of supply to a sprinkler installation.

 

  • Gravity tank

 

A gravity tank is defined as a purpose built container.  It is erected on the site of the protected premises at such a height as to provide the requisite pressure and flow condition at the installation valves.


 

Controls

 

·        Stop valves

Typical layouts of the various systems have already been described.  The main stop valve (MSV), fitted to all installations, enables water to be cut off after the fire has been extinguished in order to reduce water damage.  It also perimeters any actuated heads to be removed and replaced.

 

MSV is of the gate valve type, operates by hand-wheel and must be right-handed (i.e. must close by rotating clock-wise).  The hand-wheel must be marked to show the direction of operation to close the valve and some indication given of whether it is open or shut.  To prevent unauthorised interference and guard against accidental closure,  MSV’s are secured in the fully open position with a strap which can be cut in case of necessity.  it must be protected from frost.

 

The BS/LPC Rules require that a plan showing the position of the MSV’s must be placed within the building where it can be seen easily by firefighters.  Where installations are arranged in zones e.g. for life safety, the plan must indicate the zone control valves.  In addition a location plate must be fixed to an external wall as near to the MSV as possible.  It must bear a legend in letters not less than 35mm in height, preferably in white on a black background.

 

 

 

Where possible the MSV must be placed close to an entrance to the premises, preferably the main entrance, in such a location as to be always readily visible to authorised persons.

 

·        Alarm Valve

This valve lifts when water enters the sprinkler system pipes, allowing water to pass to the alarm gong, causing activation.  This valve also acts as a no-return valve from the system pipes to the supply connection.

·        Alarm Stop Valve

Normally kept open, but can be shut to silence the alarm gong during an incident.


 

·        Test and Drain Valve

Used for testing the water flow of the installation and to drain the system when necessary.

There are three main gauges to sprinkler systems:

o       One to show the pressure in the installation above the mains stop and alarm valves.

o       One to show the pressure of the supply below the main stop valve.

o       One which shows the pressure in the town mains.

 

·        Fire Service Inlet

Where sprinkler installations are fed from water sources of a limited capacity, such as a pressure or gravity tank, a fire service inlet connection must be fitted.  This enables the Brigade to provide water to the sprinkler system using fire appliance pumping equipment.

 

·        Alarm Devices

 

Every installation must be fitted with an approved water motor alarm, located as near the alarm valve as practicable.  The alarm is sounded by a hammer rotated by a small pelton wheel (more generally called a turbine) actuated as water flows into the system.  The pelton wheel is fitted inside the building, and is connected by a spindle hammer which, with the gong, is positioned outside the building.

 

 

 

The gong is usually placed above and close to the doorway that leads to the main stop valve.  Where more installations are fitted to that same building, each has its own gong.  Each gong must be numbered in bold figures to correspond with the number painted on the controlling valves of each installation.  The flow of water to the turbine may also actuate an electric alarm at central point and so give immediate information as to the particular installation that has operated.


 

There are four causes which may produce a ringing of the alarm gong;

 

(i)  the opening of a sprinkler head;

 

(ii)  the opening of a drain or test valve;

 

(iii)  damage to any part of the installation which leads to an outflow of water;

 

(iv)  a rise in the pressure of the water being supplied to the installation, thus lifting the alarm valve and allowing water to pass to the turbine operating the gong.

 

Electrically Operated Alarms

 

Approved water flow alarm switches may be incorporated in the system pipework above the alarm or dry pipe valve to indicate on a central control panel the particular section of the system that is operating.  Electric alarm pressure switches, operated at either an increase or fall in pressure, they are permitted on a system to operate an auxiliary warning device, but are not acceptable as a substitute for the standard water motor alarm device already referred to.


 

 

3.4       TYPES OF SPRINKLER HEAD

 

Bulb type

 

In the bulb type head , a small barrel or cylinder made of special glass is used to hold the water valve in place.  This bulb is hermetically sealed and contains a quantity of liquid and a small bubble.  As the temperature rises, the liquid expands and the size of the bubble decreases until it disappears.  A further rise shatters the bulb, breaking it into small pieces so that it cannot obstruct the water flow, and so opens the head.  In spite of this ease of fracture, the strength of the bulb is such that it can withstand any pressure applied to the pipe.  In the pressure destruction test, it is the metal parts of the head that fail first.  The gasket (2) is held in position by the bulb (1) which rests at one end upon a hollow in the valve cap (3) which in its turn is held in place by a valve assembly (4) and a spring (5) in order that this will throw the parts clear.  At the other end the bulb is held in a conical metal cup (6).

 

 

By adjusting the composition of the liquid and to some extent the size of the bubble, the bulb type head can be set to operate at any desired temperature.

 

Sprinkler rating                      Colour of bulbs

 

57 0 C                                     Orange

68 0 C                                     Red

79 0 C                                     Yellow

93 0 C                                     Green

141 0 C                                   Blue

182 0 C                                   Mauve

204 to 260 0 C                        Black

 

Firefighters may also find in certain occupancies, a sprinkler fitted with a very thin bulb.  This is described as a ‘fast-response’ type but operates in the same way as the conventional quartzoid bulb. 

 

 

 

3.5       RISING MAINS

 

This consists of a pipe installed vertically in a building with a fire service inlet connection at the base, and outlets situated at levels throughout the building.

 

There are two types of main:

a.  Wet Risers

These risers are kept permanently filled with water.  A storage tank will be fed by the town water supply, the tank feeds the riser by two automatic pumps.  Wet risers will be necessary in buildings over 60 metres in height, as fire service pumps are not able to achieve the quantities and pressure of water required at this height.

Each of the two automatic pumps feeding water from the mains to the riser, should be capable achieving the required pressure and have an independent power supply.

Booster pumps may be fitted at intermediate levels, along with pressure regulators, to ensure that any excessive pressure is not transmitted to the delivery hose.

Water supplies must be capable of supplying a minimum of four 13mm jets of 2.5 bar, at the highest outlet.

b.  Dry Risers

These are, as their name suggests, dry pipes with outlets at various levels.  The charging of these pipes is by Fire Service Pump only, for which an inlet is situated at the base.  Dry risers are found in buildings over 18 metres, but less than 60 metres in height.

The riser may be either 100 or 150mm in diameter.  100mm risers will have a double inlet and a single outlet per level.  150mm risers will have four inlets and a double outlet per level.

An air valve may be fitted at the highest point of the riser, this allows air to escape as the main is charged.  This air valve also allows the ingress of air during draining thus preventing a vacuum forming.  The drain valve fitted beneath the inlet is 25mm diameter, and allows drainage of the system after use.

Inlet boxes are usually fitted with a glass front and marked with the words ‘DRY RISING MAIN’ or ‘DRY RISER CONNECTION’.  The face of the inlet box will be usually be made from wired glass, or other breakable material, this enables, should a key not be provided locally, the panel to be broken and the spring lock unlocked from the inside.


 

 

Outlets

Each outlet should be fitted with a standard fire service female coupling, and fitted with a handwheel that is marked with ‘open’ and ‘shut’ directions.

          Outlets will normally be sited at the following locations:

·             In a firefighting staircase lobby

·             In an enclosed staircase, forming part of an exit

·             In a fire lift enclosure

Advantages Of Wet And Dry Risers

·             Enables a rapid attack on fires on upper floors, without the loss of time that is entailed by laying a line of hose through and up a building.

·             Obviates a risk of water damage, which might occur if a hose line was to burst in a part of the building, not affected by the fire.

·             The riser has a greater capacity than standard 70mm hose.

 


 

 

3.6       TYPES OF DRENCHER SYSTEMS

 

While a sprinkler system protects a building from internal fire, drenchers are placed on roofs and over windows and external openings to protect the building from damage by exposure to a fire in adjacent premises.

 

A drencher system is comprised of water-heads somewhat similar to those of sprinklers; these may be sealed or unsealed (open-drenchers), but in the latter case the water is turned on manually.  In a few instances drenchers may be controlled by quick-opening valves operated by loss of air pressure in a detector line system.

 

 

Drenchers are of three main types:

 

(a)  roof drencher

 

(b)  wall drencher

 

(c)  window drencher

 

 

Roof drenchers

 

Roof drenchers have a deflector rather similar to that of a sprinkler head.  From the roof ridge they throw a curtain of water upwards which then runs down the roof.  All parts of the roof and any skylights, windows or other openings must be protected.

 

Wall or curtain drenchers

 

Wall or curtain drenchers throw water to one side only of the outlet in the form of a flat curtain over those openings or portions of a building most likely to admit fire.  In order to cover all combustible portions of a wall, it is usual practice to put a line of drenchers just below the eaves if these contain flammable material, and to fit every window or opening on the top two storeys with a drencher.  Those below this level, except the ground floor and basement, are fitted on every alternate storey.

 

Window drenchers

 

As their name implies, window drenchers are used to protect window openings.  They are placed horizontally level with the top of the window, with the deflector 100mm from the surface of the wall providing a curtain of water to protect the glass.  From the tail of the deflector, a jet is thrown inwards on to the glass near the top of the window, while two streams are directed at an angle of 45 0 to the lower corners.

 

 

 

3.7       OTHER EXTINGUISHING AGENTS

Carbon Dioxide total flooding and local application systems have been used for many years on such risks as surface involving flammable liquids, gases and solids, deep-seated fires involving solids subject to smouldering, and fires involving live electrical equipment.

Carbon Dioxide extinguishes a fire by reducing the oxygen content of the fire areas, to a point where it will not support combustion.  The gas is discharged at low temperature, however, does not produce any significant cooling effect.

 

Warning and instructional signs or notices should be positioned at the entrance to protected fire risk.  In most cases where CO2 is installed, the actual hazard to personnel is rather small, but the hazard will always be greater where the enclosure is large and where carbon dioxide may enter adjacent spaces such as pits and basements.  The extent and type of warning must be designed to suit the particular site but it should always include the symbol shown.

Halons have been used to protect similar risks, except that they are not suitable for potentially deep-seated fires.  Halon extinguishes fires on the principle that the gas creates a chemical reaction with the fire, resulting in the smothering of the fire.

Although toxic concentrations above 15% in air, halons generally extinguish fires at a concentration between 5-7%, it is however still not advisable for any person to be in the risk area once a release of the gas has occurred.

There has been a gradual phasing out of the use of this type of extinguishing media through the 1990’s, since its CFC content was found to affect the earth’s ozone layer.  Extinguishing media of a halon type will no longer be found after January 2003, after which a worldwide ban on its use comes into force.


 

 

Foam Inlets


 

In many buildings rooms containing oil or other flammable liquids are protected by fixed piping through which foam can be pumped.  The piping is run from the room to an appropriate point in the street where it terminates in a fire service inlet usually protected by a glass panel and marked with the words FOAM INLET, together with an indication of the particular risk involved.

 

I 

The inlet pipes are fitted with a foam inlet adapter, a specification for which is included in BS336 (1980).  This has a tapered orifice against which the foam making branch is held by hand.  The orifice is suitable for most types of low expansion (foam-making) branch.  This arrangement ensures that foam can be applied where it is required in the early stages of what may be a fierce fire without it being necessary for firefighters to enter the compartment.

 

 

 

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