SE-1504(2012)-MOD-I CUSAT FIRE

8/16/2019 SE-1504(2012)-MOD-I CUSAT FIRE

1/33

SE 1504 PLANNING AND DESIGN OF FIRE PROTECTION SYSTEMS

MODULE- I

Fire detection- Need and importance of automatic fire detection system, principle of detection, classification of detectors; Heat detectors – fixed temperature, rate of rise ,thermistor rate of rise and rate compensated type detectors; Smoke detectors- opticaland ionization type, photo electric light scattering and light obstruction typedetectors; Flame detectors – infra red and ultra iolet detectors; Flammable gasdetection- !ellistor and laser detectors; "esting of fire detection de ices as per rele ant #ndian standards specifications; $omparison of detectors; !erformancecharacteristics of detectors; %ag time associated &ith fire detection'

MODULE -II

!rinciples of Fire (xtinguishments-extinction of premixed flames, diffusion flamesand burning metals, fire triangle, fire tetrahedron; )asic concept of fire fighting &ith&ater, carbon dioxide, po&ders, foams, inert gases halons; Need for halonreplacement and halon substitutes; (xtinguishant performance- flame extinguishingconcentration, inerting concentration, fire trials'

First aid fire protection – fire bucket, sand bucket, fire blanket, fire pails * &ater barrels, hose reels; +escription, &orking principle, method of operation of differenttypes of portable fire extinguishers-&ater type, foam type, dry po&der type, $ type,

apourizing li.uid type; $are, inspection, and maintenance of portable extinguishersas per rele ant #ndian standards specifications'

MODULE -III/utomatic &ater sprinkler system- re.uirement and source of &ater supply, automatic pumps; /utomatic sprinkler heads-0uartzoid type, fusible link type, modern types;mounting and protection of sprinkler heads; Sprinkler pipe &orks-standard andstaggered lay out, hangers; $ontrol al es for &et and dry installations; deluge al e'+renchers; High elocity and medium elocity spray system; !rinciples of &ater sprinkler system design as per rele ant standards 1#S#2'

MODULE -IV

Fixed fire fighting system using $, +ry chemical po&der, and Foam - concept of total flooding and local application, ad antages and disad antages of each system;)asic system components; +esign principles of fixed fire fighting systems for totalflooding and for local application as per rele ant standards 1#S#2'

Fire alarm system- classification of alarm system as per N)$; 3anually operatedsystem; /utomatic alarm system; $omponent and features of %ocal system, /uxiliarysystem, 4emote station system, $entral station system and !roprietary system


2/33

Text Books

1. 4on Hirst, 5Underdowns Practical Fire Precautions 6, 7o&er !ublishing$ompany %td', (ngland, 89:9'

2. ain


3/33

MODULE- I

Fire detection- Need and importance of automatic fire detection system, principle of detection, classification of detectors; Heat detectors – fixed temperature, rate of rise ,thermistor rate of rise and rate compensated type detectors; Smoke detectors- optical

and ionization type, photo electric light scattering and light obstruction typedetectors; Flame detectors – infra red and ultra iolet detectors; Flammable gasdetection- !ellistor and laser detectors; "esting of fire detection de ices as per rele ant #ndian standards1#S#2; $omparison of detectors; !erformance characteristicsof detectors; %ag time associated &ith fire detection'

4ef@- 82 < = ain 5Fire Safety in )uilding6

2 4on Hirst 5 Bnderdo&nCs !ractical Fire precautions6

1 0 FIRE DETECTION

+elay in detection of fire leads to issues like

- +ifficulty in controlling fire in the incipient stage &ith first aid firefighting appliances

- +elayed e acuation process

- +elayed the initiation of fire fighting

?hich may lead to- #ncreased loss of life and property'

/utomatic fire detection is important in unattendedAunoccupied premises during&orking hours, or off hoursAholidays'

/ fire can be detected by sensing the presence of one of the product of combustionsuch as

- Heat- 4adiation- Smoke, etc'

1 1 CLASSIFICATION OF DETECTORS

Fire detectors can be classified in different &ays'

)ased on the shapeA 4ange of +etection, they can be classified as

i2 SpotApointAblock type detector

- "he detector respond only to the conditions existing at the place they arelocated'

D#S 8E - )lock +etector; NF!/ - Spot detectorG


4/33

- %ine type detector – "he detector may be se eral meter long and &illrespond along its length'

ii2


5/33

/s heat transfer from the air to the operating element re.uires time 1mostly bycon ecti e method2, the surrounding air temperature &ill al&ays be higher than theoperating temperature of the de ice' "his difference bet&een the operatingtemperature of the de ice and the actual air temperature is kno&n as thermal lag' "hethermal lag is proportional to the rate at &hich temperature is rising'

"hermal lag describes a material s thermal mass &ith respect to time' / material &ithhigh thermal mass 1high heat capacity and lo& conducti ity2 &ill ha e a large thermallag'

"hermal lag 1hr2 I 8'J: % K18AL2

?here,

% I thickness 1m2L I thermal diffusi ity 1mAs2

(xpansion of materials &ith temperature has been considered as a reliable mechanismto de ise detector elements of this type' "here are different methods by &hich a fixedtemperature sensing elements can be made, namely by

- using )imetallic strip- using fusible alloy- using heat sensiti e cables- using expansible li.uid

1 ! 1 1 F#xe$ te%&e'(t)'e $ete*to' )s#+, #%et(..#* st'#&?hen t&o metals ha ing different coefficients of thermal expansion are bondedtogether and then heated, differential expansion causes banding or flexing to&ards themetal ha ing the lo&er expansion rate' "his action breaks or makes a circuit, causingthe detector to acti ate'

%o& expansion metal- in ar 1alloy of nickel 1J>M2 and iron 1> M2

High expansion metal – alloy of3anganese –copper-nickel;

Nickel-chromium-iron;Stainless steel)i-metals are used in the form of Strips and Snap disc

/ll bi-metal elements are self-restoring type and hence detections made of this principle need not re.uire replacement or adOustment


6/33

IL

Fig.Bimetallic type heatdetector

Fig. Fixed temperature-bimetallic-snap disctype heat detector


7/33

1 ! 1 ! F#xe$ te%&e'(t)'e $ete*to' )s#+, /)s# .e (..o

/ fusible alloy is used as solder to keep an element 1spring, metal strip etc2 in thedetector under tension' ?hen the temperature of the solder reaches its melting point, itmelts and the element &ill closeAbreak the contact and initiates an alarm'

"his is a spot type detector and its main dra&back is that it can be operated only onceand is not reusable'

"he commonly used alloy is (utectic metal 1-alloys of bismuth, lead, tin andcadmium2 &hich has an approximate melting point of >: P$

1 ! 1 F#xe$ te%&e'(t)'e $ete*to' )s#+, 2e(t se+s#t#3e *( .es

"hey are line type detectors' #n this case, t&o current carrying &ires are keptseparated by a heat-sensiti e insulation' "he insulation gets softened at its ratedtemperature and thus making the &ires to ha e electrical contact'

1 ! 1 4 F#xe$ te%&e'(t)'e $ete*to' )s#+, ex&(+s# .e .# )#$

- / .uartzoid bulb 1bulb in the shape of .uartz2 is filled &ith highly expansableli.uid &ith a small amount of gas inside' /s the temperature increases, the li.uidexpands and the pressure of li.uid causes the bulb to burst, leading to theacti ation of alarm'

Fig. Fixed temperature-spot

type heat detectorwith

fusible element

Fig. Fixed temperature heatdetector-Line type using heat sensitivecables


8/33

- "his type of detections are used in &ater sprinkler system and are a ailable atdifferent temperature ranges 1 9Q$, >Q, E , 8 8, 8>Q, Q , :JQ$2

1 ! ! R(te o/ '#se $ete*to'

"he rate of rise detector &ill respond to the rate at &hich the temperature rises' /t aslo& temperature rise it &ill not respond .uickly unless the temperature reaches a pre-set alue' +ifferent principles are used to achie e this response'

1 P+e)%(t#* '(te o/ '#se t) #+, t &e 2e(t $ete*to'

- "his is a line type detector

! P+e)%(t#* R(te o/ R#se *)% F#xe$ Te%&e'(t)'e- S&ot T &e

#n spot type, there is an air chamber and the expansion of air in this chamber due totemperature rise mo es a diaphragm and this in turn closes a circuit' "he alarm &ill beacti ated once the circuit is acti ated' / calibrated compensating ent &ithin thechamber allo&s the normal fluctuations in the temperature'

/ thermostat de ice fitted to the detector system allo&s the acti ation of alarm in casethe temperature rise is at slo& rate' "he thermostat can be set to a predeterminedtemperature 1 E' P$- : ' P$2

"he tube / 1small diameter copper tube2 isfastened in a continuous loop to ceilings or &alls

and terminates at both ends in chamber ) ha ingflexible diaphragms $, &hich control theelectrical contact +'

?hen air in the tubing expands under theinfluence of heat, pressure builds &ithin thechambers, causing the diaphragms to mo e andclose a circuit to alarm transmitter ('

Small and calibrated ents F compensate for small pressure changes in the tubing brought about bysmall changes in temperature in the protectedspaces'

Fig. : Pneumatic rate of rise tubing typeheat detector

"he air in the chamber / expands more rapidlythan it can escape from ent )'

"his causes pressure to close electrical contact+ bet&een diaphragm c and contact scre&('

Fixed-temperature operation occurs &henfusible alloy F melts, releasing spring 7,&hich depresses the diaphragm closing

contact points'Fig. : Pneumatic rate of rise cum xed temperature typeheat detector


9/33

1 ! T2e'%#sto' P'o e t &e s&ot t &e- '(te o/ '#se t &e6"hermistor is a semiconductor &ith a negati e temperature coefficient- that is, itselectrical resistance decreases &ith increase in temperature'

"he change in resistance of these thermistor is ery large' For example, at Q P$, itsresistance is 8QQ kR &hile at 8QQ P$ it has only 8QQ R resistance'

- "he circuit &ithin the detector is designed to alarm &hen the change inthe resistance reaches a pre-set alue'

- / fixed temperature setting can also be pro ided in the system so thatthe system can detect slo& temperature rise, if any'

A$3(+t(,es o/ t2e'%#sto' t &e o3e' /)s# .e .#+k t &e 2e(t $ete*to'

T2e'%#sto' T &e F)s# .e .#+k t &e%arge co erage area 1 Qm2 %ess co erage area 18Qm2?ill not malfunction due to ibration, asthey are in solid state

+uring melting, ibrations may cause problems

4eusable $annot be reused%ong life Fusible links may deteriorate3ore sensiti e and fast response %ess sensiti e and sluggish+esired temperature can be adOusted Fixed temperature type

1 ! 4 R(te Co%&e+s(te$ "e(t Dete*to'

"he rate of rise de ice are triggered by rate of increase in ambient temperature and aresubOected to false alarm caused by harmless thermal gradient such as flo& of &arm air from processes 1o en, etc2' "o o ercome this difficulty, rate compensated detectorsare used'

- Here, the outer shell of the detector is made of rapidly expanding alloy stainlesssteel, &hich is sensiti e to the changes in the surrounding air temperature'

- "he inner struts are made of alloy ha ing lesser co-efficient of expansion'

F#, 7 So.#$ st(te e.e*t'o+#* 2e(t $ete*to' 8#t2 $)(. t2e'%#sto'se+s#+, *#'*)#t


10/33

- /t slo& rate of heat de elopment, both outer shell and inner strut expandsalmost e enly and contact is established at pre-set alue'

- Bnder a rapid rate of rise in temperature, the shell expands at a faster rate andalarm is acti ated earlier &hen the air temperature reaches its pre-set alue'

- / transient temperature ariation may heat up the outer shell, but may not causealarm'

1 ! 5 Pe'/o'%(+*e o/ "e(t Dete*to'

4ef' #S@ 8E @89::2- specification for heat sensiti e fire detector for use inautomatic fire alarm system 1reaffirmed No ' 899 2'

"he code specifies that,

- heat detectors should operate at a temperature of EQ EP $ &henconstantly put in temperature for Q seconds in air stream at the rate of

:Q cmAs'

F#, 7 R(te *o%&e+s(te$ 2e(t $ete*to's - C)t se*t#o+ (+$ ,e+e'(. 3#e8

Fine silver contacts

Expansion struts

High Expansion sensing shell, 0.0 anodi!edaluminium

Heat control sleeve

"d#usting$%etting %cre&

%eal

F#, 7 Det(#.s o/ ( t *(. '(te *o%&e+s(te$ 2e(t $ete*to'


11/33


12/33

1 1 O&t#*(. s%oke Dete*to's S&ot t &e6

"he optical smoke detectors &ork based on the principle of the obscuration1obstruction6 or s*(tte'#+, of light by the smoke particles and hence are further classified as

i2 !hotoelectirc light obscuration type andii2 !hot electric light scattering type

1 1 1 P2otoe.e*t'#* .#,2t o s*)'(t#o+ t &e s%oke $ete*to'

bscuration refers to the ability of solid obOects in a beam of light to reduce theamount of light &hich arri es on a target' "he ability of solid materials to obscurelight decreases as the particle size is reduced'

!rinciple of &orking of a light obscuration type photoelectric smoke detector is asfollo&s@

- /n emitter produces a light beam in the infra-red spectrum

- "he intensity of light is sensed by a recei er aligned and kept at adistance 1may be upto 8QQm2, &hich is a photosensiti e de ice'

- ?hen there is a disturbance in the air &ithin the light beam due tosmoke , the intensity of light recei ed by the recei er &ill be affectedand this ariation, &hen reaches a preset alue1say about QM less2firealarm &ill be acti ated'

- ?hen a turbulent hot air or gas passes through the light beam, the light beam&ill be irregularly deflected and this may lead to a light flickering effect atthe recei ing end' "his flickering effect can also be sensed by the recei er fitted &ith appropriate electronic de ises and an alarm can be acti ated based

on the fre.uency of flickering recei ed 1"ypical flicker fre.uency associated&ith a fire scenario ranges bet&een Hz and Q Hz2' Hence, this type of system can detect both smoke and heat 1combined heat and smoke detector2

%ight obstruction type photoelectric smoke detectors are suitable for

- )uildings &ith high ceilings- %arge open areas – 1one detector &ill protect an area of 8QQm x 8 m2- %arge ducts, cable tunnels etc'- /reas &here the installation of indi idual point detectors in ol es danger or

difficulty 1(g@ installations abo e acid tanks, rotating machinery, li e

electrical e.uipments etc'2

Fig'@ ?orking principle of light obscuration Fig' %ight obscuration"ype smoke detectors type smoke

detector


13/33

Some of the disad antages of light obscuration type photoelectric smoke detectorsare@

- /s light is continously recei ed by the cell, its life is short'

- +irt deposited on either the light source or the cell could cause a false alarm'

1 1 ! P2otoe.e*t'#* .#,2t s*(tte'#+, t &e s%oke $ete*to'

"his is a Spot type detector

!rinciple of &orking of a light scattering type photoelectric smoke detector is asfollo&s@

#f a beam of light is directed into a cloud of particles some of the light &ill bescattered side&ays to the beam' "here is an optimum angle from &hich maximumamount of scattered light can be obser ed'

"he photocell is placed in the detector in such a &ay that it recei es no light from thesource 1emitter2 under normal condition'

?hen smoke particles enter the light path, light is scattered onto the photosensiti erecei er and causes the detector to respond 1alarm signal2

- %(+ is normally used as the light source

- +irt deposit may be a problem- $auses false alarm'

- "he life of photocell &ill be more in this case compared to obscuration typedetector due to the fact that in this case, the cell is exposed to light only &henlight is scattered'

- "he particle size less than Q'J micron are too small to scatter light and arein isible' So, a detector &hich operates by optical process &ill fail to detectthe pre-ignition particles and the in isible part of smouldering emission'

- #t is relati ely insensiti e to the isible part of smouldering emission 1due tosmaller size particles2

F#, 7 ;o'k#+, &'#+*#&.e o/ .#,2t s*(tte'#+, F#, L#,2t s*(tte'#+,T &e s%oke $ete*to's t &e s%oke $ete*to'


14/33

1 ! Io+#:(t#o+ T &e S%oke Dete*to's

"hese types of detectors are sensiti e to the in isible particles &hich are released, particularly in the initial stages of a fire'

"heir operation depends on the ionization of a small olume of air in a chamber by aradioacti e source'

"he radioacti e material is to produce alpha radiation and is usuallyA%e'#*#)% !41or R($#)% !!< ' /mericium has minimum radiation of particles other than L-radiation and hence it is preferred'

!rinciple of operation of an ionization type smoke detector is as follo&s@

- "he emission of alpha radiation keeps the air ionized in the air chamber'

- ?hen a potential is applied to the chamber electrode, the ions flo& to their respecti e electrodes 1T e ions to – e electrode and – e ion to T e electrode2and hence a small measurable electric current flo&s across the chamber air gap'

- ?hen smoke particle enter the chamber, ions are captured on the surface of the smoke particles and hence the current flo& is reduced'

- "his change in the current flo& is amplified and &hen the difference in thecurrent flo& is more than a preset alue, a signal is transmitted to the firealarm control unit'

F#, 7 ;o'k#+, &'#+*#&.e o/ #o+#:(t#o+ F#, 7 C'oss se*t#o+(. 3#e8 o/ (+ t &e s%oke $ete*to' #o+#:(t#o+ t &e $ete*to'

8- ptical $hamber; -$o er; J-$ase moulding; -!hotodiode1detector2;-#nfrared %(+

F#, 7 L#,2t s*(tte'#+, t &e s%oke $ete*to'


15/33

"he ionization type smoke detectors re.uire only lo& po&er consumption and/mericium pro ides a permanent source of alpha radiation 1the half life of /mericium

is QQ years2'7enerally, these detectors are of lo&est cost, and respond to smaller smoke particles1the result of high-energy fires2'

Since the current detected is ery small, a small ariation in the current due to other reasons many make a false alarm' "he ariation in the current may occur due to

- 4adio transmission- Bse of cellular phones- 4educed radiation due to the dirt or moisture, &hich may get deposited on the

surface of the emitterA recei er'- #f there is air mo ement –1ionized air may get displaced from the chamber due

to &ind and leading to a reduced current formation2'

#n fact, ionization type smoke detectors ha e the greatest false alarm rate amongsmoke detectors from the cooking and other non-fire sources'

1 ! Co%&('#so+ o/ P2otoe.e*t'#* (+$ Io+#:(t#o+ t &e $ete*to's

!hotoelectric smoke detectors respond faster to fire in its early, smouldering stage1before it breaks into flame2'

#onization smoke detectors respond faster in the flaming stage of a fire'

F#, 7 V#e8 o/ t *(. Io+#:(t#o+ t &e s%oke $ete*to's


16/33

"here is serious performance problem &ith ionization technology in the early,smoldering stage of fire' /lso, ionization detectors are &eaker in high air-flo&en ironments, and because of this, the photoelectric smoke detector is more reliablefor detecting smoke in both the smoldering and flaming stages of a fire'

#onization smoke alarms may not operate in time to alert occupants early enough toescape from smouldering fires' So, it has been made mandatory to use photoelectricsmoke alarms rather than ionization type in most of the recommendations meant for residential buildings 1sleeping rooms2'

1 A#' s(%&.#+, t &e s%oke $ete*to's

/n /ir Sampling +etector consists of a piping or tubing distribution net&ork that runsfrom the detector to the area1s2 to be protected'

/n aspiration fan in the detector housing dra&s air from the protected area back to thedetector through air sampling ports, piping, or tubing'/t the detector, the air is analyzed for fire products'

/ir Sampling Smoke +etectors are capable of detecting a fire at its earliest stage'

"raditional Uspot-typeU detectors passi ely detect smoke or heat in their immediatearea'

/ir Sampling Smoke +etectors acti ely pulls room air through a piping net&ork to itsdetection chamber &here it can detect the presence of particles that are created in the

ery early stages of combustion, e en before smoke is isible'"hey are best suited to detect fires &herein submicron particles are produced during pyrolysis or precombustion phase of incipient fires'

"hey are most often used &here the protected space has high alue and demands eryearly &arning of incipient fires such as in computer rooms, air conditioning ducts,archi es, etc'

'ost air-sampling smo(e detection systems are capa)le o* a highersensitivity than spot type smo(e detectors and provide multiplelevels o* alarm threshold, such as "lert, "ction, Fire + and Fire .

hresholds may )e set at levels across a &ide range o* smo(elevels.


17/33

+ifferent methods are adopted to detect the smoke from the air samples collected andaccordingly, air sampling detectors are further classified into

$loud $hamber type%aser system-Filtered type%aser system – !article $ounting type

1 1 C.o)$ *2(% e' t &e

$loud chamber 1?ilson cloud chamber2 principle detectors operate by dra&ing an air sample from the protected area into a high humidity chamber &ithin the detector 1through air sampling ports, piping, or tubing and using an aspirating fan2'

/fter the air sample has been raised to high humidity le el 1relati e humidityapproximately 8QQM2, the pressure is slightly lo&ered &ith the help of acuum pump'

#f smoke particles are there in the chamber, they act as condensation nuclei for &ater droplets and form cloud'

"he density of this cloud is measured &ith a photoelectric light scattering detector'

?hen the 5cloud6 reaches a predetermined density, the detector &ill respond &ith analarm'

he oldest and original air sampling technology is the loudham)er %ystems. Ho&ever, the maintenance o* these type o*

systems is di/cult due to the *act that, there is a re uirement o* *re uent replacement o* evaporated &ater and monitoring o* ongoing &ater levels. "lso, there are more more moving parts in thissystem than other systems, leading to more mechanical *ailures andis more la)or intensive to service and repair.

1 ! L(se' S ste%s = F#.te'e$ t &e

/ fan continually dra&ing air into a pipe net&ork attached to a detector unit, and passes the air through a dual stage filter to remo e dirt and particles larger than microns, sending the clean air to a laser detection chamber for smoke detection'

"he detector measures the light scatter caused by any smoke and processes thedetector signal'

1 L(se' S ste%s = P('t#*.e Co)+t#+, T &e

Here, a fan continuously dra&s air from the protected area through the detectionchamber' nce inside, particles pass through the laser beam &hile the photo collector measures reflected light from the particles' "he collector counts the number of discrete particles to determine the le el of smoke concentration' / particle sizediscriminator pre ents large particles, such as dust, from contributing to the smoke

concentration'


18/33

1 4 FLAME DETECTOR ELECTROMAGNETIC RADIATION DETECTOR6

"n ideal 1ame detector &ould relia)ly sense a 1ame o* interest,&hile totally ignoringall other 1ames or signal sources and &ould, in the process, )etotally una2ected )yam)ient operating conditions. Ho&ever, no completely ideal 1amedetector exists.

Flame detector detects the radiation from a fire' "he radiation from a flame &ill tra elat the speed of light' So, flame detections ha e fastest possible response time' "heyare of sur eillance type 1single unit protects large olume2' "he ultra iolet andinfrared region of the radiation spectra is considered for the fire detection'

Ho&e er, e en the sunlight contains the complete spectrum of radiation, &hichincludes B< and #4 radiation' 4adiations caused other than from a fire, burning and&elding operations, reflections from rotating machinery, ehicle head lights, etc' maycause a false alarm in flame detectors'

So, the characteristic of/.(%e /#*ke'#+, is identified to detect the B< * #4 radiationfrom a fire' / continuous radiation is ignored by the detector' "he detectors areusually set to respond to fre.uencies bet&een and 8 Hz'

Fig. : U !"#$pectrum

Fig. : %ypical &ydrocarbon Fire 'mission$pectrum


19/33

Flame detectors cannot respond to smouldering combustion, unless a sufficientlyglo&ing surface is exposed to the detector'

+epending on the type of radiation detected, the flame detecors are grouped into

#nfra red detectors andBltra iolet detectors

1 4 1 I+/'( Re$ T &e F.(%e Dete*to's

#nfra red radiation from the sun is absorbed by carbon dioxide molecules and &ater apour molecules' "he &a e lengths affected are bet&een 8' and 8': microns and bet&een ' and ' microns' Since $ and H are the main product of combustion,and &ill al&ays be released at flame temperature, photocells sensiti e to these&a elengths are suitable for an #4 detector'

/n #4 detector essentially consists of a lens, optical filter, a photo electric cell, &a eform filterAamplifier and an integratorA timer

"he photoelectric cell con erts light energy into electric energy' "hey are usually

made of materials such as thallons sulphide, lead sulphide, lead telluride, leadselenide, selenium and silicon'

Lensandoptical3lter

4hotoelectric cell

Filtercumampli3er

5elay

"larm

6isual

Indictor

Fig. : $chematic diagram of "# type(ame detector

F#, 7 T2'ee %(>o' s&e*t'(. ('e(s /o' F.(%e Dete*t#o+

%olar radiation-%ta)le

5adiation*romenvironment

5adiation*rom lightsources

5adiation *rom3re


20/33


21/33

"he electrodes are close together and a oltage is applied bet&een them' "he metal of the electrode is selected in such a &ay that, &hen a photon of radiation at the right&a elength is absorbed, it releases electron and this in turn ionizes the gas in the tube'"his ionization sets up a small current bet&een the electrodes and is fed to theamplifier'

"he amplifier sets up the current and transmits it to the relay, &hich acti ates thealarm &hen the signal to it persists for a preset time period'

#t is important to ensure that the glass &indo& is kept clean, particularly of oildeposits1thin film of oil &ill absorb the B< radiation2' /lso, performance of B<detector is affected by the presence of smoke and fog, as B< radiation is absorbed bythem' B< detector &ill respond to the radiation caused by &elding, W-rays, etc' HenceB< detectors are best suited for the monitoring of aircraft engines, fuel storage tanks,oil drilling rigs, etc'1 4 UV?IR T &e F.(%e Dete*to'

"he dual B


22/33

1 4 4 D)(. IR (+$ T'#&.e IR T &e F.(%e Dete*to's

+ual #4 1#4A#42 flame detectors compare the threshold signal in t&o infrared ranges'#n this case one sensor looks at the ' micron range and the other sensor at areference fre.uency'

"riple #4 flame detectors 1#4J2 compare three specific &a elength bands &ithin the#4 spectral region and their ratio to each other' #n this case one sensor looks at the 'micron range and the other sensors at reference bands abo e and belo&' "his allo&sthe detector to distinguish bet&een non flame #4 sources, and flames that emit hot

$ in the combustion process 1&hich ha e a spectral characteristic peak at 'micron2' /s a result, both detection range and immunity to false alarms can be

Fig. 7 86$I5 type 1amedetector

86sensor

I5 sensor

F#, 7Dete*t#o+ o/ t2e /.(%e t2e )se o/ t2'ee IR 8(3e.e+,t2 (+$s

F#, 7Dete*t#o+ o/ /.(%e )s#+, ot2 UV (+$ IR '($#(t#o+


23/33

significantly increased' Ho&e er, "riple #4, like other #4 detector types, is susceptibleto blinding by a layer of &ater on the detector s &indo&'

1 4 5 V#s# .e se+so's 8#t2 UV (+$ IR t &e $ete*to's

#n some detectors a sensor for isible radiation is added to the design in order to beable to discriminate against false alarms better or impro e the detection range'

(xample@ B


24/33

• Metal 'ires• Indoors

• Low cost and oil deposits on t edetector s window

ual&and(U"*IR)

• Hydrocarbon fires• Hydrogen# Silane# $mmonia andot er

ydrogen%basedfuelfires

• Metal 'ires• Indoors andoutdoors

Moderate speed• Moderate sensitivity• Low false alarmrate• Unaffected by solar radiation

• $ffected by specificU"*IR ratio created byfalse stimuli

• &linded by t ic!smo!e# vapors# greaseand oil deposits on t edetector s window

+riple IR(IR,)

• Hydrocarbon fires• Indoors andoutdoors

• Moderate speed• Hig est sensitivity• Hig immunity tofalse alarms• Longer detectionrange• Unaffected by solar radiation

• $ffected by IRsources only at s ortrange in certain rare firescenarios-

..+"(IR,/"ideo)

• Hydrocarbonfires• Indoors andoutdoors

.olor video picture• More informationabout t e

a0ard• 1rovides record oft e protectedarea before# duringand after fire

scenario• $utomatic switc ingof videoupon flame detection• Moderate speed• Hig est sensitivity• Hig immunity tofalse alarms• Longer detectionrange• Unaffected by solar radiation

• $ffected by IR sourcesonly at s ort range incertain rare firescenarios-

1 4 @ F#e.$ o/ V#e8 o/ F.(%e Dete*to'

/ flame detector is an optical de ice and thus it needs to ha e a clear ie& of thearea to properly detect a fire'

Flame detectors ha e a J-+ cone of ision ranging from 9Q degrees to 8 Q degrees'Sensiti ity of flame detectors diminishes at the edges of the cone of ision' "here issome blind spot at the edges of the cone' "he detector &ould acti ate only &hen thefire becomes larger 1say about four times the surface area that needed at the center of the cone2


25/33

Since both sensiti ity and range are related to fire size1surface area of fire2, if thedetector is placed further a&ay from 1or closer to2 the fire source, the detectable firesize &ill ary according to the in erse s.uare la&'

So doubling the detection distance results in only X of the radiant energy reaching thedetector, or con ersely, for the same response time, the surface area of the fire thenneeds to be times larger'

/ single detector &ith larger range is better compared &ith many detectors ha ing

smaller range

Fig. 7 Hori!ontal Field o*vie& o* 1ame detector-

ypical

)lind spots

Fig. 7 6ertical Field o*vie& o* 1ame detector-

ypical

)lind spots

Fig. 7 Field o* vie& o* 1ame detector ;:


26/33

1 5 FLAMMABLE GAS DETECTORSFlammable gas detection apparatus may be used &hene er there is the possibility of ahazard to life or property caused by the accumulation of a flammable gas-air mixture'Such apparatus can pro ide a means of reducing the hazard by detecting the presenceof the flammable gas and issuing suitable audible or isual &arnings'

7as detectors can be used to detect flammable and toxic gases and oxygen depletion'7as detectors may also be used to initiate specific precautions 1for example plantshutdo&n, e acuation, and operation of fire extinguishing procedures2'

Flammable gas detecting apparatus may be used to monitor a gas atmosphere belo&the lo&er flammable limit in circumstances &here accumulation of gas may result in aconcentration of the gasAair mixture to potentially explosi e le els'

7as detectors are usually battery operated' "hey transmit &arnings ia a series of audible and isible signals such as alarms and flashing lights, &hen dangerous le elsof gas apours are detected' /s detectors measure a gas concentration, the sensor responds to a calibration gas, &hich ser es as the reference point or scale' /s asensorCs detection exceeds a preset alarm le el, the alarm or signal &ill be acti ated'/s units, gas detectors are produced as portable or stationary de ices'

#t is recommended that, sensing a gas concentration of Q percent %F% 1or less2 shouldacti ate a local alarm 1audible or isual, or both, as most appropriate for the location2'Sensing a gas concentration of Q percent %F% 1maximum2 or a gas detector systemmalfunction should both acti ate an alarm 1audible or isual, or both, as mostappropriate for the area2 and initiate automatic disconnection of po&er from allelectrical de ices in the area that are not suitable for +i ision 1Yone 2' D/ninade.uately entilated area containing e.uipment that could release flammable gas or

apour can be designated as +i ision 1Yone 2G

riginally, detectors &ere produced to detect a single gas, but modern units maydetect se eral toxic or combustible gases, or e en a combination of both types'

F#, 7 O+e


27/33

)asically the toxic gases or combustion gases can be detected using differenttechnologies like

!ellister technology and

#4 technology1 5 1 Pe..#ste' T &e G(s Dete*to's

!ellistors are solid-state de ices used to detect gases &hich are either combustible or &hich ha e a significant difference in thermal conducti ity to that of air' 1"hedetecting elements consist of small ZpelletsC of catalyst-loaded ceramic &hoseresistance changes in the presence of the target gas hence the term ZpellistorC being acombination of ZpelletC and ZresistorC2

!ellistors &ere originally de eloped for the mining industry during the early 89>QCs;

+epending on the mode of operation in detecting gas, there are t&o types of pellistor,namely

$atalytic type and"hermal $onducti ity 1"$2 type

"he catalytic type sensor &orks by burning the target gas; the heat generated producing a change in the resistance of the detecting element of the sensor proportional to the gas concentration' 3ost of the pellister type gas detectors are of catalytic type'

"he thermal conducti ity sensor &orks by measuring the change in heat loss 1andhence temperatureAresistance2 of the detecting element in the presence of the targetgas'

"he earliest form of catalytic gas sensor used heated bare coils of platinum &ire to burn the gas' "he heat generated by the burning process produced a change in theresistance of the coil' "his change &as measured using a simple ?heatstone bridgecircuit' "he lo& catalytic acti ity of the bare coil necessitated ha ing to run the coilsat high temperatures 1:QQ – 8QQQ P$2 to be able to oxidise the target gas' /t thesetemperatures it &as found that significant e aporation of the &ire &as taking place'

"his produced a reduction in the &ire diameter and a subse.uent change in theresistance' "his produced a significant le el of zero drift and a lifetime of as short asse eral days'

"he present day pellistor detectors consist of t&o matched platinum coils, eachembedded in a bead of alumina' "he detecting element is coated &ith a catalyst &hich promotes oxidation &hen in contact &ith flammable gases and the compensatingelement is treated so that catalytic oxidation does not occur' "he compensatingelement is fitted to ensure that signals are not generated due to en ironmental effects1eg changes in ambient temperature or gas flo& rate2'

F#, 7 Me*2(+#s% o/ Pe..#ste't &e ,(s $etet*#o+


28/33

!ellistor-based systems operate in a ?heatstone )ridge circuit &hereby the pellistor and compensator in the detector represent one half of the bridge, the other half beingfitted to the control card usually located in the control room' "he control card suppliesa oltage to the bridge 1typically < to J'


29/33

• !ellistors do not fail-safe; poisoned pellistors remain electrically operational;thus the control system &ill continue to display zero gas &hen flammable gasmay be present'

• Sensiti ity to flammable gas is reduced in the presence of some compounds1notably hydrogen sulphide and halogens2'

• !ellistors need at minimum of 8 M olume oxygen present to operate' "heir efficiency reduces in oxygen deficient atmospheres'

• !ellistors may burn-out and re.uire replacement if exposed to gasconcentrations greater than 88QM %(% 1%o&er (xplosi e %imit2 D%F%G

• !ellistor sensiti ity degrades o er time'

• !ellistors ha e a limited life-span, sensors typically last J- years'

• !ellistors re.uire regular gas testing to ensure they are operational, and regular calibration of offset signal loss due to poisoning or bead contamination'

1 5 ! I+/'('e$ T &e G(s Dete*to's

3ost gases absorb #4 radiation at a characteristic &a elength and this beha iour is the basis in #4 type gas detection' ?hen #4 radiation transmitted is absorbed by a particular gas, the strength of reflected #4 radiation ha ing &a elength correspondingto the gas reduces at the recei ing end' "his difference in radiation intensity is

measured and processed for detecting the gas'#nfrared 1#42 gas detectors o ercome all of the limitations associated &ith pellistors to pro ide fast and reliable detection of hydrocarbon gases' #4 detectors pro ide rapidgas detection and fail-safe operation'

A$3(+t(,es o/ IR Te*2+o.o,

•


30/33

• #mmune to signal inhibition by contaminant gases'• No consumable parts; life-span typically [ 8Q years'• 4educed maintenance costs'• +oes not re.uire oxygen to be present'•

?ill not burn-out in high gas concentrations'• !remium models do not utilize a sinter 1flame arrestor2, and thus associated blockages cannot occur'

D#s($3(+t(,es o/ IR Te*2+o.o,

• !rice is higher than pellistor based detectors'• #4 detectors cannot detect hydrogen'• #4 detectors cannot pro ide a linear response to a group of different gases@ the

detector is ZlinearisedC for a particular gas, and &ill respond to others but in anon-linear fashion'

1 < Co%&('#so+ o/ Dete*to's

he parameters that are important &hile comparing detectors are7

a. %ensitivity

). 5elia)ility- the a)ility o* the system and its components to )ein proper &or(ing condition at all times, so as to )e ready toper*orm their intended *unction.

c. 'aintaina)ility and

d. %ta)ility - relates to its a)ility to sense 3res over extendedperiods o* time &ith no change o* sensitivity.

/ practical detector must be robust, reliable and sensiti e' #t should also ha e longlife, should not gi e false alarms and should be easily tested and readily replaced'"able sho&s the comparison of the performances of detectors

a)le7 omparison o* 4er*ormances

%l.=o.

smo(e?

High 'edium 'edium 'edium

@ 6isi)lesmo(e

'edium 'edium 'edium 'edium


31/33

A Flameultraviolet

High 'edium 'edium 'edium

Flame -in*rared

medium 'edium medium Lo&

"pproximate coverage area o* di2erent types o* detectors may )eta(en as sho&n in ta)le.

a)le7 "pproximate coverage area o* detectors

%.=o. ype o* detector overage+ Fusi)le alloy +C-+ m

Bimetallic + -@0 m: 4neumatic @ m

hermistor +A-@0 m@ %mo(e detector ioni!ation

type@ to C0 m

A %mo(e detector photoelectrictype

+00 m

5ate compensated heatdetector

+@ m apart eitherside

D 8ltraviolet 1ame detector one o* visison max.

C00

C In*rared 1ame detector +000 m

" 3re develops typically in *our stages namely,

• Incipient stage - =o visi)le smo(e, no 1ame and very littleheat. " signi3cant amount o* invisi)le com)ustion particlesmay )e created. his stage usually develops slo&ly.

• %mouldering stage - %mo(e, )ut no 1ame and little heat.

• Flame stage - 6isi)le 1ame, more heat, o*ten less or nosmo(e, particularly &ith 1amma)le li uids and gas 3res.

• Heat stage - Large amounts o* heat, 1ame, smo(e and toxicgases are produced. he transition *rom the previous stagecan )e very *ast.

Fire detectors are designed to detect some characteristic e2ect o* one or more o* these stages

Flame detector and optical type smo)e detector are *ast andcan operate &ithout any time delay, )ut time delays are purposelyinserted &hich may )e : to :0 seconds. Ho&ever, detection o* 3re is


32/33

di/cult in congested area or in smoldering 3res, as visi)ility o* 1ame is needed to detect the 3re.

$mo)e detectors and gas re detectors should not )e providedin areas &here am)ient temperature are li(ely to exceed :D or

*all )elo& 0 , unless they are speci3cally made *or this purpose.5adioactive ha!ard$level should )e less than +0 micro curies.

Fixed temperature type heat detectors &ill operate only &hen*ourth stage o* 3re has )een reached >heat stage?. hey may ta(e+.@ to +. @ minutes to operate &hen *ourth stage is reached andtemperature changes at the rate o* 0 $min. ut o* the 3xedtemperature type detectors, the slo&est in operation may )e*usi)le alloy type and then )imetallic type.

#ate of rise type heat detector &ill respond uic(ly to *ast heat

rise ranging *rom A to + $min &hen compared to 3xedtemperature type detectors.

%hermistor type have more *aster response out o* all the heatdetectors.

%hermistor type and rate compensated type detectors cansense rate o* rise as slo& as : $min.

*irculation of air near detectors a2ects their per*ormance. Heat

detectors are not suita)le *or areas &here ventilated air exist, as aircirculation &ill constantly remove the heat *rom the detectionsystem. In such areas even the e/ciency o* smo(e detectors isdependent on amount o* air change.

he e2ective area o* smo(e detectors )ased on the num)er o* airchanges recommended )y =F4" E-+C D is given in the ta)le)elo&

a)le7 E2ect o* "ir change in %mo(e


33/33

$ingle chamber ioni+ation type smo)e detector is cheaper, )utis suscepti)le to am)ient changes, &hich is compensated in dualcham)er smo(e detectors.

"oni+ation detectors respond )est to particles si!e ranging *rom +

micron do&n to 0.0+ micron, &hereas photoelectric detectorsrespond )est to particle si!es *rom approximately +0 microns do&nto 0. micron.

1 < SITTING OF DETECTORS

4ecommendations for sitting of detectors are specified in #S 8:9@ 89::- code of practice for selection, installlation and maintanence of automatic fire detection andalarm system 1/mendment No'82

Documents

SE-1504(2012)-MOD-I CUSAT FIRE