detector selection

8/4/2019 Detector Selection

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DETECTORSELECTION..........................................

.................7 TECTOR

SELECTION......................

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...............41ecognitiontechniques are

now beingcombined with

CCTVtechnologyproviding

antion basedon

monochrome



and full colour

technology isavailable from

as.Manufacturers’early resultswith full coloursystems seem

encouragingr,the



INTENDEDUSE ANDREGULATOR

Y

CONSIDERA TIONSdefinitions

AidedDesignFluid



DynamicsControlSystemGasand Smoke

detectorSafety and

EnvironmentProtective

Functio



nProtectiveSystemEmittingDiodeof

SightExposure

Limitof Failure on

DemandRisk



AssessmentFailureRobustnessIntegrity

LevelTermExposure

LimitLimitValuePower

Supply



GAS AND

SMOKEDETECTOR

SELECTIONown Fire & Gas

Mappingsoftware hasbeen used

widely by Shelland

Contractors to



Shell,are may

not be requiredfor all designs.

For example,where designs(point)monitoringe data

transmission(typically 0 –20 mA)



between the

detector andthe rest of

themonitoringGAS

DETECTORSELECTION

d detectors arenow availableas drop-in



replacements

for catalytic(pellistor)

detectors.of point gasdetectors

absorptiontype;gas turbines:onthresholds for



gas turbine

protectionshould be set

to 15 % LFLand 40 %LFLngress/egressthresholds for

gas turbineprotection varywidely



throughout the

Group. Gas

type

detectorstype

detectorsgas detections

detectorssuffer fromboth short-



term and long-

term drift.Short-term

drift mayresultetectorsalso suffer fromboth short-term and long-

term drift, butthis is smallwhens.s



detectors are

used, 20 % LFLand 60 % LFL

should be setas respectiveLow/High

gasdetectionof open pathgas detectors



monitoringpath gasmonitors

:recommended)

minimumalarm levelsetting of 0.5

LFLm (50 %LFL extended

foring



distances from

4 m to 200 m.However, an

optimumdistance foroffshore

LEAK DETECTIONalvesoperating at



highflowratesandhightools

operatingoff

instrumentair;valves

and relief



valves;windsand flaringoperations.a detailedmapping

review isundertaken to

establish thelevel of background



ultrasound

,acoustic leakdetection is

employed, ahigh-passfrequencythreshold inthe 25KHz

MISTDETECTION



GASDETECTORSELECTIONbe fast and

reliable andpreference

shall begiven to

speed of



responseof HSE shall beincluded inthe design

study.shall be

reliable andprecise;limit

values for



an 8 hourworkingday) shallbe

monitored;aspects

shall beincluded in

the design



study;controlsystem withcapabilities

such asstatistical

analysis anda data base

to



electrochemical cell-type.

semi-conductor

type.toxic gasdetectors



monoxide is

sometimesmeasured with

infrared typeinstruments.Point detectorsaregas detection

thresholds



TimeWeightedAverage(TWA) for an

8 hour day,40 hour

week as 5mL/m



– Short TermExposureLimit ((4) x10 minutes

exposuresper day) as

10 mL/mAmericanConference of



Governmental

IndustrialHygienists

(ACGIH) is arecognisedbody and a

AND SMOKEDETECTORSELECTIONtype selection



by persons(withmanual callpoints);(IR)

flamedetectors

;flamedetectors

;detectors,



such as:typedetectors;detectors.bulbs;alloy

links orplugs;

bypersonstype

fire



detectorsfiredetectorstype fire

detectors havean upper

ambienttemperaturelimit of 75 °C.d flamedetectors have



the advantage

of improvedfalse alarm

rejectiontype fire

detectorsetectors aresubject tointerferencefrom welding



activities, X-

rays used innon-

destructiveupper ambienttemperaturelimit of 150 °C.

flame

detectors



detectorssmokedetectors

smokedetectorsapplication of this type of detector may

be restricted



due to the fact

that thedetection

principlesensitivity

smokedetectors

detectors



heat andsmokedetectorsC.ENGINEERING,SPECIFICATIO

N ANDINSTALLATION

PRACTICESvisual

alarms/mess



ages in thecontrolcentreand/or in the

plant.Additiona

lemergencysituations to

local



communityservices,e.g. firebrigades,

etc.;firefighting

equipment,e.g. fire

water



pumps,water sprayand fogsystems,of

safeguarding and

depressurising

(blowdown



systems);closure of airventilation

inlets;evacuation

systems(barriers,

howlers,



etc.).shallbe normallyclosedcontacts

unlessotherwise

specified bythedetection

is provided



for specificplantequipment,such as a

turbinewhich

videodisplay

units; andif



the Fire &Gas IPF isSIL 1 orhigher, and

theconfirmed

fire orINTERFACE

(HMI)



mimic panels

toxic gas :yellow,flammablegas :bluefire :red,systemfault :white,pump



runninglights :green,otheralarms :

red.

gas

,gas,pump



auto-startstand-byindication,

fault

,fault,fault.a non-

latching



push buttonto test allindicationlights on the

mimic.non-latching

push buttonto change

all alarm



lights(except forthe plantnon-latching

push buttonto reset all

visual andaudible

alarms,



providedthat allnon-latchingpush button

to initiate anall-clear

signal in thebuildings

and innon-



latchingpush buttonto manuallyinitiate a fire

alarm witheffect

sAlarm: anon-latching

push button



to manuallyinitiate atoxic gasalarm in

theAlarm: anon-latching

push buttonto manually

initiate a



flammablegasPumps:one or morenon-latching

pushbuttons to

manuallystart the fire



Dampers:latchingpushbuttons to

manuallyclose the

dampers.valves:

three-



positionswitcheswith thepositions

and relatedtext:

open,valvereset: non-

latching



pushbuttons toreset thewater spray

valves.control system

- This shallshow therelevant



plants as asimplifiedplot plan. If Displays -

One plantoverview

display shallbe provided

for each



plant.splays- A unitdetaileddisplay shall

be availablefor each

processunit,



of events

recorder (SER)of

communication

interfaces withother systems

STANDARDS



of construction

andperformance

Heatdetectors

EN 54andionisation-

typedetectors



EN54(flammable)

gasdetectors

EN 61779Parts 1

through 5



of certification

purpose)detectorsmay beused onlyfor fire, toxicgas andsmokendgas



detectors foruse inprocessareas shall

be certifiedfor use in

zonefor usein all areas

shall be



certified foruse in zone1 areas as

MODULESloop

detection(input and

output)



;circuit(input andoutput);

fault(s)

;supplyfailure, e.g.

low battery



voltage (of UPS);unitfailure;LEVEL

SETTINGSasminimum

for pointdetectors,

see (2.2.2.1)



forrecommendedalarmpically

for openpath

detectors,see (2.2.3.2)

for



recommended LOSalarmtypical long-term random

drift of flammable gas

detectors is inthe order of 3



% LFL. Setting

thetypical long

term randomdrift of H

FOR CIRCUITINTEGRIT

Yuld beindividually

wired to the



controlmodule or tothe FGSIPS.initiators

may beapplied in

buildings.Zoned

circuitry



shall beachieved bySYSTEMS

REQUIREMENTSspecificationand testingfacilities



requirements

and errormessagesMagneticCompatibility(EMC)supplyof sensors



PRACTICESFORDETECTORSAND

ASSOCIATEDEQUIPMENTmay bepositioned atapproximately

the same



elevation as

the potentialsource ofs are

generally thepreferredtechnology fordetecting gasleaks in open

areas.tioned sothat they areeasily



accessible for

calibrationandply and

electronicmeasuringcircuits shall belocated in anon-hazardous

area, e.g. thedefinitions



(firedetection)

Theprobability

that anassigned set

of(gasdetection)

The



probabilitythat anassigned setoftarget The

minimumacceptable

performanceof

atolerance



Ability of afire or gasdetectionsystem

todegree of fault

tolerance If the

minimum



degree of faulttolerance is

T,

of failure Afailure of a

set of fire orgas

detectors is



requirements

for F&Gsystems

requirementfor

establishingtheperformanceof a set of detectors



of flammable

gas detectors

inlets for

HVAC(heating,

ventilationand air

conditioning);outlets of



enclosedhazardousareas/modules,

etc.;inlets toanalyser

houses;suction of

instrument



aircompressors;to furnacesin gas

plants;to aircompressors

in gasplants;to



breathingair systems.the temperture

and molecularweight of a gas

have an impacton buoyancy.In particular,of acousticleak detectors



of H

andpositioning of

smoke and firedetectors

detectorsntilation

patterns, i.e.draught due

to air



conditioning;dilutingeffects of airconditioning

andventilation

systems.type

detector



sfloors incomputerrooms,auxiliary

rooms, andinside

electricalandcable

trays in



buildings.

detector

sceiling anddepth to

which thedetector

projects



below theceiling;patterns inthe

building/room;blocking

the heatflow to the

detector,



e.g. systemcabinets.detectiontubing

DEP

32.30.20.11-Gen.Septem

ber



2002Page36resistantto ultravioletlight; for

example,“Polyflo 44-

PF”. Suchtubing is

supplied



byImperialEastman orby SamuelMoore;

however, anequivalent

may beused

followingapp



roval by thePrincipal.The instrumentair in the

tubing shallbe

maintainedat an

appropriate



pressure,typically1.5bar (ga),for the

transmitterit is to

operate, asthis relates

to rupture



temperature.NOTE: The

instrument airlines for inter-

connectionsand forconnecting thetubing to theinstrument



airheader shall

be of plastic-sheathed

copper tubing.For a typical

applicationof fire

detectiontubing, refer

to Standard



Drawings S88.020 andS88.021.Systems based

on firedetection

tubing arevulnerable

and prone to



failuresinducedbyexposureto chemicals

or bymechanical

damage. The

Principal



shall beconsulted ontheuse of fire

detectiontubing.A

sturdyalternative,

although



possiblyslower torespond tofire, is a

pointdetection

systemwithfrangible

bulb



detectors inAISI 316 teefittingsinterconnect

ed by AISI316 tubing

andmountedat two-

metre



intervals.Fusibleplugs maybe used

instead of frangible

bulbs.3)Optical type

fire



detectorsOptical typefiredetectors

are line-of-sight

devices andshall

therefore be



positionedso thattheycan see theentire

section tobe

protected. They shall

be mounted



so that theyare freefromthe effectsof vibration

and shock,and spaced

inaccordance

with the



detectionobjectives, see(AppendixIV).Infrared

(IR) lensesshall be

protectedagainst the

effects of



water andthepossibilityoffreezing.NOTE: Certain

hydrocarbonsand other

gases, e.g.,carbon dioxide,may interfere



with the signal

to theIRdetector.

Ultraviolet(UV)

detectorsshall be

protectedfrom



possiblefouling of theirwindows /

lensesbutsuch

protectionshall not

impair their



operation.Optical typefiredetectors

providerapid

responseand good

space



detection -see(2.6.1.3).3.9.8Positioning of

beaconsBeacons

shall bepositioned



so that theywill bevisible in thearea for

which theyare

toprovide awarning, but

they should



beaccessibleformaintenanc

e.Suggested

locationsarepipe

racks, top



corners of buildingsand theprincipal

passagesinside

auxiliarybuildings.



3.9.9

Positioning of manual call

pointsManual call

points shallbe

positioned(see DEP



80.47.10.30-Gen) so thatthey standoutagainst

thebackground,

i.e. theyshall be

clearly



recognisablefrom adistance. If necessaryth

ey shall beprovided

with signs toenhance

their



visibilityfrom accessroads.Manual call points

should bepositioned

as follows:-along roads

in the plant



area atintervals notexceeding100 m,

preferablyat or near

tolampposts;-

along roads



in storage /tank areasnotexceeding

intervals of 200 m;-

near or atlocations

having a



higher risksuch asremotepump floors,

oilcatchers,ma

nifolds,motor

control



centres, jetty heads;

-

on offshorelocations, at

escaperoutes

(entrance tobridges and

staircases);-



insidebuildings,officeentrance,

canteens,warehouses,

medicalcentres,

gate



andguardhouses, etc.;-inside theplant and

positioned:-outside

powerstation(s);-

outside



analyserhouse(s);-outsidecontrol

room(s);-outside

utilitybuildings;-

outside



hazardousenclosedareas;

DEP


ber2002Page

37- along



logicalescaperoutes.

DEP


ber2002Page

383.10



DETECTORVOTINGDetector votingis one

method of ensuring

that fire orgas detector

configuratio



ns arerobustagainst failureand robust

againstspurious

alarms. Butdetector

voting may



notberequired;for example,where

detectors ordetector

systemsthemselves

are robust,



orwhereappropriateactions aretaken by

experiencedoperators.Cl

early,combining

detectors to



votelogically inanyconfiguratio

n requiresadditionalde

tectors toprovide the

same



degree of coverage.Generally,the number

of detectorsreq

uiredincreases as

the voting



architecturebecomemorecomplex –

(AppendixIV)

listspossibleconfiguratio

ns.An



architecturefindingwidespreaduse is that

referred toas 1oo2D.

Thisstrategy

requires2



detectors forconfirmedFire or Gasas with

2ooN,except that

underdetector

faultconditio



ns, e.g. if adetector hasfailed, thelogic reverts

to 1ooN (i.e.the logic

considersfailed detectors

as alarms,



which is theequivalentof votingHigh on

detectorfault).

Thishas themajor

advantage



increased. Theconcept,however, is

slightly lessrobust

againstspurious trips

when alarms



areproducedfrom F&Gzones that

have faileddetectors,

butthislower

robustness



does notaffect theentirefacility.

Furthermore, modern

detectorshave a typical

MTBF of 10



years ormore, sothisdrawback is

marginaland

inconsequentialwhen

judged



against theimprovement in safetyperformance

.Nevertheles

s, thishighlightsth

e need for



promptaction torepair faultyinstruments.

The mainreason for

adopting1oo2D

detector



voting isthat therequiredperformance

(coverage)is delivered

with theminimum

number of



detectors.Other

detectorvotingconfig

urationsmay be

required toachieve

identified



safety oreconomicneeds, butsuchconfigu

ti ill

detector selection

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