DETECTOR SELECTION.. .................... .................... .................7 TECTOR SELECTION.. .................... ....................

.................... ......13 .................... .................... ....27 .................... ........40

...............41
ecognition techniques are now being combined with CCTV technology providing antion based on monochrome

and full colour technology is available from as. Manufacturers early results with full colour systems seem encouragingr, the

INTENDED USE AND REGULATOR Y CONSIDERA TIONS

definitions

Aided DesignFluid

Dynamic sControl SystemGas and Smoke detecto rSafety and Environmen tProtective Functio

nProtective Syste mEmitting Diodeof Sigh tExposure Limitof Failure on DemandRisk

Assessmen tFailure Robustnes sIntegrity LevelTerm Exposure LimitLimit ValuePower Supply

GAS AND SMOKE DETECTOR SELECTION own Fire & Gas Mapping software has been used widely by Shell and Contractors to

Shell,are may not be required for all designs. For example, where designs (point) monitoring e data transmission (typically 0 20 mA)

between the detector and the rest of themonitoring

GAS DETECTOR SELECTION

d detectors are now available as drop-in

replacements for catalytic (pellistor) detectors. of point gas detectors

absorption type;
gas turbines:on thresholds for

gas turbine protection should be set to 15 % LFL and 40 % LF Lngress/egress thresholds for gas turbine protection vary widely

throughout the Group. Gas

type detectors type detectors

gas detections detectors suffer from both short-

term and longterm drift. Short-term drift may resultetectors also suffer from both shortterm and longterm drift, but this is small whens.s

detectors are used, 20 % LFL and 60 % LFL should be set as respective Low/High

gas detection
of open path gas detectors

monitoring
path gas monitors : recommended) minimum alarm level setting of 0.5 LFLm (50 % LFL extended foring

distances from 4 m to 200 m. However, an optimum distance for offshore

LEAK DETECTION alves operating at

high flowrates and hightools operating off instrument air;valves and relief

valves;winds and flaring operations.

a detailed mapping review is undertaken to establish the level of background

ultrasound ,acoustic leak detection is employed, a high-pass frequency threshold in the 25KHz

MIST DETECTION

GAS DETECTOR SELECTION be fast and reliable and preference shall be given to speed of

responseof HSE shall be included in the design study. shall be reliable and precise;limit values for

an 8 hour working day) shall be monitored ;aspects shall be included in the design

study ;control system with capabilities such as statistical analysis and a data base to

electrochem ical celltype. semiconductor type.

toxic gas detectors

monoxide is sometimes measured with infrared type instruments. Point detectors are gas detection thresholds

Time Weighted Average (TWA) for an 8 hour day, 40 hour week as 5 mL/m

 Short Term Exposure Limit ((4) x 10 minutes exposures per day) as 10 mL/m
American Conference of

Governmental Industrial Hygienists (ACGIH) is a recognised body and a

AND SMOKE DETECTOR SELECTION

type selection

by persons (with manual call points);(IR) flame detectors ;flame detectors ;detectors,

such as:type detectors ;detectors. bulbs;alloy links or plugs; by personstype fire

detectorsfire detectors
type fire detectors have an upper ambient temperature limit of 75 C. d flame detectors have

the advantage of improved false alarm rejection

type fire detectors

etectors are subject to interference from welding

activities, Xrays used in nondestructiv eupper ambient temperature limit of 150 C.

flame detector s

detector ssmoke detectors smoke detectors

application of this type of detector may be restricted

due to the fact that the detection principle

sensitivity smoke detectors detectors

heat and smoke detectorsC.

ENGINEERING, SPECIFICATIO N AND INSTALLATION PRACTICES

visual alarms/mess

ages in the control centre and/or in the plant. Additiona lemergency situations to local

community services, e.g. fire brigades, etc.;fire fighting equipment, e.g. fire water

pumps, water spray and fog systems,of safeguardin g and depressurisi ng (blowdown

systems) ;closure of air ventilation inlets ;evacuation systems (barriers, howlers,

etc.).shall be normally closed contacts unless otherwise specified by thedetection is provided

for specific plant equipment, such as a turbine which video display units; andif

the Fire & Gas IPF is SIL 1 or higher, and the confirmed fire or INTERFACE (HMI)

mimic panels

toxic gas : yellow ,flammable gas : bluefire : red,system fault : white,pump

running lights : green,other alarms : red . gas ,gas,pump

auto-start stand-by indication , fault ,fault,fault. a nonlatching

push button to test all indication lights on the mimic.nonlatching push button to change all alarm

lights (except for the plant non-latching push button to reset all visual and audible alarms,

provided that allnonlatching push button to initiate an all-clear signal in the buildings and innon-

latching push button to manually initiate a fire alarm with effect sAlarm: a non-latching push button

to manually initiate a toxic gas alarm in theAlarm: a non-latching push button to manually initiate a

flammable gasPumps: one or more non-latching push buttons to manually start the fire

Dampers: latching push buttons to manually close the dampers .valves: three-

position switches with the positions and related text: open,valve reset: nonlatching

push buttons to reset the water spray valves.

control system

- This shall show the relevant

plants as a simplified plot plan. If Displays One plant overview display shall be provided for each

plant.splays - A unit detailed display shall be available for each process unit,

of events recorder (SER) of communicatio n interfaces with other systems

STANDARDS

of construction and performance

Heat detectors EN 54and ionisationtype detectors

EN 5 4 (flammable) gas detectors EN 61779 Parts 1 through 5

of certification

purpose) detectors may be used only for fire, toxic gas and smokend gas

detectors for use in process areas shall be certified for use in zonefor use in all areas shall be

certified for use in zone 1 areas as MODULE Sloop detection (input and output)

;circuit (input and output) ; fault(s) ;supply failure, e.g. low battery

voltage (of UPS);unit failure; LEVEL SETTINGSas minimum for point detectors, see (2.2.2.1)

for recommend ed alarmpically for open path detectors, see (2.2.3.2) for

recommend ed LOS alarm

typical longterm random drift of flammable gas detectors is in the order of 3

% LFL. Setting the typical long term random drift of H

FOR CIRCUIT INTEGRIT Yuld be individually wired to the

control module or to the FGS IPS.initiators may be applied in buildings. Zoned circuitry

shall be achieved by SYSTEMS REQUIREME NTS

specification and testing facilities

requirements

and error message sMagnetic Compatibilit y (EMC )supplyof sensors

PRACTICES FOR DETECTORS AND ASSOCIATED EQUIPMENT

may be positioned at approximately the same

elevation as the potential source ofs are generally the preferred technology for detecting gas leaks in open areas.tioned so that they are easily

accessible for calibration andply and electronic measuring circuits shall be located in a non-hazardous area, e.g. the definitions

(fire detection) The probability that an assigned set of(gas detection) The

probability that an assigned set oftarget The minimum acceptable performance of atolerance

Ability of a fire or gas detection system todegree of fault tolerance If the minimum

degree of fault tolerance is T, of failure A failure of a set of fire or gas detectors is

requirements for F&G systems requirement for establishing the performance of a set of detectors

of flammable gas detectors

inlets for HVAC (heating, ventilation and air conditioning );outlets of

enclosed hazardous areas/modul es, etc.;inlets to analyser houses ;suction of instrument

air compressors ;to furnaces in gas plants;to air compressors in gas plants;to

breathing air systems.

the temperture and molecular weight of a gas have an impact on buoyancy. In particular, of acoustic leak detectors

of H and positioning of smoke and fire detectors

detectors ntilation patterns, i.e. draught due to air

conditioning ;diluting effects of air conditioning and ventilation systems .type detector

sfloors in computer rooms, auxiliary rooms, and inside electrical andcable trays in

buildings . detector sceiling and depth to which the detector projects

below the ceiling ;patterns in the building/roo m;blocking the heat flow to the detector,

e.g. system cabinets .detection tubing DEP 32.30.20.11Gen.Septem ber

2002Page 36resistant to ultraviolet light; for example, Polyflo 44PF. Such tubing is supplied

byImperial Eastman or by Samuel Moore; however, an equivalent may be used followingapp

roval by the Principal.Th e instrument air in the tubing shall be maintained at an appropriate

pressure, typically 1.5bar (ga), for the transmitter it is to operate, as this relates to rupture

temperature .
NOTE: The instrument air lines for interconnections and for connecting the tubing to the instrument

airheader shall be of plasticsheathed copper tubing.

For a typical application of fire detection tubing, refer to Standard

Drawings S 88.020 andS 88.021.Syst ems based on fire detection tubing are vulnerable and prone to

failures induced byexposure to chemicals or by mechanical damage. The Principal

shall be consulted on theuse of fire detection tubing.A sturdy alternative, although

possibly slower to respond to fire, is a point detection systemwith frangible bulb

detectors in AISI 316 tee fittings interconnect ed by AISI 316 tubing andmounted at twometre

intervals. Fusible plugs may be used instead of frangible bulbs.3) Optical type fire

detectorsOp tical type fire detectors are line-ofsight devices and shall therefore be

positioned so thatthey can see the entire section to be protected. They shall be mounted

so that they are freefrom the effects of vibration and shock, and spaced in accordance with the

detectionobj ectives, see (Appendix IV).Infrared (IR) lenses shall be protected against the effects of

water and the possibility offreezing.

NOTE: Certain hydrocarbons and other gases, e.g., carbon dioxide, may interfere

with the signal to the IRdetector.

Ultraviolet (UV) detectors shall be protected from

possible fouling of their windows / lensesbut such protection shall not impair their

operation.O ptical type fire detectors provide rapid response and good space

detection see (2.6.1.3).

3.9.8 Positioning of beacons

Beacons shall be positioned

so that they will be visible in the area for which they are toprovide a warning, but they should

be accessible for maintenanc e. Suggested locations arepipe racks, top

corners of buildings and the principal passages inside auxiliary buildings.

3.9.9 Positioning of manual call points

Manual call points shall be positioned (see DEP

80.47.10.30Gen) so that they stand outagainst the background, i.e. they shall be clearly

recognisable from a distance. If necessaryth ey shall be provided with signs to enhance their

visibility from access roads.Manu al call points should be positioned as follows:along roads in the plant

area at intervals not exceeding 100 m, preferably at or near tolamp posts;along roads

in storage / tank areas not exceeding intervals of 200 m; near or at locations having a
-

higher risk such as remote pump floors, oil catchers,ma nifolds, motor control

centres, jetty heads; on offshore locations, at escape routes (entrance to bridges and staircases);-

inside buildings, office entrance, canteens, warehouses, medical centres, gate

andguardho uses, etc.;inside the plant and positioned:outside power station(s);outside

analyser house(s);outside control room(s);outside utility buildings;outside

hazardous enclosed areas; DEP 32.30.20.11Gen.Septem ber 2002Page 37- along

logical escape routes. DEP 32.30.20.11Gen.Septem ber 2002Page 383.10

DETECTOR VOTINGDete ctor voting is one method of ensuring that fire or gas detector configuratio

ns are robustagain st failure and robust against spurious alarms. But detector voting may

not berequired; for example, where detectors or detector systems themselves are robust,

orwhere appropriate actions are taken by experienced operators.Cl early, combining detectors to

vote logically in any configuratio n requires additionalde tectors to provide the same

degree of coverage. Generally, the number of detectorsreq uired increases as the voting

architecture become more complex (Appendix IV) listspossible configuratio ns.An

architecture finding widespread use is that referred to as 1oo2D. This strategy requires2

detectors for confirmed Fire or Gas as with 2ooN, except that under detector faultconditio

ns, e.g. if a detector has failed, the logic reverts to 1ooN (i.e. the logic considersfail ed detectors as alarms,

which is the equivalent of voting High on detector fault). Thishas the major advantage

that detection coverage is not lost if a detector has failed, as with2ooN in fact coverage is

increased. The concept, however, is slightly less robust againstspuri ous trips when alarms

are produced from F&G zones that have failed detectors, butthis lower robustness

does not affect the entire facility. Furthermore , modern detectorsha ve a typical MTBF of 10

years or more, so this drawback is marginal and inconsequen tialwhen judged

against the improvemen t in safety performance . Nevertheles s, this highlightsth e need for

prompt action to repair faulty instruments. The main reason for adopting 1oo2D detector

voting is that the required performance (coverage) is delivered with the minimum number of

detectors. Other detector votingconfig urations may be required to achieve identified

safety or economic needs, but suchconfigu rations will require a greater number of detectors.