as
oN-
rEST
ala
for every
Gasexplosions
canbedeadly- soit makes
sense
boatwithgasaboard
to haveanalarm.Butwhichto choose?
PBO
testedsevenfor easeof useandabilityto detectgas
s most peopleknow
Liquef,edPetroleumGas
(LPG)of eitherpropaneor
butaneis heavierthan air
and will collectin the bilge
or bottom ofa locker.It only
takesa smallvolume of LPGto producean
explosivemixture,and when the
concentrationofgasin air fully reachesits
Iowerexplosivelimit (LEL)the mixture will
iSniteifyou strikea match or if thereis a
sparkfrom an electricalsystem.The LELof
bulaneis only about2ubgdsto 98u",rir.
GasalarmsshoulddetectLPGbeforethe
concentrationrcaches2570of LEL.To put
that in perspective,
a normal nosewill
detecta very strongsmellofgaswhen the
concentrationis about 10'1,6
of LEL,which is
beforenost ofthe alarmswill be triggered.
Get an alarm!
Gasinstallationand maintenanceattractsa
nountain ofpaperworkin the form of
Iegislationand codesofpractice,and
becau\e
of thi\ the riskof a gasexplo<ion
ir
small,though of coursethe consequences
arecatastrophic.
The investigationafteran
explosionusuallyconcludesthat the gas
systemwould havebeenpe ectlysafeif
installedand maintainedcorrectly.
A gasalarmis mandatoryon commercial
vessels,
charterand sailingschoolboatsand
it makessenseto fit one to a cruisingboat.
An alarmwill not stopa gasleak,but it will
alertyou to its presence.
It shouldnot be
usedasa substitutefor a goodinstallation
practices.It is always
or goodhousekeeping
goodpracticeto turn the gasoffat the
cylinderwhen it's not in use.
How the sensors work
A LPGsensoris madefrom a sinteredmetal
oxidethat is heated.When gaspasses
over
this componentit increases
in electrical
conductivity.Meanwhileanotherpart of
the sensoris enclosedand not exposedto
60
a Thesensorswere
installed
inasealed
chamher
gaswasinjecled
belore
andlhendishihuted
bylans
I PeterSpreadborough
led
thePBOtestteam.Heworksat
Southampton
CalorGas
Centreandhasspent20years
inthemarine
Heisa
industry
regularcontributorto
PBO'sAsk
theExperts
matters
columnon gasinstallation
the gas.l'his is used as a control and the
differencebet\ een the two is u\ed to trigger
the alarm. Some ofthe units tested had two
alarm levels - low and full -with the early
'low level'warning set to go off at a lower
gas concentration than the'full level'.
Other gas sources
In recentyea$ LPGhasbeenusedasa
and
CFC-fteereplacementin refrigerators
aerosols.
lt is alsousedin gaslighters,
cordlesscurlingtongs,gaslightsand other
portableappliances.
This meansoverzealoususeof an uDderarmdeodorantor
hairspraylrlay leadto a build-upof LPG
with potentiallythe sameresultsasa leak
ftom the backofvour cooker.
will alsodetectother
The sensors
llammablehydrocarbonssuchaspaint
thinnen and solvents,not forgcttlngthe
obviousoneslike petrol,die5eland alcohol.
Anotherreasonfor the alann going off is
to warn of a fault in the system-Th€
problemis how do you know if it's a fault
or a gasleak?All of the alarns testedhave
lights to warn of a fault, while someusea
c o m b i n , r t i oonf l i g h t sa n da u d i ow a r n i n S s .
Eitherway they makeit obvioussomething
is not right and needsattention.
DavidStoppardof MarineSystems
Enginee ng, which specialises
in gas
installationson boatsrangingfrom sail
training vessels
to superyachts
like Mi/dlrcl1.r
y, saysthereis a casefor itting aLarmswith
''lhey
the cheapestreplacementsensors.
willneed replacingfrom time to time
an).wat and continuedfalsealarmsonly
leadto mistrustin the alarmsystemand to
crewsdisconnectingit to avoid annoyance.'
Whena gas alarm sounds
l. Don't paniclGasalarmsaredesiSnedto
operatewell belowthe lowerlimit of
flammability(LEL)of the gas.
2. Extinguishall nakedflames.
3. Do not operateelectdcalappliances.
4. Switchoff all engines.
5. Tum off all gasappliances.
6. Tum off all gascylinders.
7, If safeto do soopen all hatches,doors
and windowssoair circulationcandisperse
the gas.
8, l'ump out the bilgewith a manualbilge
punp (not an electricone) and continueto
pump when the bilgeis dry. Any
accumulatedgaswill be pumpedoverboard.
Remember,
the gasyou areusingis heavier
Practical Boat Owner 471 March2006 . www.pbo.co.uk
"-a.rE=:
There is no substitute for a good gas
installation.Alwaysconsiderusinga
gasengineer.A list of
professional
madnegasinstallencanbe found at
r-w'r{.calormadneshop.co.uk-
than air and will collectin the bilgeor the
bottom of a locker,sopumping out could
takesometime.
9. Re-trythegasalarmfrom time to time
until it ceases
to'sound off'.
lO. Oncethishappens,
do not operate
your gassystemuntil it hasbeeninspected
and testedby a competentgasengineer.
Godes and regulations
Fitting a gas alarm
I Agasalarminstallationwill requirea
tusedelectdcalsupply.
I Although 24V alarmsareavailablethe
vastmajority soldare 12V
I The control module shouldbe locatedin
a prominent area- Somewhere
aroundthe
chafi tablewith other instrumentsis a
common location.
I Youmay want the alarmpoweredwhen
the boat is left unattended.This hasthe
advantageof alertingyou to a problemas
soonasyou retum to the boat.The
disadvantage
is that the alarmdraws
elect cal power and you may be left with flat
battedes.Anotheroption is to havethe
alalm wircd in so it comeson when you tum
on the batte es.Thls savesbatterypowet
but there is a sk that the battery switch may
causea sparkandigniteany leakedLPG.But
if the cylinder is tumed off in a properly
drainedlocker,that shouldn'tbea problem.
I Singleor multi-sensoralarmsareavailable.
I The codesof practice suggestthat one
alarmis frttedin eachcabinthat hasa gas
appliance.It would alsomakesenseto f,t
a Theteslswerecaniedoulwilhthehelp0lslallal
theSouthamolon
Calor
GasCenlre
one in areasofthe boat that gasis likely to
collect-in the spaceunder the gaslockeror
in a spacewheregaspipe ioints arenot easy
to inspect,for instance.In somecasesa
multi-sensorsystemwould suit.
Other safety devices
It alsofollows that if there areno leak iu
your gassystem,then the risk of explosion is
alrnostnon-existent.All installations should
have a method of checkingthe soundnessof
the gassystem.Although the minimum
requtuementis to have iust a testpoint a
built-in Alde bubble leaktesteris
a quick and simple method of checkingyour
gassystemeverytime you tum it on.
Gasalarminstallation
tips
I Theidealplacetoinstallasensoris atthe lowestpoinlgasis likelylo colleqt
THE SEI{SORSHOULD OTBEI STALLED:
I In an enclosedspaceawayfroma sourceol gas
I Directlybeloworaboveacooker
I Nextto a hatch,portholeol extractorlan
I Anywheredirt anddustcanblockthesensorandslop il wolking
I Anwhere it is likelyio getwet
Praclical Boat Owner 471 March2006. www.Dbo.co.uk
Surpdsinglt thereareno Bdtishor
EuropeanStandards
for the performance
ofa marinegasalarm- althoughthereare
ma ne codesof practicefor the installation
of gasalarmsin boats.Most manufacturen
thereforeusethe domesticgasalarm
standardBSEN50194:2000
and apply it
wherepossibleto the ma ne environment.
A CEmark usuallymeansthe alarmhas
beentestedfor electricalsafetvand radio
ftequencyinteference,It doesnot mean
it hasbeentestedfor pedormancein
detectinggas.
How the alarms were tested
All the LPGalarmswereplacedin a test
chambet and in orderto monitor the gas
industrialgas
concentrationtlvo separate
detectorswereplacedin the chamberwith
them. Thesehad recentlybeencalibrated
and werecapableof detectinggas
concentrationsin 1oloincrementsof the LEL.
All the alarmswerepoweredup and left to
warmup - imporlanla5lhey requiretime
to heatthe sensorunits and go through a
self-testand calibrationprocedure.
Gaswasaddedto the chamberusinga
syringe(left)sothe amount ofgas
couldbe controlled.A pat of
fansin the chambermlxed
the gasand air to givean
even mixture. The
concentrationof gaswas
recordedat every stage.
Oncethe gastestswere
complete,eachalarmwas
connectedto a 6xed power
supply and the current
drawnwasrecorded.
tr
6l
tr
EZSense
PilotMini
+
f,
gaaLtr
Retail price t4O
Star rating ***
This is a smallhandheld
I alarmw th a banery ifeof
abouteight hours,meaningit
would not be suitablefor
periodsof e)dendeduse. lt
would besuitableas a meansof
detectingthe locationofa leak
orcheckingthosehardto reach
placesin a boatthatwouldnot
normallyhavean alarm.lwas
very impressedwiththe EZ
Sense'lowlevel'alarm,which
soundedat 5oloLEL.Atthis level
it would be hardto detectthe
presenceof gas by smell.
;
A[T:;:lfii,::',ffi'
the boat'ssupply,the Pilot
l\,4ini
comessuppliedwltha controlpaneland a loosesensor The 3.5m
wiresuppliedwith the sensoris 5mm in diameter,so it only requires
smallholesto be drilledduringinstallation.
The installationkitdoes not
comewith a powercable.The backingplateis smalland a bitfiddly,
and the controlpanelattacheswithtlvo screwsthat requireside
access whichwouldlimitwhereit couldbe installed.lflt
detectsa
faultwth thesensorthecontrolpanelwillgive
an audioalarm.The
Pilotl\,1iniis
available
in l2Vor 24Vversions
withsingleortwinsensor
pleasing,bul it s
options.lt might not beihe most aesthetically
functionalandhas a provenlrack record.
Dualwatch
SFDetection
Z10b
a--
a
Retailprice €1OO
Star rating ***
t-
Retail price €15O
Retail price €75
Star rating ****
D;?::;fl:1i:i::?"
supply,thisunitcomes
BEST
wltha 1.8mpowercable.
SUDGET
Thesensorcableis ihin,
BI'Y
but has a plug measuring
'15mm
acrossthatwill
requirea largeholeto be drilledduringinstallation.
The controlpanelis
the sizeof adouble domesticpowersocket,and can be surfaceorflush
mounted.The sensoris locatedwithinasolid plastichousingand care
shouldbe takenwith its fixinglocationas it protrudes30mmfrom the
mountingsurface-The Z'10bgivesan early'lowlevel warningofthe
presenceofgas. In ourtest itsoundedat 9% LEL,beloregoing intofull
alarmmode at 14olo.
lt wasthe onlyiixedalarmtestedthat had this
feature.The conirolpanelcanalso detectafault withthe sensorand
givean audioalarm.The alarmis designedto acceptan inputvoltage
of betweenSVand 27Vmakingit suitableforeithet12Vot 24V
installaiions.lt has asingle ortlvin sensoroption.
Model
Fullalarm
",6ol LEL
Lowlevel Voltage
alarm
% of LEL
EZSense
9/.
5./.
N/A
N/A
PilotMini
240/6
N/A
12124V
sF z10b
14%
9%
Dualwatch
10%
N/A
ROM203
11%
Power
consumption
on stand-by
Star rating ****
The DJalwatchlro.n Marinecareis the o'rly alarn_tl'al also has a
! bu ll-i r carbonnororide detector.Altl'oJgl' tl'is makesil one of
the most expensivealafrnswe tested,itdoes giveextraprotectionfor
you and your crew.lt's designedto be hardwired intothe boat s supply
and comeswith a3m powercable.The sensorcablehas a largep ug
on the end measuring13mm.The attractivecontrolpanel,designedto
fit ln with otherboat instruments.can beflush orsurfacemounted.Of
allthe alarmstested,it had the
lowestpower
consumption.
The alarmis
designedwlth
--ra singleLPG
sensor,ou an
additional
sensorcan be
'daisy-chained'
on to makeit atlvin
sensorunit.The
Dualwatchis only availablewith
a 12Vpowerinput,however
Sensors
-_t
Fault
atarm
Hush
button
Relay
outlet
Gasswitch
outlet
LJNE
None
NO
No
No
95mA
One/two
Lightand audio
No
No
Yes
12124V
103m4
One/two
Liqhtandaudio
Yes
Yes
Yes
12V
65mA
Oneortwo
Lightonly
NO
Yes
No
12V
163m4
One
Lightonly
NO
No
No
NereusWG1000127o
12V
70mA
Oneortwo
Lightand audio
Yes
Yes
Yes
VetuscDgoo
12124V
114mA
Oneor tvvo
Lightonly
No
Yes
Yes
62
247"
Practical Boat Owner 471 March2006 . wwwpbo.co.uk
RDM203
WG1000
Nereus
Retail price €45
Star rating ***
Retail price E2OO Star rating *****
The cheapestfixedalarm
I tested,the RDM203's
controlpanelhas avery short
(0.3m)powercablefor wiring
-!ilillll
intothe boat'ssupply.The 3m
i
sensorcable has a plug on the
I
end measuring
16mm,
:
requiring
a majorholetobe
The
drilledduringinstallation.
controlpanelcomeswith a
mountingplateand can only
be surfacemounted.Although
the cheapestfixedalarm,
detectionperformancewas not
compromisedby its low price.Power
consumption,however,was by far the
timesas muchas the lowest
highestat 18mA nearlyone-and-a-half
consumingunit.Forperformancewhereelectricaiconsumptionand
aestheticsare not important,this alarmisworth considering.
=t
, t -
VetusGD900
Retail price e245
Star rating **
Thrs alarmis desrgnedto be hardwired into the boal s supply.The
I controloanelis desroneoto be flushfittedand comeswith 0.8mof
powercable.The sensoihas exposedcontactsthatcould be
vulnerableto damagewheninstalled.The 5m ofsensor cablecan be
easiiyinstalledthrougha 7mm hole and is joinedto ihe controlpanel
via a multi-blockplug.
Unliketheotheralarms,whichonlycome
with an explanatoryleaflet,the
Vetuscomeswith a
comprehensivemultilingua
nstallationguide.The wiring
diagramis clearand the
wlresarecolourcoded.
The alarmworks on either
12Vor 24Vand additional
sensorscan be added. lt
was the most expensve
alarmwe tested,yet its
performancewas no better
than anotheralarmcostingless
than halfits price.
Approximate Lengthot
warm-uDtime sensorwite
Flush and/ol
surface litting
Control box
dimensions
20secs
2 -3 mins
N/A
N/A
N/A
J.5m
Surfaceonly
53mmx 100mm
1 5m i n s
2 -3 mins
6m
Flushor Surface
100mmx 160mm
6m
Flushor Surface
108mmx 122mm
3 mins
3m
Surfaceonly
71mmx 125mm
2 mins
6m
Surfaceonly
65mmx65mm
2 mins
5m
Flushonly
90mmx90mm
PracticalBoal Owner 471 March2006 . wvvw.pbo.co.uk
Theonething that
I willnormally
stop a gas detector
workingis water
gettingon the
is
sensor;this
wherethe
Nereusalarm
scoreshighly-it
has a waterproof
sensor Although
beingone of the
most expensive
alarmswetested,
not havingto replacewaterdamagedsensorsat 130-!50 a
Inaddition
timewillmakethisalarmawofthwhileinvestment.
becausetherewill be no'down time'with damagedsensors,
this alarmwillaffordthe best protectionand avoidthe
annoyanceoffalse alarms.The Nereusis designedto be hardwired
intothe boat'ssupply and a shortlengthof powercableis supplied
alongwitha fusedconnectotThe controlpanelcandetectafaLlltwith
the sensorandgive an audioalarm.The waterproofsensoris supplied
with 6m of cablethatis4mm in diameter,with no plugs,which makesit
veryeasyto conceal.The controlpanel,thoughsmall,is easytofix and
functional.Theysay lookscan be deceptiveand the Nereusalarmis
LEL
notthe best looking,but a waterproofsensorsoundingat 12olo
coupledwith lts low powerconsumptionmakesthis, in nnyop n on,
the beston test.Atlvin sensoralarmunlt is also available.
Conclusion
lwas very pleasedthat allthe alarmsperformedas requiredbythe marine
codes of practicesoundingbefore25%oi LEL.Withinthe gas detectLon
industryalarmsare normallydesigned10soundat between5ol.and 20oloof
LEL,whichis whatthe majoriryofthe alarmsdid.Any ofthe
protection,but,asthetabe
alarmstestedwouldprovide
doso.
shows,someusea lotlesselectricalpowerto
Costmayalsobe an issueandthereisalargeprice
rangeto choosefrom.
llly viewis that it'sbettertofit any ofthetested
alarmsthan noneat all.Basedon priceand
functionality,
the RDM203 has a lotto otfer,but
theprizeforbestbudgetbuygoestotheSFZl0b.
TheEZSensealso
scoreshighlyforitsflexibility.
lf choosing
analarmon meritalone,theNereus
sensor
because
of itswaterprool
WG1000wins
(right).
itcouldprovetobea
Although
expensive
investment.
worthwhile
lono-term
Dualwatch,tel: 01474855699,web: \4 44tr.marinecare.co.uk
NereusWG1000,tel: 01202731886,web: !wvw.nereusalarms.co.uk
Pilot Mini, tel: 02476680088,web: vw'ryr'.technisolltd.co.uk
EZ Sense and SF 210b, tel:01202645587,web: lvvw.sfdetection.com
Vetus GD900,tel: 02380454507,web: w\,/wvetus.nl
RDM 203,tel: 0 t444 831550,web: lvvvw.gasalarms.biz
Replacementsensor costs
Dualwatchf40, NereusWG1000€60, PilotMinil30, EZ SenseN/A,
SF DetectionZ'10b130,VetusGD900!45.Withthe RDM203 it is more
to buy a completenewaiarm
cost-effective
ThankstoSouthampton
CalorGasCenlrefor useof itsworkshopfacilities
andtothemembersof thegasdetectionindustrywhoprovidedtechnical
thisarticle.
in carryingoutlhetestsandin preparing
assistance
63