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8/9/2019 50RS12 333
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www.hsl.gov.uk An Agency of the Health and Safety Executive
www.hsl.gov.uk An Agency of the Health and Safety Executive
UKELG 50th A!"E#SA#$ %EE&!G#E'E& (EL)*%E&S ! A#EA
'LASS!+!'A&!) +)# GASES
#)GE# SA&), HEAL&H - SA+E&$ LA)#A&)#$, U/&)
8/9/2019 50RS12 333
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An Agency of the Health and Safety Executive
')&E&S
'u11ent standa1ds *1evious wo1k on gases 2UA("E&
atu1al ventilation esti3ation 'onst1aints Exa34les
(e3onst1ation +utu1e develo43ents #efe1ences
8/9/2019 50RS12 333
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An Agency of the Health and Safety Executive
'U##E& S&A(A#(S
S E 006789089:;007, Elect1ical a44a1atusfo1 ex4losive gas at3os4he1es < *a1t 90:'lassification of ha=a1dous a1eas.
A1ea classification code fo1 installations
handling fla33a>le fluids, %odel 'ode of safe41actice, !* 95 ?1d edition, &he Ene1gy
!nstitute, ;005.
!GE%@S#@;5, Edition ;, Ha=a1dous a1ea
classification of natu1al gas installations,
!nstitution of Gas Enginee1s and %anage1s,
;090.
8/9/2019 50RS12 333
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An Agency of the Health and Safety Executive
'U##E& S&A(A#(S
S E 006789089:;007, Elect1icala44a1atus fo1 ex4losive gasat3os4he1es < *a1t 90: 'lassification of
ha=a1dous a1eas.
< one definitions
< Sou1ce te13s
< "=
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An Agency of the Health and Safety Executive
'U##E& S&A(A#(S
"=
< Hy4othetical gas cloud volu3e
< %ean concent1ation of 50B LEL Cfo1 seconda1y
1eleasesD
< (ete13ines level of ventilation < !f "= is less than 0.93?, ventilation is 1ega1ded as
high and =one is classified egligi>le Extent CED
and no 41ecautions against ignition a1e 1eui1ed.
< Euations fo1 the calculation of "= a1e included inS E 006789089:;007
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An Agency of the Health and Safety Executive
GASES
8/9/2019 50RS12 333
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Gases
"= esti3ated f1o3 S E 006789089found to >e 900 to ?000 ti3es la1ge1than values o>tained f1o3 '+(
#e4o1ted at Ha=a1ds /!/ CGant et alD
8/9/2019 50RS12 333
8/41 An Agency of the Health and Safety Executive
GASES
Vz from BS EN is 2 – 3 orders of
magnitude larger
In every case Vz from CFD is less
tan !"#m3
8/9/2019 50RS12 333
9/41 An Agency of the Health and Safety Executive
GASES
S E 006789089 calculation is >asedon 41e3ise that 1atios: Actual ventilation rate / Ventilation rate
required to dilute gas escape tospecified level
And
Enclosure volume / V z A1e eual.
&his has no scientific >asis.
8/9/2019 50RS12 333
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GASES
;00 Steel wo1ks so1ted atu1al gas indust1y su>Fect to (SEA#
< Una>le to co34ly with thei1 own code !GE%@S#@;5
< o lowe1 41essu1e li3it fo1 =one ;
Una>le to Fustify a44lication of E =oning Una>le to 1each ag1ee3ent with HSE on
th1eshold fo1 =oning low 41essu1e installations S E 006789089 3ethodology in dou>t
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GASES
atu1al Gas 8 oint !ndust1y *1oFect;008;006 < HSL 1e4o1t ##?0 and Ha=a1ds //! 4a4e1
!GE%@S#@;5 1evised to include one ;
E, 4u>lished ;090
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)&HE# GASES
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13/41 An Agency of the Health and Safety Executive
)&HE# GASES
2UA("E&I ased on an integ1al gas Fet 3odel Jell esta>lished scientific c1edi>ility
+ull 3athe3atical de1ivation 4u>lished;099, CJe>>e1 et alD
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2UA("E&
Unchoked flow will 1esult if:
a P
P
9.7
whe1e P is the gas sto1age 41essu1e and
P a is at3os4he1ic 41essu1e.
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2UA("E&
Jhen the flow is choked CsonicD it isnecessa1y to define a 4seudo sou1cehole 1adius r s, whe1e r o is the o1ifice
1adius
−+= 9.15.01
0
a
s P
P r r
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2UA("E&
"=
ρb Ckg@3?D is the density of the >ackg1ound Cwhich no13ally
a441oxi3ates to that of ai1D ρs Ckg@3?D is the density of the sou1ce gas
is the ent1ain3ent coefficient C1eco33ended value 0.05D
x b Cv@vD is the >ackg1ound concent1ation
x crit Cv@vD is the concent1ation of inte1est C50B LEL fo1seconda1y 1eleasesD
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16
9
−
−
bcrit
b
s
b s
x x
xr
ρ
ρ
α
π
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2UA("E&
&he >ackg1ound concent1ation of fla33a>le gas
x b in the enclosu1e is
q9 C3?@sD is the ventilation 1ate
qs C3?@sD is the sou1ce gas volu3e flow1ate
ε is the efficiency of >ackg1ound 3ixing Csee >elowD.
&he leak 1ate qs can >e de1ived f1o3 standa1d 3ethods fo1 the
esti3ation of leak flow1ates. A441o41iate 3ethods a1e included in
S E 006789089:;007, Annex A.
1q
q x sb
ε =
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An Agency of the Health and Safety Executive
2UA("E&
)utdoo1s the1e is =e1o >ackg1oundconcent1ation, x b0, and the >ackg1ound
density is that of 4u1e ai1
32/33
1
16
9
=
crit s
a s
Z
x
r V
ρ
ρ
α
π
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An Agency of the Health and Safety Executive
2UA("E&
&he axial distance z to a concent1ation x zone 3ay >ede1ived as an a441oxi3ation to the =one extent. An
a441o41iate value of x zone should >e chosen. S E
006789089 uses 900B LEL fo1 exa34le.
( )
( )b zone
zone s
x x
xr z
−−
= 1
µ
b
s
ρ
ρ α µ 2≡
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An Agency of the Health and Safety Executive
"AL!(A&!)
2uadvent has >een validated against detailed '+(si3ulations which the3selves have >een validatedagainst ex4e1i3ental data.
&he validation data includes si3ulations of a 1ange offla33a>le gas 1elease 1ates in enclosu1es of va1ious
si=es at a 1ange of diffe1ent ventilation 1ates. All of the si3ulations a1e fo1 uno>st1ucted 1eleases of3ethane in a ventilation cont1olled cha3>e1.
&he ag1ee3ent >etween the 2UA("E& 3odel andthe '+( si3ulations is su141isingly good conside1ing
how si34le the 2UA("E& calculation is.
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An Agency of the Health and Safety Executive
"AL!(A&!)
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An Agency of the Health and Safety Executive
E'L)SU#E "E&!LA&!)
&he ventilation 1ate of an enclosu1e is a key
in4ut to an a1ea classification assess3ent.
+o1ced ventilation 1ates can >e esta>lishedf1o3 design o1 eui43ent s4ecifications.
&he natu1al ventilation 1ate will va1y th1oughti3e as it is st1ongly influenced >y the weathe1
conditions. Si34le a441oaches fo1 the
esti3ation of ventilation 1ates, suita>le fo1 use
as 4a1t of HA' 3ethodologies, a1e the1efo1e
1eui1ed.
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An Agency of the Health and Safety Executive
E'L)SU#E "E&!LA&!)
S57;5:9779 contains 3ethods fo1 ve1y
si34le enclosu1es
A s41eadsheet containing a si34le 3odel ofwind and >uoyancy d1iven ventilation is
availa>le f1o3 the 'ha1te1ed !nstitution ofuilding Se1vices Enginee1s C'!SED
')%!S o1 ')&A% 3ulti=one 3odels
Ex4e1i3ental 3easu1e3ents, o1 '+(si3ulations 2uadvent contains an esti3ation 3ethod
8/9/2019 50RS12 333
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An Agency of the Health and Safety Executive
2UA("E& ')SA!&S
Hole si=e Local congestion and confine3ent < "entilation efficiency facto1 ε
Safety facto1 Su>8cha3>e1s *1essu1e "= value fo1 s3all enclosu1es
Availa>ility of ventilation ackg1ound concent1ation "alidation li3ited to 3ethane
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An Agency of the Health and Safety Executive
2UA("E& ')SA!&S
Hole si=e < "= is a function of the cu>e of the hole1adius
< "= 3ust not >e unde18esti3ated
< %ini3u3 of 0.;533; is 1eco33ended
Cexce4t unde1 s4ecified ci1cu3stancesD
< +u1the1 guidance in 'ox Lees and Ang
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An Agency of the Health and Safety Executive
2UA("E& ')SA!&S
'ongestion and confine3ent < Guidance in !GE%@S#@;5 A44endix < Efficiency of 3ixing ε
ε 9 1e41esents an uno>st1ucted 1elease
ε M 1e41esents a 3ode1ate deg1ee of
o>st1uction
ε N 1e41esents a significant o>st1uction to the
ventilation flow
< )ve1 900 3? ve1ify local ventilation
effectiveness with s3oke tests etc.
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An Agency of the Health and Safety Executive
2UA("E& ')SA!&S
Safety facto1 < &o allow fo1 unce1tainty
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An Agency of the Health and Safety Executive
2UA("E& ')SA!&S
Su> cha3>e1s < 'o34ute "= fo1 the volu3e of the su>8cha3>e1 with1educed ventilation 1ate
o1
< Set "= to su>8cha3>e1 volu3e
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An Agency of the Health and Safety Executive
2UA("E& ')SA!&S
*1essu1e < Li3it E =ones to syste3s at less than 90 >a1g < Li3it to ;0 >a1g >ased on 1isk assess3ent taking
the conseuences of ignition, i.e. the 1isk of inFu1y,
into account
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An Agency of the Health and Safety Executive
2UA("E& ')SA!&S
"= si=e c1ite1ion < +o1 enclosu1e volu3es of less than 903? the c1ite1ion of 0.9 3? fo1 "= should >e
1educed to 9B of the enclosu1e volu3e.
&his const1aint is taken f1o3 S E 006789089:;007
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An Agency of the Health and Safety Executive
2UA("E& ')SA!&S
"entilation availa>ility < &he guidance in S E 006789089:;007should >e o>se1ved
E =ones not allowed if availa>ility is 4oo1
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An Agency of the Health and Safety Executive
2UA("E& ')SA!&S
ackg1ound concent1ation < Suggested li3it ;5B LEL < Unde1 conside1ation fo1 inclusion in
softwa1e
< %anual check
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An Agency of the Health and Safety Executive
2UA("E& ')SA!&S
"alidation < Jhilst this 3ethodology is valid fo1 allgases, it should >e noted that the validation
of the c1ite1ion of 0.9 3? fo1 the value of "=
leading to an E classification has only>een ca11ied out fo1 natu1al gas.
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An Agency of the Health and Safety Executive
2UA("E& E/A%*LES
)utdoo1 >utane gas 4i4ewo1k, seconda1y1eleases
* O.5 >a1a Hole si=e 0.;533;
"=, 3? one
S E 00678
9089:;007
0.? one ;
2UA("E& 0.00;9 one ; E
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An Agency of the Health and Safety Executive
(E%)SA&!)
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An Agency of the Health and Safety Executive
')'LUS!)S
S E 006789089:;007 it1a1y 1esults < o scientific foundation
< "= u4 to ? o1de1s of 3agnitude too high
2UA("E& < Scientific >asis
< )ften 1educes =oning 1eui1e3ents
< 'a4ital and 3aintenance costs of 41otected
eui43ent can >e 1est1icted to genuine 1isks
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An Agency of the Health and Safety Executive
+U&U#E (E"EL)*%E&S U(E#
')S!(E#A&!)
Softwa1e < now availa>le fo1 gases CSeeleafletD +lashing liuids CL*G, A33oniaD C*1oFect
in 41og1essD
*lu3es !34inge3ent
Liuid 4ools Gas 3ixtu1es %ist C!* in 41og1essD
8/9/2019 50RS12 333
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An Agency of the Health and Safety Executive
#E+E#E'ES
S E 006789089:;007, Elect1ical a44a1atus fo1ex4losive gas at3os4he1es < *a1t 90: 'lassification ofha=a1dous a1eas.
A1ea classification code fo1 installations handlingfla33a>le fluids, %odel 'ode of safe 41actice, !* 95
?1d edition, &he Ene1gy !nstitute, ;005.
'ox, A.J., Lees, +. *. and Ang, %. L., 'lassification ofHa=a1dous Locations, ! 'he3 E, 9770.
A1ea classification fo1 seconda1y 1eleases f1o3 low41essu1e natu1al gas syste3s, HSL #esea1ch #e4o1t##?0.
8/9/2019 50RS12 333
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An Agency of the Health and Safety Executive
#E+E#E'ES ;
"entilation theo1y and dis4e1sion 3odelling a44lied to ha=a1dous
a1ea classification, (.%. Je>>e1, %.. !vings and #.'. Santon, ou1nal of Loss *1evention in the *1ocess !ndust1ies 2$ C5D
Se4te3>e1 ;099, 9;8;9
tt%&''d("doi"org'#!"#!#)'*'*l%"2!##"!$"!!2
Gant, S.E., !vings, %.., ones, A., and Santon, #., Ha=a1dous
A1ea 'lassification of Low *1essu1e atu1al Gas Syste3s using'+( *1edictions. Ha=a1ds /!/, %ancheste1, ;00
ew %ethods fo1 Ha=a1dous A1ea 'lassification fo1 Ex4losiveGas At3os4he1es, #.'. Santon, %..!vings, (.%. Je>>e1 and A
Kelsey, Ha=a1ds //!!!, South4o1t ;09;
http://dx.doi.org/10.1016/j/jlp.2011.04.002http://dx.doi.org/10.1016/j/jlp.2011.04.002
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A'K)JLE(GE%E&S
%at !vings 8 HSL (avid Je>>e1 8 HSL Ad1ian Kelsey8 HSL
HSE HSL