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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/&)

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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

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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.

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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

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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

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    GASES

     

    Vz from BS EN is 2 – 3 orders of

    magnitude larger 

    In every case Vz from CFD is less

    tan !"#m3

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    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.

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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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    )&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 

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    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

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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

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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.

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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