T ansac ions o he VSB - Technical Uni e si y o Os a a
Sa e y Enginee ing Se ies, ISSN 1805-3238
Vol. XV, No. 1, 2020
38
COMPARISON OF VARIOUS APPROACHES FOR DETERMINATION
OF SEPARATION DISTANCES
Daniela PITELKOVÁ1, Pe HEJTMÁNEK2, Vladimí MÓZER3
1 Facul y o Ci il Engine ing, Czech Technical Uni e si y in P ague, P ague, Czech Republic,
[email p o ec ed]
2 Facul y o Ci il Engine ing, Czech Technical Uni e si y in P ague, P ague, Czech Republic,
pe [email p o ec ed]
3 Facul y o Ci il Engine ing, Czech Technical Uni e si y in P ague, P ague, Czech Republic,
ladimi [email p o ec ed]
Abs ac : The ex en o i e sp ead by adia ion is delimi ed by sepa a ion dis ances, equi ed
o p e en ex e nal i e sp ead due o excessi e adia ion hea o alling bu ning b ands.
The simpli ied calcula ion me hod uses a se ies o p ecalcula ed abula ed alues.
Al e na i ely, a mo e p ecise analy ical calcula ion app oach can be used. The esolu ion
o he me hod can de e mine he equi ed sepa a ion dis ances signi ican ly. This pape
e alua es analy ical calcula ion me hods and CFD simula ions o de e mine hei
accu acy o sepa a ion dis ances p edic ion. The mos app op ia e a e s anda d analy ical
calcula ion me hods wi h su icien numbe o e alua ion poin s along he adia ing
su ace.
Keywo ds: Sepa a ion dis ances, Fi e sp ead zone, S e an-Bol zmann law, View ac o , Radia ion
in ensi y.
Resea ch a icle
In oduc ion
A zone o po en ial i e sp ead is p esen a ound
a building in i e. This zone is bound by sepa a ion
dis ances, beyond which i e sp ead isk is conside ed
su icien ly low. Inside he zone i e may sp ead by
adian hea o alling bu ning b ands.
Sepa a ion dis ances a e hence an impo an
aspec o building i e sa e y design in he dense
u ban a eas. The p ima y goal is o a oid po en ial
i e sp ead among he buildings, which becomes
a p oblem on small lo s whe e buildings a e placed
close o he p ope y bounda ies.
Acco ding o he Czech echnical s anda ds
(ČSN 73 0802 (ČSN 73 0802, 2020) and ČSN 73
0804 (ČSN 73 0804, 2020)), he zone o po en ial
i e sp ead mus no ex end beyond he p ope y
bounda ies o he owne . The e a e a ew excep ions
om his equi emen , such as he p ojec ion o
he zone on o he public a eas, such as oads,
pa emen s and o he simila a eas whe e i e sp ead
is no expec ed. None heless, he zone canno
p ojec on o a p i a e p ope y, ega dless o i s use,
unless he owne o he a ec ed p ope y ag ees and
building con ol app o es such exemp ion. In any
case, i is always ad isable ha he zone o po en ial
i e sp ead does no ex end beyond he p ope y on
which he conside ed building is loca ed, and does
no a ec neighbou ing buildings, ega dless o hei
owne ship.
Sepa a ion dis ances a e de e mined by wo
me hods in he Czech Republic. The i s me hod
is a simpli ied app oach which uses abula ed
p ecalcula ed alues om he echnical s anda ds
o building i e sa e y design ČSN 73 0802 (ČSN
73 0802, 2020), ČSN 73 0804 (ČSN 73 0804, 2020).
The second me hod is mo e p ecise and uses analy ical
calcula ion app oach based, he desc ip ion o which
may be ound in ČSN EN 1991-1-2 (ČSN EN 1991-
1-2, 2004) and (Reichel, 1989). The c i ical hea
adia ion in ensi y in his case is aken om ČSN 73
0802 (ČSN 73 0802, 2020), ČSN 73 0804 (ČSN 73
0804, 2020).
The simpli ied app oach akes he poin wi h
he highes in ensi y o hea adia ion, usually
he cen e o he adia ing su ace, and applies
he equi ed sepa a ion dis ance o he en i e
adia ing su ace. This means ha he sepa a ion
dis ance is o e es ima ed, pa icula ly a he edges
o he adia ing su ace, howe e , e s on he side
o sa e y.
pp. 38-46, DOI 10.35182/ ses-2020-0005
T ansac ions o he VSB - Technical Uni e si y o Os a a
Sa e y Enginee ing Se ies, ISSN 1805-3238
Vol. XV, No. 1, 2020
39
The e is no uni e sal in e na ionally applied
me hod o he de e mina ion o su icien sepa a ion
dis ances. None heless he majo i y o he me hods
a e based on he physics laws o adia i e hea
ans e . They also use, implici ly o explici ly,
di e en c i ical adia ion in ensi ies conside ed as
limi s o i e sp ead.
The sepa a ion dis ances a e usually dependen
p ima ily on he adia ion in ensi y, which is
desc ibed h ough he S e an-Bol zmann law.
In p ac ice, he law can be ma hema ically exp essed
h ough he equa ion o he in ensi y o adian hea
lux (Blahož and Kadlec, 1996; Kuče a, 2009):
[kW.m-2] (1)
whe e
σ = 5,67∙10-8 [W.m-2.K-4] S e an-Bol zmann cons an ;
ε emissi i y [-];
ϕ iew ac o [-];
TN gas empe a u e inside i e compa men [°C];
T0 ini ial empe a u e (usually 20 °C) [°C].
The in ensi y o adian hea lux is calcula ed
om he empe a u e o bu ning gases in he i e
enclosu e o compa men . This empe a u e - TN
- may be es ablished in a ious ways. A simpli ied
way o de e mina ion o TN o a gi en ime is o
use he ISO 834 ime- empe a u e cu e ela ionship
(ČSN 73 0802, 2020):
[°C] (2)
whe e
ime [minu es];
T0 ini ial empe a u e (usually 20 °C) [°C].
Along wi h he empe a u e o he emi ing
su aces (equal o he gas empe a u e inside
he i e enclosu e), he iew ac o has a signi ican
impac on he esul ing adian hea lux a
he ecei ing su ace. The iew ac o is dependen
on he ollowing:
• shape and size o he emi ing and ecei ing
su aces;
• dis ance be ween he emi ing and ecei ing
su aces;
• mu ual o ien a ion (angle) o he emi ing and
ecei ing su aces.
The iew ac o is calcula ed di e en ly o
a ious combina ions o shapes and o ien a ions o
he emi ing and ecei ing su aces.
The basic con igu a ion (as pe ČSN 73 0802
(ČSN 73 0802, 2020), ČSN 73 0804 (ČSN 73 0804,
2020)) is a pa allel con igu a ion o he emi ing and
ecei ing su aces. I is ep esen a i e o a case o
wo building ex e io walls pa allel o each o he .
Fo an exposu e poin o iew, his con igu a ion
also ep esen s he mos se e e exposu e along he
emi ing su ace wid h.
The pa ial iew ac o s o his con igu a ion a e
calcula ed as ollows:
[-] (3)
whe e
a = h/s;
b = w/s;
s (sepa a ion) dis ance be ween he adia ing and
ecei ing su aces [m];
h heigh o he i- h segmen (1, 2, 3, 4) o
he adia ing su ace [m];
w wid h o he i- h segmen o adia ing su ace
[m].
Subsequen ly he esul ing iew ac o s o
he en i e adia ing su ace (opening) is calcula ed
in h ee di e en ways, depending on he loca ion o
he elemen ep esen ing he ecei ing su ace:
1. iew ac o s o he ecei ing su ace di ec ly
opposing he adia ing su ace (opening) - Fig. 1
a):
[-] (4)
2. iew ac o s o he ecei ing su ace di ec ly
opposing he adia ing su ace (opening) - Fig. 1
b):
[-] (5)
3. iew ac o s o he ecei ing su ace beyond
he edges away om he adia ing su ace
(opening) - Fig. 1 c):
[-] (6)
44
N0
[( 273) ( 273) ]
ITT
σεφ
= ⋅ + −+⋅⋅
( )
N0
345 log 8 1TT
=+⋅ +
( ) ( )
( ) ( )
1
11
22
22
1
11
22
22
an
11
1
2
an
11
i
ab
aa
bb
bb
φ
π
−
−




⋅+



++


= ⋅





+⋅



++



1234
φφφ φφ
=+++
12
φφφ
= +
ABEF BCDE 3 4
φφ φ φφ
= + −−
pp. 38-46, DOI 10.35182/ ses-2020-0005
T ansac ions o he VSB - Technical Uni e si y o Os a a
Sa e y Enginee ing Se ies, ISSN 1805-3238
Vol. XV, No. 1, 2020
40
F om he o e all adia ion in ensi y di ec ly a he
emi ing su ace and he equi ed c i ical adia ion
in ensi y, he c i ical iew ac o can be es ablished:
[-] (8)
whe e
Ic c i ical adia ion in ensi y (13-18.5 (Reichel,
1989)) [kW.m-2].
The sepa a ion dis ance s (see equa ion (7)),
i.e. he dis ance a which he adia ion in ensi y
dec eases o he equi ed c i ical adia ion in ensi y,
is eached when:
(9)
F om he enginee ing pe spec i e, he e is
a numbe o app oaches o implemen ing he abo e
calcula ion p ocedu e. They di e in accu acy,
p ima ily due o educ ion o he numbe o poin s
o he emi ing su ace e alua ed.
Me hods
The echnical s anda ds o building i e
sa e y design in he Czech Republic a e based on
he p inciples desc ibed abo e. De ailed desc ip ion
o indi idual app oaches may be ound o example
in ČSN 73 0802, ČSN 73 0804 and ČSN EN 1991-
1-2.
The e alua ion o he di e en app oaches is
based on a simple model case wi h a single opening,
which ep esen s he adia ion emi ing su ace.
The ocus was pu on he ex en and shape o
he zone in which he adia ion in ensi y was abo e
he c i ical limi 18.5 kW.m-2, which was aken om
ČSN 73 0802 and ČSN 73 0804 (ČSN 73 0802,
2020; ČSN 73 0804, 2020).
c) beyond he edges o opening
Fig. 1 Possible con igu a ions o calcula ion o
he iew ac o o he emi ing su ace
The iew ac o o wo su aces wi h an angle θ
(Fig. 2) can be calcula ed as ollows (ČSN EN 1991-
1-2, 2004) wi h Equa ion (7).
Fig. 2 Con igu a ion o calcula ion o iew ac o
o ecei ing and emi ing su aces wi h angle θ
(ČSN EN 1991-1-2, 2004)
a) cen e and along
he opening
b) a he edges
o opening
( ) ( )
( ) ( ) ( )
( )
( ) ( )
11
1 11
2 2 22
2 22
11
11
22 22
22
1 cos
an an
1 2 cos 1 2 cos sin
1
2cos cos
an an
sin sin
b
aa
a
bb bb a
b
aa
θ
θ θθ
φ
πθθ
θθ
−−
−−


−


− ⋅ +⋅



+− +− +


= ⋅




−



⋅+




++





[-] (7)
whe e
a = h/s;
b = w/s;
s (sepa a ion) dis ance be ween he adia ing and
ecei ing su aces [m];
h heigh o he i- h segmen (1, 2, 3, 4) o
he adia ing su ace [m];
w wid h o he i- h segmen o he adia ing
su ace [m];
θ angle be ween he adia ing and ecei ing
su ace.
c
c
I
I
φ
=
c
φφ
≤
pp. 38-46, DOI 10.35182/ ses-2020-0005
T ansac ions o he VSB - Technical Uni e si y o Os a a
Sa e y Enginee ing Se ies, ISSN 1805-3238
Vol. XV, No. 1, 2020
41
es ablish he side ex en (Fig. 3 d) -
he alues o sepa a ion dis ances a e
es ablished o he adia ing su ace
ho izon al cen e line, using iew ac o
calcula ion con igu a ions shown in
Fig. 1 a), b) and c).
Calcula ions desc ibed in i ems 2. and 3. a e
sel -con ained p og ammes, and me hod 4. was
sc ip ed in Py hon.
a) Me hod 1
b) Me hod 2
c) Me hod 3
d) Me hod 4
Fig. 3 G aphical ep esen a ion o adia ion
in ensi y calcula ion me hods
In addi ion o he analy ical calcula ion me hods
and simpli ied abula ed app oach adia ion
in ensi y was e alua ed also in he Fi e Dynamics
Simula o (FDS) de eloped by he Na ional
Ins i u e o S anda ds and Technology (NIST).
I is a eely a ailable simula ion so wa e which
is complemen ed by a isualisa ion pos p ocesso
Smoke iew (NIST, 2020).
The heigh o he opening was cons an -
1.25 m; his ep esen s a s anda d window heigh
ound in many buildings. The wid h o he opening
was g adually inc eased om 1.0 m o 3.0 m
in inc emen s o 0.5 m.
To calcula e he adia ion in ensi y, which
inc eases wi h ime - see equa ions (1) and (2),
i e du a ion was aken as 45 minu es. This
alue is ep esen a i e o dwelling houses and
esiden ial accommoda ion as pe ČSN 73 0802.
The i e du a ion o 45 minu es co esponds o he
empe a u e TN = 902.32 °C and o he adia ion
in ensi y a he emi ing su ace I = 108.5 kW.m-2.
The indi idual app oaches o he de e mina ion
o he sepa a ion dis ance s e alua ed we e as
ollows:
Me hod 1 - abula ed da a me hod om ČSN 73
0802 wi h in e pola ion (Fig. 3 a) -
he abula ed alues o sepa a ion
dis ances a e es ablished o
he adia ing su ace cen e poin
(ho izon ally and e ically), using
iew ac o calcula ion con igu a ion
shown in Fig. 1 a);
Me hod 2 - de ailed calcula ion based on
he poin s posi ioned along he opening
ho izon al cen eline in he middle and
a he edges wi h he app oxima ion
o he side ex en by a semi-ci cula
shape (Poko ný, 2017) (Fig. 3 b) -
he alues o sepa a ion dis ances a e
es ablished o he adia ing su ace
ho izon al cen e line, using iew
ac o calcula ion con igu a ions shown
in Fig. 1 a) and b) in combina ion wi h
he semi-ci cula app oxima ion o
he side ex en ;
Me hod 3 - de ailed calcula ion based on he poin s
posi ioned along he opening ho izon al
cen eline in he middle, qua e s and
a he edges wi h he app oxima ion
o he side ex en by an angula shape
(Kuče a, 2009) (Fig. 3 c) - he alues o
sepa a ion dis ances a e es ablished o
he adia ing su ace ho izon al cen e
line, using iew ac o calcula ion
con igu a ions shown in Fig. 1 a) and
b) in combina ion wi h he angula
app oxima ion (equa ion (7)) o he
side ex en ;
Me hod 4 - de ailed calcula ion based on 100
e alua ion poin s along he wid h
(ho izon al cen eline) o he opening
and addi ional 0.01 m inc emen s o
pp. 38-46, DOI 10.35182/ ses-2020-0005
T ansac ions o he VSB - Technical Uni e si y o Os a a
Sa e y Enginee ing Se ies, ISSN 1805-3238
Vol. XV, No. 1, 2020
42
Fo compa ison wi h he ou analy ical
me hods an e alua ion using CFD simula ion
in he Fi e Dynamics Simula o was conduc ed.
The compu a ion mesh had a cell size o
25×25×100 mm. The con igu a ion o he adia ing
su ace was iden ical o he abo e desc ibed scena ios
o analy ical calcula ions. The en i e adia ing
su ace had a uni o m empe a u e acco ding o
he ISO 834 ime- empe a u e cu e - 902.34 °C
ep esen ing he 45 h minu e o a ully de eloped
i e. Simila ly o he analy ical calcula ion me hods,
adia ion in ensi y was moni o ed along on a plane
aligned wi h he ho izon al cen eline. This was
done in wo di e en ways:
1. INTEGRATED INTENSITY - he command
moni o s he o e all adian hea lux ecei ed a
any poin in he plane om all di ec ions. This
spa ial in eg a ion o ecei ed adian hea lux a
each poin se ed as a e e ence o he maximum
adian hea exposu e any poin is able o ecei e.
2. RADIATIVE HEAT FLUX GAS - he command
ep esen s a adiome e o a gi en o ien a ion.
The e o e, he measu ing poin ecei es adian
hea lux wi h espec o i s o ien a ion. This is
an analogy o he in ini ely small agmen o
ecei ing su ace, which is used in he analy ical
me hods.
Since FDS uses a di e en adia ion hea ans e
model, he shape o c i ical adia ion in ensi y
bounda ies a e sligh ly di e en . I s esolu ion
and accu acy is dependen on he le el angula
disc e isa ion, i.e. in o how many spa ial angles
he compu a ional domain is di ided (NIST, 2020).
Resul s
The esul s ob ained h ough he calcula ion
me hods and simula ions desc ibed abo e a e
summa ised in Table 1. The able has h ee pa s
which indica e he de e mined sepa a ion dis ances
o he ollowing:
• cen e o he adia ing su ace (opening) wi h
maximum hea adia ion in ensi y;
• edges o he adia ing su ace (opening);
• side p ojec ion beyond he edges o he adia ing
su ace (opening).
The esul s o he cen e o he adia ing su ace
(opening) indica e a ela i ely good ag eemen
in he e alua ed ange. The maximum di e ence is
be ween Me hod 1 (in e pola ion o abula ed da a)
and In eg a ed in ensi y om FDS o he wid h o
3 m - 0.21 m. O e all he di e ences a e smalle
han 10 %.
The indi idual calcula ion me hods esul
in di e en shapes (ex en ) o he zone in which
he adia ion in ensi y is abo e he c i ical alue
o 18.5 kW.m-2. This is appa en om Fig. 3 and
is caused by he simpli ica ions and numbe o
e alua ion poin s in he e alua ion me hods.
Me hod 1 (Fig. 3 a) is he mos one ous one since
he en i e zone is based on one e alua ion poin . This
poin is loca ed in he cen e o he emi ing su ace
and ep esen s he highes exposu e. The sepa a ion
dis ance s is hen p ojec ed om his poin along
he en i e opening and o i s sides up o an angle o
20°. I should be no ed, ha he sepa a ion dis ances
we e based using 100 %-open adia ing su aces,
i.e. he wo s -case scena ios o a pa icula leng h
and wid h wi hin he abula ed alues. These we e
selec ed as he nea es g ea e alues o he ac ual
dimensions o he adia ing su ace (opening).
Me hod 2 (Fig. 3 b) e alua es he sepa a ion
dis ance s in he cen e o he opening as well as a
i s edges. Then a cu e is p ojec ed h ough he h ee
poin s ob ained o ob ain app oxima e alues o
he emainde o he opening wid h. The zone by
he sides o he opening is p ojec ed as semi-ci cles
wi h a diame e , which is equal o he sepa a ion
dis ance calcula ed a he edge o he opening.
Fu he desc ip ion o his calcula ion me hod may
be ound in (Poko ný, 2017).
Me hod 3 (Fig. 3 c) he uses h ee e alua ion
poin s along he wid h o he opening - a he edges
and in ¼, ½ and ¾ o he wid h. The zone by he sides
o he opening is ep esen ed by a cu e p ojec ed
h ough e alua ion poin s based a he edge o
he opening and wi h a ying exposu e angle, i.e.
he ecei ing su ace is g adually il ed om 0°
o 90°, in 10° inc emen s. The esul ing in ensi y
beyond he edges o he opening Iθ is calcula ed
using he Lambe ’s cosine law, using Equa ion (10).
The p og am ha calcula es sepa a ion dis ances
using his me hod ounds he esul s o 0.1 m, which
leads o somewha coa se esul s.
[kW.m-2] (10)
Me hod 4 is an implemen a ion o equa ions
(1)-(6) and (8)-(9) in o he Py hon p og amming
language. The objec i e was o main ain he pa allel
o ien a ion o he ecei ing su ace o all posi ions
(wi hin, a edges and ou side he adia ing su ace).
This was due o he ac ha he ecei ing su ace’s
shape/o ien a ion does no usually change o one
case. The numbe o e alua ion poin s is explained
abo e. This app oach was adop ed om Annex A
o Ex e nal Fi e Sp ead - Building Sepa a ion and
Bounda y dis ances (Chi y, 2014).
cosII
θ
θ
= ⋅
pp. 38-46, DOI 10.35182/ ses-2020-0005

T ansac ions o he VSB - Technical Uni e si y o Os a a
Sa e y Enginee ing Se ies, ISSN 1805-3238
Vol. XV, No. 1, 2020
43
he sides o he opening). The sepa a ion dis ances
ob ained om Me hod 1 a e 2- imes g ea e han
hose calcula ed using Me hods 2-4. In e es ingly,
he In eg a ed in ensi y FDS esul s a e smalle han
hose ob ained om Me hods 1-4.
To e alua e whe he he analy ical calcula ion
esul s di e ences hold simila ends o la ge
adia ing su aces, he wid h o he opening was
u he inc eased up o 10 m. This was done in
1 m inc emen s. The esul s a e p esen ed in Tab. 2.
Wi h he excep ion o Me hod 1 he di e ences
among he o he me hods a e ela i ely small and
ange om 0.01 m o 0.1 m a bo h e alua ion poin s
- adia ing su ace cen e poin and i s edges.
G ea e di e ences may be obse ed a he edges
o he adia ing su ace. Due o he simpli ica ion
o Me hod 1, he sepa a ion dis ances a e iden ical
o he alues o he cen e o he opening.
The maximum di e ence be ween Me hod 1 and
o he analy ical me hods is 0.69 m and he minimum
0.17 m. The o he analy ical Me hods (2-4) esul s
show again a ela i ely good ag eemen wi h
maximum di e ences o 0.1 m, which is less han
10 %. G ea e di e ences may be also obse ed when
he analy ical Me hods 2-4 esul s a e compa ed
o he simula ion esul s, whe e hey ange om
app ox. 0.1 m o 0.3 m; signi ican di e ences a e
also p esen among he esul s om CFD simula ions
app ox. 0.3 m o 0.5 m.
The mos signi ican di e ences a e p esen
in he esul s o he p ojec ion o he hea adia ion
beyond he edges o he adia ing su ace ( o
Opening
wid h
Sepa a ion dis ance [m]
Analy ical calcula ions CFD simula ion
Me hod 1 Me hod 2 Me hod 3 Me hod 4 In eg a ed Radiome e
In he cen e o he adia ing su ace (maximum in ensi y)
1.00 1.37 1.40 1.40 1.39 1.50 1.28
1.50 1.68 1.70 1.70 1.70 1.80 1.57
2.00 1.92 1.95 2.00 1,94 2.15 1.82
2.50 2.12 2.15 2.20 2.14 2.30 2.08
3.00 2.29 2.30 2.40 2.31 2.50 2.25
A he edges o he adia ing su ace
1.00 1.37 1.20 1.30 1.21 1.35 1.08
1.50 1.68 1.40 1.40 1.40 1.55 1.26
2.00 1.92 1.50 1.60 1.51 1.75 1.32
2.50 2.12 1.55 1.60 1.58 1.85 1.37
3.00 2.29 1.60 1.70 1.63 1.90 1.43
To he sides o he adia ing su ace
1.00 1.29 0.60 0.65 0.72/0.28* 0.50 0.20
1.50 1.58 0.70 0.71 0.76/0.31 0.55 0.25
2.00 1.80 0.75 0.78 0.81/0.32 0.60 0.26
2.50 1.99 0.78 0.78 0.77/0.33 0.70 0.27
3.00 2.15 0.80 0.85 0.84/0.33 0.60 0.28
*The sepa a ion dis ance ( alue in on o he slash) is shown a he maximum dis ance om he edge o he adia ing
su ace whe e he adia ion in ensi y eaches he limi o 18.5 kW.m-2.
Tab. 1 Sepa a ion dis ances ob ained h ough calcula ions and simula ions
pp. 38-46, DOI 10.35182/ ses-2020-0005
T ansac ions o he VSB - Technical Uni e si y o Os a a
Sa e y Enginee ing Se ies, ISSN 1805-3238
Vol. XV, No. 1, 2020
44
along he wid h o he adia ing su ace a e
he same, so he di e ences a e caused p ima ily by
he ounding o inpu and ou pu alues.
Simila ly, he di e ences esul ing om
he di e en app oxima ions o he zones o
he sides om he adia ing su ace do no appea
o be signi ican among Me hods 2-4. Wi h
he maximum di e ence o 0.12 m he e is a good
ag eemen among he me hods wi hin he e alua ed
ange.
CFD simula ions exhibi g ea e di e ences,
bo h om he analy ical me hods as well as be ween
he In eg a ed in ensi y and Radiome e hea
lux measu emen s. In eg a ed in ensi y ends o
o e p edic he sepa a ion dis ance1 in he cen e
and a he edges o he adia ing su ace sligh ly,
by app ox. 5-10 %, when compa ed o analy ical
Me hods 2-4. On he o he hand, In eg a ed in ensi y
unde p edic ed he sepa a ion dis ances on he sides
o he opening by abou 20 %, when compa ed o
analy ical Me hods 2-4.
The adiome e measu emen s (RADIATIVE
HEAT FLUX GAS) we e below he analy ical
me hods and In eg a ed in ensi y in all cases. Abou
5-10 % o he cen e, 10-15 % o he edges and
70 % o he sides o he adia ing su ace.
The main explana ion o he di e ences is
he di e en calcula ion app oach when he CFD
simula ions a e compa ed o he analy ical me hods.
In addi ion he shape o he p oduced sepa a ion
dis ance bounda y, i.e. he ex en beyond he isk
1 A Ic i = 18.5 kW.m-2.
Discussion
The esul s p esen ed in he p e ious chap e
p o ide a use ul insigh in o he a ious calcula ion
app oaches o he de e mina ion o sepa a ion
dis ances.
F om a p ac ical s andpoin he analy ical
me hods a e he mos ly used ones, howe e ,
he di e ences be ween he abula ed alues
(Me hod 1) and de ailed calcula ions (Me hods 2-4)
a e qui e signi ican .
Me hod 1 is signi ican ly mo e one ous a
he edges and sides o he adia ing su ace. This is
an expec ed esul due o he simpli ica ion o his
me hod. I akes he cen e poin (mos in ensi e
adia ion) as ep esen a i e o all poin s along and
o he sides o he adia ing su ace. The di e ences
a he edges ange signi ican ly om 10 % o
he 1 m-wide opening o 90 % o he 10 m-wide
opening. Beyond he opening wid h o 3 m,
he abula ed alues in e als become much coa se
which is ano he sou ce o signi ican o e p edic ion.
This o e p edic ion is e en mo e p onounced on
he sides o he adia ing su ace whe e i anges
om 115 % o 170 %.
The di e ences among he de ailed analy ical
Me hods 2-4 a e ela i ely small, in gene al be ween
0.01 m and 0.1 m, i.e. well unde 10 %. The e o e,
hey may be conside ed equally accu a e conside ing
he o e all accu acy a he scale o measu emen s o
he building and i s su oundings. The calcula ions
Tab. 2 Sepa a ion dis ances ob ained h ough analy ical me hods
Opening wid h Sepa a ion dis ance [m]
Me hod 1 Me hod 2 Me hod 3 Me hod 4
In he cen e o he adia ing su ace (maximum in ensi y)
5.00 2.76 2.80 2.80 2.79
6.00 2.91 2.95 3.00 2.95
7.00 5.37 3.05 3.10 3.08
8.00 5.73 3.15 3.20 3.17
9.00 6.10 3.25 3.30 3.25
10.00 6.28 3.30 3.40 3.32
A he edges o he adia ing su ace
5.00 2.76 1.70 1.70 1.70
6.00 2.91 1.70 1.70 1.71
7.00 5.37 1.70 1.80 1.72
8.00 5.73 1.70 1.80 1.72
9.00 6.10 1.70 1.80 1.72
10.00 6.28 1.70 1.80 1.72
pp. 38-46, DOI 10.35182/ ses-2020-0005
T ansac ions o he VSB - Technical Uni e si y o Os a a
Sa e y Enginee ing Se ies, ISSN 1805-3238
Vol. XV, No. 1, 2020
45
Conclusion
Fi e sepa a ion dis ances a e an impo an pa o
building i e sa e y design. They p e en i e sp ead
in ex e io p ima ily h ough adia ing hea om i e
bu also alling bu ning b ands. This pape analysed
a numbe o me hods o de e mina ion o equi ed
i e sepa a ion dis ances - abula ed alues, analy ical
calcula ion me hods and CFD simula ions.
I was ound ha he abula ed alues end
o o e p edic he i e sepa a ion dis ances when
compa ed o he o he analy ical and CFD me hods;
in some cases o la ge adia ing su aces qui e
signi ican ly. I could, be howe e , used as a quick
p elimina y assessmen ool wi h a good ma gin
o sa e y unde he condi ion ha 100 %- i e open
adia ing su aces a e conside ed.
CFD simula ions p o ed compu a ionally
in ensi e and he esul s would equi e u he
p ocessing. Al e na i ely, he numbe o spa ial
angles could be inc eased, howe e , his would
inc ease he compu a ional demand o he simula ions
e en u he . Hence, FDS did no p o e a p ac ical
ool o he sole pu poses o sepa a ion dis ances
de e mina ion. I can be, o cou se, e y help ul, in
cases when CFD i e simula ion is desi ed, howe e ,
he use should ca e ully de e mine he app op ia e
numbe o spa ial angles o he adia ion sub-model.
Finally, all h ee analy ical calcula ion me hods
(Me hods 2-4) p o ed o be mo e o less equally
accu a e and app op ia e o he de e mina ion o
i e sepa a ion dis ances. Since hey a e based on he
same calcula ion p inciples as he abula ed alues,
hei use is app op ia e and in compliance wi h he
na ional i e sa e y design s anda ds. The inc eased
esolu ion o hese me hods, pa icula ly a he edges
and sides o he adia ing su ace (opening), allows
o mo e p ecise design.
o i e sp ead is conside ed su icien ly low, is no
a smoo h cu e (e.g. Fig. 3 d), bu a he a sinusoidal
shaped one. This would equi e u he smoo hing o
ob ain be e esul s.
This sinusoidal shape is explained in FDS
Ve i ica ion guide (McG a an e al., 2020) and i s
ex en depend on he numbe o he spa ial angles.
By inc easing he numbe o spa ial angles, he shape
becomes smoo he , howe e , he compu a ional
demand inc eases oo. This dependence is shown
in Fig. 4. Hence, when using FDS as a ool o
sepa a ion dis ance p edic ion, he has o be awa e
o his e ec and e alua e he p edic ed c i ical hea
lux bounda y in de ail. In he in es iga ed ange,
his app oach esul ed in unde p edic ion when
adia ion in ensi y was moni o ed by adiome e s -
e e o Tab. 1, column Radiome e .
Fig. 4 Dependence o inciden adian hea lux
p edic ion on he numbe o spa ial angles
in he ange o 50-2000 in Fi e Dynamics Simula o
(McG a an e al., 2020)
Re e ences
Blahož, V., Kadlec, Z. 1996. In oduc ion o Hea T ans e . Os a a: Associa ion o Fi e and Sa e y Enginee ing.
ISBN 978-80-902001-1-1. (in Czech)
Chi y, R. 2014. Ex e nal i e sp ead: building sepa a ion and bounda y dis ances. 2. ed. B acknell: IHS BRE P ess.
BR, 187. ISBN 978-1-84806-319-8.
ČSN 73 0802:2020. Building i e sa e y - Non-indus ial buildings ed.2. (in Czech)
ČSN 73 0804:2020. Building i e sa e y - Indus ial buildings ed.2. (in Czech)
ČSN EN 1991-1-2:2004. Eu ocode 1: Ac ions on s uc u es - Pa 1-2: Gene al ac ions - Ac ions on s uc u es
exposed o i e.
Kuče a, P., Kaise , R., Poko ný, J., Pa lík, T. 2009. Fi e Enginee ing: Fi e Dynamics. Os a a: Associa ion o Fi e
and Sa e y Enginee ing. ISBN 978-80- 7385-074-6. (in Czech)
NIST - Na ional Ins i u e O S anda ds And Technology. FDS and Smoke iew [so wa e]. U.S. Depa men od
Comme ce, 2020 [ci . 2020-12-02]. A ailable a : h ps://pages.nis .go / ds-sm /.
pp. 38-46, DOI 10.35182/ ses-2020-0005
T ansac ions o he VSB - Technical Uni e si y o Os a a
Sa e y Enginee ing Se ies, ISSN 1805-3238
Vol. XV, No. 1, 2020
46
McG a an, K., McDe mo , R., Vanella, M., Hos ikka, S., Floyd, J. 2020. Fi e Dynamics Simula o Technical
Re e ence Guide Volume 2: Ve i ica ion [online]. U.S. Depa men o Comme ce, Na ional Ins i u e o
S anda ds and Technology, 2020 [ci . 2020-12-02]. A ailable a : h ps://pages.nis .go / ds-sm /manuals.h ml.
Poko ný, M. 2017. Calcula ion o i e sepa a ion dis ances o adia ian hea exposu e [so wa e]. (in Czech)
Reichel, V. 1989. Fi e sa e y design o indus ial buildings. IV. P aha: Czech na ional insu ance ins i u e. Loss
p e en ion, 27. (in Czech)
pp. 38-46, DOI 10.35182/ ses-2020-0005