NFPA 68 2012 Revised 20130122

8/9/2019 NFPA 68 2012 Revised 20130122

1/99

Revision History

6/2/2007 Initial Release6/5/2007 Added disclaimer

6/13/2007 Corrected errors in Partial volume calculation for nclosures! Added calculation of to"#do$n and %7/2/2007 Corrected error in volume calculation for cylindrical &o""ers!7/3/2007 Corrected s"&erical vessel to s&o$ */+ al$ays 1! C&an)ed all */+ calculation formulae to allo$ c

11/2/2007 "dated comments to reflect IA as( rou" modification of limits on &res&old ass 4uation2/12/200 "dated Hi)& tren)t& +ust solver cell formula "er comments received! o c&an)e in results!8/21/200 Added notes in */+ ta% to e9"lain to"#mounted vent a""lication!

7/ /200 Added )uidance in +ust nclosures ta% descri%in) duct diameter used for calculation and ma9imu7/2:/200 C&an)ed */+ ta% note 3, to correctly state t&at total enclosure volume is used for vent si;in) $it& a

Added ne$ ote 8, to address multi"le vents alon) central a9is and renum%ered su%se4uent note Added c&ec( of

8/9/2019 NFPA 68 2012 Revised 20130122

2/99

ottom u" $&en vent is in side '"ic( lon)est */+&e,! Added s"&erical vessel */+! Corrected calculation of ve

lculatin) */+ 1- %ut $it& $arnin) format!

1!5 times area for vent ducts sin)le vent- no matter $&ere vent is "laced! !

sures,

Aeff calculation for to"#do$n "ro"a)ation!&an 1 '$as already correct in +ust# nclosures ta%,t&at met&odosure ta%s use */+ ta% for in"ut- %ut %uildin) ta%s ot&er$ise assume ventin) at one end of lon)est dimension!

n t&e e4uation is set e4ual to ;ero 'not allo$ed to %e ne)ative,

sing Paste"#pecial"$aluesunds. This is not yet uni'ersal.

8/9/2019 NFPA 68 2012 Revised 20130122

3/99

ted volume to %e entire section volume- not .eff '.eff is only used to determine t&e $orst case */+ to t&e ven

8/9/2019 NFPA 68 2012 Revised 20130122

4/99

location,

8/9/2019 NFPA 68 2012 Revised 20130122

5/99

isclaimer " This spreadsheet is the personal wor of #amuel &odgers, gi'en freely without any impliThis is not authori ed !y any employer, !y 0 P(, or !y any other organi ation.se of this spreadsheet is solely the responsi!ility of the user and the user should 'erify th

0 P( 4"2))5 *'aluate L/ for *+uipment #hapes

Calculate t&e .ent Area for eac& section of t&e nclosure or for t&e $&ole enclosureotes@1, The original printed 'ersion of the anne6 inserts the incorrect diameter of the conical hopp2, Placin) a sin)le vent some$&ere alon) t&e central a9is does not c&an)e t&e volume to %e vented-3, 7hen a single 'ent is used, the 'olume to use in the 'ent area e+uations is the entire enclo8, 7hen multiple 'ents are placed along the central a6is, the 'olume to use in the 'ent area e+5, &en su%dividin) alon) ori)inal central a9is- at t&e "oint t&e section *en)t& e4uals +&e- t&en */+6, 8loser placement of 'ents does not reduce L/ or change the orientation of the a6is, since7, &en vents are "laced suc& t&at */+ is less t&an or e4ual to 2- t&ere is no furt&er reduction in re4, or +ust Collectors- if t&e .olume %et$een %a)s is considered- t&en loo( at a to"#do$n &ei)&t and

&ectangular $essels with 1 $ent at end of section no hopper e6tension-

*en)t& 2 meters &e lon)est distance from one end of t&e vessel to t&e o""osite end of t&e vidt& 1 2 meters ' easured alon) central a9is,idt& 2 2 meters

.olume cu%ic meters

H 2 meters Aeff 8 s4 meters

" meters+&e 2 meters

*/+ 1 */+ can not %e less t&an 1- %y definition

ummary

8/9/2019 NFPA 68 2012 Revised 20130122

6/99

idt& a2 1! meters +imension of strai)&t sideidt& %2 1!5 meters +imension of o""osite strai)&t side

.olume 2!7 cu%ic meters .olume of Rectan)ular ection a%ove t&e ventIf t&e .ent is mounted &ori;ontally on t&e to" of vessel- t&en

8/9/2019 NFPA 68 2012 Revised 20130122

7/99

H 2!5 meters.eff 6!75 cu%ic meters Aeff 2!7 s4 meters If vent is mounted on to"- sets AeffBa2D%2

As"ect 1!2 ratio a/% &is uses t&e as"ect ratio of t&e a%ove rectan)ular sectionide a 1! meterside % 1!5 meters" 6!6 meters

+&e 1!636368 meters

*/+ 1!52777 Top" own */+ can not %e less t&an 1- %y definition

etermine 7orst"8ase either Top" own or :ottom"up- for L/ 9/ he-, Total $olume is the same*/+'ma9, 3!8762 1 :ottom"up

ummary

8/9/2019 NFPA 68 2012 Revised 20130122

8/99

ummary

8/9/2019 NFPA 68 2012 Revised 20130122

9/99

If no Ho""er- t&en

8/9/2019 NFPA 68 2012 Revised 20130122

10/99

8/9/2019 NFPA 68 2012 Revised 20130122

11/99

d warranty or guarantee.

t the methods and e+uations are consistent with the controlling 0 P( standard.

r top into the e+uations.%ut c&an)es t&e effective $orst/case */+ correction!ure 'olume, no matter where the 'ent is placed.uations is the section 'olume $eff-.1!he su!di'ision is only 'irtual walls, not real ones.ired vent area/section volume!calculate a smaller +&e- lar)er */+ for t&e %a) section!

ent!

8/9/2019 NFPA 68 2012 Revised 20130122

12/99

o""er!

!5 from "icture,!

r!

8/9/2019 NFPA 68 2012 Revised 20130122

13/99

o$n '.olume must %e same,

8/9/2019 NFPA 68 2012 Revised 20130122

14/99

rom "icture,

r!

8/9/2019 NFPA 68 2012 Revised 20130122

15/99

o$n '.olume must %e same,

8/9/2019 NFPA 68 2012 Revised 20130122

16/99

8/9/2019 NFPA 68 2012 Revised 20130122

17/99


0 P( 4"2))5 Gases in :uildings " Low #trength ;ethod*o$ tren)t& et&od limited to u of 60 and F of 130

&oom imensions*en)t& 7!5 meters 9am"le +ata u Fidt& 3 meters Acetone 58

Hei)&t 8 meters Iso"ro"anol 81 3.olume :0 cu%ic meters et&anol 56 75

t&anol 7

8/9/2019 NFPA 68 2012 Revised 20130122

18/99

H 7!5 meters Aeff 12 s4 meters

" 18 meters+&e 3!82 571 meters

*/+ 2!1 75 If */+ e9ceeds 3- vents must %e "laced alon) lon)est dimension

n 1 num%er of "anels

formula 82:!:03 ()/mE280 ( )/mE2 is minimum of 80 ()/mE2 or t&e formula a%ove! If )reater t&an 80 ()/mE

.ent area is increased if "anel density e9ceeds t&e t&res&old or 80 ()/mE2- $&ic&ever is smaller!80 ()/mE2 l%/s4 ft If "anel density is in units- en

etric B 3:!1 ()/mE2

GA 0 s4 meters If - t&en t&ere is no area correction for inertia Av 80!6 s4 meters

:uildings do not generally ha'e 'ent ducts, so this is not included here.

&e effective area- A eff , shall be (etermine( b) (ivi(ing eff b) + !base( on the longestentral axis flame length$. -his ass#mes all venting at one en(.

&e effective &ydraulic diameter- + he, for the en los#re shall be (etermine( base( #pon thegeneral shape of the en los#re ta en normal to the entral axis.+ he = 4 * A eff / p, Where p is the perimeter of the general shape

8/9/2019 NFPA 68 2012 Revised 20130122

19/99



is t&e +efla)ration Inde9!o$ and enter at left@

B 100- uB86 for "ro"ane

rom PA#6

d must %e less t&an t&e room $all stren)t&!

8/9/2019 NFPA 68 2012 Revised 20130122

20/99

- consult an e9"ert

ter &ere and enter metric units at left

ss t&an - t&en no correction is needed!ntainin) $alls and floor Pred values- t&at is

8/9/2019 NFPA 68 2012 Revised 20130122

21/99


0 P( 4"2))5 Gases in :uildings " 9igh #trength ;ethod

&oom imensions*en)t& 6!:1 :6 meters 9am"le +ata u Fidt& 6!30:36 meters Acetone 58

Hei)&t 8!8 056 meters Iso"ro"anol 81 3.olume 1:5!5:53 cu%ic meters et&anol 56 75

t&anol 7

8/9/2019 NFPA 68 2012 Revised 20130122

22/99

Aeff 2 !26:87 s4 meters

" 21!57: 8 meters+&e 5!23::77 meters

*/+ 1 If Red- */+ &as %een set to L1L %y enterin) a > a%ove!

L/ 8orrectionIf */+ e9ceeds 2- a vent area correction is added

GABA0D F '*/+#2,E2J/750 GAB 0!0000 4! eters

$&ere *imits A0B 25!3:21F B 100

8/9/2019 NFPA 68 2012 Revised 20130122

23/99


8/9/2019 NFPA 68 2012 Revised 20130122

24/99



&is ta% does not use t&e */+ ta% for in"ut values! nless noted %elo$- it is assumed t&at all ventit&e $all at t&e end of t&e lon)est dimension! If ventin) $ill %e evenly distri%uted alon) t&e lon)estsuc& t&at */+ is evaluated as 1- enter > in t&e cell %elo$@

>

o$ and enter at left@

B 100- uB86 for "ro"ane

anne9rom PA#6

ide .+I %oundset to L;eroL

8/9/2019 NFPA 68 2012 Revised 20130122

25/99

ation i.e. @GB>>) !ar"m/sec-

- consult an e9"ert

ter &ere and enter metric units at left

ction is needed! If Av is lar)er t&an t&e

r Pred values- t&at is ma(e t&em stron)er!

8/9/2019 NFPA 68 2012 Revised 20130122

26/99

8/9/2019 NFPA 68 2012 Revised 20130122

27/99

8/9/2019 NFPA 68 2012 Revised 20130122

28/99

8/9/2019 NFPA 68 2012 Revised 20130122

29/99

8/9/2019 NFPA 68 2012 Revised 20130122

30/99

isclaimer " This spreadsheet is the personal wor of #amuel &odgers, gi'en freely without any implThis is not authori ed !y any employer, !y 0 P(, or !y any other organi ation.se of this spreadsheet is solely the responsi!ility of the user and the user shoul

0 P( 4"2))5 Gases in *nclosures " 9igh #trength ;ethod9am"le +

*nclosure #ection imensions Acetonesee LC Ta! to calculate these terms- Iso"ro"an

et&anol*en)t& 'H, 8!5 meters t&anol.olume '., 18!27 : cu%ic meters ' &is is total volume- not .eff, Hydro)en

Area 'Aeff, 3!1730 7 s4uare meters+iameter '+&e, 2!01 meters If F not a

F is t&e defla)ration inde9Pred is t&e ma9imum "ressure develo"ed durin) t&e vented e9"losionPstat is t&e static release "ressure of t&e vent "anel

u;aterial Hydro)en F

F 550 %ar#m/secPred 0!1:252 %ar 313Pstat 0!1 %ar etric B 0!18: 65

8u!ical $essel, Low

8/9/2019 NFPA 68 2012 Revised 20130122

31/99

formula 5!::021 ()/mE25!::021 ()/mE2 is minimum of 80 ()/mE2 or t&e formula a%ove!

.ent area is increased if "anel density e9ceeds t&e t&res&old or 80 ()/mE2- $&ic&ever is smaller!80 ()/mE2 l%/s4 ft If "anel density is in

etric B 3:!1 ()/mE2 If )reater t&an 80 ()/

GA 0!72::8: s4 meters Av 5!3:01 s4 meters .ent Area can not e9ceed cross#section 'Aeff,

$ent uct *ffect As t&e vent duct increases Pred- a "seudo#value PNred is used in t&e initial e4uations!

&is section iterates to t&e value of PNred and vent area t&at $ill ac&ieve t&e overall Pred )oal!

Calculate +uct &ydraulic diameter ?nly enter > / ? for Round +uct- as Rectan)ular is t&e automatic ot&er c&oice

Round +uct > / ?Round +uct +&e 2!61:721 meters

Rectan)ular +uct > As"ect 1!5 ratio a/%

ide a 2! 8385 meterside % 1! :5638 meters" :!87 16 meters

Rectan)ular +uct +&e 2!27876 meters

C&osen +uct +&e 2!27876 metersC&ose correct relation %et$een PNred and Pred

*duct 2!1 meters+uct */+&e, 0!:23178 or *duct 3 meters and */+&e 8

PNredB 0!1:252 %ar nter +esi)n oal for Pred $it& +uct

Pred oalB 0!3 %ar PNredB 0!01672 %ar

PNredB 0!1:252 %ar

ser must ;(0 (LLY 8opy the 'alue of PDred a!o'e into the initial entry for Pred at cell :22 and$*&< Y that the same chosen PDred 'alue is 'alid at cell :E> This could change if the 'ent area gets

If - t&en t&ere is no area correction for inertia

or *duct of 3 to 6 meters or */+&e M 8

( ) ( )7.1

5.0

.0%.07.

=

G

red T K

V n P M

( )%.0.0

5.0.00075.0

red

Gvi

P V n

K M A A =

8/9/2019 NFPA 68 2012 Revised 20130122

32/99

ied warranty or guarantee.

d 'erify that the methods and e+uations are consistent with the controlling 0 P( standard.

ata u F58

l 81 356 75

7550

vaila%le- estimate from u as %elo$ and enter at left@

8/9/2019 NFPA 68 2012 Revised 20130122

33/99

units- enter &ere and enter metric units at leftE2- consult an e9"ert

much larger as a result-

8/9/2019 NFPA 68 2012 Revised 20130122

34/99

8/9/2019 NFPA 68 2012 Revised 20130122

35/99

P0 0 %ar#) intial "ressure in t&e enclosureCd 0!7 vent flo$ disc&ar)e coefficient- ta(en as 0!7! Can %e increased to 0! $&enPa 0!013 am%ient "ressure outside t&e vent B 0!013 %ar#)

;aterial Pro"aneu 0!86 m/secPma9 7!: %ar#)Ost 0!055 stoic&imetric volume fraction fuel in air etric B

1! 0 #05383 un%urned )as#air mi9ture sound s"eed B 383 m/sec for )as concentrations l1!2

1!15230!1

Av 15!5:80: s4uare meters

+ifference 0!0000 s4uare meters se olver to ac&ieve difference of and Panel

efault Parameters

0!3:

Q1 1!23Q2 0!08 7 m/sec

7!8 08

3!1331

312!7 32 m/sec

+iameter of vent is iterated 'av/"i,E0!5

8!65 07

u un%urned )as#air mi9ture dynamic viscosity B 1! #05 ()/m#sec for )as cona uSu un%urned )as#air mi9ture mass density B 1!2 ()/m 3 for )as concentrations lT% ratio of s"ecific &eats for %urned )as#air mi9ture B 1!1 to 1!2 de"endin) on t

u un%urned )as#air mi9ture sonic flo$ mass flu9 B 230!1 ()/m 2#sec for an encl

etermination of Tur!ulent lame *nhancement actor,

of .ent Area t&at must %e iterated '+ v is used

ote t&at "ressure terms in formula for u v are in a%solute units- $&ile t&e standard a""ro

*'aluation of )

Re f

1

uv

Rev

( )otherwisea P P if

P P u uared

u

ared v ,'.1

%00000

8/9/2019 NFPA 68 2012 Revised 20130122

36/99

1! 867

5!7 5

urface area of o%structions includes@1! &e surface of conduits- "i"es and suc& over 1/2 inc& diameter 2! &e surface area of structural columns- %eams and Uoists3! &e surface area of stair$ays and railin)s8! &e surface area of e4ui"ment $it& c&aracteristic dimension in t&e ran)e of 2 to 20 in

Ao%s 0 s4uare meters Ao%s/As 0

5!7 5

< PP*& L* T i11--BFYF,1, ..- " This artificially sets L/ to 1

*/+ 1!5000

5!7 5

Low Pressure, Low

8/9/2019 NFPA 68 2012 Revised 20130122

37/99

15!5:81 4! eters .ent Area can not e9ceed cross#section 'Aeff,

Partial $olume 8orrection

.)as 100 volume of )as at am%ient "ressure $&ic& could esca"e from t&e credi%le ev

OrB :!2 :8220!075:8:8

If Or is )reater t&an 1- "artial volume does not a""ly and Av8BAv3

15!5:81 s4uare meters

:ased on the Tas Group (cti'ities, the inertia e+uations are applica!le up to #u limit of the !asic e+u


formula 2500!22 ()/mE2

80 ()/mE2

.ent area is increased if "anel density e9ceeds t&e t&res&old or 80 ()/mE2- $&ic&ever is smaller!&e amount of vent area increase de"ends on t&e mode of o"enin)- eit&er &in)ed or translatin)!

10 ()/mE2 2 l%/s4 ft If "anel density is inHin)ed .ent > / ? etric B :! ()/mE2 If )reater t&an 80 ()/

A v0B

Calculate t&e $orst#case %uildin) "artial volume fraction- Xr - from t&e follo$in) e4uation@

B

If Or is less t&en - t&en no ventin) is re4uired

A v1B

8/9/2019 NFPA 68 2012 Revised 20130122

38/99

1

Av 15!5:81 s4 meters.ent Area can not e9ceed cross#section 'Aeff,




Round +uct > / ?Round +uct +&e 8!855 :6 meters


ide a 8! 3683 meterside % 3!2282:2 meters" 16!12186 meters

Rectan)ular +uct +&e 3! 6:151 meters

C&osen +uct +&e 3! 6:1505 metersC&ose correct relation %et$een PNred and Pred

*duct 2!1 meters+uct */+&e, 0!582758 or *duct 3 meters and */+&e 8

PNredB 0!120236 %ar nter +esi)n oal for Pred $it& +uct


PNredB 0!1202357 %ar

ser must ;(0 (LLY 8opy the 'alue of PDred a!o'e into the initial entry for Pred at cell :22 and$*&< Y that the same chosen PDred 'alue is 'alid at cell :E> This could change if the 'ent area gets m

H



( )

+= %.0.05.0.0

1%$05.0!

1red

uSH vv P V n

S M F A A

8/9/2019 NFPA 68 2012 Revised 20130122

39/99

warranty or guarantee.

'erify that the methods and e+uations are consistent with the controlling 0 P( standard.

alues! nless noted %elo$- it is assumed t&at all ventin) is "ut on! If ventin) $ill %e evenly distri%uted alon) t&e lon)est dimension-n t&e cell %elo$@

ata u Pma90!58

l 0!810!560!8 7!

3!12 6!0!86 7!:

8/9/2019 NFPA 68 2012 Revised 20130122

40/99

t&e vent is essentially an entire $all/side of t&e enclosure

313 "sf 0!18: 65 %ar

ss t&an 5 vol at am%ient tem"eratures

Inertia Corrected .ent Area B 0

entrations less t&an 5 vol at am%ient tem"eratures

ss t&an 5 vol at am%ient tem"eraturese )as mi9ture

sure at am%ient tem"eratures

to determine and is ta(en as Av 0!5,

ac& is to use )au)e values!

8/9/2019 NFPA 68 2012 Revised 20130122

41/99

&es '5!1 to 51 cm,

if 'enting is pro'ided well distri!uted

lso c&an)in) to not use PredE0!5 %elo$

8/9/2019 NFPA 68 2012 Revised 20130122

42/99

nt- cu%ic meters

tion i.e. #u B 3 m/sec-


tion is needed! If Av is lar)er t&an t&e e9terior $all ofat is ma(e t&em stron)er!

8/9/2019 NFPA 68 2012 Revised 20130122

43/99

uch larger as a result-

8/9/2019 NFPA 68 2012 Revised 20130122

44/99

8/9/2019 NFPA 68 2012 Revised 20130122

45/99

7!8 08

3!1331

312!7 32 m/sec


8!65 07

1! 867

5!7 5


Ao%s 0 s4uare meters

Ao%s/As 0

5!7 5

Re f

1

uv

Rev

2

0B

#urface (rea of H!structions 8orrection to

If Ao%sM 0!8 As- is increased! ?t&er$ise 1 B 0

1B

L/ 8orrection to

$.0!01 sobs A A+=


P P u uared

u

ared v ,'.1

%00000

8/9/2019 NFPA 68 2012 Revised 20130122

46/99

*/+ 1!5000

5!7 5

Low Pressure, Low

8/9/2019 NFPA 68 2012 Revised 20130122

47/99

8/9/2019 NFPA 68 2012 Revised 20130122

48/99

C&ose correct relation %et$een PNred and Pred*duct 2!1 meters+uct */+&e, 0!582758 or *duct 3 meters and */+&e 8



PNredB 0!1:251:7 %ar



8/9/2019 NFPA 68 2012 Revised 20130122

49/99



ata u Pma90!58

l 0!810!560!8 7!

3!12 6!0!86 7!:

>


313 "sf 0!18: 65 %ar

ss t&an 5 vol at am%ient tem"eratures



ss t&an 5 vol at am%ient tem"eraturese )as m 9ture


to determine and is ta(en as Av 0!5,


8/9/2019 NFPA 68 2012 Revised 20130122

50/99

&es '5!1 to 51 cm,

8/9/2019 NFPA 68 2012 Revised 20130122

51/99

nt- cu%ic meters

8/9/2019 NFPA 68 2012 Revised 20130122

52/99




8/9/2019 NFPA 68 2012 Revised 20130122

53/99


8/9/2019 NFPA 68 2012 Revised 20130122

54/99

isclaimer " This spreadsheet is the personal wor of #amuel &odgers, gi'en freely without any implieThis is not authori ed !y any employer, !y 0 P(, or !y any other organi ation.se of this spreadsheet is solely the responsi!ility of the user and the user should

0 P( 4"2)12 Gases in *nclosures " 9igh #trength ;ethod

&oom imensions*en)t& 7!3152 meters &is ta% does not use t&e */+ ta% for in"utidt& 7!3152 meters t&e $all at t&e end of t&e lon)est dimension

Hei)&t 3!6576 meters suc& t&at */+ is evaluated as 1- enter > i.olume 1:5!72608 cu%ic meters o

8/9/2019 NFPA 68 2012 Revised 20130122

55/99

P0 0 %ar#) intial "ressure in t&e enclosureCd 0!7 vent flo$ disc&ar)e coefficient- ta(en as 0!7! Can %e increased to 0! $&enPa 0!013 am%ient "ressure outside t&e vent B 0!013 %ar#)

;aterial Pro"aneu 0!86 m/secPma9 7!: %ar#)Ost 0!055 stoic&imetric volume fraction fuel in air etric B

1! 0 #05383 un%urned )as#air mi9ture sound s"eed B 383 m/sec for )as concentrations l1!2 un%urned )as#air mi9ture mass density B 1!2 ()/m3 )as concentrations less

1!15230!1

Av 15!:55 : s4uare meters

+ifference 0!0000 s4uare meters se olver to ac&ieve difference of and Panel

efault Parameters

0!3:

Q1 1!23Q2 0!08 7 m/sec

7!8 08

3!1331

312!7 32 m/sec


8!70 07

u un%urned )as#air mi9ture dynamic viscosity B 1! #05 ()/m#sec for )as cona uSuT% ratio of s"ecific &eats for %urned )as#air mi9ture B 1!1 to 1!2 de"endin) on t

u un%urned )as#air mi9ture sonic flo$ mass flu9 B 230!1 ()/m 2#sec for an encl

etermination of Tur!ulent lame *nhancement actor,

of .ent Area t&at must %e iterated '+ v is used

ote t&at "ressure terms in formula for u v are in a%solute units- $&ile t&e standard a""ro

*'aluation of )

Re f

1

uv

Rev


P P u uared

u

ared v ,'.1

%00000

8/9/2019 NFPA 68 2012 Revised 20130122

56/99

1! 8 :

5!7:2


Ao%s : s4uare meters Ao%s/As 0!8157:38

5! 83

< PP*& L* T i11--BFYF,1, ...- " This artificially sets L/ to

*/+ 1!5000

5! 83

9igh Pressure, Low

8/9/2019 NFPA 68 2012 Revised 20130122

57/99

8/9/2019 NFPA 68 2012 Revised 20130122

58/99

&e amount of vent area increase de"ends on t&e mode of o"enin)- eit&er &in)ed or translatin)!

10 ()/mE2 l%/s4 ft If "anel density is inHin)ed .ent > / ? etric B 3:!1 ()/mE2 If )reater t&an 80 ()/

1

Av 15!:55: s4 meters.ent Area can not e9ceed cross#section 'Aeff,






ide a 8! :2222 meterside % 3!2618 1 meters" 16!30781 meters

Rectan)ular +uct +&e 3!:1377 meters

C&osen +uct +&e 3!:137775 metersC&ose correct relation %et$een PNred and Pred






H



( ) += %.0.05.0.0

1% $05.0!1red

uSH vv P V n

S M F A A

8/9/2019 NFPA 68 2012 Revised 20130122

59/99

8/9/2019 NFPA 68 2012 Revised 20130122

60/99


313 "sf 0!18: 65 %ar

ss t&an 5 vol at am%ient tem"eratures t&an 5 vol at am%ient tem"eratures



e )as mi9ture


o determine and is ta(en as Av 0!5,


8/9/2019 NFPA 68 2012 Revised 20130122

61/99

&es '5!1 to 51 cm,

if 'enting is pro'ided well distri!uted

8/9/2019 NFPA 68 2012 Revised 20130122

62/99

8/9/2019 NFPA 68 2012 Revised 20130122

63/99



8/9/2019 NFPA 68 2012 Revised 20130122

64/99

isclaimer " This spreadsheet is the personal wor of #amuel &odgers, gi'en freely without any implieThis is not authori ed !y any employer, !y 0 P(, or !y any other organi ation.se of this spreadsheet is solely the responsi!ility of the user and the user should

0 P( 4"2)12 Gases in *nclosures " 9igh #trength ;ethod9am"le

*nclosure #ection imensions Acetonesee LC Ta! to calculate these terms- Iso"ro"an

et&anol*en)t& 'H, 7!3152 meters et&ane.olume '., 1:5!72608 cu%ic meters ' &is is total volume- not .eff, Hydro)en

Area 'Aeff, 26!756076 s4uare meters Pro"ane+iameter '+&e, 8! 76 metersInternal urface 'As, 218!08 6 s4uare meters + ? + R I HI I */+ A

8/9/2019 NFPA 68 2012 Revised 20130122

65/99

7!8 08

3!1331

312!7 32 m/sec


8!70 07

1! 8 :

5!7:2


Ao%s : s4uare meters

Ao%s/As 0!8157:38

5! 83

Re f

1

uv

Rev

2

0B

#urface (rea of H!structions 8orrection to

If Ao%sM 0!8 As- is increased! ?t&er$ise 1 B 0

1B

L/ 8orrection to

$.0!01 sobs A A+=


P P u uared

u

ared v ,'.1

%00000

8/9/2019 NFPA 68 2012 Revised 20130122

66/99

*/+ 1!5000

5! 83

9igh Pressure, Low

8/9/2019 NFPA 68 2012 Revised 20130122

67/99

15!:55: s4uare meters

:ased on the Tas Group (cti'ities, the inertia e+uations are applica!le up to #u limit of the !asic e+u


formula 2865!2265 ()/mE2

80 ()/mE2

.ent area is increased if "anel density e9ceeds t&e t&res&old or 80 ()/mE2- $&ic&ever is smaller!&e amount of vent area increase de"ends on t&e mode of o"enin)- eit&er &in)ed or translatin)!

10 ()/mE2 l%/s4 ft If "anel density is inHin)ed .ent > / ? etric B 3:!1 ()/mE2 If )reater t&an 80 ()/

1

Av 15!:55: s4 meters.ent Area can not e9ceed cross#section 'Aeff,






ide a 8! :2222 meters

A v1B

8/9/2019 NFPA 68 2012 Revised 20130122

68/99

ide % 3!2618 1 meters" 16!30781 meters

Rectan)ular +uct +&e 3!:1377 meters

C&osen +uct +&e 3!:137775 metersC&ose correct relation %et$een PNred and Pred







8/9/2019 NFPA 68 2012 Revised 20130122

69/99



ata u Pma90!58

l 0!810!560!8 7!

3!12 6!0!86 7!:

>


313 "sf 0!18: 65 %ar

ss t&an 5 vol at am%ient tem"eratures t&an 5 vol at am%ient tem"eratures



e )as m 9ture


o determine and is ta(en as Av 0!5,


8/9/2019 NFPA 68 2012 Revised 20130122

70/99

&es '5!1 to 51 cm,

8/9/2019 NFPA 68 2012 Revised 20130122

71/99

8/9/2019 NFPA 68 2012 Revised 20130122

72/99




8/9/2019 NFPA 68 2012 Revised 20130122

73/99


8/9/2019 NFPA 68 2012 Revised 20130122

74/99

8/9/2019 NFPA 68 2012 Revised 20130122

75/99

Av1 13!76:33 s4 meters

:uilding re+uires a factor of 1.5 on 'ent area

Av2 23!807 6 s4 meters

or Panel ;ass I %) g/m=2, 0 P(" 4 recommends use of the (nne6 not included here-:ased on the Tas Group (cti'ities, the inertia e+uations are applica!le up to @#t limit of the !asic e+


formula 215:! 51 ()/mE280 ( )/mE2 is minimum of 80 ()/mE2 or t&e formula a%ove! If )reater t&an 80 ()/mE

Intended .ent Panel +ensity80 ()/mE2 2!5 l%/s4 ft If "anel density is in units- en

etric B 12!2 ()/mE2 If )reater t&an 80 ()/mE2- consul

Av3 23!807 6 s4 meters If - t&en t&ere is no area correction for inertia


8/9/2019 NFPA 68 2012 Revised 20130122

76/99

f 18 )m stimate ill raction > > or ? Afs 0!37 s4 meters If > f/Afs B 680 )m/m2 (ssumed ust on lC$ 500 )m/mE3 s/Ass B 680 )m/m2 orst Case allo$edH 7!3 meters C$ B 200 )m/m2s 100 )m

Asur 20 s4 meters Calculated from In"uts at *eft Ass 0!37 s4 meters If ? f/Afs B 800 )m/m2. 313!: mE3 s/Ass B 270!2703 )m/m2

C$ B 500 )m/m2 Al$ays nter t&e mass of com%usti%les t&at could %e released from e4ui"ment or stora)e %elo$@

e 8! ()8 00 )m

Or 0!71 7 fill fraction

If Or is less t&en V- t&en no ventin) is re4uiredIf Or is )reater t&an 1- "artial volume does not a""ly and Av8BAv3

Av8 22!1311 s4 meters


=

11

4r

r vv

A A

8/9/2019 NFPA 68 2012 Revised 20130122

77/99



elo$- it is assumed t&at all ventin) is "ut onnly distri%uted alon) t&e lon)est dimension-

8/9/2019 NFPA 68 2012 Revised 20130122

78/99

uation i.e. @#tB4)) !ar"m/sec-

- consult an e9"ert

ter &ere and enter metric units at leftt an e9"ert

8/9/2019 NFPA 68 2012 Revised 20130122

79/99

oor of Hperational &oomssum"tions "er section !3!8

8/9/2019 NFPA 68 2012 Revised 20130122

80/99

isclaimer " This spreadsheet is the personal wor of #amuel &odgers, gi'en freely without any implied wThis is not authori ed !y any employer, !y 0 P(, or !y any other organi ation.se of this spreadsheet is solely the responsi!ility of the user and the user should 'erif

0 P( 4"2))5 ust in *+uipment

*nclosure #ection imensionssee LC Ta! to calculate these terms-

*en)t& 'H, 1 meters.olume '., 2 cu%ic meters ' &is is total volume- not .eff,

Area 'Aeff, 8 s4uare meters+iameter '+&e, 1 meters

F t is t&e defla)ration inde9Pred is t&e ma9imum "ressure develo"ed durin) t&e vented e9"losionPma9 is t&e ma9imum "ressure develo"ed in a closed e9"losion testPstat is t&e static release "ressure of t&e vent "anelV is t&e ratio of Pred/Pma9

F t 31 %ar#m/secPred 0! %ar Pma9 !8 %ar Pstat 0!1 %ar 0!5 "si)V 0!108762 Pred/Pma9 etric B 0!038878 %ar)

Av0B 0!167518 s4 meters .ent Area can not e9ceed cross#section 'Aeff,

8hec for L/ less than 2' se in"uts a%ove,

*/+ 'H/+&e, 1

If */+ M2- increase vent area- else Av1BAv0 Av1B 0!167518 s4 meters .ent Area can not e9ceed cross#section 'Aeff,

Tur!ulence 8orrectionelect as many o"tions as a""lica%le for t&e enclosure and t&is "ic(s t&e &i)&est correction!

*/+ 6 ' for silos,

+= )redP.exp(.

DL

.vAvA %'50

750%0101

[ ] 154.11101 max4//440 += red

St stat v P

P V K P A

8/9/2019 NFPA 68 2012 Revised 20130122

81/99

/ ? Correction factor of 1!7 if a %uildin) 'occu"ia%le, Av2/Av1B 0

lo$#CreatedW > / ?Inlet Air 20 mE3/secInlet Pi"e +iam 1 m?utlet Pi"e +iam 1 m Correction.a9ial 10 meter/sec &is $ould.tan)ential 12!7328 meter/sec '0!5 .tan=ma9, Av2/Av1B

Rotatin) 4ui"W > / ? CorrectionRotational Radius 0!5 meter &is $ouldRotational "eed 1000 RP Av2/Av1B.tan)ential 26!17::8 meter/sec '0!5 .tan=ma9,

Pic( &i)&est value of selected L> L o"tions a%oveHi)&est Av2/Av1B 0 o adUustment made if calculated Av2/Av1 is 1

If .elocities are less t&an 20 meters/sec- t&en Av2BAv1!

Av2B 0!167518 s4 meters .ent Area can not e9ceed cross#section 'Aeff,

or Panel ;ass I %) g/m=2, 0 P(" 4 recommends use of the (nne6 not included here-:ased on the Tas Group (cti'ities, the inertia e+uations are applica!le up to @#t limit of the !asic e+uati


formula 0!5:0121 ()/mE20!5:0121 ()/mE2 is minimum of 80 ()/mE2 or t&e formula a%ove!

Intended .ent Panel +ensity7!85 ()/mE2 0!75 l%/s4 ft If "anel density is in

etric B 3!7 ()/mE2 If )reater t&an 80 ()/

Av3 0!205 5 s4 meters If - t&en t&ere is no area correction for inertia.ent Area can not e9ceed cross#section 'Aeff,


8/9/2019 NFPA 68 2012 Revised 20130122

82/99

f 18 )m stimate ill raction > > or ? Afs 0!37 s4 meters If > f/Afs B 680 )m/m2 (ssumedC$ 500 )m/mE3 s/Ass B 680 )m/m2 orst CasH 1 meters C$ B 200 )m/m2s 100 )m

Asur 20 s4 meters Calculated from In"uts at *eft Ass 0!37 s4 meters If ? f/Afs B 800 )m/m2. 2 mE3 s/Ass B 270!2703 )m/m2


e 8! ()8 00 )m

Or 87!2 fill fraction

If Or is less t&en V- t&en no ventin) is re4uiredIf Or is )reater t&an 1- "artial volume does not a""ly and Av8BAv3

Av8B 0!205 5 s4 meters .ent Area can not e9ceed cross#section 'Aeff,

$ent uct *ffect

nter a uess for t&e final Avf! A su))estion is to start $it& a%out 20 )reater t&an Av8! Avf ')uess,B 0!205 5 mE2

=

11

4r

r vv

A A

8/9/2019 NFPA 68 2012 Revised 20130122

83/99


Round +uct > / ?Round +uct +&e 0!511:63 meters Guidance

1. The duct area used in the $ent uct *Rectan)ular +uct > 2. 7hen duct area is larger than the 'ent

As"ect 1!5 ratio a/% 3. The actual duct area should !e no moide a 0!5556 6 meterside % 0!370857 meters" 1! 522 6 meters

Rectan)ular +uct +&e 0!88858: meters

C&osen +uct +&e 0!88858: meters

nter +uct Confi)uration

*duct 0 meterse"silon 0!26 mm &is is t&e rou)&ness- used in friction factor!F el%o$s 0F &at 0

Calculate riction actor

fB 0!0172 6

8/9/2019 NFPA 68 2012 Revised 20130122

84/99

8/9/2019 NFPA 68 2012 Revised 20130122

85/99

arranty or guarantee.

that the methods and e+uations are consistent with the controlling 0 P( standard.

8/9/2019 NFPA 68 2012 Revised 20130122

86/99

8/9/2019 NFPA 68 2012 Revised 20130122

87/99

ust on loor of Hperational &oom e allo$ed assum"tions "er section !3!8

8/9/2019 NFPA 68 2012 Revised 20130122

88/99

fect is that e+ual to the 'ent area.area, actual Pred can !e higher or lower.e than 1.> times the 'ent area.

eff to )et a sin)le solution!

- t&e constraint of Av/Aeff is not met and Cells

8/9/2019 NFPA 68 2012 Revised 20130122

89/99

8/9/2019 NFPA 68 2012 Revised 20130122

90/99

isclaimer " This spreadsheet is the personal wor of #amuel &odgers, gi'en freely without any iThis is not authori ed !y any employer, !y 0 P(, or !y any other organi ation.se of this spreadsheet is solely the responsi!ility of the user and the user shoul

etermine Pred for F

8/9/2019 NFPA 68 2012 Revised 20130122

91/99

Tur!ulence 8orrectionelect as many o"tions as a""lica%le for t&e enclosure and t&is "ic(s t&e &i)&est correction!

/ ? Correction factor of 1!7 if a %uildin) 'occu"ia%le, Av2/Av1B 0

lo$#CreatedW > / ? or lo$#Created ur%ulence- use t&e ma9imum A9ial orInlet Air 20 mE3/sec &is $ould %e ty"ical for a cycloneInlet Pi"e +iam 1 m Av2/Av1B 0?utlet Pi"e +ia 1 m.a9ial 16!66667 meter/sec.tan)ential 12!7328 meter/sec '0!5 .tan=ma9,

Rotatin) 4ui"W > / ? Correction factor if Rotatin) 4ui"mentRotational Radiu 0!5 meter &is $ould %e ty"ical for a )rinder or &ammermillRotational "ee 1000 RP Av2/Av1B 0.tan)ential 26!17::8 meter/sec '0!5 .tan=ma9,

i)&est Av2/Av1B 0 '"ic(s &i)&est value of selected L> L o"tions a%ove,

If .elocities are less t&an 20 meters/sec- t&en Av2BAv1!inimum value of Av2/Av1 is 1!

Av2B 0!1666:8 s4 meters .ent Area can not e9ceed cross#section 'Aeff,


f 18 )m stimate ill ractio> > or ? Afs 0!37 s4 meters If > f/Afs B 680 )m/m2 (ssumed ust on

Cal #late the 3orst ase b#il(ing partial vol#me fra tion, r , from the follo3ing e #ation

8/9/2019 NFPA 68 2012 Revised 20130122

92/99

C$ 500 )m/mE3 s/Ass B 680 )m/m2H 2 meters C$ B 200 )m/m2s 100 )m

Asur 20 s4 meters Calculated from In"uts at *eft Ass 0!37 s4 meters If ? f/Afs B 800 )m/m2. 2!8 mE3 s/Ass B 270!27 )m/m2


e 8! ()8 00 )m

Or 5! 6667 fill fraction

If Or is less t&en V- t&en no ventin) is re4uired

Av8B 0!1666:8 s4 meters .ent Area can not e9ceed cross#section 'Aeff,

(nne6 (lternate

8/9/2019 NFPA 68 2012 Revised 20130122

93/99

F B 261!1166 0!13 27 3!318:6

0! 560:: %ar) 0!75672 = 0!6118

0!7538: 1!716657 %ara

( B f 'P v, B P ri B

3!0 #" r- for inertialess vents6!0 # +etermine vent "aram

10!0 # +etermine e9"onent

15!0 # +e (

" r B B P ri B

7!0 # +etermine vent "aram (

11!0 # +etermine P vi 'P stat $it&inertia ,

16!0 # +eover ventde"loyme

( B P vi B P ri B

8/9/2019 NFPA 68 2012 Revised 20130122

94/99

plied warranty or guarantee.


26

Correction 1!8000 %ar 1!8000 %ar

8/9/2019 NFPA 68 2012 Revised 20130122

95/99

an)ential ur%ulence

loor of Hperational &oom

8/9/2019 NFPA 68 2012 Revised 20130122

96/99

2!8000

vent "anel as"ect ratio 's&ort side/lon) side 1,

ermine P ri for ( 1

ermine P ri for 1

8/9/2019 NFPA 68 2012 Revised 20130122

97/99

2!3671

1! 561

2!8000 %ara

ermine P ri for 3

ermine increase"ressure afternt P ri

8/9/2019 NFPA 68 2012 Revised 20130122

98/99


Insert Pru)& *e#C&atalier for Hy%rid i9 from *oss Prevention

Xuestion $&et&er t&e s&a"e of t&e curve can %e estimated usin) t&e same

8/9/2019 NFPA 68 2012 Revised 20130122

99/99



NFPA 68 2012 Revised 20130122

Documents

Transcript of NFPA 68 2012 Revised 20130122