FLARES WET GAS FLARES H2S PROCESS PLANTS HAZARDOUS EQUIPMENT
LIQU. HYDROC. STORAGE TANKS 60 (n.i.) 60 (n.i.) n.v. LPG STORAGE TANKS > 5 m3 60 (n.i.) 60 (n.i.) n.v.
LIQU. HYDROC. LOADING BAYS 30 (n.i.) 60 (n.i.) n.v.
LPG LOADING BAYS 60 (n.i.) 60 (n.i.) n.v.
WELLS 30 (n.i.) 60 (n.i.) n.v.
OIL TREATMENT PLANTS 60 (n.i.) 60 (n.n.) n.v.
GAS TREATMENT PLANTS 30 (n.i.) 60 (n.i.) n.v.
COMPRESSION STATIONS 30 (n.i.) 60 (n.i.) n.v.
GLYCOL HEATING AND RECOND. 30 (n.i.) 60 (n.i.) n.v.
GLYCOL TANKS 30 (n.i.) 60 (n.i.) n.v.
OILY WATERS TREAT. BASINS 30 (n.i.) 60 (n.i.) n.v.
OIL PIPELINES/GAS PIPELINES 30 (n.i.) 60 (n.i.) n.v.
PROCESS SAFETY VALVES 15 (n.n.) 15 (n.n.) n.v.
DRY GAS FLARES 10log(Q-2)/2 10log(Q-2)/2 n.v.
WET GAS FLARES 10log(Q-2)/2 10log(Q-2)/2 n.v.
PRESSURE REDUCER 30 (n.i.) 60 (n.i.) n.v.
MEASUREMENT CABIN 30 (n.i.) 60 (n.i.) n.v.
FREE FLAME EQUIPMENT 30 (n.i.) 60 (n.i.) n.v.
GLYCOL PUMPS 30 (n.i.) 60 (n.i.) n.v.
MANUAL SOV 30 (n.i.) 60 (n.i.) 30 (m.c.)
FITTINGS INSIDE THE PLANT
OFFICES, CONTROL ROOM 30 (n.i.) 60 (n.i.) 30 (m.c.)
FIRE FIGHTING PUMPS 30 (n.i.) 60 (n.i.) n.v.
FIRE FIGHTING VALVES 30 (n.i.) 60 (n.i.) n.v.
AERIAL POWER LINES 30 (n.i.) 60 (n.i.) n.v.
FITTINGS OUTSIDE THE PLANT
CARRIAGE ROADS 30 (n.i.) 60 (n.i.) 100 (m.c.)
NON-CARRIAGE ROADS 30 (n.i.) 60 (n.i.) 30 (m.c.)
RAILWAYS AND TRAMWAYS 30 (n.i.) 60 (n.i.) 30 (m.c.)
PUBLIC PREMISES 30 (n.i.) 60 (n.i.) 100 (m.c.)
Annex 6 Pool fire - Computational method
The relation for round base flame height computing is drawn from:
(1) H =D ⋅42 0 06 1 27 ⋅( , / , ⋅ 9 8 ⋅. D)0 61, where: H is the flame height in metres
D is the round base flame height
0,06 is the liquid hydrocarbons combustion rate in kg/(m2
·
s)If the base flame were square shaped (i.e. into a duct or a control basin or an annulus of a floating roof tank), the following relations would be adopted:
(2) Fr=0 48, / D1
where: Fr is the discriminating factor for flame height determination D1 is the lower dimension of the flame base in meters.
If Fr ≥ 0.25, the flame height is: (3) H = 2,2
·
D1otherwise is:
(4) H = 0,88
·
(Fr)-0,65·
D1
For radiation computing, the following relations are used: (5) E = 130
·
e-0,12 ·D+ 20·
(1 - e-0,12 ·D)where: E is the flame radiating flux in kW/m2 (For flames with a diameter >20
m fixed value E = 130 kW/m2 shall be to adopt).
Radiation reaching the observer is: (6) q = F
·
Ewhere: q is the radiation in kW/m2
(Annex 6)
• if the flame is round shaped, C is the distance in metres from the flame centre to the observer and B is the flame radius:
H/B = 0,1 C/B = 2 F = 0,028 H/B = 0,5 C/B = 2 F = 0,129 H/B ≥ 2 C/B = 1 F = 0,580 H/B ≥ 2 C/B = 1,2 F = 0,517 H/B ≥ 2 C/B = 1,5 F = 0,392 H/B ≥ 2 C/B = 2 F = 0,267 H/B ≥ 2 C/B = 3 F = 0,141 H/B ≥ 2 C/B = 4 F = 0,083
• if the flame base is square shaped, C is the distance in metres from the flame surface to the observer:
H/C = 0,5 D/C = 0,5 F = 0,06 H/C = 0,5 D/C = 0,2 F = 0,027 H/C = 0,5 D/C = 0,1 F = 0,014 H/C = 0,5 D/C = 0,05 F = 0,007 H/C = 0,1 D/C = 0,2 F = 0,006 H/C = 0,1 D/C = 0,1 F = 0,003 H/C = 0,1 D/C = 0,05 F = 0,002
In order to evaluate the equilibrium radius of an unconfined pool fire, that is the flame radius relating to the steady phase when as much product leaks and burns, the following relation is considered:
(7) 3
·
log R = 1,6·
log Q + 0.89 (log = common logarithm) where: R = pool equilibrium radius, in metresQ = leaking product flowrate, in kg/s
When the flame radius is determined, radiation can be evaluated by (1) to (6) formulas.
That is, with an oil leakage of 5 kg/s, R is 4.67 m, flame height is H = 15,3 m and radiating flux is E = 55.8 kW/m2.
Annex 7 Jet fire - Computational method
For gas jet fires can be used some correlations for the flame spacing (it corresponds to a 1% of gas concentration by volume) according to the hole diameter.
The correlations are:
(1) X = 1,33
·
(d'/d)·
dwhere: X is the distance in meters from the leakage point to the point where concentration is 1% (with an equipment pressure of 50 bar);
(2) d'/d = 0,625 ln p + 0,0625 where: d is the hole diameter in cm
d' is the jet diameter in cm
Annex 8 Unconfined gas cloud explosion (pressurised) - Computational method
The relation for the mass of flammable gas in a cloud arising from a pressurised gas leakage is the following/Ref.2/:
(1) Q=45400⋅ T ⋅a d3 ⋅1067 / To1 5,
where: Q is the mass in kg of flammable gas into the cloud ; Ta is the ambient temperature in K
d is the jet diameter of the already expanded gas (meters) (see Annex 7)
To is the gas temperature in K (generally 288 K)
The relation (1) is valid only for natural gas whose composition is defined by CEI 64.2 codes.
Once determined the mass into the explosive zone, the “hazard circumference” shall be to evaluate, that is the distance where the consequences of a possible explosion are detected.
The hazard circumference is from the following relation /Ref. 4/: (2) R = K
·
(0.1·
E ) 1/3where: R is the radius of the circumference limiting the hazard zone K is a coefficient with value:
- 0,03 if the hazard circumference is considered for the plants equipment;
- 0,06 if the hazard circumference is considered for the fittings into the Plant;
- 0,15 if the hazard circumference is considered for the fitting out of the Plant.
E is the energy content of the explosive part of the cloud whose value is 5
·
107·
Q (in Joule)Q is the mass in kg of the flammable gas into the cloud
In order to obtain the extension of the explosive zone downwind of the leakage, the following correlation is considered:
(3) log Q1 = 2
·
log L + 2 (log = common logarithm)where: Q1 is the gas flowrate in m3 / g
L is the downwind spacing from the Explosivity Lower Limit (ELL) in atmosphere with a medium stability.
(Annex 8)
The values obtained by the application of this computational model and listed in table of Annex 5 have been determined by the following operative scheme which can help for verifying also real conditions substantially different from those assumed :
• has been considered a pipe 120 mm in diameter and then a leakage from a hole 12 mm in diameter (10% of the pipe diameter, as sta ted in 2.4.2.1.2) • from the relation (2) of Annex 7 the jet diameter can be determined ( 3 cm at
50 bar pressure)
• from the relation(1) the explosive mass Q can be determined ( 6 kg)
• from the relation (2) the hazard radius can be calculated as the minimum distance for the installations equipment ( 20 m)
• from the relation (2) the hazard radius can be calculated as the minimum distance for the fittings into the Plant, usually offices and control room( 40 m)
• from the relation (2) the minimum distance towards the fittings out of the Plant can be calculated ( 100 m)
• the gas flowrate is evaluated (1 kg/s at 50 bar pressure)
• from the relation (3) the ELL is evaluated ( 30 m) which represents the minimum distance from heaters, reconditioners and free burning flame equipment.
Annex 9 Unconfined gas cloud explosion (not pressurised) - Computational method
The relation for the mass of flammable gas in a cloud arising from non- pressurised gas leakage is the following/Ref.2/:
(1) Q = (12 / Ta)
·
V1.2·
63 / (1 - 0.55 T a / To) 0.6where: Q is the mass in kg of flammable gas into the cloud ; Ta is the ambient temperature in K
V is the gas flowrate in m3/s To is the gas temperature in K
The relation (1) is valid only for natural gas whose composition is defined by CEI 64.2 codes.
Once determined the mass into the explosive zone, the “hazard circumference” shall be to evaluate, that is the distance where the consequences of a possible explosion are detected.
The hazard circumference is from the following relation /Ref. 4/:
(2) R = K
·
(0.1·
E ) 1/3where: R is the radius of the circumference limiting the hazard zone K is a coefficient with value:
- 0.03 if the hazard circumference is considered for the plants equipment;
- 0.06 if the hazard circumference is considered for the fittings into the Plant;
- 0.15 if the hazard circumference is considered for the fitting out of the Plant.
E is the energy content of the explosive part of the cloud whose value is 5
·
107·
Q (in Joule)Q is the mass in kg of the flammable gas into the cloud
The values obtained by the application of this computational model and listed in table of Annex 5 have been determined by the following operative scheme which can help for verifying also real conditions substantially different from those assumed :
• has been considered a pipe 120 mm in diameter and then a leakage from a hole 12 mm in diameter (10% of the pipe diameter, as stated in 2.4.2.1.2)
(Annex 9)
• the gas flowrate is evaluated (0.17 kg/s)
• from the relation(1) the explosive mass Q can be determined (0.8 kg)
• from the relation (2) the hazard radius can be calculated as the minimum distance for the installations equipment (6 m)
• from the relation (2) the hazard radius can be calculated as the minimum distance for the fittings into the Plant, usually offices and control room(10 m)
• from the relation (2) the minimum distance towards the fittings out of the Plant can be calculated too (25 m).
Annex 10 Heavy vapours dispersion - Computational method
The vapours quantity that can overflow from a basin containing oily products has been considered by Kletz /Ref.2/; it has been evaluate d about 1 ton.
It is necessary to evaluate the volume into the explosive field. Different criteria can be used: 10% of the volume released in 30” can be considered ( Bureau of Mines), or 2% of the total volume of released vapours ( Industrial Risk Insurers), or 7% of the total mass released ( TNO, "Report of the Committee for the Prevention of Disasters" published by General Directorate of Work of the Ministry of Social Affairs, 1979).
Once determined the mass into the explosive zone, the “hazard circumference” shall be to evaluate, that is the distance where the consequences of a possible explosion are detected.
The hazard circumference is from the following relation /Ref. 4/:
(2) R = K
·
(0.1·
E ) 1/3where: R is the radius of the circumference limiting the hazard zone K is a coefficient with value:
- 0.03 if the hazard circumference is considered for the plants equipment;
- 0.06 if the hazard circumference is considered for the fittings into the Plant;
- 0.15 if the hazard circumference is considered for the fitting out of the Plant.
E is the energy content of the explosive part of the cloud whose value is 5