California Code of Regulations › Title 8 - Industrial Relations › Division 1 - Department of Industrial Relations › Chapter 4 - Division of Industrial Safety › Subchapter 7 - General Industry Safety Orders › Group 20 - Flammable Liquids, Gases and Vapors › Article 145 - Tank Storage › Section 5593 - Emergency Relief Venting for Fire Exposure for Aboveground Tanks

Current through Register 2024 Notice Reg. No. 28, July 12, 2024
(a) Except as
						provided in (b), every aboveground storage tank shall have some form of
						construction or device that will relieve excessive internal pressure caused by
						exposure fires.
(b) Tanks larger
						than 12,000 gallons capacity storing liquids with a flashpoint greater than
						199.4 °F (93 °C) (formerly designated Class IIIB Combustible liquids)
						and not within the diked area or the drainage path of Category 1, 2 or 3
						flammable liquids do not require emergency relief venting.
(c) In a vertical tank the construction
						referred to in (a) may take the form of a floating roof, lifter roof, a weak
						roof-to-shell seam, or other approved pressure relieving construction. The weak
						roof-to-shell seam shall be constructed to fail preferential to any other
						seam.
(d) Where entire dependence
						for emergency relief is placed upon pressure relieving devices, the total
						venting capacity of both normal and emergency vents shall be enough to prevent
						rupture of the shell or bottom of the tank if vertical, or of the shell or
						heads if horizontal. If unstable liquids are stored, the effects of heat or gas
						resulting from polymerization, decomposition, condensation, or self-reactivity
						shall be taken into account. The total capacity of both normal and emergency
						venting devices shall be not less than that derived from Table FL-16 except as
						provided in (f) or (g). Such device may be a self-closing manhole cover, or one
						using long bolts that permit the cover to lift under internal pressure, or an
						additional or larger relief valve or valves. The wetted area of the tank shall
						be calculated on the basis of 55 percent of the total exposed area of a sphere
						or spheroid, 75 percent of the total exposed area of a horizontal tank and the
						first 30 feet above grade of the exposed shell area of a vertical
						tank.
(e) For tanks and storage
						vessels designed for pressures over 1 psig, the total rate of venting shall be
						determined in accordance with Table FL-16, except that when the exposed wetted
						area of the surface is greater than 2,800 sq. ft., the total rate of venting
						shall be in accordance with Table FL-17 or calculated by the following formula:
CFH = 1,107
						  A0.82
Where:
CFH = venting requirement, in cubic feet of free air
						  per hour.
A = exposed wetted surface, in square feet.
The foregoing formula is based on Q = 21,000
						  A0.82
(f) The total emergency relief venting
						capacity for any specific stable liquid may be determined by the following
						formula:
Cubic feet of free air per hour =
								  V
1337
L[TICK]M.
V = cubic feet of free air per hour from Table
						  FL-16.
L = latent heat of vaporization of specific liquid in
						  BTU per pound.
M = molecular weight of specific liquids.
Table FL-16
Wetted Area Versus Cubic Feet Free Air Per
						  Hour* (14.7 psig and 60°F.)
Sq.
								  Ft.
CFH
Sq.
								  Ft.
CFH
Sq.
								  Ft.
CFH
20
21,100
200
211,000
1,000
524,000
30
31,600
250
239,000
1,200
557,000
40
42,100
300
265,000
1,400
587,000
50
52,700
350
288,000
1,600
614,000
60
63,200
400
312,000
1,800
639,000
70
73,700
500
354,000
2,000
652,000
80
84,200
600
392,000
2,400
704,000
90
94,800
700
428,000
2,800
742,000
100
105,000
800
462,000
see (e)
120
126,000
900
493,000
140
147,000
1,000
524,000
160
168,000
180
190,000
200
211,000
*
								  Interpolate for intermediate values.
Table FL-17
Sq.
								  Ft.
CFH
Sq.
								  Ft.
CFH
2,800
742,000
9,000
1,930,000
3,000
786,000
10,000
2,110,000
3,500
892,000
15,000
2,940,000
4,000
995,000
20,000
3,720,000
4,500
1,100,000
25,000
4,470,000
5,000
1,250,000
30,000
5,190,000
6,000
1,390,000
35,000
5,900,000
7,000
1,570,000
40,000
6,570,000
8,000
1,760,000
(g) For tanks containing stable liquids, the
						required air-flow rate of (d) or (f) may be multiplied by the appropriate
						factor listed in the following schedule when protection is provided as
						indicated. Only one factor may be used for any one tank.
.5 For drainage in accordance with Section
						  5595(b) for tanks
						  over 200 square feet of wetted area.
.3 For approved water spray in accordance with Standard
						  for Water Spray Fixed Systems for Fire Protection, NFPA No. 15, and drainage in
						  accordance with Section
						  5595(b).
.3 For approved insulation in accordance with
						  (g)(1).
.15 For approved water spray with approved insulation
						  in accordance with (g)(1) and drainage in accordance with Section
						  5595(b).
(1) Insulation systems for which credit is
						taken shall meet the following performance criteria and shall be subject to
						approval of the authority having jurisdiction:
(A) Remain in place under fire exposure
						conditions.
(B) Withstand
						dislodgment when subjected to hose stream impingement during fire exposure.
						This requirement may be waived where use of solid hose streams is not
						contemplated or would not be practical.
(C) Maintain a maximum conductance value of
						4.0 Btu's per hour per square foot per degree °F (Btu/hr./sq.ft./ °F)
						when the outer insulation jacket or cover is at a temperature of 1,660° F
						and when the mean temperature of the insulation is 1,000°
						F.