Section 14a.8. Vents

(a) Normal venting. The normal venting requirements for construction and use of tanks shall conform to the following:

(1) Atmospheric tanks shall be adequately vented to prevent, as a result of filling or emptying and atmospheric temperature changes, development of pressure or vacuum sufficient to distort the roof of a cone roof tank or pressure exceeding the design pressure in the case of other atmospheric tanks.

(2) Low pressure tanks shall be adequately vented to prevent development of pressure or vacuum, as a result of filling or emptying and atmospheric temperature changes, from exceeding the design pressure of the tank. Protection shall also be provided to prevent overpressure from any pump discharging into the tank where the pump discharge pressure may exceed the design pressure of the tank.

(3) If a tank has more than one fill or withdrawal connection and simultaneous filling or withdrawal can be made, the vent size shall be based on the maximum anticipated simultaneous flow.

(4) Unless the vent is designed to limit the internal pressure to 2 1/2 psig or less, the outlet of vents and vent drains shall be arranged to discharge in such a manner as to prevent localized overheating of any part of the tank in the event vapors from such vents are ignited.

(5) Tanks storing class IA liquids shall be equipped with venting devices which shall be normally closed except when venting under pressure or vacuum conditions. Tanks storing class IB and class IC liquids shall be equipped with venting devices which shall be normally closed except when venting under pressure or vacuum conditions, or with approved flame arresters. This paragraph shall not apply to tanks with capacities of 3,000 barrels or less containing crude petroleum in crude producing areas and outside aboveground atmospheric tanks with capacities under 1,000 gallons containing other than class IA liquids which may have open vents.

(6) Flame arresters or venting devices required in paragraph (5) may be omitted for class IB and class IC liquids if conditions are such that their use may, in case of obstruction, result in tank damage. Liquid properties justifying the omission of such devices include, but are not limited to, condensation, corrosiveness, crystallization, polymerization, freezing, or plugging. When any of these conditions exist, consideration may be given to heating, use of devices employing special materials of construction, the use of liquid seals, or inerting; for further information, see Standard No. 69—1978, Explosion Prevention Systems.

(7) Normal vents shall be sized in accordance with either the American Petroleum Institute, Standard No. 2000—1982, Venting Atmospheric and Low-Pressure Storage Tanks, or other accepted standard, or shall be at least as large as the filling or withdrawal connection, whichever is larger, but shall not in any case be less than the requirements set forth in the following table:

Capacity of Tank (in gallons)	Diameter of Vent Fitting Iron Pipe Size (in inches)
500 or less	1¼
501 to 3,000	1½
3,001 to 10,000	2
10,001 to 20,000	2½
20,001 to 35,000	3

(8) Skid tanks and similar portable equipment shall be provided with a free opening vent of the following nominal pipe size, to relieve vacuum or pressure which may develop in normal operation or from fire exposure:

Tank Size	Vent Size (in inches)
0- 275	1½
276- 660	2
661- 900	2½
901-1,000	3

(i) Vents shall be arranged to discharge in such a way as to prevent localized or overheating of, or flame impingement on, any part of the tank in the event vapors from such vents are ignited.

(ii) Drums equipped with dispensing devices must be provided with pressure and vacuum relief vents with flame arresters. These vents are to be in addition to any vent which may be an integral part of the dispensing device being used in connection with the drum.

(9) For tanks in excess of 1,100 gallons capacity, emergency relief venting for fire exposure shall be as provided under subsection (b).

(b) Emergency relief venting for fire exposure. Every aboveground storage tank shall have some form of construction or device that will relieve excessive internal pressure caused by exposure fires, and such construction or device shall conform to the following:

(1) In a vertical tank, the construction 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. Where entire dependence for such additional relief is placed upon some device other than a weak roof seam or joint, 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. Such device may be a self-closing manhole cover, or one using long bolts that permit the cover to lift under internal pressure.

(2) If emergency venting is not provided in accordance with paragraph (1), the total capacity of both normal and emergency venting devices shall be not less than that derived from the following table, except as provided in paragraphs (4) and (5):

Wetted Area Versus Cubic Feet Free Air per Hour
at 14.7 p.s.i.a. and 60°F.

Square Feet	CFH	Square Feet	CFH	Square Feet	CFH
20	21,100	160	168,000	900	493,000
30	31,600	180	190,000	1,000	524,000
40	42,100	200	211,000	1,200	557,000
50	52,700	250	239,000	1,400	587,000
60	63,200	300	265,000	1,600	614,000
70	73,700	350	288,000	1,800	639,000
80	84,200	400	312,000	2,000	662,000
90	94,800	500	354,000	2,400	704,000
100	105,000	600	392,000	2,800	742,000
120	126,000	700	428,000	and over
140	147,000	800	462,000

(3) The wetted area of the tank, when such term is used in paragraph (2), shall be calculated on the basis of 55% of the total exposed area of a sphere or spheroid, 75% of the total exposed area of a horizontal tank, and the first 30 feet abovegrade of the exposed shell area of a vertical tank. Approximate wetted areas for horizontal tanks may be found in the following table:

Tank	Approximate Wetted Areas for Horizontal Tanks
Diameter	(Wetted Area Equals 75% Total Area)
(feet)	3	4	5	6	7	8	9	10	11	12
Tank Length	Approximate Wetted Area Of Tanks With Flat Heads
(feet)
3	32
4	39	55
5	46	65	88
6	53	74	100	128
7	60	84	112	142	173
8	67	93	124	156	190	226
9	74	102	136	170	206	245	286
10	82	112	147	184	223	264	308	353
11	88	121	159	198	239	283	329	377	428
12	95	131	171	213	256	301	350	400	454	509
13	102	140	183	227	272	320	371	424	480	537
14	109	150	194	241	289	339	393	447	506	565
15	116	159	206	255	305	358	414	471	532	594
16	123	169	218	269	322	377	435	495	558	622
17	130	178	230	283	338	395	456	518	584	650
18	137	188	242	298	355	414	477	542	610	678
19		197	253	312	371	433	499	565	636	707
20		206	265	326	388	452	520	589	662	735
21		216	277	340	404	471	541	612	688	763
22		225	289	354	421	490	562	636	714	792
23		235	300	368	437	508	584	659	740	820
24		244	312	383	454	527	605	683	765	848
25			324	397	470	546	626	706	791	876
26			336	411	487	565	647	730	817	905
27			347	425	503	584	668	754	843	933
28			359	440	520	603	690	777	869	961
29			371	454	536	621	711	801	895	989
30			383	468	553	640	732	824	921	1018
31			395	482	569	659	753	848	947	1046
32				496	586	678	775	871	973	1074
33				510	602	697	796	895	999	1103
34				524	619	715	817	918	1025	1131
35				539	635	734	838	942	1051	1159
36				553	652	753	860	966	1077	1187
37				567	668	772	881	989	1103	1216
38					685	791	902	1013	1129	1244
39					701	810	923	1036	1155	1272
40					718	828	944	1060	1181	1301
41					734	847	966	1083	1207	1329
42					751	866	987	1107	1233	1357
43					767	885	1008	1130	1259	1385
44						904	1029	1154	1284	1414
45						923	1051	1178	1310	1442
46						941	1072	1201	1336	1470
47						960	1093	1225	1362	1498
48						979	1114	1248	1388	1527
49						998	1135	1272	1414	1555
50							1157	1295	1440	1583
51						1178	1319	1466	1612
52						1199	1342	1492	1640
53						1220	1366	1518	1668
54						1246	1389	1544	1696
55						1263	1413	1570	1725
56							1437	1593	1753
57							1460	1622	1781
58							1484	1648	1809
59							1507	1674	1839
60							1531	1700	1866
61								1726	1894
62								1752	1923
63								1778	1951
64								1803	1979
65								1829	2007
66								1855	2036
67									2064
68									2092
69									2120
70									2149
71									2177
72									2205

(4) The total emergency relief venting capacity for any specific liquid may be determined by the following formula:

Cubic feet of free air per hour =

V = cubic feet of free air per hour from the table of paragraph (2).

L = latent heat of vaporization of specific liquid in Btu per pound.

M = molecular weight of specific liquid.

(5) The required air flow rate, as set forth in paragraphs (2) and (3), may be multiplied by the following appropriate factor set forth when protection is provided as indicated; only one factor may be used for any one tank:

(i) Factor .5 for drainage in accordance with the drainage provisions of § 14a.6 (relating to dikes, walls and drainage) for tanks over 200 square feet of wetted area.

(ii) Factor .3 for approved water spray.

(iii) Factor .3 for approved insulation.

(iv) Factor .15 for approved water spray with approved insulation.

(6) Venting devices shall be certified by the manufacturer as to actual rated flow capacity in cubic feet of free air per hour, specifying the pressure in psig at which the flow capacity was determined. The stamping of such information on the devices by the manufacturer shall be acceptable as certification for this purpose.

(7) The outlet of all vents and vent drains on tanks equipped with emergency venting to permit pressures exceeding 2½ psig shall be arranged to discharge in such a way as to prevent localized overheating of any part of the tank in the event vapors from such vents are ignited.

(c) Vent piping for aboveground tanks. Vent piping for aboveground tanks shall conform to the following:

(1) Vent piping shall be constructed under § § 14a.51—14a.58 (relating to piping, valves and fittings). Where vent piping for tanks storing class I liquids is adjacent to buildings or public ways, the vent piping shall be located so that the vapors are released at a safe point away from buildings and not less than 12 feet above the adjacent ground level. In order to aid their dispersion, vapors shall be discharged upward so that flammable vapors will not be trapped by eaves or other obstructions and shall be at least 5 feet from building openings. Vent outlets for all classes of flammable and combustible liquids shall be above normal snow accumulation on top of tanks.

(2) When tank vent piping is manifolded, pipe sizes shall be able to discharge, within the pressure limitations of the system, the vapors they may be required to handle when manifolded tanks are subject to the same fire exposure. The manifolding of tank vent piping shall be avoided except if required for special purposes such as vapor recovery, vapor conservation or air pollution control.

(3) Vent piping for tanks storing class I liquids shall not be manifolded with vent piping for tanks storing class II or class III liquids unless positive means are provided to prevent the vapors from class I liquids from entering tanks storing class II or class III liquids to prevent contamination and possible change in classification of the less volatile liquid.

The provisions of this § 13.8 amended through June 22, 1984, effective June 18, 1984, 14 Pa.B. 2131; transferred from 37 Pa. Code and renumbered as 34 Pa. Code § 14a.8, February 28, 2014, effective March 1, 2014, 44 Pa.B. 1233. Immediately preceding text appears at serial pages (259913) to (259919)

Notation

Authority

The provisions of this § 13.8 issued under act of April 27, 1927 (P. L. 450, No. 291) (35 P. S. § § 1181—1194); transferred from 37 Pa. Code and renumbered as 34 Pa. Code § 14a.8 under section 4(b) of the Combustible and Flammable Liquids Act (35 P. S. § 1244(b)).

Cross References

This section cited in 34 Pa. Code § 14a.25 (relating to vents for underground tanks); 34 Pa. Code § 14a.111 (relating to storage and handling); 34 Pa. Code § 14a.141 (relating to scope and application); 34 Pa. Code § 14a.151 (relating to scope and application); and 34 Pa. Code § 14a.161 (relating to general provisions).