Pennsylvania Code › Title 34 - LABOR AND INDUSTRY › Part I - Department of Labor and Industry › Chapter 14a - STORAGE AND USE OF FLAMMABLE AND COMBUSTIBLE LIQUIDS › Subchapter A - GENERAL PROVISIONS › OUTSIDE AND ABOVEGROUND STORAGE › Section 14a.8 - Vents

Current through Register Vol. 54, No. 28, July 13, 2024
(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).