EL DORADO COUNTY AIR POLLUTION CONTRO DISTRICT
 

Rule 909 Standards.

ADOPTED April 17, 1989
AMENDED September 18, 1990
 

Description.
The purpose of this Rule is to limit emissions from storage tanks for organic liquids. A person shall not place, store, or hold in any stationary tank, reservoir, or other container of more than 40,000 gallons capacity, any organic liquid having a Reid vapor pressure greater than 25.8 mm Hg (0.5 psia) at actual storage temperature and/or conditions, unless such tank, reservoir or other container is in a pressure tank maintaining working pressures sufficient at all times to prevent organic vapor or gas loss to the atmosphere.
 
909.1 Storage Tanks Storing Organic Liquids with a Vapor Pressure Greater than 11 psia. A person shall not store organic liquid with a vapor pressure greater than 11 psia under storage conditions in any tank unless such tank is a pressure tank maintaining working pressures sufficient at all times to prevent organic vapor or gas loss to the atmosphere, or designed and equipped with a vapor loss control device which meets the requirements of this Rule.

909.2 External Floating Roof. The vapor loss control device may be a floating roof, consisting of a pontoon-type or double-deck-type cover that rests on the surface of the liquid contents and is equipped with the closure device between the tank shell and roof edge. The closure device shall consist of two seals, one above the other; the one below shall be referred to as the primary seal and the one above shall be referred to as the secondary seal. Seal designs shall be submitted to the Air Pollution Control Officer as meeting the criteria set forth within this rule, as applicable.

909.3 Internal Floating Roof.

  1. The vapor loss control device may be a fixed roof with an internal-floating-type cover, provided the cover prevents the release or emission to the atmosphere of organic vapors or gasses at an efficiency equivalent to a floating roof closure device which meets the requirements of Section 909.5. The Air Pollution Control Officer shall determine whether equivalence exists.
  2. A fixed roof container with an internal-floating-type cover shall not be used if the organic liquid stored has a vapor pressure greater than 11 psia under storage conditions.
 
909.4 Vapor Recovery System.
  1. Any installed vapor recovery system shall be a CARB certified vapor recovery system capable of collecting organic vapors and gasses, and include a vapor return or disposal system capable of processing such vapors and gasses, so as to prevent their emission to the atmosphere at an efficiency of at least 95 percent by weight.
  2. Any tank gauging or sampling device on a tank vented to the vapor recovery system shall be equipped with a gas-tight cover which shall be closed at all times except during gauging or sampling.
  3. All piping, valves and fittings shall be constructed and maintained in a gas tight condition, such that no organic vapor or gas leaks are detectable.

909.5 Metallic-Shoe-Seal Criteria.

  1. Metallic-Shoe-type seals shall be installed so that one end of the shoe extends into the stored liquid and the other end extends a minimum vertical distance of 61 cm (24 inches) above the stored liquid surface.
  2. The geometry of the shoe shall be such that the maximum gap between the shoe and the tank shell is no greater than double the gap allowed by the seal gap criteria for a length of at least 46 cm (18 inches) in the vertical plane above the liquid surface.
  3. There shall be no holes or tears in, or openings through the secondary seal or in the primary seal envelope surrounding the annular vapor space enclosed by the roof edge, stored liquid surface, shoe, and seal fabric.
  4. The secondary seal shall extend from the roof to the tank shell and shall not be attached to the primary seal.
  5. Any roof drain which opens directly into the organic liquid content in the tank shall be provided with as slotted membrane fabric cover, or equivalent, that covers at least 90% of the area of the opening.
  6. All openings in the roof, except pressure-vacuum valves, shall provide a projection below the liquid surface to prevent belching of liquid and to prevent entrained or formed organic vapor from escaping from the liquid contents of the tank and shall be equipped with a cover, seal or lid. The cover, seal, or lid shall at all times be in a closed position, with no measurable gap exceeding 0.32 cm (1/8 in.), except with the device or appurtenance is in use. Pressure-vacuum valves located in the roof shall be set to within ten percent of the maximum allowable working pressure of the roof.

909.6 Welded Tanks with Metallic-Shoe-Seals. Any welded tank shell which uses a metallic-shoe type seal shall meet the following conditions:

  1. No gap between the tank shell and the primary seal shall exceed 3.8 cm (1-1/2 inches). The cumulative length of all primary seal gaps exceeding 1.3 cm (1/2 inch) shall be not more than 10% of the circumference; the cumulative length of all primary seal gaps exceeding 0.32 cm (1/8 inch) shall not be more than 40 percent of the circumference. No continuous gap greater than 0.32 cm (1/8 inch) shall exceed 10% of the circumference of the tank.
  2. No gap between the tank shell and the secondary seal shall exceed 1.3 cm (1/2 inch). The cumulative length of all secondary seal gaps exceeding 0.32 cm (1/8 inch) shall not exceed 5 percent of the circumference of the tank.
  3. The secondary seal shall allow each insertion of probes up to 3.8 cm (1-1/2 inches) in width in order to measure gaps in the primary seal.
 
909.7 Riveted Tanks with Metallic-Shoe-Seals. Any welded tank shell which uses a metallic-shoe-type seal shall meet the following conditions:
  1. No gap between the tank shell and the primary seal shall exceed 6/4 cm (2-1/2 in.). The cumulative length of all primary seal gaps exceeding 3.8 cm (1-1/2 in.) shall not be more than 10% of the circumference.
  2. The secondary seal shall consist of at least two sealing surfaces, such that the sealing surfaces prevent the emission of organic compounds around the rivets. Serrated sealing surfaces are allowable if the length of serration does not exceed 15.2 cm (6 in.). No gap between the tank shell and the secondary seal shall exceed 1.3 cm (1/2 in.). The cumulative length of all secondary seal gaps exceeding 0.32 cm (1/8 in.) shall not be more than 5% of the circumference.
  3. The secondary seal shall allow easy insertion of the probes up to 3.8 cm (1-1/2 inches) in width in order to measure gaps in the primary seal.

909.8 Resilient-Toroid-Seal Criteria. Any storage tank which uses a resilient-toroid-type seal shall meet the following conditions:

  1. No gap between the tank shell and the primary seal shall exceed 1.3 cm (1/2 inch). The cumulative length of all gaps exceeding 0.32 cm (1/8 inch) shall not be more than 5% of the circumference.
  2. No gap between the tank shell and the secondary seal shall exceed 1.3 cm (1/2 inch). The cumulative length of all gaps exceeding 0.32 cm (1/8 inch) shall not be more than 5% of the circumference.
  3. The secondary seal shall allow easy insertion of probes up to 1.3 cm (1/2 inch) in width in order to measure gaps in the primary seal.
  4. There shall be no holes or tears in, or openings through the secondary seal or in the primary seal envelope surrounding the annular vapor space enclosed by the roof edge, stored liquid surface, shoe, and seal fabric.
 
909.9 Welded Tanks with Zero Gap Secondary Seals. Any welded tank shell which uses a zero gap secondary seal must meet the following conditions:
  1. No gap between the tank shell and the primary seal shall exceed 3.8 cm (1-1/2 inches). The cumulative length of all primary seal gaps exceeding 1/3 cm (1/2 inch) shall be not more than 10% of the circumference and the cumulative length of all primary seal gaps exceeding 0.32 cm (1/8 inch) shall not be more than 40% of the circumference. No continuous gap greater than 0.32 cm (1/8 inch) shall exceed 10% of the circumference of the tank.
  2. No gap between the tank shell and the secondary seal shall exceed 1.5 mm (0.06 in.). The cumulative length of all secondary seal gaps exceeding 0.5 mm (0.02 inch) shall not exceed 5% of the circumference of the tank excluding gaps less than 5 cm (1.79 in.) from vertical weld seams.
  3. The secondary seal must exert a positive pressure against the tank shell such that the seal surface in contact with the tank shell does not pull away from the tank shell more than the gaps allowed in Section 909.9B.