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Subchapter 7. General Industry Safety Orders
Group 20. Flammable Liquids, Gases and Vapors
Article 136. Dip Tanks

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§5426. Construction of Dip Tanks.

NOTE: Closed system quench tanks of integral quench furnaces are not included in this Article.

(a) Dip tanks, including drain boards if provided, shall be constructed of substantial noncombustible material, and their supports shall be of steel, reinforced concrete or masonry, or equivalent fire resistant material.

NOTE: Where dip tanks extend through a floor to the story below or where the weakening of the tank supports by fire may result in the tank collapse, supports should be of material having not less than one-hour fire resistance.

(b) Dip tanks of over 150 gallons in capacity or 10 square feet in liquid surface area shall be equipped with a properly trapped overflow pipe leading to a safe location outside buildings.

(c) Overflow pipes shall be of sufficient capacity to overflow the maximum delivery of dip tank liquid fill pipes but shall not be less than 3 inches in diameter and shall be increased in size depending upon the area of the liquid surface and the length and pitch of pipe.

(d) If the liquid surface area of dip tank (and drain board, unless drain board is arranged to positively prevent drainage into dip tank) is 75-150 square feet, diameter of overflow pipe shall be not less than 4 inches; if 150-225 square feet, not less than 5 inches; if 225-325 square feet, not less than 6 inches.

NOTE: 1. On large dip tanks, multiple overflow connections are preferable to a single large pipe, provided the aggregate cross sectional area is equivalent.

NOTE: 2. Overflow pipes should be connected to dip tanks through a flared outlet where the accumulation of caked or dried material may clog the overflow opening.

(e) Piping connections on drains and overflow lines shall be designed so as to permit ready access for inspection and cleaning of interior.

(f) The bottom of the overflow connection shall be not less than 6 inches below the top of the tank.

(g) Dip tanks over 500 gallons in liquid capacity shall be equipped with bottom drains automatically and manually arranged to quickly drain tank in event of fire, unless the viscosity of the liquid at ambient temperature makes this impractical. Manual operation shall be from a safely accessible location. Where gravity flow is not practicable, automatic pumps shall be required.

(h) Such drain shall be trapped and discharge to a closed properly vented salvage tank or to a safe location outside which will not endanger property.

(i) According to tank capacity the diameter of bottom drain pipe shall be not less than the following:

500 to 750 gallons--3 in.
750 to 1,000 gallons--4 in.
1,000 to 2,500 gallons--5 in.
2,500 to 4,000 gallons--6 in.
over 4,000 gallons--8 in.

(j) Where the drain line is long or of poor pitch the pipe size shall be increased to at least the next larger size.

NOTE: Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code.


1. Amendment of subsection (b) filed 7-8-85; effective thirtieth day thereafter (Register 85, No. 28).

2. Amendment file 12-5-86; effective thirtieth day thereafter (Register 86, No. 51).

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