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Subchapter 7. General Industry Safety Orders
Group 20. Flammable Liquids, Gases and Vapors
Article 143. Processing Plants

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§5556. Construction.

(a) Processing buildings shall be of not less than noncombustible construction, except heavy timber construction with load-bearing walls may be permitted for plants utilizing only stable Class II or Class III liquids. Except as provided in Section 5555(b) or in the case of explosion resistant walls used in conjunction with explosion relieving facilities, see (f), load-bearing walls shall be prohibited. Buildings handling Class I or Class II liquids shall be without basements or covered pits.

(b) Areas shall have adequate exit facilities arranged to prevent occupants from being trapped in the event of fire (see Article 2).

(c) Exits shall not be exposed by the drainage facilities described in Section 5546(a) and (b).

(d) Enclosed processing buildings handling Class I or Class II liquids shall be ventilated at a rate of not less than one cubic foot per minute per square foot of solid floor area. This shall be accomplished by natural or mechanical ventilation with discharge or exhaust to a safe location outside of the building. Provision shall be made for introduction of make-up air in such a manner as not to short circuit the ventilation. Ventilation shall be arranged to include all floor areas or pits where flammable vapors may collect. Local (or spot) ventilation may be needed for the control of special fire or health hazards. Such ventilation, if provided, may be utilized for up to 75 percent of the required ventilation.

(e) Equipment used in a building and the ventilation of the building shall be designed so as to limit flammable vapor-air mixtures under normal operating conditions to the interior of equipment, and to not more than five feet from equipment which exposes Class I liquids to the air. Examples of such equipment are dispensing stations, open centrifuges, plate and frame filters, open vacuum filters, and surfaces of open equipment.

(f) Areas where Class IA or unstable liquids are processed shall have explosion venting through one or more of the following methods:

(1) Open air construction;

(2) Lightweight walls and roof;

(3) Lightweight wall panels and roof hatches;

(4) Windows of explosion venting-type. (Title 24, T8-5556)


1. Amendment filed 7-16-76; effective thirtieth day thereafter (Register 76, No. 29).

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