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Subchapter 7. General Industry Safety Orders
Group 20. Flammable Liquids, Gases and Vapors
Article 138. Hydrogen

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§5485. Piping, Tubing and Fittings.

(a) Piping, tubing and fittings and gasket and thread sealants shall be suitable for hydrogen service at the pressures and temperatures involved. Cast iron pipe and fittings shall not be used.


1. Consideration shall be given to the thermal expansion and contraction of piping systems when exposed to temperature fluctuations of ambient to liquefied hydrogen temperatures.

2. Some materials suitable for liquefied hydrogen temperature are austenitic chromium-nickel alloys, certain copper alloys, and aluminum which retain ductility and do not become brittle at the temperature of liquefied hydrogen.

(b) Hydrogen piping and tubing.

(1) Hydrogen piping and tubing installed after May 30, 1999, shall conform to ASME B31.3-1996, Process Piping, which is hereby incorporated by reference.

(2) Hydrogen piping and tubing installed on or before May 30, 1999, shall conform to either the American National Standard Code for Pressure Piping, Petroleum Refinery Piping, ANSI B31.3-1973, or the updated version of the ANSI/ASME B31.3 standard in effect at the time of installation.

(3) For temperatures of -20oF to -320oF, hydrogen piping shall be approved as defined Section 3206 of the General Industry Safety Orders.

(c) Joints in piping and tubing shall preferably be made by welding or brazing; flanged, threaded, socket or suitable compression fittings may be used.

(d) Means shall be provided to minimize exposure of personnel to piping operating at low temperatures and to prevent air condensate from contacting piping, structural members and surfaces not suitable for cryogenic temperatures. Only those insulating materials which are rated nonburning in accordance with ASTM Procedure D-1692-68 may be used. Other protective means may be used to protect personnel. The insulation shall be designed to have a vapor-tight seal in the outer covering to prevent the condensation of air and subsequent oxygen enrichment within the insulation. The insulation material and outside shield shall also be of adequate design to prevent attrition of the insulation due to normal operating conditions.

(e) Uninsulated piping and equipment which operate at liquefied-hydrogen temperature shall not be installed above asphalt surfaces or other combustible materials in order to prevent contact of liquid air with such materials. Drip pans may be installed under uninsulated piping and equipment to retain and vaporize condensed liquid air.


:(a) Separate buildings shall be of light, noncombustible construction on a substantial frame. Walls and roofs shall be lightly fastened and designed to relieve at a maximum internal pressure of 25 pounds per square foot. Windows shall be of shatterproof glass or plastic in metal frames. Doors shall be located in such a manner that they will be readily accessible to personnel in an emergency.

(b) Adequate ventilation to the outdoors shall be provided. Inlet openings shall be located near the floor level in exterior walls only. Outlet openings shall be located at the high point of the room in exterior walls or roof. Both the inlet and outlet vent openings shall have a minimum total area of one square foot per 1,000 cubic feet of room volume. Discharge from outlet openings shall be directed or conducted to a safe location.

(c) There shall be no sources of ignition.

(d) Electrical wiring and equipment shall comply with Section 5489 except that the provisions of Subsection (b) of Section 5489 shall apply to all electrical wiring and equipment in the separate building.

(e) Heating, if provided, shall be by steam, hot water, or other indirect means. (Title 24, T8-5495)


1. Amendment of subsection (d) filed 3-2-76; effective thirtieth day thereafter (Register 76, No. 10).

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

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