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

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§5492. Specific Requirements.

(a) The location of liquefied hydrogen storage, as determined by the maximum total quantity of liquefied hydrogen, shall be in the order of preference as indicated by Roman numerals in the following Table H-3:

                          Table H-3 
Maximum Total Quantity of Liquefied Hydrogen Storage Permitted 

                                   Size of Hydrogen Storage (Capacity in Gallons) 
                            39.63                                    In excess  
Nature of Location       (150 liters)    51 to 300  301 to 600        of 600    
                            to 50 
Outdoors                       I             I           I              I 
In a separate building         II            II          II         Not permitted 
In a special room              III           III    Not permitted   Not permitted 
Inside buildings not in 
  a special room and 
  exposed to other 
  occupancies                  IV            Not         Not           Not 
                            permitted     permitted   permitted 

NOTE: This table does not apply to the storage in dewars of the type generally used in laboratories for experimental purposes.

(b) The minimum distance in feet from liquefied hydrogen systems of indicated storage capacity located outdoors, in a separate building, or in a special room to any specified exposure shall be in accordance with Table H-4.

                          Table H-4 
Minimum Distance (feet) from Liquefied Hydrogen Systems to Exposures 
                                           Liquefied Hydrogen Storage  
                                     39.63      3,501         15,001 
Type of Exposure                  (150 liters)    to             to 
                                     3,500       15,000       30,000 
1. Fire-resistive Building and          5          5               5 
  Fire Walls* 
2. Noncombustible Building*            25         50              75 
3. Other Buildings*                    50         75             100 
4. Wall Openings, Air Compressor       75         75              75 
  Intakes, Inlets for Air- 
  Conditioning or Ventilating Equipment 
5. Flammable Liquids (Above-           50         75             100 
  ground and Vent or Fill 
  Openings if Below Ground) 
  (See 5491(c) and (d)) 
6. Between Stationary Liquefied         5          5               5 
  Hydrogen Containers 
7. Flammable Gas Storage               50         75             100 
8. Liquid Oxygen Storage and          100        100            100 
  other Oxidizers (See 5491(c) and (d)) 
9. Combustible Solids                  50         75             100 
10. Open Flames, Smoking and           50         50              50 
11. Concentrations of People**         75         75              75 
12. Public Ways, Railroads, and        25         50              75 
  Property Lines 

* Refer to NFPA No. 220, "Standard Types of Building Construction," for definitions of construction types.

** In congested areas such as offices, lunchrooms, locker rooms, time clock areas, and places of public assembly.

NOTE: 1: The distances in Nos. 2, 3, 5, 7, 8, 9 and 12, in Table 2, may be reduced where protective structures, such as fire walls equal to height of top of the container, to safeguard the liquefied hydrogen storage system, are located between the liquefied hydrogen storage installation and the exposure. (See definition of Outdoor Location, Section 5415.)

NOTE: 2: Where protective structures are provided, ventilation and confinement of product shall be considered. The 5-foot distance in Nos. 1 and 6 facilitates maintenance and enhances ventilation.


1. Amendment of Table H-4 filed 3-2-76; effective thirtieth day thereafter (Register 76, No. 10).

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