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

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§5473. Specific Requirements.

(a) The location of a system, as determined by the maximum total contained volume of hydrogen, shall be in the order of preference as indicated by Roman numerals in Table H-1.

                        Table H-1  

                               Size of Hydrogen System                
                          Less         3,000 CF  In Excess 
Nature of Location        than           to         of 
                         3,000 CF     15,000 CF  15,000 CF 

Outdoors                     I            I          I 
In a separate building       II           II         II 
In a special room            III          III        Not 
Inside buildings not in a                 Not        Not 
  special room and exposed   IV           Permitted  Permitted 
  to other occupancies 

(b) The minimum distance in feet from a hydrogen system of indicated capacity located outdoors, in separate buildings or in special rooms to any specified outdoor exposure shall be in accordance with Table H-2.

(c) The distance in Table H-2, Items 1, 14 and 3 to 10 inclusive do not apply where protective structures such as adequate fire walls are located between the system and the exposure.

(d) Hydrogen systems of less than 3,000 CF when located inside buildings and exposed to other occupancies shall be situated in the building so that the system will be as follows:

(1) In an adequately ventilated area as in Section 5475(b).

(2) 20 feet from stored flammable materials or oxidizing gases.

(3) 25 feet from open flames, ordinary electrical equipment or other sources of ignition.

(4) 25 feet from concentrations of people.

(5) 50 feet from intakes of ventilation or air conditioning equipment and air compressors.

(6) 50 feet from other flammable gas storage.

(7) Protected against damage or injury due to falling objects or working activity in the area.

(8) More than one system of 3,000 CF or less may be installed in the same room, provided the systems are separated by at least 50 feet. Each such system shall meet all of the requirements of this Section.

                                  Table H-2 
                                          Size of Hydrogen System     

                                                Less    3,000 CF     In Excess 
Type of Outdoor Exposure                        than      to             of        
                                               3,000 CF 15,000 CF    15,000 CF 

1. Building or     Wood Frame Construction*       10        25           50 
   Structure       Heavy Timber, Noncom-
                     bustible or Ordinary Con- 
                     struction*                    0        10           25* 
                   Fire Resistive 
                   Construction*                   0         0            0 

2. Wall Openings    Not above any part of a       10        10           10 
                    Above any part of a system    25        25           25 

3. Flammable 
    liquids          0-1,000 gallons              10        25           25 
  above ground    In excess of 1,000 gallons      25        50           50 

4. Flammable 
    liquids               Tank                    10        10           10 
    below ground-- 
    gallons      Vent or fill opening of tank     25        25           25 

5. Flammable 
    liquids               Tank                    20        20           20 
    below ground-- 
    in excess of 
    gallons       Vent or fill opening of tank    25        25           25 

6. Flammable gas 
    storage           0-15,000 CF capacity        10        25           25 
    age, either high 
  pressure or 
  low                 in excess of 15,000 CF 
  pressure            capacity                    25        50           50 

7. Oxygen 
    Storage             12,000 CF or less         Refer to NFPA No. 51, Gas  
                                                   for Welding and Cutting 
                         More than 12,000 CF      Refer to NFPA No. 50, Bulk 
                                                   Systems at Consumer Sites 

8. Fast burning solids such as ordinary lumber,   50        50             50 
     excelsior or paper 

9. Slow burning solids such as heavy timber or    25        25             25 

10. Open flames and other sources of ignition     25        25             25 

11. Air compressor intakes or inlets to           50        50             50 
     ventilating or air-conditioning equipment 

12. Concentration of people***                    25        50             50 

13. Public Sidewalks                              15        15             15 

14. Line of adjoining property which may be built  5         5              5 

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

** But not less than one-half the height of adjacent side wall of the structure.

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


1. Editorial correction of Table H-2 (Register 76, No. 9).

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