Didn’t know if you wanted to see what 99 said??
NFPA 99, 2012
11.3.1* Storage for nonflammable gases equal to or greater than 85 m3 (3000 ft3) at STP shall comply with 5.1.3.3.2 and 5.1.3.3.3.
5.1.3.3.2* Design and Construction. Locations for central supply systems and the storage of positive-pressure gases shall meet the following requirements:
(1) They shall be constructed with access to move cylinders, equipment, and so forth, in and out of the location on hand trucks complying with 11.4.3.1.1.
(2) They shall be secured with lockable doors or gates or otherwise secured.
(3) If outdoors, they shall be provided with an enclosure (wall or fencing) constructed of noncombustible materials with a minimum of two entry/exits.
(4) If indoors, they shall be constructed and use interior finishes of noncombustible or limited-combustible materials such that all walls, floors, ceilings, and doors are of a minimum 1-hour fire resistance rating.
(5) They shall be compliant with NFPA 70, National Electrical Code, for ordinary locations.
(6) They shall be heated by indirect means (e.g., steam, hot water) if heat is required.
(7) They shall be provided with racks, chains, or other fastenings to secure all cylinders from falling, whether connected, unconnected, full, or empty.
(8) *They shall be supplied with electrical power compliant with the requirements for essential electrical systems as described in Chapter 6.
(9) They shall have racks, shelves, and supports, where provided, constructed of noncombustible materials or limited-combustible materials.
(10) They shall protect electrical devices from physical damage.
5.1.3.3.3 Ventilation.
5.1.3.3.3.1 Venting of Relief Valves. Indoor supply systems shall have all relief valves vented per 5.1.3.5.6.1(4) through (9).
5.1.3.3.3.2 Ventilation for Motor-Driven Equipment. The following source locations shall be adequately ventilated to prevent accumulation of heat:
(1) Medical air sources (see 5.1.3.6)
(2) Medical–surgical vacuum sources (see 5.1.3.7)
(3) Waste anesthetic gas disposal (WAGD) sources (see 5.1.3.8.1)
(4) Instrument air sources (see 5.1.3.9)
11.3.2* Storage for nonflammable gases greater than 8.5 m3 (300 ft3), but less than 85 m3 (3000 ft3), at STP shall comply with the requirements in 11.3.2.1 through 11.3.2.3.
11.3.2.1 Storage locations shall be outdoors in an enclosure or within an enclosed interior space of noncombustible or limited-combustible construction, with doors (or gates outdoors) that can be secured against unauthorized entry.
11.3.2.2 Oxidizing gases, such as oxygen and nitrous oxide, shall not be stored with any flammable gas, liquid, or vapor.
11.3.2.3 Oxidizing gases such as oxygen and nitrous oxide shall be separated from combustibles or materials by one of the following:
(1) Minimum distance of 6.1 m (20 ft)
(2) Minimum distance of 1.5 m (5 ft) if the entire storage location is protected by an automatic sprinkler system designed in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems
(3) Enclosed cabinet of noncombustible construction having a minimum fire protection rating of 1/2 hour