Gas Max

From NFPA 45 - Fire Protection for Laboratories using Chemicals, Chapter 8, Table 8-2:
Maximum Quantity and Size Limitation for Compressed or Liquefied Gas Cylinders in Laboratory Work Areas.

The allowed quantity is based on a 500 ft² area, and depends on whether the lab is sprinklered or not.

In instructional labs the total number of cylinders shall be reduced to three maximum.   In all other cases 25 2 x 23" cylinders, or equivalent volume shall be permitted.

*Note that the BOCA and UBC codes have additional requirements for gases with health hazard rating of 3 & 4, such as the mandatory use of gas cabinets, toxic gas monitoring, automatic safety & shut down system, signal to central station & evacuation alarms, etc.

NFPA ratings.  From BOC Gases MSDSs, Spring 2000.  Health hazards are based on toxicity; simple asphyxiants such as nitrogen and carbon dioxide are not toxic, per se.  Chemical asphyxiants such as hydrogen cyanide and carbon monoxide, as well as other gases having toxic effects on biological systems in relatively small quantities, are the gases which will be rated as health hazard 3 or 4.