This is the defining code for propane.
There are still people out there who think that it is OK to keep propane inside. So, without further ado, here are the salient portions of NFP 58:
6.2 Location of Containers
6.2.1 LP-Gas containers shall be located outside buldings unless they are specifically allowed to be inside of buildings.
6.2.2 LP-Gas containers shall be allowed in buildings only for the following applications:
(1) Cylinders as specifically provided for under Section 6.19 (see below).
(2) Containers of less than 125 gallons for the purpose of being filled.
(3) Containers on LP-Gas vehicles complying with and parked or garaged in accordance with Chapter 9.
(4) Containers used with LP-Gas stationary or portable engine fuel systems complying with Chapter 11.
(5) Containers used with LP-Gas fueled trucks complying with Chapter 11.
(6) Containers used on LP-Gas fueled vehicles garaged in accordance with Chapter 11.
(7) Cylinders awaiting use, resale or exchange when stored in accordance with Chapter 8.
***NOTE: These are the only allowed inside storage of LP cylinders under the code.
Other parts of the code that might interest you:
6.6.2 Installation of cylinders
126.96.36.199 Containers shall be installed only above ground and shall be set upon a firm foundation or otherwise be firmly secured. The cylinder shall not be in contact with the soil.
188.8.131.52 Flexibility shall be provided in the connecting piping. Where flexible connectors are used they shall comply with 6.9.6.
Section 6.19 covers allowable inside use and storage of propane cylinders. These are limited to a maximum liquid capacity of 100 pounds. Additionally, it states “limited to those conditions where operational requirements make the indoor use of cylinders necessary and outside location is impractical.”
6.19.4 Building undergoing construction or major renovation
6.19.5 Building undergoing major renovation where frequented by the public
6.19.6 Buildings housing industrial occupancies
6.19.7 Buildings housing institutional and educations occupancies
184.108.40.206 The use of cylinders in classrooms shall be prohibited unless they are used temporarily for classroom demonstrations in accordance with 220.127.116.11.
18.104.22.168 Where cylinders are used in buildings housing institutional and educational laboratory occupancies for research and experimental purposes. Cylinders must not be stored (in use or not) in the laboratory room.
6.19.8 Temporary heating and food service applications in buildings in emergencies
6.19.9 Use in buildings for demonstrations or training and use of small cylinders for self-contained torch assemblies and food service appliances.
22.214.171.124 Limit 5 lb propane capacity, for self-contained torch assemblies, the limit is 1 lp propane capacity.
6.19.10 Use in a building for flame effects before a proximate audience
6.19.11 Cylinders on roofs and balconies
***NOTE: many major restrictions i.e.: building shall be of fire-resistant construction or non-combustible construction AND essentially non-combustible contents or contents are protected with automatic sprinklers.
6.19.12 Liquid LP-Gas piped into buildings or structures
***NOTE: the above (6.19.4 – 6.19.12) are the ONLY indoor usages allowed under the code.