National Fire Protection Association (NFPA):
NOTE: To view online (read-only) documents NFPA requires users to REGISTER.  
              Read-only access allows users to view all editions.
NFPA 58: Liquefied Petroleum Gas Code, (RRC adopted 2008 Edition on February 1, 2008)
NFPA 54: National Fuel Gas Code, (RRC adopted 2006 Edition on February 1, 2008) 

LP-Gas Safety Rulebook (PDF)
CNG/LNG Safety Rulebook (PDF)

Texas Administrative Code (TAC), Title 16, Chapter 9 - LP-Gas Safety Rules

Texas Natural Resources Code, Title 3, Chapter 113 - Liquefied Petroleum Gas
Texas Natural Resources Code, Title 3, Chapter 116 - CNG and LNG