Excerpts from ASME (ANSI) ••••••• A 13.1-1996

2. Definitions:

2.2 Materials Inherently Hazardous

2.2.1 Flammable or Explosive
This classification includes materials which are easily ignited. It includes materials known as fire producers or those creating an explosive atmosphere.

2.2.2 Chemically Active or Toxic
This classification includes materials which are corrosive, or are in themselves toxic or productive of poisonous gases.

2.2.3 At Temperatures or Pressures
This classification includes materials which when released from the piping would have a potential for inflicting injury or property damage by burns, impingement, or flashing to vapor state.

2.2.4 Radioactive
This classification includes those materials which emit ionizing radiation.

2.3 Materials of Inherently Low Hazard
This classification includes all materials which are not hazardous by nature, and are near enough to ambient pressure and temperature that people working on systems carrying these materials run little risk through the release of these materials.

2.4 Fire Quenching Materials
This classification includes sprinkler systems and other piped fire fighting or fire protection equipment. This includes water (for fire fighting), foam, CO2 , Halon, etc.3.

3. Method of Identification:

3.1 Legend
This Standard considers legend to be primary and explicit for identification of contents. Positive identification of the contents of a piping system shall be by lettered legend giving the name of the contents in full or abbreviated form. Arrows shall be used to indicate direction of flow. Contents shall be identified by legend with sufficient additional details such as temperature, pressure, etc. as are necessary to identify the hazard. Legend shall be brief, informative, pointed, and simple for greatest effectiveness. Legends shall be applied close to valves or flanges and adjacent to changes in direction, branches, and where pipes pass through walls or floor; and at intervals on straight pipe runs.

3.2 Color
Color should be used to identify the characteristic hazards of the contents (see Table 2).

3.4 Type and Size of Letters
Contrast shall be provided between color field and legend for readability. Table 2 gives recommendations for color of legend on various color fields covered in this Standard. Use of letters of standard style1, in sizes 1/2 in. 13 (mm) and larger, is recommended. Refer to Table 3 for specific size recommendations. For identification of materials in pipes of less than 3/4 in. (19mm) in diameter, and for valve and fitting identification, the use of a permanently legible tag is recommended.
• 1Sans serif gothic bold lettering provides high readability.

• *Previously specified radioactive markers using yellow and purple are acceptable if already installed and/or until existing supplies are depleted, subject to pertinent Federal Regulations.
• *Previously specified radioactive markers using yellow and purple are acceptable if already installed and/or until existing supplies are depleted, subject to pertinent Federal Regulations.