Flammable solids are any materials in the solid phase

Phase (matter)

In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, and chemical composition...

 of matter that can readily undergo combustion

Combustion

Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 in the presence of a source of ignition

Combustion

Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 under standard circumstances, i.e. without:

• Artificially changing variables such as pressure or density; or
• Adding accelerant
  Accelerant
  Accelerants play a major role in chemistry. Most chemical reactions can be hastened with an accelerant. Accelerants alter a chemical bond, speed up a chemical process, or bring organisms back to homeostasis. Accelerants are not necessarily catalysts as they may be consumed by the process...
  
  s.

Divisions

Division 4.1: Flammable Solid

Flammable solids are any of the following three types of materials:

1. Desensitized Explosives: explosives that, when dry, are Explosives of Class 1 other than those of compatibility group A, which are wetted with sufficient water, alcohol, or plasticizer
   Plasticizer
   Plasticizers or dispersants are additives that increase the plasticity or fluidity of the material to which they are added; these include plastics, cement, concrete, wallboard, and clay. Although the same compounds are often used for both plastics and concretes the desired effects and results are...
   
    to suppress explosive properties; and are specifically authorized by name either in the 49CFR 172.101 Table or have been assigned a shipping name and hazard class
   Dangerous goods
   Dangerous goods are solids, liquids, or gases that can harm people, other living organisms, property, or the environment. They are often subject to chemical regulations. "HazMat teams" are personnel specially trained to handle dangerous goods...
   
    by the Associate Administrator for Hazardous Materials Safety.
2. Self-Reactive Materials: materials that are thermally unstable and that can undergo a strongly exothermic decomposition
   Exothermic reaction
   An exothermic reaction is a chemical reaction that releases energy in the form of light or heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:-Overview:...
   
    even without participation of oxygen (air). Certain exclusions to this group do apply under 49 CFR.
3. Generic Types: Division 4.1 self-reactive materials are assigned to a generic system consisting of seven types. A self-reactive substance identified by technical name in the Self-Reactive Materials Table in 49CFR 173.224 is assigned to a generic type in accordance with that Table. Self-reactive materials not identified in the Self-Reactive Materials Table in 49CFR 173.224 are assigned to generic types under the procedures of paragraph (a)(2)(iii) of this section.
4. Readily Combustible Solids: materials that are solids which may cause a fire through friction
   Friction
   Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
   
   , such as match
   Match
   A match is a tool for starting a fire under controlled conditions. A typical modern match is made of a small wooden stick or stiff paper. One end is coated with a material that can be ignited by frictional heat generated by striking the match against a suitable surface...
   
   es; show a burning rate
   Burn rate (chemistry)
   In chemistry, the burn rate is a measure of the linear combustion rate of a compound or substance such as a candle or a solid propellant. Burn rate is measured in length over time, such as "mm/second" or "inches/second". Burn rate is a property of combustible substance and it quantifies the...
   
    faster than 2.2 mm (0.087 inches) per second when tested in accordance with UN Manual of Tests and Criteria; or are any metal powders that can be ignited and react over the whole length of a sample in 10 minutes or less, when tested in accordance with UN Manual of Tests and Criteria.

Division 4.2: Spontaneously Combustible

Spontaneously combustible material is:

1. Pyrophoric Material: A pyrophoric material
   Pyrophoricity
   A pyrophoric substance is a substance that will ignite spontaneously in air. Examples are iron sulfide and many reactive metals including uranium, when powdered or sliced thin. Pyrophoric materials are often water-reactive as well and will ignite when they contact water or humid air...
   
    is a liquid or solid that, even in small quantities and without an external ignition source, can ignite within five (5) minutes after coming in contact with air when tested according to the UN Manual of Tests and Criteria.
2. Self-Heating Material: A self-heating material is a material that, when in contact with air and without an energy supply
   Energy supply
   Energy supply is the delivery of fuels or transformed fuels to point of consumption. It potentially encompasses the extraction, transmission, generation, distribution and storage of fuels...
   
   , is liable to self-heat.

Division 4.3: Dangerous When Wet

Dangerous when wet material is material that, by contact with water, is liable to become spontaneously flammable or to give off flammable or toxic gas at a rate greater than 1 liter per kilogram of the material, per hour, when tested in accordance with the UN Manual of Tests and Criteria.

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