Here are some common flammable chemical and their classifications and characteristics:

Flammable Gases
- Hydrogen (H₂)
  - Characteristics: Colorless, odorless, highly flammable gas. Widely used in chemical synthesis and fuel cells.
  - Safety: Forms explosive mixtures with air (explosive limits: 4.1%–74.2%). It is extremely dangerous when exposed to ignition sources.
- Liquefied Petroleum Gas (LPG)
  - Characteristics: Mainly composed of propane and butane. Commonly used for domestic fuel and industrial applications.
  - Safety: Forms explosive mixtures with air. It is heavier than air and can spread to distant areas, igniting when exposed to a flame.
- Propane (C₃H₈)
  - Characteristics: Flammable gas. Explosive limits with air: 2.1%–9.5%.
  - Safety: Heavier than air, can spread and ignite when exposed to a flame.
- Ethylene (C₂H₄)
  - Characteristics: Flammable gas. Explosive limits with air: 2.7%–36%.
  - Safety: Can ignite and explode when exposed to an ignition source or oxidizer.

Flammable Liquids
- Gasoline
  - Characteristics: Commonly used as fuel for internal combustion engines. Flash point below or equal to 61°C.
  - Safety: Highly volatile, ignites easily when exposed to a flame.
- Ethanol (C₂H₅OH)
  - Characteristics: Commonly used as a solvent and disinfectant. Flash point between 23°C and 61°C.
  - Safety: Highly flammable, ignites easily when exposed to a flame.
- Acetone (C₃H₆O)
  - Characteristics: A common organic solvent. Low flash point, highly volatile.
  - Safety: Extremely flammable, ignites easily when exposed to a flame.
- Toluene (C₇H₈)
  - Characteristics: Commonly used as a solvent. Low flash point.
  - Safety: Highly flammable, ignites easily when exposed to a flame.

Flammable Solids
- Sulfur
  - Characteristics: Low ignition point, ignites easily when exposed to friction or impact. Commonly used in matches and fireworks.
  - Safety: Forms toxic sulfur dioxide when burned.
- Red Phosphorus
  - Characteristics: Commonly used in matches and fireworks. Low ignition point.
  - Safety: Ignites easily when exposed to friction or impact.

Pyrophoric Substances
- White Phosphorus
  - Characteristics: Ignites spontaneously in air, producing highly toxic phosphine gas.
  - Safety: Extremely dangerous; must be stored under water or in an inert atmosphere.

Water-Reactive Substances
- Sodium (Na)
  - Characteristics: Reacts violently with water, producing hydrogen gas and heat.
  - Safety: Can cause explosions when exposed to water.
- Potassium (K)
  - Characteristics: Reacts violently with water, producing hydrogen gas and heat.
  - Safety: Can cause explosions when exposed to water.

Classification Criteria
According to the national standard "General Rules for Classification and Labeling of chemical" (GB13690-2009), flammable chemical are classified as follows:
- Flammable Gases:
  - Class I: Explosive limit less than 10%, or regardless of the lower explosive limit, the explosive range is greater than or equal to 12 percentage points.
  - Class II: Explosive limit greater than or equal to 10% and less than or equal to 13%, and the explosive range is less than 12 percentage points.
- Flammable Liquids:
  - Low Flash Point: Below -18°C.
  - Medium Flash Point: -18°C to 23°C.
  - High Flash Point: 23°C to 61°C.
- Flammable Solids: Low ignition point, ignites easily when exposed to friction or impact.

These flammable chemical require special attention to fire prevention, sun protection, and heat insulation during storage, transportation, and use to prevent fire or explosion accidents.