Functions of Class A Foam Fire Extinguishing Agent
When putting out fires with foam extinguishers, large amounts of carbon dioxide and foam will be ejected. These substances adhere to combustibles and isolate them from air to achieve fire suppression.

Applicable Fire Types
- Class A solid fires: wood, cotton fabrics and other solid combustibles
- Class B liquid fires: gasoline, kerosene, vegetable oil, diesel oil and other liquids (suitable for high-expansion foam extinguishers)

It can be used for live electrical equipment conditionally. It is applicable to low-voltage electrical facilities such as computer room main units and small common equipment.

Class A foam agents are divided into high-expansion and low-expansion types.
High-expansion foam features an expansion ratio of 201 to 1000 times. It can fill fire spaces rapidly, ideal for large-area fires with fast fire extinguishing efficiency.
Low-expansion foam covers burning surfaces to cut off air and put out fires, leaving water stains after use. It cannot tackle flowing liquid fires. Water contained in foam may cause electric shock and leakage hazards when used on electrical fires.

Selection Requirements for Fire Extinguishers
1. Dry powder, foam, halon and carbon dioxide extinguishers are optional. Chemical foam extinguishers apply to common Class B fires, but not water-soluble Class B fires.
2. Dry powder and carbon dioxide extinguishers shall be adopted for Class C fires.
3. Carbon dioxide and dry powder extinguishers are used for live equipment fires.
4. Dry powder extinguishers are suitable for Class A, B, C fires and live electrical fires.
5. Special dry powder extinguishers shall be used for Class D fires.