Carbon Dioxide (CO2) Fire Extinguishers
The Carbon Dioxide (CO2) fire extinguisher is a specialised suppression unit designed primarily for risks involving energised electrical equipment. It is a “clean” agent, meaning it leaves no residue after discharge, which is a critical factor for protecting sensitive electronic infrastructure managed by Fireshift.
Identification and Construction
In accordance with AS/NZS 1841.1, CO2 extinguishers are distinguished by a black band on a Signal Red cylinder. Unlike other types, CO2 extinguishers are easily identified by their lack of a pressure gauge and the presence of a large, non-conductive discharge horn or a high-pressure hose and horn assembly.
Fire Classes and Technical Ratings
The FPA Australia classifies CO2 extinguishers for use in specific environments based on the following ratings:
- Class E: Electrically energised equipment. CO2 is a non-conductive gas, making it the primary choice for server rooms, switchboards, and telecommunications hubs.
- Class B: Limited effectiveness on small flammable liquid fires (petrol, oils, or solvents). It works by displacing oxygen, though it has no post-fire cooling effect, posing a risk of re-ignition.
Suppression Mechanism
The discharge of a CO2 extinguisher involves the release of highly pressurised liquid carbon dioxide, which rapidly expands into a gas. This process achieves suppression through two primary methods:
- Oxygen Displacement: It replaces the oxygen surrounding the flame, effectively “smothering” the fire.
- Heat Absorption: While less significant than its smothering effect, the discharge temperature is extremely low (approximately −78°C), providing limited cooling to the fuel source.
Technical Limitations and Safety Hazards
Standard operating procedures and AS 2444 identify several technical constraints for CO2 units:
- Confined Spaces: CO2 displaces oxygen; therefore, discharge in small, unventilated rooms can lead to asphyxiation.
- Thermal Shock: The extreme cold can damage sensitive electronic components or cause brittle fractures in certain materials.
- Discharge Range: CO2 has a shorter effective range compared to Dry Chemical Powder units, typically requiring the operator to be within 1 to 3 metres of the fire.
- Static Electricity: The high-velocity discharge can generate static electricity; hence, horns are manufactured from non-conductive materials to prevent user shock.
Maintenance and Compliance Requirements
Under AS 1851, CO2 extinguishers require specific maintenance intervals to ensure operational readiness:
- Six-Monthly Inspection: Verification of weight, seal integrity, and physical condition.
- Hydrostatic Testing: Due to the high internal pressure (approx. 58 bar at 20°C), the cylinders must undergo hydrostatic testing and internal inspection every five years.
- Weight Loss: Because they do not have gauges, the only way to verify the contents is by weighing the unit. A loss of more than 10% of the rated contents requires a recharge.
Data Table: CO2 Extinguisher Specifications
| Feature | Technical Specification |
| Australian Standard | AS/NZS 1841.6 |
| Identifying Colour | Red with a Black Band |
| Primary Use | Electrical (Class E) |
| Secondary Use | Flammable Liquids (Class B) |
| Discharge Agent | Carbon Dioxide (CO2) |
| Typical Pressure | 5.8 MPa (58 bar) at 20°C |