Water Fire Extinguishers

The Water fire extinguisher is the most traditional form of fire suppression, designed specifically for deep-seated fires in carbonaceous materials. It remains a standard installation for office environments, warehouses, and timber storage areas managed by Fireshift.

Identification and Construction

Under AS/NZS 1841.1, Water extinguishers are distinguished by being Solid Red with no coloured band. Because the entire unit is Signal Red, it is often referred to simply as a “Water” or “Air-Water” unit. Most high-quality units, such as those provided by Fireshift, feature a stainless steel cylinder to prevent internal corrosion from the water storage.

Fire Classes and Technical Ratings

According to FPA Australia, Water extinguishers are rated for:

  • Class A: Ordinary combustibles (wood, paper, textiles, rubber, and plastics).
  • Not Suitable for Class B/C: Water is ineffective on flammable liquids or gases as it can cause the fire to spread or “splash.”
  • Not Suitable for Class F: Discharge onto hot cooking oils will cause a violent steam explosion.

Suppression Mechanism (Thermal Cooling)

Water extinguishers operate on the cooling principle of the fire triangle:

  1. Heat Absorption: Water has a high high thermal capacity, allowing it to absorb massive amounts of energy from the fire.
  2. Saturation: The steady stream allows for deep penetration into porous materials (like timber or hay), cooling the fuel to below its ignition point.
  3. Steam Conversion: As the water hits the fire, it converts to steam, which can provide a secondary displacement of oxygen in confined areas.

Danger: Electrical Conductivity

Under AS 2444:2001, Water extinguishers carry a critical safety warning:

  • Electrical Hazard: Water is a conductor of electricity.
  • Warning: They must never be used on Class E fires (energised electrical equipment).
  • Risk: Using a water extinguisher on a live electrical fire poses a fatal risk of electrocution to the operator. For areas with high electrical density, Fireshift recommends CO2 or ABE Powder alternatives.

Maintenance and Compliance Requirements (AS 1851)

Water extinguishers have the most frequent internal maintenance requirements under AS 1851:

  • Six-Monthly Service: Visual inspection, pressure gauge check, and nozzle clearance.
  • Annual Discharge: In many commercial applications, the water must be discharged and the unit refilled every 12 months to ensure the water remains clean and the propellant is effective.
  • Five-Year Hydrostatic Test: Like all pressure vessels, the cylinder must undergo hydrostatic testing and internal inspection every five years.
  • Anti-Freeze Additives: For installations in alpine or cold-storage environments, a specific anti-freeze additive must be included to prevent the unit from freezing and rupturing.

Technical Specification Table

FeatureSpecification
Australian StandardAS/NZS 1841.2
Identifying ColourSolid Red (No Band)
Primary RiskClass A (Wood, Paper, Textiles)
Agent TypePotable Water (with/without additives)
ConductivityHigh (Dangerous for Electrical Fires)
Operating PressureApprox. 700–1000 kPa