Wet Chemical Fire Extinguishers
The Wet Chemical extinguisher is a highly specialised unit developed specifically for fires involving high-temperature cooking oils and fats. Unlike other agents that may react violently with hot oil, the wet chemical agent is engineered to suppress the fire safely and prevent re-flash.
Identification and Construction
As per AS/NZS 1841.1, Wet Chemical extinguishers are identified by an oatmeal-coloured band (sometimes referred to as light yellow or cream) around the top of a Signal Red cylinder. Most commercial units, such as those serviced by Fireshift, are constructed with stainless steel cylinders to resist the corrosive nature of the alkaline extinguishing agent.
Fire Classes and Technical Ratings
The FPA Australia provides the following classification for Wet Chemical units:
- Class F: Cooking oils and fats (lard, vegetable oil, butter, and grease). This is the primary and most critical application.
- Class A: Ordinary combustibles (wood and paper). While effective, they are typically reserved for kitchen-specific Class A risks to ensure the agent is available for Class F emergencies.
Suppression Mechanism (Saponification)
The wet chemical agent—usually a solution of potassium acetate, potassium citrate, or potassium carbonate—extinguishes fire through a process known as saponification:
- Chemical Reaction: The alkaline solution reacts with the fatty acids in the burning oil.
- Soap-Like Blanket: This reaction creates a thick, soapy foam layer on the surface of the fat.
- Smothering & Cooling: The blanket cuts off the oxygen supply and seals in flammable vapours, while the high water content in the solution provides a cooling effect to bring the oil below its auto-ignition temperature.
Safety Hazard: Electrical Conductivity
Under AS 2444:2001, it is mandatory to note that Wet Chemical agents are electrically conductive.
- Danger: They must not be used on Class E (electrical) fires.
- Risk: Discharge onto live electrical components can lead to operator electrocution. In kitchen environments, it is critical to isolate the power or gas supply before or during discharge if safe to do so.
Maintenance and Compliance Requirements (AS 1851)
Due to the specific chemical properties of the agent, Fireshift adheres to strict maintenance intervals:
- Six-Monthly Inspection: Verification of the pressure gauge, nozzle integrity (to ensure no crusting of the agent), and weight.
- Five-Year Overhaul: In line with AS 1851, the unit must be discharged, hydrostatically pressure tested, and refilled with fresh wet chemical agent every five years.
- Corrosion Management: Because the agent is alkaline, any discharge must be thoroughly cleaned from kitchen surfaces (especially aluminium) immediately after the fire is extinguished to prevent permanent material damage.
Technical Specification Table
| Feature | Specification |
| Australian Standard | AS/NZS 1841.3 |
| Identifying Colour | Red with an Oatmeal Band |
| Primary Risk | Class F (Cooking Oils & Fats) |
| Secondary Risk | Class A (Wood/Paper) |
| Conductivity | High (Dangerous for Class E) |
| Common Sizes | 2.0L and 7.0L |