In case you missed any of the previous posts in the Vehicle Fire Suppression Basics series…

• Blog post 1: Extinguishing Agents
• Blog post 2: Detection Systems
• Blog post 3: Control Module

Part 4 of 9: Extinguishing Agent Tanks (Part 1)

No fire suppression system is complete without the correct extinguishing agent tanks. In this blog post, we look at the two main types of agent tanks: cartridge operated and stored pressure.

Understanding Agent Tank Types

Cartridge operated and stored pressure agent tanks will both perform well when used in the right application and in the right environment. However, it is important to understand when and where to use each type of canister. Of the two, cartridge operated tanks are currently favoured industry-wide in the vehicle and mobile plant market for the following reasons:

• Heavy duty construction
• Simple design eliminates failure points
• Easily serviced on-site
• Low maintenance
• No special tools required

Stored pressure units are often used as hand held portable extinguishers, but side cartridge operated units are also available. These are effective in protecting stationary situations such as restaurant cooking hoods and electrical sub-stations. For complete peace of mind, it is recommended that all vehicle and mobile plant systems are supported by hand held extinguishers, as these provide additional fire suppression if needed.

Stored pressure tanks

Stored pressure extinguishers contain compressed nitrogen gas. This is used as the propellant for the extinguishing agent and is stored in the same canister as the extinguishing agent.

Cartridge operated tanks

Cartridge operated units store the extinguishing agent in a non-pressurised container and the nitrogen gas in a separate cartridge. When activated the extinguisher is under pressure for a relatively short time.

Cartridge Operated versus Stored Pressure

Compaction

Dry chemical does not stay in suspension in either cartridge operated or stored pressure tanks, but in cartridge operated ones, it is stored at atmospheric pressure so compaction is less severe.

In cartridge operated systems, when the system is discharged 1800-2015 PSI gas mixes the powder up, then flows from a large hole in the side of the tank after reaching burst-disc release pressure. In storage pressures systems, the gas must push through the compacted gas entraining the powder up and out of the dip tube.

Maintenance/ Recharge costs

Cartridge operated tanks are low maintenance and have low recharge costs, and can be easily serviced on site. They don’t require special equipment, just replacement of the burst disc, agent and cartridge to restore system to working order.

Stored pressure tanks are also low maintenance and have low recharge costs, but equipment needed to recharge requires pressurising the cylinder on site, which can lead to related elated health and safety issues.

Energy density

Energy density of the expellant gas in cartridge operated systems is very high. This means longer, more powerful discharges using less space compared to stored pressure systems.

Discharge pressure

Cartridge operated systems will hold a constant discharge pressure throughout the duration of the discharge, while stored pressure system will lose discharge pressure. Cartridge operated systems discharge pressure will start at 100 PSI and remain at 100 PSI and over until all agent has been discharged. Stored pressure systems discharge pressure will start at 16 Bar and drop to 0 across the discharge.

Next blog post in the Vehicle Fire Suppression Basics series: Extinguishing Agent Tanks (Part 2)