Foam Suppression Firefighting System is a vital tool in extinguishing fires, particularly in industries dealing with flammable liquids and chemicals. The NFPA 11 standard outlines various types of foam concentrate proportioning systems, each designed to deliver accurate and efficient foam ratios for fire suppression. Foam systems are indispensable for controlling fires in storage tanks, refineries, and other high-risk environments. This article explores the common foam proportioning systems, their components, advantages, and limitations.
Understanding Foam Concentrate Proportioning
The success of a foam firefighting system depends on the precise proportioning of foam concentrate into the firewater stream. NFPA 11 sets strict guidelines for the proportioning rate, ensuring fire suppression effectiveness. Below are some key aspects:
- Proportioning Limits: The foam concentrate proportioning rate must not be lower than the prescribed values. For example, a 3% foam concentrate requires a proportioning rate of at least 3%, while a 6% foam concentrate requires 6%. Exceeding the proportioning rate by more than 30% is not recommended. However, it is permissible to exceed by 1% (i.e., 3.9% for a 3% foam concentrate, or 7.8% for a 6% foam concentrate).
- Annual Testing: To ensure accurate proportioning, foam systems must be tested annually, including checking the proportioner’s performance and foam concentrate quality.
Types of Foam Proportioning Systems
There are several foam concentrate proportioning systems, each offering unique advantages for fire suppression. Here, we look at the three most common systems:
1. Bladder Tank with Proportioner
Bladder tanks with proportioners are widely used in foam suppression systems due to their cost-effectiveness and simple design. This system involves a pressurized bladder tank filled with foam concentrate, which is connected to a proportioner. The proportioner works on the Venturi principle, where the flow of firewater creates a vacuum that pulls foam concentrate into the water stream.
Advantages:
- Simple design with no moving parts.
- Low operational costs.
- No external energy required.
Disadvantages:
- Requires regular testing and refilling of foam concentrate.
- Limited capacity for handling large fluctuations in firewater flow.
- Sensitive bladder material can lead to contamination if damaged.
2. Driven Proportioning Pump with Flow Meter
This foam suppression system uses an electric or diesel-powered foam concentrate pump, a flow meter, and an electronically controlled valve to regulate the foam proportioning. When the fire pumps are activated, the flow meter adjusts the foam concentrate injection rate based on the extinguishing water flow.
Advantages:
- Accurate, real-time foam concentrate proportioning.
- Can handle a wide range of foam concentrates, including highly viscous types.
- Foam concentrate can be topped up during operation.
Disadvantages:
- Requires a stable energy supply.
- Higher installation costs.
- Possible delay in foam concentrate adjustment during flow rate changes.
3. Water Motor with Proportioning Pump
The water motor-driven foam proportioning system operates by using a water motor coupled directly with the foam concentrate pump. When the fire pumps are activated, the water motor generates rotational force to drive the foam concentrate pump, instantly adjusting foam concentrate flow in response to changing water pressure.
Advantages:
- No external energy source required.
- Immediate and precise foam concentrate injection.
- Capable of proportioning highly viscous foam concentrates.
Disadvantages:
- Larger system size and higher purchase costs.
- Requires regular maintenance and testing.
Mobile Foam Suppression Systems
In some cases, stationary foam suppression systems may be damaged during large-scale fires, especially in tank farms or areas prone to explosions. In such cases, mobile foam extinguishing systems come into play. These systems provide flexibility and can be deployed rapidly in case of an emergency.
Mobile Foam Fire Monitors
Mobile foam monitors are mounted on vehicles or trailers and can discharge up to 60,000 liters of foam per minute. These monitors are capable of reaching distances of up to 180 meters and can be used to fight fires in tank farms, storage facilities, and other high-risk areas. Foam monitors are supplied either by stationary fire pumps or mobile pumps.
Advantages:
- Flexibility: Can be positioned around the tank or fire site.
- Energy independence: Water-motor driven proportioning pumps.
- High extinguishing power: Suitable for large fires.
Disadvantages:
- Requires careful placement and setup to ensure effective foam delivery.
- May not be effective against certain types of fires or situations.
Regulatory Considerations & Testing for Foam Suppression Systems
The NFPA 11 guidelines are clear about the standards for foam proportioning and annual testing. Regular testing ensures that the foam concentrate proportioning system works efficiently under actual fire conditions. The testing typically involves:
- Activation of the foam system.
- Verification of foam concentrate proportioning through a laboratory analysis.
- Disposal of premix foam and refilling of foam concentrate.
- Inspection of foam discharge devices and system components.
Lessons Learned from Real-World Incidents
Tank farm fires, particularly in the oil and petrochemical industries, demonstrate the importance of effective foam suppression systems. For instance, the Deer Park, Texas fire in 2019 resulted from a faulty valve leak that led to a massive fire. The local fire service struggled to control the fire due to insufficient equipment and a lack of mobile foam systems. The fire continued for over 63 hours, consuming over 500,000 liters of foam concentrate.
Key takeaways:
- Regular system maintenance and annual testing are crucial.
- Mobile foam systems can be a lifesaver in large-scale fires.
- Prompt action and sufficient foam resources are critical to minimize damage and loss.
Conclusion
A foam suppression firefighting system is a crucial element of fire safety, especially in industries where flammable materials pose significant risks. Whether using bladder tanks, foam concentrate pumps, or water motor-driven systems, foam systems offer highly effective protection against fires. Compliance with NFPA 11 guidelines and regular testing ensures that these systems perform efficiently in emergencies. By combining mobile extinguishing units, precise foam proportioning, and energy-independent operation, foam suppression systems are key to mitigating fire risks in industrial and commercial settings.
