Concrete and Fire: The Ultimate Guide to Fire-Resistant Precast Concrete Solutions
This guide is designed for companies that handle or store combustible materials on their premises. It provides them with essential information about using concrete, particularly precast concrete, to construct fire-resistant retaining walls and storage facilities.
Our goal is to help you understand concrete’s role in fire prevention and how it can be used effectively in your operations.
While this guide offers valuable insights, it does not constitute a design or fire prevention plan.
Understanding the Environment Agency’s Fire Prevention Objectives
The Environment Agency outlines three critical objectives for fire prevention, which all companies handling combustible materials must meet:
1. Minimise the likelihood of a fire: Implementing robust fire prevention strategies is essential to reduce the fire risk on your site.
2. Aim to extinguish a fire within 4 hours. An effective fire response plan is crucial for controlling and extinguishing fires quickly.
3. Minimise the spread of fire within the site and to neighbouring sites: Designing your site layout and storage areas to contain fires is vital for preventing widespread damage.
Addressing these objectives in your fire prevention plan should help you secure approval from regulatory bodies.
Types of Combustible Waste Material
Different types of waste materials present varying levels of fire risk. Common combustible materials include:
- Paper and cardboard
- Plastics
- Rags and textiles
- Scrap metals contaminated with oils or plastics
- End of Life Vehicles (ELVs), both de-polluted and un-depolluted
- Refuse Derived Fuel (RDF) and Solid
- Recovered Fuel (SRF)
- Compost and plant material
- Biomass
- Rubber and tyres (whole, baled, or shredded)
- Wood (planks, sawdust, pellets, logs)
- Electronic equipment (fridges, computers, televisions)
These materials can self-combust if not stored carefully, especially in large volumes or for extended periods.
Minimising storage time and reducing the volume and height of stored materials are simple yet effective ways to lower the risk of self-combustion.
Designing Fire-Resistant Storage Bays
The design of storage bays is critical in preventing and controlling fires.
Key considerations include:
Storage Bay Dimensions: The maximum pile height for waste in transfer stations is 4 meters, with a maximum length and width of 20 meters. Ensuring compliance with these dimensions is crucial for fire safety.
Firewalls and Segregation: Construct fire-resistant walls to separate different types of combustible materials. These walls must be capable of withstanding heat and flames for at least 120 minutes and remain structurally sound for an additional 2 hours, giving a total fire resistance time of 4 hours.
Preventing Fire Spread: Best Practices
Two primary methods exist for controlling or preventing the spread of fire:
- Physical Separation: Maintain a minimum distance of 6 meters between piles of combustible waste and between waste piles and buildings or site boundaries.
- Fire-Resistant Barriers: Construct fire-resistant walls and create storage bays that can contain fires within specific areas, limiting the risk of spread.
In addition to these methods, your fire prevention plan should include:
- Rotating Materials: Implement a first-in, first-out policy to minimise the time combustible materials remain on-site.
- Monitoring Temperature: Regularly check the temperature of waste in storage bays to detect potential fire risks early.
- Ensuring Proper Sealing: Segregation walls should provide a thermal barrier and be properly sealed to prevent fire spread.
- Calculating Flame Heights: Accurately assess potential flame heights to design walls that prevent fire from spreading over them.
- Creating a Quarantine Area: Designate a quarantine area to isolate burning waste in an emergency and prevent the fire from spreading to other areas.
The Role of Concrete in Fire Prevention
Concrete is an exceptional material for use in fire-prone environments, especially in waste transfer stations, due to its inherent fire-resistant properties.
Here’s why concrete is the material of choice:
- Non-Combustible: Concrete does not burn, making it ideal for constructing fire-resistant walls.
- High Fire Resistance: Concrete can withstand high temperatures without losing its structural integrity.
- No Smoke or Toxic Gas Emission: Unlike other materials, concrete does not produce smoke or toxic gases when exposed to fire.
- Ease of Repair: Concrete structures are relatively easy to repair after a fire, minimising downtime.
- Water Resistance: Concrete is not adversely affected by the water used to extinguish fires, ensuring its durability even after a fire event.
Fire Classification of Building Materials
Building materials are classified based on their reaction to fire, with Eurocode EN 13501–1: 2002 providing the relevant standards.
The classifications range from A1 to F, with A1 being the highest, indicating non-combustibility.
- A1 Classification: Concrete and its components (aggregate, cement, and water) fall into this category, making it an ideal material for fire-resistant construction.
When designing a structure that requires fire protection, Eurocode 2 mandates certain criteria:
- Resistance (R): The structure must retain its load-bearing capacity during a fire.
- Separation (E): The structure must prevent the passage of flames and hot gases.
- Isolation (I): The structure must restrict the rise in temperature on the non-exposed side.
These criteria are expressed in minutes (e.g., REI 120 means the structure provides resistance, separation, and isolation for 120 minutes).
Designing Storage Bay Push Walls and Dividing Walls
When designing retaining walls for waste storage, especially in environments where fire risk is a concern, several factors must be considered:
- Material Flammability: Determine if the stored waste is flammable and design the wall accordingly, with increased reinforcement cover if necessary.
- Fire-Rated Walls: Ensure that retaining walls designed to resist fire have a minimum of one meter of freeboard above the maximum retained material height.
- Wall Dimensions: Design storage bays based on a maximum retained height of four meters, with a total wall height of up to five meters, including freeboard.
Using low-level retaining walls with materials heaped above the top of the walls is not recommended for flammable materials. Instead, design your retaining walls and storage bays to accommodate the full volume of materials within the specified height limits, in line with your fire prevention plan.
Fire Ratings for Precast Retaining Walls
While interlocking concrete blocks, prestressed concrete panels, and precast retaining walls are not classified as firewalls under building regulations – they are still considered acceptable for use in waste transfer stations.
These structures can effectively contain and separate flammable materials, providing essential protection to buildings and other assets in the event of a fire.
Wall Design Considerations
Types of Retaining Walls
Several types of precast concrete retaining walls are suitable for use in fire-prone environments:
Precast Concrete Frames: These include ‘A’, ‘L’, and inverted ‘Y’ frames, which are ideal for segregation walls but may need to be anchored down if used as push walls.
Kingpost and Infill Panel Construction: This type of construction is not recommended for waste retaining walls due to the vulnerability of the exposed flanges to impact damage.
Interlocking Concrete Blocks (Lego-Type): These blocks are solid concrete and rely on their mass and friction for stability. However, they are vulnerable to impact, particularly at the top rows, and should not be used as push walls.
Greedy Board Design
Greedy boards, which are extensions to push walls, should be designed with several key elements in mind:
Material: Use mild steel plate to combat deflection, possibly with insulation for noise reduction or fire protection.
Strength: Ensure the board is thick enough to minimise deflection and has supporting fins at regular intervals to prevent buckling.
Angle of Emplacement: Design the angle to be greater than 50 degrees to the horizontal, allowing materials to slide back into the bay rather than accumulating on the board.
Connections: Secure the greedy board to the external fascia materials and to the top of the push wall to prevent damage and maintain structural integrity.
Protective Coatings and Joint Sealing
Steel elements in fire-prone environments should be protected with intumescent paint or encased in concrete to prevent damage during a fire.
Additionally, all joints in concrete structures should be properly sealed to prevent the spread of fire and to maintain the integrity of the fire-resistant barriers.
Conclusion
Concrete is an outstanding material for use in fire-resistant construction, particularly in environments where combustible materials are stored or handled.
By understanding the principles outlined in this guide, you can design, construct, and maintain precast concrete retaining walls that meet regulatory requirements and provide robust protection against fire risks.
Need expert advice on designing fire-resistant concrete structures? Contact us today to learn how our precast concrete solutions can help protect your assets and ensure compliance with fire safety regulations.
