James Mountain, sales and marketing director at Fire Shield Systems, explores the rubber and plastic fire risks and shares his tips to mitigate them, in order to turn around the waste and recycling sector’s troubling fire record.
As the effort towards sustainable materials increases worldwide, the UK is seeing a rise in rubber and plastic recycling. Before recycling, these materials are often stored for extended periods of time, and require intense processing to repurpose them, creating significant fire risks.
Plastics today have evolved significantly since their origin and now contain a complicated mix of materials. This is also true for rubber, with tyres today containing over 200 different materials. Many of these ingredients are combustible, producing significant fire risks.
Both rubber and plastic are oil-based materials, with the potential to act much like flammable liquids when alight. Fire suppression, therefore, is more challenging, and it is particularly important to understand all the risks and mitigation measures to ensure safety.
Rubber
Rubber fires have the potential to spread rapidly and burn at incredibly high temperatures. Once these high temperatures have been reached, rubber will often begin to flow as a hot mass. This entraps the flammable vapours being released from the material and can create an explosive force if not quickly managed.
Rubber is also a natural water repellent, meaning many extinguishing mediums will simply be shed and drained away. Therefore, traditional suppression systems, like ceiling sprinkler systems, are often limited in controlling the spread of fire.
A particularly common type of rubber fire is tyre fires, as waste tyres for recycling are often stored for extended lengths of time. These tyre stockpiles have the potential for high heat output, a risk increased further by the air spaces between tyres.
Tyres can also burn for a staggering amount of time, such as the Heyope Tyre Fire, which burned beneath the surface for 15 years before being fully extinguished in 2004. Burning tyres also release large amounts of oil, making water alone an even less effective extinguishing material.
Plastic
Plastic flames spread rapidly and can reach as high as two feet per second, or 10 times that of wood on the surface. Burning plastic will also melt and run, causing the fire to spread in different and unpredictable ways.
Recycled plastics are commonly used to produce refuse derived fuel (RDF) and solid recovered fuel (SRF), both of which carry key fire risks. Subcoal technology can also now be used to repurpose RDF and SRF into pellets, used for fuelling lime or cement kilns, for instance. These pellets have a high calorific value, meaning they are also highly susceptible to ignition.
Responsibilities and regulations
All waste sites must have a clear fire prevention plan (FPP), outlining all fire safety measures that are in place, as is mandated by the Environment Agency. This is agreed upon by the Regulatory Reform (Fire Safety) Order (2005), which stipulates the reasonable steps that should be taken to mitigate fire risk.
There is voluntary guidance pertaining to the suppression measures for different materials (NFPA 11, EN 13565), and there is also guidance specifically referencing the storage of rubber (ISO 2230:2002).
How to reduce the risk
- When bulk storing raw materials
- Minimise pile sizes and storage times
- Regularly monitor sub-surface temperatures
- Ensure sufficient ventilation
- Separate stockpiles – physically or using fire walls.
Water-based suppression solutions are often unsuitable for rubber and plastic storage. In these situations, compressed air foam systems will often be more effective, as the agent will stick to the materials and eliminate oxygen supply.
- During processing
- Ensure regular maintenance on all machinery to monitor friction and avoid mechanical failure
- Regularly clean all machinery to prevent build-up of combustible particles.
Localised protection may be needed for parts of the processing machinery. Detection systems can also reduce risk by monitoring for flames or sparks, for instance with video or infra-red flame detection.
- When storing processed materials
- Rotate piles where risk of combustion is high
- Monitor temperatures regularly below the surface
- Control any additional material risks, such as exposed metal content.
The high calorific value in RDF or SRF makes water alone ineffective for suppressing fires. In this case, Class A penetrating foam, using cannons, hose reel or deluge systems, is often more effective. These systems focus suppression towards a particular area or hotspot, penetrating the surface to suppress at point of ignition.
A full fire risk assessment should inform your site’s fire mitigation measures, ensuring that your solutions are tailored to the site’s individual risks.