The global drive towards sustainability is causing businesses to continually search for alternative fuel sources, seeing an increase in rubber and plastic recycling across the UK. However, recycling these materials tends to relies on high volume storage for lengthy periods of time, as well as intense processing. This creates unique fire risks, as evidenced in the troubling fire record for recycling plants in the UK.
James Mountain, sales and marketing director, Fire Shield Systems, explains the key fire risks associated with rubber and plastics, and how these risks can best be mitigated.
Over the past century, the plastic industry has rapidly evolved, creating a diverse family of materials comprising various types of plastics. The same can be said for the rubber industry, which uses a range of raw materials, with modern tyres being made up of over 200 different materials, and the average car tyre comprising around 30 types of synthetic rubber and eight types of natural rubber. Many of the diverse ingredients in modern rubber and plastic are combustible, creating unique fire risks and making it crucial for business owners to understand the appropriate mitigation measures.
The rubber risk
Many of the diverse ingredients in modern rubber and plastic are combustible, creating unique fire risks.When ignited, the spread of fire and smoke from rubber can be rapid. It also burns at extreme temperatures. At 200°C, rubber flows as molten rubber, and at 230°C, it emits flammable vapours, which can become trapped in the hot mass. If not promptly controlled, those vapours can set alight with an explosive force.
As rubber naturally repels water, many extinguishing measures are often shed and drained away. This makes suppression extremely challenging, with many common measures, such as ceiling height sprinkler systems, unable to successfully control rubber fires.
Prior to recycling, rubber tyres can be stored for extended periods of time. This creates unique fire risks, due to the air spaces between each tyre and their potential for high heat output.
When alight, tyres release a range of toxic chemicals and a large amount of oil, with one million tyres releasing up to 55,000 gallons (208,198 litres) of oil. This means water is generally an ineffective extinguishing material.
|The average car tyre comprises of around 30 types of synthetic rubber and eight types of natural rubber|
In addition, tyre fires often burn for shocking amounts of time. For example, the Heyope Tyre Fire in Wales begin in 1989 and wasn’t fully extinguished for an incredible 15 years, as the tyres were so densely packed together.
During the recycling process, tyres are sometimes shredded into smaller chips, known as tyre shred or rubber crumb. In this state, rubber is extremely vulnerable to self-combustion. However, these fires often take a long period of time to ignite, meaning prevention is possible in many situations.
The plastic risk
The naturally occurring and synthetic polymers found in plastics react similarly to fire, typically creating highly toxic chemicals when ignited. Additionally, plastic flames can spread rapidly, as high as two feet per second or 10 times that of wood on the surface.
Recycled plastics can be used for the production of renewable fuels, such as solid recovered fuel (SRF) and refused derived fuel (RDF). Subcoal technology is now being used to upgrade these fuels into pellets, which can be used as a substitute for coal or lignite to fuel industrial furnaces. However, this pellet material often has a high calorific value, which means it is extremely susceptible to fire risk when stored in stockpiles.
Responsibilities and regulations
The Environment Agency (EA) outlines that every waste and recycling site must have a fire prevention plan (FPP), which details the mitigation measures and policies in place to reduce a site’s fire risk. The Regulatory Reform (Fire Safety) Order (2005) also stipulates business owners’ responsibility to take appropriate measures to reduce fire risk.
Specific voluntary guidance for the storage of rubber exists (ISO 2230:200), as well as guidance for the suitable use of suppression systems and how to mitigate specific types of fires (NFPA 11, EN 13565).
Mitigating the risk
Methods for safeguarding sites and mitigating fire risk for rubber and plastics can be broken down into three key areas: initial storage, the recycling process and storage of the newly formed materials.
- Initial bulk storage of raw materials
When reducing fire risk in bulk raw material storage, you should:
- Monitor the sub-surface temperature regularly
- Control moisture levels
- Ensure adequate ventilation
- Reduce the size of piles
- Create separation (either physically or using fire walls) between all waste piles
- Minimise storage times.
When it comes to suppression measures, water-based solutions will generally have a limited impact on rubber and plastic fires. Instead, you could use a compressed air foam system, which allows the agent to stick to the materials to remove the oxygen supply and effectively suppress the fire.
- Processing rubber and plastics
When processing rubber and plastic for SRF or RDF, the risk of fire is extremely high and mitigation will often need a holistic approach. Key things to consider include:
- Cleaning machinery frequently to remove any small, highly combustible particles released during shredding.
- Regular maintenance of machinery to minimise the risk of mechanical failure or friction.
- Implementing the right fire prevention systems. Different machinery will require localised application protection. For example, detection systems such as linear heat detection, infra-red flame detection or video flame detection, are important for identifying flames, sparks or embers, which can be created from the metallic presence within the material.
- Storing processed materials
Mitigating fire risk in the storage of processed materials may include:
- Turning piles frequently where the risk of self-combustion or spontaneous heating is higher
- Monitoring sub-surface temperatures
- Controlling moisture levels
- Managing material risk factors.
Processed rubber and plastic, such as SRF or RDF, has a high calorific value, so water alone will often not effectively suppress a fire. Instead, a Class A penetrating foam systems, using deluge systems, cannons/monitors or hose reel systems, is likely to be more effective.
To create an effective fire protection strategy, a full risk assessment is crucial, as it helps to generate a unique solution, tailored to the individual site and its risks.