The global drive towards sustainability has seen businesses continually looking for alternative fuel sources, resulting in an increase in rubber and plastic recycling across the UK. However, rubber and plastic recycling often requires high volume storage for extended periods of time, as well as intense processing. This creates unique fire risks, as shown in the troubling fire record for recycling plants in the UK.
James Mountain Explains how Key Fire Risks can be Reduced
Over the past century, the plastic industry has evolved rapidly, resulting in a diverse family of materials. The rubber industry has also developed at fast pace, with the modern material comprising a range of raw ingredients. Modern tyres, for example, use a wide range of different materials, and the average car tyre includes around 30 types of synthetic rubber and eight types of natural rubber. The complex range of ingredients in modern rubber and plastics contribute to a number of unique fire risks, and it is crucial for business owners to understand these risks and introduce the right fire protection measures to mitigate them.
The Rubber Risk
When alight, fire and smoke spread from rubber can be rapid, as it burns at extremely high temperatures. At 200°C, rubber flows as a molten rubber, and at 230°C, it can release highly flammable vapours which may become trapped in the hot mass. If left uncontrolled, these vapours can ignite with explosive force. (Though extensive trials by London Fire Brigade have failed to self ignite tyre stockpiles – Ed.)
As rubber naturally repels water, many extinguishing methods are shed and drained away. This can prove suppression to be extremely difficult, as many common measures, such as sprinkler systems at ceiling height, are unable to effectively mitigate rubber fires.
Prior to recycling, rubber tyres can be stored for significant periods of times. 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 substantial amount of oil, with one million tyres releasing up to 55,000 gallons (201,198 litres) of oil. This often makes water alone an ineffective extinguishing material.
Additionally, tyre fires can burn for shocking lengths of time. For example, the Heyope Tyre Fire (The Heyope fire, like many others was a suspected case of arson and is recorded as such in Hansard) in Wales began in 1989 and burned for an astonishing 15 years before it was fully extinguished, due to the tyres being so tightly packed together.
The recycling process of tyres often involves them being shredded into smaller chips, known as tyre shred or rubber crumb. In this condition, rubber may be susceptible to self-combustion according to Fire Shield Systems. However, fires of this type often take a long period of time to ignite, meaning prevention is perfectly possible in many scenarios.
The Plastic Risk
The natural and synthetic polymers in plastics react similarly to fire, often emitting highly toxic chemicals when alight. Plastic flames can also spread extremely quickly, 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 refuse derived fuel (RDF). Subcoal technology is now being used to repurpose these fuels into pellets, which can be used as an alternative for coal or lignite to fuel industrial furnaces. However, these pellets often have a high calorific value, which means they have an extremely high fire risk when stored in stockpiles.
Responsibilities and Regulations
The Environment Agency (EA) requires every waste and recycling site to have a fire prevention plan (FPP) in place, which details fire prevention measures and policies, tailored the specific site and its individual risks. The Regulatory Reform (Fire Safety) Order (2005) also stipulates the business owner responsibility to take the appropriate measures to reduce and control fire risk.
For the storage of rubber, there is specific voluntary guidance (ISO 2230:200), and there is also guidance for the suitable use of suppression systems and how to minimise specific types of fire risk (NFPA 11, EN 13565).
Minimising the Risk
Guidance for protecting sites and mitigating fire risk for rubber and plastics can be broken down into three key areas: initial storage of raw materials, 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.
Water-based suppression solutions will often have very little impact for rubber and plastic fires. Alternatively, you could use a compressed air foam system, in which the agent sticks to materials to remove oxygen supply and stop the fire.
Processing rubber and plastics
Processing rubber and plastic for SRF or RDF creates a substantially high fire risk, and prevention measures will often require a holistic and localised 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 risk of mechanical failure or friction.
Implementing the right fire prevention systems. Different machinery will need 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 produced from metallic presence within the material.
Storing processed materials
Minimising fire risk in the storage of processed materials may include:
Turning piles frequently where 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 and RDF, has an extremely high calorific value, meaning water alone will often not effectively suppress a fire. Class A penetrating foam systems, using deluge systems, cannons/monitors or hose reel systems, are often likely to be more effective.
An effective fire protection strategy should be the result of an in-depth risk assessment to ensure the solution is tailored to the individual site and its unique risks.