Minimising the risk: rubber and plastic fires

The global shift towards sustainability is seeing businesses continually search for alternative fuel sources, causing an increase in rubber and plastic recycling across the UK. However, rubber and plastic recycling often relies on high-volume storage for extended periods of time, as well as intense processing methods. This presents 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, explores the key fire risks of rubber and plastics and explains how these risks can best be mitigated.

The past century has seen the plastic industry rapidly evolve, creating a diverse family of materials. As with plastic, the rubber industry has also developed quickly, with the modern material using a range of raw ingredients. For example, modern tyres are now made up of over 200 different materials, and the average car tyre includes around 30 types of synthetic rubber and eight types of natural rubber. The diverse range of ingredients in modern rubber and plastics creates a number of unique fire risks, making it crucial for business owners to understand and implement the right fire protection measures.

The rubber risk

When set alight, the spread of fire and smoke from rubber can be rapid, burning at extreme temperatures. At 200°C, rubber flows as a molten rubber, and at 230°C, it releases highly flammable vapours, which can become trapped in the hot mass. If not controlled quickly, these vapours can ignite with explosive force.

Rubber naturally repels water, meaning many extinguishing methods are shed and drained away. This makes suppression extremely difficult, with many common measures, such as sprinkler systems, often unable to effectively control rubber fires.

Tyre fires

When awaiting recycling, rubber tyres can be stored for lengthy periods of time. This poses 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 emitting up to 55,000 gallons (201,198 litres) of oil. This proves water alone to often be an ineffective extinguishing agent.

Additionally, tyre fires often burn for astonishing lengths of time. For example, the Heyope Tyre Fire in Wales began in 1989 and burned for a staggering 15 years before it was fully extinguished, as the tyres were so tightly packed together.

The recycling process often involves tyres being shredded into smaller chips, known as tyre shred or rubber crumb. In this state, rubber is extremely susceptible to self-combustion. However, fires of this kind often take a long period of time to ignite, so prevention is entirely possible in many scenarios.

The plastic risk

The natural and synthetic polymers in plastics react similarly to fire, often creating highly toxic chemicals when ignited. In addition, 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 refuse derived fuel (RDF). Subcoal technology is now being used to enhance 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 carry a substantially high fire risk when stored in stockpiles.

Responsibilities and regulations

The Environment Agency (EA) stipulates every waste and recycling site must have a fire prevention plan (FPP), which details fire prevention measures and policies, unique to the specific site and its own risks. The Regulatory Reform (Fire Safety) Order (2005) also stipulates the business owner’s responsibility to take the appropriate measures to mitigate fire risk.

For the storage of rubber, there is specific voluntary guidance (ISO 2230:200). There is also guidance for the suitable use of suppression systems and how to reduce specific types of fire risk (NFPA 11, EN 13565).

Reducing the risk

Methods 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.

1. Initial bulk storage of raw materials

When minimising 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 a limited impact for rubber and plastic fires. Instead, you could use a compressed air foam system, in which the agent sticks to the alight materials to remove oxygen supply and effectively suppress the fire.

2. Processing rubber and plastics

Processing rubber and plastic for SRF or RDF creates an extremely high fire risk and prevention measures 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 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.

3. Storing processed materials

Reducing 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. Instead, Class A penetrating foam systems, using deluge systems, cannons/monitors or hose reel systems, are likely to be more successful.

An effective fire protection strategy requires a full risk assessment, as this will ensure the solution is bespoke and tailored to the individual site and its unique risks.

For more information, go to http://bit.ly/fireshield-systemsltd or call 0800 975 5767