Stopping the spread of rubber and plastic fires

James Mountain, Sales and Marketing Director, Fire Shield Systems, discusses the risks associated with rubber and plastics, business owner responsibilities when it comes to protection, and what that protection may include.

The global drive towards preserving our fossil fuel supplies has seen many businesses continually searching for alternative fuel sources and ways to reuse commonly wasted materials, such as rubber and plastic. The shift towards sustainability is accelerating this further, resulting in a rise in rubber and plastic recycling across the UK. As recycling drives to keep pace with production of new materials, these rates are only expected to rise.

The recycling of rubber and plastic often requires high volume storage for long periods of time, as well as intense processing to repurpose the materials for fuel, construction or other uses. This creates significant fire risks, shown in the troubling fire record for recycling centres across the UK.

The plastics industry has rapidly evolved since World War II, with countless types of plastics being created, resulting in a complex family of materials. Similarly, the rubber industry 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 these ingredients, in both rubber and plastic, are combustible, resulting in increased fire risk. This makes it vital for business owners to understand the appropriate mitigation measures.

The risk of rubber

Rubber doesn’t readily ignite. However, when it does, the spread of fire and smoke can be rapid and burn at extreme temperatures. At 200°C, rubber flows as a molten rubber, and at 230°C, this releases flammable vapours, which may become trapped in the hot mass. If not controlled quickly, these vapours can alight with explosive force.

As rubber naturally repels water, many extinguishing mediums are shed and drained away. This proves suppression to be extremely challenging, as many common methods are unable to effectively control these fires.

Tyre fires

Prior to recycling, rubber tyres are often stored for an extended period of time. This presents unique fire risks, due to air spaces between each tyre and their potential for high heat output.

When alight, tyres release a range of harmful, toxic chemicals. They can also release a large amount of oil, with one million tyres releasing up to 55,000 gallons (208,198 litres) of oil. As a result, water is often an unsuitable extinguishing material. In addition, tyre fires tend to burn for an extreme period of time. For example, the Heyope Tire Fire in Wales, began in 1989 and continued to burn for a staggering 15 years, as extinguishing was so challenging, due to tyres being tightly packed together.

During the recycling process, tyres are often shredded into smaller chips, known as tyre shred or rubber crumb. In this state, rubber is extremely susceptible to self-combustion. However, fires from tyre shred or rubber crumb often take a long time to initiate, meaning it is possible to prevent ignition in many scenarios.

The risk of plastic

Naturally occurring and synthetic polymers found in plastics react similarly to fire, and often produce highly toxic chemicals when ignited. Additionally, plastic flames often spread quickly, as high as two feet per second or 10 times that of wood on the surface.

Recycled plastics are commonly used for the production of renewable fuel sources, such as solid recovered fuel (SRF) and refused derived fuel (RDF). Subcoal technology is also now being used to upgrade SRF and RDF into pellets, which can be utilised as a substitute to coal or lignite to fuel industrial furnaces, such as lime or cement kilns. This material often has a high calorific value, so it is extremely susceptible to fire 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 prevention measures and policies to reduce fire risk. The Regulatory Reform (Fire Safety) Order (2005) also outlines responsibilities for business owners to take the appropriate measures to minimise fire risk.

Specific voluntary guidance (ISO 2230:2002) also exists for the storage of rubber, as well as guidance for the appropriate use of suppression systems and how to handle specific types of fires (NFPA 11, EN 13565).

Reducing the risk

For safeguarding sites handling rubber and plastics, guidance can be split into three key areas: initial storage, the recycling process and the bulk storage of the newly formed materials.

Initial bulk storage of raw materials

For reducing fire risk in the storage of bulk raw materials, you could:

Monitor the sub-surface temperature regularly

• Control moisture levels
• Ensure adequate ventilation
• Reduce the size of storage piles

• Create separation (either physically or using fire walls) between all waste piles
• Minimise storage times.

Water-based solutions will often have a limited effect for the suppression of rubber and plastic fires. Instead, you may consider using a compressed air foam system, where the agent will stick to the material to eradicate oxygen and suppress the fire effectively.

Processing rubber and plastics

Processing rubber and plastic for SRF or RDF brings about extremely high fire risks, and effective mitigation often requires a holistic approach. The key measures to consider include:

Cleaning regularly to remove small, highly combustible particles which can be released during shredding.

• Regular maintenance of machinery to reduce risk of mechanical failure or friction.
• Introducing appropriate fire prevention systems. Different machinery will require concentrated application protection. For example, detection systems such as linear heat, infra-red flame or video flame detections, are key for identifying flames, sparks or embers, which may form from metallic presence within the material.

Storing processed materials

Minimising fire risk in the storage of processed materials may include:

Turning piles at regular intervals, where risk of self-combustion or spontaneous heating is higher

• Monitoring sub-surface temperatures
• Controlling moisture levels
• Managing material risk factors.

SRF, RDF and other processed rubber and plastic has a high calorific value. This means water alone will 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 successful.

Effective mitigation of fire risks will require a full risk assessment, in order to create a bespoke solution which is unique to the individual site and its risks.